WO2024223841A1

WO2024223841A1 - Measurement system for in-situ black carbon measurement in gas pipe

Info

Publication number: WO2024223841A1
Application number: PCT/EP2024/061567
Authority: WO
Inventors: Casper Laur BYG; Jakob BRØNS; Martin Edvard Thomsen MATTESEN; Peter Mariager; Steffen Elb MØLLER; Daniel Hagedorn DITH
Original assignee: Green Instruments AS
Current assignee: Green Instruments AS
Priority date: 2023-04-26
Filing date: 2024-04-26
Publication date: 2024-10-31
Anticipated expiration: 2025-10-26

Abstract

The invention provides an in-situ measurement system for measurement of a property of black carbon in a stream of gas, such as gas streaming inside an exhaust gas pipe of a combustion engine. A first light transceiver comprises a light source, e.g. a laser light source, and a light detector, and wherein the first light transceiver is arranged so as to allow transmission and receipt of light along a measurement axis through the gas. One or more scattering light detectors, such as only one single scattering light detector, arranged for mounting, such as mounting in an opening of a wall of a pipe in which the gas streams, to detect incoming light along a scattering axis forming a non-zero angle, with the measurement axis, e.g. at an angle of 15°-30°. A processor system is arranged for connection to the first light transceiver and to the one or more scattering light detectors, so as to perform a light extinction measurement and a light scattering measurement, and wherein the processor system is arranged to determine the property of black carbon in response to the light extinction measurement and the light scattering measurement, and wherein the processor system is arranged to generate an output accordingly. Such system has been tested and found to produce black carbon results that are comparable with reference standardized method, and thus suited to document black carbon outlet e.g. from maritime vessels.

Description

MEASUREMENT SYSTEM FOR IN-SITU BLACK CARBON MEASUREMENT IN GAS

PIPE

FIELD OF THE INVENTION

The present invention relates to the field of measuring particles in a gas, specifically to the field of measuring a property of black carbon particles in a gas. More specifically, the invention relates to a measurement system for in-situ black carbon measurement in a gas stream, such as a measurement system for mounting in a chimney stack with exhaust gas outlet from a combustion engine, e.g. on a maritime vessel. More specifically, the measurement system may be capable of real time measurements of a quantity of black carbon particles.

BACKGROUND OF THE INVENTION

Recently, there has been focus on black carbon particle pollution, especially black carbon particle emission from combustion engine exhaust gas. Quantification of black carbon particles in exhaust gas from combustion engines of large maritime vessels is complicated. The golden standard is to take a small sample of air from the chimney stack and analyse the gas sample based on a method involving leading the gas sample through a filter paper and then determine the quantity of black carbon particles with an optical method on particles absorbed by the filter paper to arrive at a Filter Smoke Number (FSN).

At a large ship, the golden standard for quantification of black carbon particles in requires that a person guides a suction pipe into the exhaust gas at the chimney top to take a gas sample. This gas sample is then analysed to determine an FSN value. It may be a complicated task to enter the top of the chimney stack for gas sampling, and therefore it is only feasible to provide a momentary value of black carbon particles in the exhaust gas, for example a daily FSN measurement during a trip of maybe several weeks.

Thus, with the present technique, it is only possible to provide a very coarse estimate of the actual quantity of black carbon particle outlet during a period of time. It is well known that black carbon particle emission in exhaust gas varies significantly over time, depending on engine load conditions as well as with variation in the fuel quality, e.g. diesel, crude oil or heavy fuel oil, supplied to the engine.

It is well known that exhaust gas from a combustion engine, e.g. a diesel engine, will contain a significant amount of black carbon particles during run up or other load conditions, while the black carbon level may be lower at steady load conditions. Therefore, the present technology does not allow a precise quantification of black carbon particle outlet from combustion engine exhaust gas during practical operating conditions. E.g. it may be a goal to be able to determine the total carbon particle outlet during a full trip of a container ship or the like. Such full trip includes manoeuvring in a harbour with varying engine load conditions, where the black carbon pollution may be especially high, and with the current technique, this can not be taken into account.

SUMMARY OF THE INVENTION

In particular, it may be seen as an object of the present invention to provide an easy and reliable method and system for black carbon measurement of a stream of gas, e.g. exhaust gas from a combustion engine.

Preferably, the measurement system should be possible to calibrate for accordance with the current filter paper based measurement standard in order to allow generation of measurement values equivalent with the current standard.

Preferably, the measurement system should be capable of providing real time measurement values, such as measurement values with an interval of less than 1 minute, such as less than 10 seconds.

Preferably, the measurement system should be configured for being in-situ mounted in an exhaust gas pipe from a combustion engine, such as in the chimney stack of a maritime vessel, so as to allow continuous measurements or monitoring of black carbon particle outlet during normal operating conditions. In a first aspect, the invention provides a measurement system configured for in- situ measurement of a property of black carbon in a stream of gas, such as a quantity or distribution of black carbon particles in the gas, such as gas streaming along a stream axis, such as a stream axis in a pipe, such as gas streaming inside an exhaust gas pipe of a combustion engine,

- at least a first light transceiver, such as first and second light transceivers, where the first light transceiver comprises a light source and a light detector, and wherein the first light transceiver is arranged so as to allow transmission and receipt of light along a measurement axis through the gas, such as a measurement axis non-parallel with an axis along which the gas streams, preferably such as a measurement axis perpendicular to an axis along which the gas streams,

- one or more scattering light detectors, such as only one single scattering light detector, arranged for mounting, such as mounting in an opening of a wall of a pipe in which the gas streams, to detect incoming light along a scattering axis forming a non-zero angle, with the measurement axis, preferably both of the scattering axis and the measurement axis are arranged in one plane which is perpendicular to an axis along which the gas streams, and

- a processor system arranged for connection to the first light transceiver and to the one or more scattering light detectors, so as to perform a light extinction measurement and a light scattering measurement, and wherein the processor system is arranged to determine the property of black carbon in response to the light extinction measurement and the light scattering measurement, and wherein the processor system is arranged to generate an output accordingly.

Such measurement system is highly suited for permanent installation in the chimney stack with outlet of exhaust gas from a combustion engine, e.g. on a maritime vessel. This allows real time measurements of black carbon particles in the exhaust gas, and therefore a high precision monitoring of total black carbon particle emission over a period of time is possible.

The system has been tested to be capable of being permanently installed in the harsh environment inside the chimney stack of a maritime vessel with existing light source (laser light source) and detector components. Tests have verified that the measurement system can be calibrated to generate black carbon particle quantity data which are equivalent with the present golden standard measurement filter paper based technique.

Even further, since the measurement system of the invention allows real time measurements of black carbon particle outlet, and this may be provided as feedback data to the engine control. Thus, e.g. fuel injection or other parameters can be controlled in response to the real time black carbon quantity data with the aim of reducing black carbon emission from the engine exhaust gas or to quantify the effectiveness of Black Carbon reduction techniques.

Software based solutions to compensate for dirt or soot on the measurement equipment during normal operation has been proposed, as well as software based solutions to compensate for misalignment of the measurement transducers - either to facilitate correct mounting, and/or to compensate for vibration based misalignments during normal operating conditions.

Components of the first light transceiver and the scattering light detector can especially be mounted in three or four openings in the wall of the pipe, wherein these three or four openings are arranged in a plane perpendicular to or substantially perpendicular to the gas stream. In preferred embodiments, four openings in one plane may be used for optical access to the gas stream, wherein the four openings form two measurement axes, wherein the two measurement axes form an angle of 15°-30°, such as at an angle of 20°-24°.

In this way, the measurement system only requires a limited height, e.g. for mounting on a chimney stack, and this can be a practical feature for mounting in spaces with limited access, and such four identical openings or holes in one plane only has a limited impact on mechanical stability of the chimney stack or other pipe. Still, this allows installation of a measurement system capable of performing high precision measurements.

It is to be understood that by "light transceiver" is understood a light source and a light detector which may either 1) form one unit and thus be arranged for optical access to the gas in the pipe via one opening in the wall of the pipe, or 2) form separate light source unit and a light detector unit arranged for optical access to respective openings in the wall of the pipe. The one-unit embodiments has the advantage of requiring only one opening in the wall of the pipe, while the combined light source and detector function may have disadvantages with respect to a limited optical performance compared to separate solutions.

By using a light detector or light detectors in the form of a 2D or 3D camera combined with a high precision light intensity detector, the processor system can be used to detect anomalies or errors which can be used to generate an alarm in case poor measurement quality can be expected. Further, at least some of these detected errors or anomalies can be corrected by the processor system.

Especially, by using a camera, 2D movements or displacement can be detected, e.g. due to misalignment of light sources and detectors or due to vibrations, while a high precision light intensity detector, e.g. photodiode or pyroelectric detector, can be used by the processor system to compensate for variations in light sensitivity of the camera, e.g. linearity errors in light intensity sensitivity of the camera.

Various types of compensations of errors or anomalies can be used to improve long-term stability of the measurement system in spite the harsh environment involving high temperatures, high vibration levels, a pulsating gas stream and dirt which can all lead to optical imprecise measurements. Furthermore, procedures for compensations, e.g. involving performing special compensation or calibration measurements, can be used to counteract long-term variation in precision of the optical components, especially light intensity variation in both light sources and light detectors. For example, use of one or more reference light sources can be used to perform reference measurements that can improve light intensity level precision of the measurements of the black carbon property.

In the following, preferred features and embodiments will be described.

The one or more scattering light detector preferably comprises a camera, such as a 2D colour camera or a high precision light intensity detector. This allows detection of the scattered light as well as allowing an intelligent image analysis based detection and compensation in case of contamination, e.g. dirt or soot, on the optical window in contact with the gas. Especially, the camera may have an adjustable lens to allow focal adjustment, thereby allowing the camera to switch focus between the gas side and the far side of the optical window, thereby allowing detection of contamination on the gas side of the optical window. Thus, in preferred embodiments, the processor system is arranged to detect a transmission change of the optical window, such as caused by contamination such as dirt or soot on the optical window. Further, the processor system may be arranged to control a focal point of the camera, preferably the focal point of the camera can be controlled to focus on an optical window which is arranged for contact with the gas, so as to allow detection of the transmission change of the optical window.

In some embodiments, the processor system is configured to execute an algorithm serving to compensate for change of transmission of the optical window, such as caused by contamination such as dirt or soot on the optical window, in a calculation of the property of black carbon.

In some embodiments, the first light transceiver is arranged to generate light and detect with a wavelength within 500-900 nm, such as 500-800 nm, such as 600- 800 nm, such as 700-800 nm, such as 750-800 nm, such as 500-550 nm. Especially, the first light transceiver may comprise a laser light source. The selected wavelength depends on the type of black carbon particles which is expected to be detected in the gas as well as the gas type.

The first light transceiver and the one or more scattering light detectors may be arranged for mounting on a pipe, such as a wall of the pipe, to provide a measurement axis which is perpendicular or substantially perpendicular to the stream axis. Thus, in a chimney stack, the first light transceiver and the one or more scattering light detectors can be position in openings on the side walls of the pipe leading gas to an outlet.

In preferred embodiments, at least one of the one or more scattering light detectors is mounted to provide a scattering axis forming an angle of 15°-30°, such as at an angle of 20°-24°, with the measurement axis. Especially, the one or more scattering light detectors consists of one single scattering light detector mounted to provide a scattering axis forming an angle of 15°-30°, such as 20°- 24°, with the measurement axis. Such scattering axis angle even with only one scattering light detector has been found in tests to be suitable for measurement of black carbon in exhaust gas from a combustion engine, and to provide reliable results comparable and possible to calibrate to standardized reference methods. Thus, in preferred embodiments the processor system is programmed to determine the property of black carbon as a value which is calibrated to correspond to a standardized reference method, such as Filter Smoke Number, and wherein the control system is arranged to generate an output indicative of said value.

In preferred implementations, the scattering light detector and the first light transceiver are both mounted on a first mounting element arranged for mounting in a single opening in a wall of a pipe. This facilitates mounting, since the first mounting element can be prefabricated, e.g. of metal, to ensure a selected angle between the scattering axis and the measurement axis.

In preferred implementations, a second light transceiver is mounted on a second mounting element for mounting in an opening in a wall of a pipe.

With such embodiment with only two mounting elements, only a minimal installation on a gas pipe is necessary, i.e. only two openings are required. Preferably, the first and second mounting elements are configured to allow the sensitive components, i.e. the light transceivers and the scattering light detector (e.g. CMOS camera) to be positioned at a distance away from the gas inside the pipe. This is advantageous, since which can in some applications the gas can be aggressive and have a high temperature.

In some embodiments, the one or more scattering light detector and the first light transceiver have separate optical windows which are arranged for connection to the gas in the pipe. In other embodiments, at least one of the one or more scattering light detectors and the first light transceiver share one common optical window which is arranged for connection to the gas in the pipe. In preferred embodiments, the processor system is arranged for continuously and in real time determining the property of black carbon in response to the light extinction and the light scattering measurement, and to generate outputs accordingly. This allows logging or tracking black carbon outlet of an entire event, e.g. from a maritime vessel arrives to a harbour to it leaves the harbour including various manoeuvring, or logging of an entire trip at sea from one harbour to another.

In preferred embodiments, the processor system is arranged to calculate a measure of a total property, such as a total quantity, of black carbon in response to a series of quantities of black carbon particles determined over a period of time. This can be used to document a total black carbon outlet during an event, e.g. during a total travel by a maritime vessel.

In preferred embodiments, the system comprise of first and second light transceivers, wherein each of the first and second light transceivers comprises a light source and a light detector, and wherein the first and second light transceivers are both arranged to allow transmission and receipt of light along a measurement axis through the gas, so as to allow mutual light extinction measurements, e.g. along measurement axes which are arranged perpendicular to an axis along which the gas streams. Especially, the light extinction measurement may involve a first measurement of transmitting light from the light source in the first light transceiver and detecting light accordingly by the light detector in the second light transceiver. More specifically, the light extinction measurement may further involve a second measurement of transmitting light from the light source in the second light transceiver and detecting light accordingly by the light detector in the first light transceiver. Such measurement system allows reliable and precise measurement results. More specifically, the processor system may be arranged to calculate a measure of light extinction as a function of said first and second measurements and the backward light extinction measurement, such as to calculate an average of the forward light extinction measurement and the backward light extinction measurement. More specifically, the processor system may be arranged to calculate a measure of light scattering in response to light scattering detected by the one or more light scattering detectors during both of said first and second measurements. In some embodiments, first and second light transceivers are arranged relative to each other so as to allow performing mutual light extinction measurements along one common measurement axis.

In some embodiments, the first and second light transceivers are arranged to generate light with different polarization. This can allow further advantages with respect to measurement accuracy, and especially if only one or a few detector angles are used, the use of two or more different light polarizations can provide a measurement accuracy similar to that obtained with the use of more detector angles.

In some embodiments, the light scattering measurement involves detecting light by the one or more scattering light detectors during transmission of light by the light source emitted by the first light transceiver, such as detecting light by the one or more scattering light detectors simultaneous or non-simultaneous with performing of the light extinction measurement.

Preferably, the processor system is arranged to calculate the property of black carbon, such as a quantity or distribution of black carbon particles, in response to a function between a measure of light extinction and a measure of light scattering.

In some embodiments, the processor system comprises a front-end device arranged for connection with the at least first light transceiver and to the one or more scattering light detectors, such as an electric or fibre optic connection. Especially, the processor system may comprise a calculation module comprising a processor and being in wired or wireless connection with the front-end device to receive measurement signals or data from the first light transceiver and the one or more scattering light detectors, such as to receive measurement signals or data from the first and a second light transceiver and the one or more scattering light detectors.

It has been found that the measurements described can be used to determine or calculate various black carbon properties. Thus, in some embodiments, the processor system is arranged to determine a measure of one or more properties selected from : a mass of black carbon particles, a number of black carbon particles, a toxicity level of black carbon particles, a size of black carbon particles, and a distribution of sizes of black carbon particles in response to the light extinction measurement and the light scattering measurement, and wherein the processor system is arranged to generate an output indicative of said measure.

In some embodiments, the measurement system forms a kit arranged for mounting on a pipe or a duct or a tank. Thus, such kit can be used for fitting the measurement system on existing pipe, ducts or tanks etc.

In some embodiments, the processor system is arranged to execute an alignment algorithm serving to eliminate or at least reduce an effect of misalignment of the first light receiver and/or the one or more light scattering detectors. Specifically, the alignment algorithm involves detecting measurement outliers and/or detecting minimum or maximum values among a series of measurements. More specifically, the alignment algorithm may serve to facilitate a mechanical alignment during mounting of the measurement system. More specifically, the alignment algorithm may serve to eliminate or at least reduce measurement errors caused by mechanical vibrations during the light extinction measurements.

Some embodiments comprise a plurality of scattering light detectors arranged to detect light incoming at different angles relative to the measurement axis, such as each of the scattering light detectors comprising a camera, such as comprising 2- 10 separate scattering light detectors. This may further increase measurement accuracy, however as mentioned, tests have verified that one single scattering light detector at a specific angle can be enough to provide a high accuracy.

The measurement system is preferably configured to generate an output indicative of a property of black carbon, such as a total quantity of black carbon particles, which is outlet in gas from the chimney stack during a period of time, such as during an hour, such as during a day, such as during a plurality of days.

In some embodiments, the light source and the light detector of first light transceiver are integrated to form one single unit, such as the light source and the light detected being positioned within one common housing and being configured to transmit and receive light via one common optical window connection with the gas. In embodiments with first and second light transceivers, both light transceivers may be of such integrated light transceivers as described above for the first light transceiver. Especially, both light transceivers may be laser light transceivers, i.e. each comprising a laser light source.

In some embodiments, the light source and the light detector of the first light transceiver are formed as separate units. Especially, the light source and the light detector of the first light transceiver may be arranged at different positions, so as on opposite sides of a wall of a pipe or duct, so as to allow the light source to transmit light through the gas and to allow the light detector to receive light transmitted through the gas, so as to allow performing the light extinction measurement. This allows a simple measurement setup.

The light source in the first light transceiver can in principle be based on different light source technology. E.g. the light source can be configured to generate monochromatic or polychromatic light. Especially, in case of a light source generating polychromatic light, it may be preferred to have an optical filter in front of the light source to limit the spectrum of emitted light.

In some embodiments the first light transceiver comprises a laser light source, and in some embodiments the measurement system comprises a second light transceiver comprising a laser light source.

In some embodiments, the first light transceiver comprises a Light Emitting Diode (LED) based light source, such as a light source comprising a LED and an optical filter, and in some embodiments the measurement system comprises a second light transceiver comprising a LED based light source, such as a light source comprising a LED and an optical filter.

In preferred embodiments, the first light transceiver and the scattering light detector(s) are arranged for mounting in openings of the wall of the pipe in which the gas streams such that the openings of the wall of the pipe are arranged in one plane which is perpendicular to the stream axis. Also, in case of embodiments where three or four or more openings of the wall of the pipe are required for light source, light detectors and scattering light detector(s), it may be preferred that all openings are in one plane which is perpendicular to the stream axis. In this way, only a minimal impact on the wall of the pipe is required, e.g. in the form of small drilled holes in the wall, and thus installation of the measurement system only results in a minimal mechanical impact on the pipe. In case of a pipe with a circular cross section, openings for the light transducers are thereby arranged at different angular positions on the wall of the pipe. Such arrangement of measurement transducers allows the measurement system to be accepted for installation e.g. on an exhaust gas pipe of a maritime vessel.

It may be preferred that some of or all of the openings of the wall of the pipe for mounting of light source(s) and light detector(s) are in a plane which is different from a plane perpendicular to the stream axis. However, to do so, a larger opening in the wall may be required, and this can in some cases be unacceptable with respect to mechanical stability of the pipe.

It is to be understood that the first light source and the first light detector may be arranged in the same housing to form one single unit. Alternatively, the first light source and the first light detector may be arranged in separate housings so as to allow the first light source to be arranged at one position relative to the wall of the pipe, while the first light detector is arranged at another position relative to the wall of the pipe.

In preferred embodiments, the first transceiver and the one or more scattering light detectors are arranged for mounting in openings in the wall of the pipe which are all in a plane which is perpendicular to the stream axis. In this way, only a limited part of the pipe, e.g. a chimney stack, is occupied by the measurement system, and with three or four distributed openings or holes each of a few centimetres, the mechanical impact on the pipe is limited. Especially, the first transceiver, such as one single unit or separate light source and light detector units, and the one or more scattering light detectors may be mounted on respective tubes, wherein the tubes are mounted in openings of the wall of the pipe. Said tubes are preferably all mounted so as to extend in one plane, most preferably a plane which is perpendicular or substantially perpendicular to the stream axis. Especially, at least one of the one or more scattering light detectors is mounted to provide a scattering axis forming an angle of 15°-30°, such as at an angle of 20°-24°, with the measurement axis. Especially, the first transceiver and the one or more scattering light detectors are mounted so that the measurement axis and the scattering axis intersect at a centre of the pipe, such as the pipe having a circular cross section. In preferred embodiments, four openings in the wall of the pipe, such as comprising a tube arranged in each of said four openings, are arranged to form two measurement axes in a plane perpendicular or substantially perpendicular to the stream axis, wherein said two measurement axes form an angle of 15°-30°, such as at an angle of 20°-24°.

In some embodiments, a camera is mounted to serve as the scattering light detector, and wherein at least one optical fibre connects a light source of the first transceiver to the camera as a reference, e.g. to transfer light from a reference light source to the camera. Especially, the camera is connected so that one area of its optical coverage area serves as the scattering light detector while another area of its optical coverage area is connected to receive light from the optical fibre. In this way the same camera serves as detector for scattering light, and via an optical fibre it may connect to a position for detection of the extinction measurement as well. Preferably, the processor system is arranged to compensate for the absolute light measurement intensity of the camera, e.g. in case where light from a reference light source can be used to calibrate light sensitivity of the camera and thus improve precision of measurement of the scattering light by means of the camera. Further, the processor system may be arranged to compensate for changes in light intensity of the light source of the first transceiver.

In some embodiments, one laser light source is connected via at least two optical fibres to provide light to respective optical positions for the light extinction measurement. Especially, the laser light source is connected to a controllable shutter to control optical connection between the laser light source and the at least two optical fibres. Especially, a photodiode or a camera may be arranged as a light detector for both of the light extinction measurement and the light scattering measurement. Especially, a beamsplitter may be arranged in connection to said one laser light source so as to transfer a fraction of light from said one laser light source to a reference photodiode or camera, and wherein the processor system is arranged to compensate for changes in light intensity from said one laser light source based on measurements made by said reference photodiode or camera. Especially, a third optical fibre may be connected to the controllable shutter. Use of optical fibres allow all electronic components including light source(s) and light detector(s) to be collected at one location, e.g. in one single housing at or near a position for one opening in the wall of the pipe, whereas optical connection to two or three other positioned openings in the wall of the pipe is provided by means of optical fibres.

In some embodiments, a photodiode and a camera are arranged for detection of light at the same optical position, and wherein the processor system is arranged to detector compensate for at least one of: 1) fouling or contamination of an optical window in contact with the gas stream, 2) heat haze phenomenon, 3) heat lens phenomenon, and 4) misalignment of a laser light source, based on measurement performed with the photodiode and camera. Especially, the processor system may be arranged to detect and/or compensate for two or more of l)-4). In this way measurement precision and reliability of the measurement system can be improved.

In some embodiments, a camera and a photodiode are arranged as light detectors at the same optical position, and a reference laser source connected to provide light to the camera and the photodiode, and wherein the processor system is arranged to calibrate or compensate errors accordingly. Especially, the reference laser source may be controlled to generate a light intensity sweep, and wherein the processor system is arranged to determine or compensate for linearity errors in light intensity level detection.

In some embodiments, four openings are arranged in the wall of the pipe, such as comprising a tube arranged in each of said four openings, to form two measurement axes in a plane perpendicular or substantially perpendicular to the stream axis, wherein said two measurement axes form an angle of 15°-30°, such as at an angle of 20°-24°, and wherein one single laser light source provides light at one opening, and wherein three separate light detectors are arranged to detect light at respective ones of the further openings. In some embodiments, three openings are arranged in the wall of the pipe, such as comprising a tube arranged in each of said three openings, to form one measurement axis and a scattering axis which are all in a plane perpendicular or substantially perpendicular to the stream axis, and wherein the scattering axis and the measurement axis form an angle of 15°-30°, such as at an angle of 20°- 24°. Especially, one light transceiver may be arranged at a first opening, wherein a laser light source is arranged at a second opening opposite the first opening, and wherein a light detector is arranged at a third opening. Especially, one light transceiver comprising a camera may be arranged at a first opening, wherein a laser light source is arranged at a second opening opposite the first opening, and a light detector comprising a camera is arranged at a third opening.

In some embodiment, at least one of the optical windows in openings of the wall of the pipe and being arranged for the extinction measurements and the light scattering measurements have a diameter of more than 20 mm, such as more than 25 mm. Use of a rather large optical window, such as a focal lens, serves to reduce problems with dirt on the optical window, heat haze phenomenon, heat lens phenomenon, robustness to misalignment or other effect that causes changes of the intensity or shape of the beam.

In an alternative formulation, the first aspect provides a measurement system configured for in-situ measurement of a property of black carbon in a stream of gas, such as a quantity or distribution of black carbon particles in the gas, such as gas streaming along a stream axis, such as a stream axis in a pipe, such as gas streaming inside an exhaust gas pipe of a combustion engine,

- at least a first light source and a first light detector arranged so as to allow transmission and receipt of light along a measurement axis through the gas, such as a measurement axis non-parallel with an axis along which the gas streams,

- one or more scattering light detectors, such as only one single scattering light detector, arranged for mounting, such as mounting in an opening of a wall of a pipe in which the gas streams, to detect incoming light along a scattering axis forming a non-zero angle, with the measurement axis, and

In a second aspect, the invention provides a maritime vessel, such as a ship, comprising

- a chimney stack for outlet of gas from a combustion process, such as a combustion engine or a boiler or the like.

- the measurement system according to the first aspect, wherein the at least first light transceiver and the one or more scattering light detectors are mounted in openings in walls of the chimney stack or in openings in walls of a pipe leading the gas from the combustion process to the chimney stack.

Especially, the measurement system may be configured to generate an output indicative of a property of black carbon, such as a total quantity of black carbon particles, which is outlet in gas from the chimney stack during a period of time, such as during an hour, such as during a day, such as during a plurality of days, such as during an entire travel of the maritime vessel from one harbour to another harbour, such as during a stay in a harbour of the maritime vessel.

In preferred embodiments, components of the first light transceiver and the one or more scattering light detectors are mounted in three or four openings in the walls of the chimney stack or in openings in the walls of a pipe leading the gas, wherein said three or four openings are arranged in a plane perpendicular to or substantially perpendicular to the stream of gas, such as components mounted in four openings arranged to form two measurement axes form an angle of 15°-30°, such as at an angle of 20°-24°.

In a third aspect, the invention provides a method for in-situ measuring a property of black carbon in a gas streaming along a stream axis in a pipe,

- a) mounting a first light transceiver in an opening of a wall of the pipe to allow transmission and receipt of light along a measurement axis through the gas, wherein the measurement axis is non-parallel with the stream axis, wherein the first light transceiver comprises a light source and a light detector, - b) mounting at least one scattering light detector, such as comprising a camera, in an opening of the wall of the pipe to detect incoming light along a scattering axis forming a non-zero angle with the measurement axis,

- c) performing at least one light extinction measurement by operating the first light transceivers, during the gas streaming in the pipe,

- d) performing a light scattering measurement by means of the at least one scattering light detector, during the gas streaming in the pipe,

- e) determining the property of black carbon in response to a result of the light extinction measurement and a result of the light scattering measurement, and

- f) generating an output according to the determined black carbon, such as a quantity of black carbon particles.

Especially, the method may comprise continuously performing steps c), d) and e), and generating the output continuously in real time accordingly.

The method may comprise determining a measure of a total property of black carbon in response to a series of properties of black carbon determined over a period of time.

The method may especially comprise performing light scattering measurements by one single scattering light detector arranged at a fixed angle with the measurement axis.

In preferred embodiments, the method comprises mounting a second light transceiver in an opening of a wall of the pipe to allow transmission and receipt of light along the measurement axis, wherein both of the first and second light transceivers comprises a light source and a light detector, and further comprising performing at least one light extinction measurement by operating the second light transceiver, during the gas streaming in the pipe.

Especially, the method may comprise performing at least steps a)-d), such as all of steps a)-f), on a maritime vessel, such as performing at least steps a)-d) on a pipe for outlet of combustion gas on the maritime vessel. For example, steps e) and f) may be performed at another location based on measurement data obtained in steps a)-d) on a maritime vessel, e.g. based on wirelessly transmitted data indicative of measurement results obtained in steps a)-d).

Especially, the method may comprise executing an alignment algorithm serving to compensate the determined property of black carbon due to misalignment of the first light transceiver caused by mechanical vibrations during the measurements.

In some embodiments, the method comprises generating a report, such as in the form of a document in the form of paper or in a file format, wherein the report is generated based on determined properties of black carbon based on measurements performed over a period of time, e.g. the report may comprise values indicating a total quantity and/or distribution of black carbon particles which has been measured over a predetermined period of time. This can be used e.g. to document a total output of black carbon from a gas pipe during a period of time.

The method may comprise mounting components of the first light transceiver and the scattering light detector in three or four openings in the wall of the pipe, wherein the three or four openings are arranged in a plane perpendicular to or substantially perpendicular to the gas stream or to a longitudinal extension of the pipe.

In a fourth aspect, the invention provides use of the measurement system according to the first aspect. Especially, the use may be on a maritime vessel, or the use may be on a gas outlet from a stationary combustion process.

The individual aspects of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from the following description with reference to the described embodiments.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

FIG. 1 illustrates the basic measurement principle of light absorption and scattering of a light black carbon particle in a gas and the principle of light extinction,

FIG. 2-4 illustrate various measurement system embodiments,

FIG. 5 illustrates a sketch maritime vessel with a combustion gas outlet chimney stack on which the measurement system of the present invention is mounted, FIG. 6 illustrates steps of a method embodiment,

FIG. 7-13 illustrate various embodiments based on four openings for optical access in the wall of the pipe arranged in one plane which is perpendicular to the gas stream or the longitudinal extension of the pipe, and

FIG. 14 and 15 illustrate embodiments with three openings for optical access in the wall of the pipe arranged in one plane which is perpendicular to the gas stream or the longitudinal extension of the pipe.

DETAILED DESCRIPTION OF AN EMBODIMENT

FIG. 1 illustrates the basic measurement principle of light absorption and scattering of a light black carbon particle in a gas and the principle of light extinction. Thus, by transmitting light, e.g. from a laser light source with a wavelength of 500-900 nm, through a gas containing black carbon particles BC, the black carbon particles BC will absorb and scatter the light. Light extinction is the difference between the incoming light and the transmitted light, which can be detected by a light detector. By measuring the scattered light in addition to the light extinction, a property of the black carbon BC in the gas can be derived.

This is the basic principle behind the measurement system of the invention. However, scattered light is generally complicated to measure, since in principle all scattering angle should be covered. The inventors have found in experiments that even one single light detector at one single scattering angle can be used to provide valid measured results for properties of black carbon in combustion exhaust gas, such as the exhaust gas of a combustion engine in a maritime vessel. FIG. 2 shows a preferred embodiment installed at a pipe P guiding a gas stream GS including black carbon BC particles. In this embodiment two laser light transceivers LLT1, LLT2 are mounted opposite each other for performing mutual light extinction measurements along a measurement axis. One single scattering light detector SLD is mounted close to the first laser light transceiver LLT1 at an angle a, e.g. between 20° and 24°, relative to the measurement axis. Especially, it may be preferred that the first laser light transceiver LLT1 and the scattering light detector SLD are mounted on one common mounting element, so as to be mounted on the wall of the pipe P using only one single opening.

FIG. 3 shows another embodiment where only one single laser light transceiver LLT1 is used, e.g. mounted on the same mounting element as a scattering light detector SLD, as described above. However, instead of the second laser light transceiver, a light reflector RFL is positioned to reflect light transmitted by the laser light source in the laser light transceiver.

FIG. 4 shows yet another embodiment, where two scattering light detectors SLD1, SLD2 are used, positioned on opposite sides of the pipe P wall. In this embodiment, the double scattering light detector arrangement is further combined with the laser light transceiver being split into two separate units, one laser light source LLS unit and one transmission detector TD unit. One scattering light detector SLD1 is mounted close to the laser light source LLS, while the one scattering light detector SLD2 is mounted close to the transmission detector TD.

In the embodiments of FIG. 2-4 the measurement axis is shown as perpendicular to the gas stream axis GS, and the scattering axis or axes are shown to form a plane together with the measurement axis which is parallel with the gas stream axis GS, thus this plane is also parallel with the wall of the pipe P.

FIG. 5 shows a measurement system MS mounted on a chimney stack CS of a ship S. The chimney stack guides a stream of gas GS away from a combustion process CMB, e.g. the main engine of the ship S. The gas stream GS contains black carbon particles BC which are outlet from the ship S. Properties, e.g. a quantity of such black carbon BC outlet from the ship S can be measured and reported by means of the measurement system MS.

FIG. 6 illustrates steps of a method embodiment, i.e. a method for in-situ measuring a property of black carbon in a gas streaming along a stream axis in a pipe. First a) mounting a first laser light transceiver in an opening of a wall of the pipe to allow transmission and receipt of light along a measurement axis through the gas, wherein the measurement axis is non-parallel with the stream axis, wherein the first laser light transceiver comprises a laser light source and a light detector. Further, b) mounting at least one scattering light detector, such as comprising a camera, in an opening of the wall of the pipe to detect incoming light along a scattering axis forming a non-zero angle with the measurement axis. Further, c) performing at least one light extinction measurement by operating the first laser light transceivers, during the gas streaming in the pipe. Further, d) performing a light scattering measurement by means of the at least one scattering light detector, during the gas streaming in the pipe. Further, e) determining the property of black carbon in response to a result of the light extinction measurement and a result of the light scattering measurement. Finally, f) generating an output according to the determined black carbon, such as a quantity of black carbon particles.

The described method applies as well for other light transceivers than laser light source based transceivers, e.g. light transceivers based on LED light sources.

An important part of precise measurement of opacity and scattering light levels is to handle nonlinearities of both light source light detector. Measuring the light source intensity can be obtained by directly measuring the light intensity either through a separate light detector (reference detector) or by transferring the emitted light using an optical fibre (reference light fibre) to the measurement detector for direct comparison.

Introduction of a separate reference light detector introduces a new source of error: nonlinearity of the reference detector. This method described here aims to: 1) Compensate for the nonlinearities of both the reference light detector/optical fibre and the light detector by obtaining the difference between the reference detector/ reference optical fibre and the light detector across a range of light intensities.

2) Compensate for the nonlinearities of the light detector.

By measuring opacity or scattering with different light intensity levels, it is possible to determine linearity errors and thereby compensate for this. This is done by determining the ratio between generated light intensity and measured light intensity at the other end of the gas pipe at different light intensity levels. Ideally, this ratio should be the same at all light intensity levels in a small time window. However, when linearity errors occur, the ratio will change.

In case a camera is used as light detector, it is possible to track a moving beam and other abnormalities. There are also other options as detection of fouling/contamination of protection optical window. Detection of heat haze phenomenon, heat lens phenomenon and misalignment of opacity/scattering lasers. However, using a camera as an absolute light intensity detector may be problematic. By introducing an LED/laser, photodiode, and beam splitter, it is possible to calibrate the camera by performing a light intensity sweep. The light intensity from the LED/laser is measured by the photodiode and the camera, and the camera can then be calibrated accordingly. Also, changing exposure time and gain on the camera in different light intensity levels can be used for compensation for errors. With the combination of a camera and a photodiode it is also possible to determine linearity errors by changing light intensity levels.

In case of using only photodiodes as light detector for opacity and scattering light intensity, it is preferred that the light source contains laser and a local reference measurement photodiode. In this way it is possible to determine the light intensity from the laser. By changing the light intensity on the laser it is possible to measure opacity/scattering in different light intensity levels. Thereby, it is possible to determine linearity errors and compensate for the error.

In the following, various types of calibration procedures will be described which may be used for the measurements system to improve its measurement performance. This can be implemented e.g. by means of a user interface of the processor system which may be preprogrammed to perform one or more of the following calibrations. Once the one or more calibration procedures has been performed, the processor system can be switched to a normal mode of operation.

1) Calibration using a device that generates a mist of various character, e.g. a mist based on salt, aerosols, polymers, dust etc.

2) Calibration with a device that generates smoke of various character.

3) Calibration with a stabilized atmosphere enriched with media that has characteristics emulating black carbon. This media could have scattering, absorptive or similar characteristics. The media(s) could be retained inside a vessel/container that could be pressurized. The media could be any media including solids, gasses, and liquids.

4) Calibration with a light scattering element that in turns is inserted into the beams of lights. This could be a material in which scattering material such as black carbon is entrapped or a material that has inherent scattering properties. The insertion could be manually, automatic, periodic or event based.

5) Calibration using the exhaust gas/media itself. The system can be calibrated if the dynamic range of the media changes ideally from lowest range to highest range, e.g. from white smoke to black smoke.

6) Calibration/linearity of opacity and scattering can be obtained by linearizing the detector using any of the above methods. This could be by inserting one or a series of neutral density filter(s) in the light beam and adjusting the characteristics/linearity of the detector output. It will now be possible to disconnect and relocate this linearized detector to any of the other light beams placed at different angles/orientations (opacity beam, forward beam and backward beam etc.). The relationship between beam intensity and detector response can be adjusted for each individual beam. This makes it possible to trim each response relative to the detector.

7) Correct angles/orientation relative to the beams can be verified by a mechanical jig that ensure angular orientation and parallel coherence to the optical plane at the time of installation or permanently mounted. The same can be achieved by making the construction of the orientation between beams in advance on precision machinery.

8) Calibration of the system can be carried out in a test-rig/jig that orientates the beams and detectors and makes it possible to apply various calibration methods as mentioned above without having constrains related to the in-situ placement in/onto the exhaust gas pipe. In FIG. 7-13 various light source and light detector embodiments are illustrated which are all based on a configuration with four openings in the wall of the pipe leading a gas stream, where these four openings are all in one plane which is perpendicular to the gas stream or to the longitudinal extension of the pipe. In this way only a minimal height of a vertical pipe is used. Further, with rather small openings or holes in one plane only, only a minimal mechanical impact on the pipe is caused. Especially, the openings are positioned in the plane such that two optical measurement axes are provided, namely measurement axes with a mutual angle of 15°-30°, or preferably 20°-24°.

FIG. 7a and 7b serve to illustrate the one plane concept where four openings or holes H1-H4 are arranged in a wall of the P such that all four openings H1-H4 are in one plane which is perpendicular to gas stream inside the P. Thus, in this concept the light scattering and extinction (opacity) are measured in the same horizontal plane. This makes it easier to mount this system on ships, where small space in height is often a constrain. E.g. four identical holes H1-H4 can be drilled. This makes it easier to install/align the tubes. Alignment can be made by passing a pipe through the installed tubes.

When all light/measurements are pointed in the center of the smokestack, measurement is more precise.

FIG. 7a shows a cross section view of the pipe P and thus the plane where the four openings H1-H4 are arranged to form two measurement axes Ml, M2 for optical measurements with a mutual angle of most preferably 22°, however an angle of 15°-30° may be used. Each of the openings H1-H4 has an optical window, e.g. a glass lens, serving to protect light source(s) and detector(s) from the gas inside the pipe P. As seen, the measurement axes Ml, M2 intersect at the centre of the pipe P, here illustrated as a circular cross section pipe P.

FIG. 7b shows a 3D sketch of the four openings in one plane, here illustrated with tubes inserted through the wall of the pipe P to allow optical access to the gas inside the pipe P, and where light source(s) and light detector(s) are arranged at an outside end of the tubes, thereby protecting this equipment from the harsh environment inside the pipe P. Inside the pipe P gas streams along the longitudinal extension of the pipe P, indicated by the vertical arrow. E.g. four identical holes can be drilled and the tubes are installed an aligned. Alignment can be made by passing a pipe through.

FIG. 8 shows an embodiment where optical fibres OF via beam splitters transfer light from laser light sources L1-L3 to a camera CM serving as light detector. These three signals are provided to the camera CM to create reference signals Rl- R3. To the top right the camera image CI is illustrated where the scattering and opacity light image SC is shown in the centre of the image CI, while the three laser signals R1-R3 are also provided to the camera and guided to other parts of the image CI.

The idea with this embodiment is that the camera CM measures the reference signals R1-R3 and the measurement signal SC on the same image. Using a large CMOS allows measurement light and reference light signals to hit different parts of the CMOS, in the same image CI as illustrated. Thereby, it is possible to compensate for errors caused by the camera's absolute light intensity measurement and the light intensity that changes from the laser sources L1-L3.

FIG. 9 shows an embodiment where optical fibres OF are used to transmit light from a laser light source LS to three light source positions. At one position a photo diode PD serves a light detector. The three light source positions are switched on alternately with a shutter arrangement SH. A beamsplitter is used to transfer a small percentage of laser light to a reference photodiode PDR. This makes it possible to compensate for errors caused by changes in light intensity generated by the laser light source LS.

FIG. 10 shows an embodiment with the same optical fibre OF and shutter arrangement SH as in FIG. 9 to guide light from the laser light source LS to three light source positions. However, here a camera CM is used as light detector at a measurement position. The camera image CI is illustrated to the right, and this shows that the camera CM detects both the measured light MS at the measurement position and a reference signal RL via a beamsplitter from the laser light source LS. Using a large CMOS allows measurement ML and reference light RL to hit two different parts of the CMOS, in the same image. This makes it possible to compensate for errors caused by the camera's absolute light intensity measurement and laser light source LS intensity changes.

FIG. 11 shows an embodiment with the same optical fibre OF and shutter arrangement SH as in FIG. 9 and 10 to guide light from the laser light source LS to three light source positions. However, in this embodiment a combined light detector arrangement comprises a camera CM, a photodiode PD and a reference photodiode PDR as shown also in FIG. 9. The camera CM in this solution is used for tracking movements of the detected light beam and other abnormalities, e.g. to generate an alarm in case a fatal measurement error is detected. There are also other options as detection of fouling/contamination of protection glass window, and detection of heat haze phenomenon, heat lens phenomenon and misalignment of scattering lasers.

FIG. 12 shows an embodiment with three laser light sources L1-L3 and a reference laser light source LRF. In this way a shutter arrangement is eliminated. Light detection arrangement comprises a camera CM and a photodiode PD.

The camera CM is good at tracking a moving beam and other abnormalities. There are also other options as detection of fouling/contamination of protection glass window. Detection of heat haze phenomenon, heat lens phenomenon and misalignment of scattering lasers.

However, using a camera CM as an absolute light intensity measurement can be difficult. By introducing a reference light source LRF, a photodiode PD and a beam splitter, it is possible to calibrate the camera CM by performing a light intensity sweep using the reference light source LRF, e.g. an LED based light source. The light intensity from the reference light source LRF is measured by the photodiode PD and the camera CM, whereby the camera CM can be calibrated accordingly. The combination of camera CM and photodiode PD also allows determination of linearity errors by changing light intensity levels.

FIG. 13 illustrates an embodiment with one light source LS and three light detectors PD1-PD3 e.g. in the form of photodiodes, however one or more of these may comprise camera as well. With only one light source LS this embodiment is simple, and there is no need for turning on/off light sources alternately, thus no timing of light sources needed, and all measurements can be done instantaneously or nearly instantaneously.

FIG. 14 and 15 illustrate embodiments based on a configuration with only three openings in the wall of the pipe leading a gas stream, where these three openings are all in one plane which is perpendicular to the gas stream or to the longitudinal extension of the pipe P. Especially, two openings are positioned in the plane such that on optical measurement axis Ml is provided, and a third opening is positioned to provide an angle of 15°-30°, or preferably 20°-24° with the measurement axis. The same advantages apply as for the four opening embodiments, however practical installation is facilitated with only three openings or holes are required.

FIG. 14 illustrates a three-opening embodiment based on a light transceiver TC with one unit having a combined light source LI and light detector PD1 with access to one opening in the wall of the pipe P along the measurement axis. This solution is more complex due to the combined light source and light detector. Further, a second light detector PD2 is arranged to measure scattered light, and opposite the transceiver TC, a second light source L2 is positioned to allow forward/backward light together with the light source LI in the transceiver TC.

FIG. 15 illustrates a three-opening embodiment based on two light sources LI, L2 at respective positions. At the position of the first light source LI, a light detector with a photodiode PD1 and a camera CM1 is seen. Further, at this position, a reference laser light source LRF is provided. Further, at the scattering light position a light detector with a photodiode PD2 and a camera CM3 is seen along with another reference laser light source LRF. The cameras CM1, CM2 are advantageous for tracking moving beam and other abnormalities as already mentioned above. There are also other options as detection of fouling/contamination of protection glass window and detection of heat haze phenomenon, heat lens phenomenon and misalignment of scattering lasers.

However, the use of two cameras CM1, CM2 causes this embodiment to be more complex. Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is to be interpreted in the light of the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features may be possible and advantageous.

Claims

1. A measurement system configured for in-situ measurement of a property of black carbon in a stream of gas, such as a quantity or distribution of black carbon particles in the gas, such as gas streaming along a stream axis, such as a stream axis in a pipe, such as gas streaming inside an exhaust gas pipe of a combustion engine,

- at least a first light transceiver, such as first and second laser light transceivers, where the first light transceiver comprises a light source and a light detector, and wherein the first light transceiver is arranged so as to allow transmission and receipt of light along a measurement axis through the gas, such as a measurement axis which is perpendicular to an axis along which the gas streams,

- one or more scattering light detectors, such as only one single scattering light detector, arranged for mounting, such as mounting in an opening of a wall of a pipe in which the gas streams, to detect incoming light along a scattering axis forming a non-zero angle, with the measurement axis, preferably the scattering axis is perpendicular to an axis along which the gas streams, and

2. The measurement system according to claim 1, wherein the one or more scattering light detector comprises a camera, such as a 2D colour camera.

3. The measurement system according to claim 2, wherein the processor system is arranged to detect a transmission change of the optical window, such as caused by contamination such as dirt or soot on the optical window.

4. The measurement system according to claim 2 or 3, wherein the processor system is arranged to control a focal point of the camera, preferably the focal point of the camera can be controlled to focus on an optical window which is arranged for contact with the gas, so as to allow detection of the transmission change of the optical window.

5. The measurement system according to any of the preceding claims, wherein the processor system is configured to execute an algorithm serving to compensate for change of transmission of the optical window, such as caused by contamination such as dirt or soot on the optical window, in a calculation of the property of black carbon.

6. The measurement system according to any of the preceding claims, wherein the first light transceiver is arranged to generate light and detect light with a wavelength within 500-900 nm, such as 500-800 nm, such as 600-800 nm, such as 700-800 nm, such as 750-800 nm, such as 500-550 nm, such as the first light transceiver comprising a laser light source.

7. The measurement system according to any of the preceding claims, wherein the first light transceiver and the one or more scattering light detectors are arranged for mounting on a pipe, such as a wall of the pipe, to provide a measurement axis which is perpendicular or substantially perpendicular to the stream axis, preferably both of the scattering axis and the measurement axis are arranged in one plane which is perpendicular to an axis along which the gas streams.

8. The measurement system according to any of the preceding claims, wherein at least one of the one or more scattering light detectors is mounted to provide a scattering axis forming an angle of 15°-30°, such as at an angle of 20°-24°, with the measurement axis.

9. The measurement system according to claim 8, wherein the one or more scattering light detectors consists of one single scattering light detector mounted to provide a scattering axis forming an angle of 15°-30°, such as 20°-24°, with the measurement axis.

10. The measurement system according to any of the preceding claims, wherein the processor system is programmed to determine the property of black carbon as a value which is calibrated to correspond to a standardized reference method, such as Filter Smoke Number, and wherein the control system is arranged to generate an output indicative of said value.

11. The measurement system according to any of the preceding claims, wherein the scattering light detector and the first light transceiver are both mounted on a first mounting element arranged for mounting in a single opening in a wall of a pipe.

12. The measurement system according to any of the preceding claims, wherein a second light transceiver is mounted on a second mounting element for mounting in an opening in a wall of a pipe.

13. The measurement system according to claim 11 or 12, wherein the one or more scattering light detector and the first light transceiver have separate optical windows which are arranged for connection to the gas in the pipe.

14. The measurement system according to claim 11 or 12, wherein at least one of the one or more scattering light detectors and the first light transceiver share one common optical window which is arranged for connection to the gas in the pipe.

15. The measurement system according to any of the preceding claims, wherein the processor system is arranged for continuously and in real time determining the property of black carbon in response to the light extinction and the light scattering measurement, and to generate outputs accordingly.

16. The measurement system according to any of the preceding claims, wherein the processor system is arranged to calculate a measure of a total property, such as a total quantity, of black carbon in response to a series of quantities of black carbon particles determined over a period of time.

17. The measurement system according to any of the preceding claims, comprising first and second light transceivers, wherein each of the first and second light transceivers comprises a light source and a light detector, and wherein the first and second light transceivers are both arranged to allow transmission and receipt of light along a measurement axis through the gas, so as to allow mutual light extinction measurements.

18. The measurement system according to claim 17, wherein the light extinction measurement involves a first measurement of transmitting light from the light source in the first light transceiver and detecting light accordingly by the light detector in the second light transceiver.

19. The measurement system according to claim 18, wherein the light extinction measurement further involves a second measurement of transmitting light from the light source in the second light transceiver and detecting light accordingly by the light detector in the first light transceiver.

20. The measurement system according to claim 19, wherein the processor system is arranged to calculate a measure of light extinction as a function of said first and second measurements and the backward light extinction measurement, such as to calculate an average of the forward light extinction measurement and the backward light extinction measurement.

21. The measurement system according to claim 19 or 20, wherein the processor system is arranged to calculate a measure of light scattering in response to light scattering detected by the one or more light scattering detectors during both of said first and second measurements.

22. The measurement system according to any of claims 17-21, wherein first and second light transceivers are arranged relative to each other so as to allow performing mutual light extinction measurements along one common measurement axis.

23. The measurement system according to claim 17-22, wherein the first and second light transceivers are arranged to generate light with different polarization, such as vertical and horizontal polarization, such as both of the first and second light transceivers being arranged to generate light with two different polarization.

24. The measurement system according to any of the preceding claims, wherein the light scattering measurement involves detecting light by the one or more scattering light detectors during transmission of light emitted by the first light transceiver, such as detecting light by the one or more scattering light detectors simultaneous or non-simultaneous with performing of the light extinction measurement.

25. The measurement system according to any of the preceding claims, wherein the processor system is arranged to calculate the property of black carbon, such as a quantity or distribution of black carbon particles, in response to a function between a measure of light extinction and a measure of light scattering.

26. The measurement system according to any of the preceding claims, wherein the processor system comprises a front-end device arranged for connection with the at least first light transceiver and to the one or more scattering light detectors, such as an electric or fibre optic connection.

27. The measurement system according to claim 26, wherein the processor system comprises a calculation module comprising a processor and being in wired or wireless connection with the front-end device to receive measurement signals or data from the first light transceiver and the one or more scattering light detectors, such as to receive measurement signals or data from the first and a second light transceiver and the one or more scattering light detectors.

28. The measurement system according to any of the preceding claims, wherein the processor system is arranged to determine a measure of one or more properties selected from : a mass of black carbon particles, a number of black carbon particles, a toxicity level of black carbon particles, a size of black carbon particles, and a distribution of sizes of black carbon particles in response to the light extinction measurement and the light scattering measurement, and wherein the processor system is arranged to generate an output indicative of said measure.

29. The measurement system according to any of the preceding claims, forming a kit arranged for mounting on a pipe or a duct or a tank.

30. The measurement system according to any of the preceding claims, wherein the processor system is arranged to execute an alignment algorithm serving to eliminate or at least reduce an effect of misalignment of the first light transceiver and/or the one or more light scattering detectors.

31. The measurement system according to claim 30, wherein the alignment algorithm involves detecting measurement outliers and/or detecting minimum or maximum values among a series of measurements.

32. The measurement system according to claim 30 or 31, wherein the alignment algorithm serves to facilitate a mechanical alignment during mounting of the measurement system.

33. The measurement system according to any of claims 30-32, wherein the alignment algorithm serves to eliminate or at least reduce measurement errors caused by mechanical vibrations during the light extinction measurements.

34. The measurement system according to any of the preceding claims, comprising a plurality of scattering light detectors arranged to detect light incoming at different angles relative to the measurement axis, such as each of the scattering light detectors comprising a camera, such as comprising 2-10 separate scattering light detectors.

35. The measurement system according to any of the preceding claims, being configured to generate an output indicative of a property of black carbon, such as a total quantity of black carbon particles, which is outlet in gas from the chimney stack during a period of time, such as during an hour, such as during a day, such as during a plurality of days.

36. The measurement system according to any of the preceding claims, wherein the light source and the light detector of first light transceiver are integrated to form one single unit, such as the light source and the light detected being positioned within one common housing and being configured to transmit and receive light via one common optical window connection with the gas.

37. The measurement system according to any of claims 1-35, wherein the light source and the light detector of the first light transceiver are formed as separate units.

38. The measurement system according to claim 37, wherein the light source and the light detector of the first light transceiver are arranged at different positions, so as on opposite sides of a wall of a pipe or duct, so as to allow the light source to transmit light through the gas and to allow the light detector to receive light transmitted through the gas, so as to allow performing the light extinction measurement.

39. The measurement system according to any of the preceding claims, wherein the first light transceiver comprises a laser light source.

40. The measurement system according to claim 39, comprising a second light transceiver comprising a laser light source.

41. The measurement system according to any of the preceding claims, wherein the first light transceiver comprises a Light Emitting Diode based light source, such as a light source comprising a Light Emitting Diode and an optical filter.

42. The measurement system according to claim 41, comprising a second light transceiver comprising a Light Emitting Diode based light source, such as a light source comprising a Light Emitting Diode and an optical filter.

43. The measurement system according to any of the preceding claims, wherein the first transceiver and the one or more scattering light detectors are arranged for mounting in openings in the wall of the pipe which are all in a plane which is perpendicular to a stream axis being an axis along which the gas streams in the pipe.

44. The measurement system according to claim 43, wherein the first transceiver, such as one single unit or separate light source and light detector units, and the one or more scattering light detectors are mounted on respective tubes, wherein the tubes are mounted in openings of the wall of the pipe.

45. The measurement system according to claim 44, wherein said tubes are all mounted so as to extend in one plane.

46. The measurement system according to claim 45, wherein said tubes are all mounted so as to extend in one plane which is perpendicular or substantially perpendicular to the stream axis.

47. The measurement system according to any of claims 43-46, wherein at least one of the one or more scattering light detectors is mounted to provide a scattering axis forming an angle of 15°-30°, such as at an angle of 20°-24°, with the measurement axis.

48. The measurement system according to claim 47, wherein the first transceiver and the one or more scattering light detectors are mounted so that the measurement axis and the scattering axis intersect at a centre of the pipe, such as the pipe having a circular cross section.

49. The measurement system according to any of claims 43-48, wherein four openings in the wall of the pipe, such as comprising a tube arranged in each of said four openings, are arranged to form two measurement axes in a plane perpendicular or substantially perpendicular to the stream axis, wherein said two measurement axes form an angle of 15°-30°, such as at an angle of 20°-24°.

50. The measurement system according to any of the preceding claims, wherein a camera is mounted to serve as the scattering light detector, and wherein at least one optical fibre connects a light source of the first transceiver to the camera as a reference.

51. The measurement system according to claim 50, wherein the camera is connected so that one area of its optical coverage area serves as the scattering light detector while another area of its optical coverage area is connected to receive light from the optical fibre.

52. The measurement system according to claim 50 or 51, wherein the processor system is arranged to compensate for the absolute light measurement intensity of the camera.

53. The measurement system according to any of claims 50-52, wherein the processor system is arranged to compensate for changes in light intensity of the light source of the first transceiver.

54. The measurement system according to any of the preceding claims, wherein one laser light source is connected via at least two optical fibres to provide light to respective optical positions for the light extinction measurement.

55. The measurement system according to claim 54, wherein the laser light source is connected to a controllable shutter to control optical connection between the laser light source and the at least two optical fibres.

56. The measurement system according to claim 54 or 55, comprising a photodiode or a camera arranged as a light detector for both of the light extinction measurement and the light scattering measurement.

57. The measurement system according to any of claims 54-56, comprising a beamsplitter arranged in connection to said one laser light source so as to transfer a fraction of light from said one laser light source to a reference photodiode or camera, and wherein the processor system is arranged to compensate for changes in light intensity from said one laser light source based on measurements made by said reference photodiode or camera.

58. The measurement system according to any of claims 54-57, comprising a third optical fibre connected to the controllable shutter.

59. The measurement system according to any of the preceding claims, comprising a photodiode and a camera arranged for detection of light at the same optical position, and wherein the processor system is arranged to detector or compensate for at least one of: 1) fouling or contamination of an optical window in contact with the gas stream, 2) heat haze phenomenon, 3) heat lens phenomenon, and 4) misalignment of a laser light source, based on measurement performed with the photodiode and camera.

60. The measurement system according to any of the preceding claims, comprising a camera and a photodiode arranged as light detectors at the same optical position, and a reference laser source connected to provide light to the camera and the photodiode, and wherein the processor system is arranged to calibrate or compensate errors accordingly.

61. The measurement system according to claim 60, wherein the reference laser source is controlled to generate a light intensity sweep, and wherein the processor system is arranged to determine or compensate for linearity errors in light intensity level detection.

62. The measurement system according to claim 49, wherein one single laser light source provides light at one position, and wherein three separate light detectors are arranged to detect light at respective positions.

63. The measurement system according to any of the preceding claims, wherein three openings in the wall of the pipe, such as comprising a tube arranged in each of said three openings, are arranged to form one measurement axis and a scattering axis which are all in a plane perpendicular or substantially perpendicular to the stream axis, and wherein the scattering axis and the measurement axis form an angle of 15°-30°, such as at an angle of 20°-24°.

64. The measurement system according to claim 63, wherein one light transceiver is arranged at a first opening, wherein a laser light source is arranged at a second opening opposite the first opening, and wherein a light detector is arranged at a third opening.

65. The measurement system according to claim 63, wherein one light transceiver comprising a camera is arranged at a first opening, wherein a laser light source is arranged at a second opening opposite the first opening, and a light detector comprising a camera is arranged at a third opening.

66. The measurement system according to any of the preceding claims, wherein at least one of the optical windows in openings of the wall of the pipe and being arranged for the extinction measurements and the light scattering measurements have a diameter of more than 20 mm, such as more than 25 mm.

67. The measurement system according to any of the preceding claims, wherein at least one of the optical windows in openings of the wall of the pipe and being arranged for the extinction measurements and the light scattering measurements comprises a focal lens, such as a focal lens having a diameter of more than 20 mm.

68. A maritime vessel, such as a ship, comprising

- the measurement system according to any of claims 1-67, wherein the at least first light transceiver and the one or more scattering light detectors are mounted in openings in walls of the chimney stack or in openings in walls of a pipe leading the gas from the combustion process to the chimney stack.

69. The maritime vessel according to claim 68, wherein the measurement system is configured to generate an output indicative of a property of black carbon, such as a total quantity of black carbon particles, which is outlet in gas from the chimney stack during a period of time, such as during an hour, such as during a day, such as during a plurality of days, such as during an entire travel of the maritime vessel from one harbour to another harbour, such as during a stay in a harbour of the maritime vessel.

70. The maritime vessel according to claim 68 or 69, wherein components of the first light transceiver and the one or more scattering light detectors are mounted in three or four openings in walls of the chimney stack or in openings in walls of a pipe leading the gas, wherein said three or four openings are arranged in a plane perpendicular to or substantially perpendicular to the stream of gas, such as components mounted in four openings arranged to form two measurement axes form an angle of 15°-30°, such as at an angle of 20°-24°.

71. A method for in-situ measuring a property of black carbon in a gas streaming along a stream axis in a pipe,

- a) mounting a first light transceiver in an opening of a wall of the pipe to allow transmission and receipt of light along a measurement axis through the gas, wherein the measurement axis is non-parallel with the stream axis, wherein the first light transceiver comprises a light source, such as a laser light source, and a light detector,

- b) mounting at least one scattering light detector, such as comprising a camera, in an opening of the wall of the pipe to detect incoming light along a scattering axis forming a non-zero angle with the measurement axis,

72. The method according to claim 71, comprising continuously performing steps c), d) and e), and generating the output continuously in real time accordingly.

73. The method according to claim 71 or 72, comprising determining a measure of a total property of black carbon in response to a series of properties of black carbon determined over a period of time.

74. The method according to any of claims 71-73, performing light scattering measurements by one single scattering light detector arranged at a fixed angle with the measurement axis.

75. The method according to any of claims 71-74, comprising mounting a second light transceiver in an opening of a wall of the pipe to allow transmission and receipt of light along the measurement axis, wherein both of the first and second light transceivers comprises a light source and a light detector, and further comprising performing at least one light extinction measurement by operating the second light transceiver, during the gas streaming in the pipe.

76. The method according to any of claims 71-75, comprising performing at least steps a)-d), such as all of steps a)-f), on a maritime vessel, such as performing at least steps a)-d) on a pipe for outlet of combustion gas on the maritime vessel.

77. The method according to any of claims 71-76, comprising executing an alignment algorithm serving to compensate the determined property of black carbon due to misalignment of the first light transceiver caused by mechanical vibrations during the measurements.

78. The method according to any of claims 71-77, comprising mounting components of the first light transceiver and the scattering light detector in three or four openings in the wall of the pipe, wherein the three or four openings are arranged in a plane perpendicular to or substantially perpendicular to the gas stream.

79. Use of the measurement system according to any of claims 1-67, such as on a maritime vessel, such as on a gas outlet from a stationary combustion process.