WO1992002724A2 - Process for converting heat into power using the stirling principle with internal combustion - Google Patents

Abstract

An exhaust gas-air mixture passes through a cycle. In each cycle a certain fraction of exhaust gas is removed at the point of lowest energy and replaced by fresh air. Integrated counterflow cooling (6) followed by gentle compression, with a small difference between isothermal and adiabatic curves avoids the drawbacks of a purely isothermal process. The valves (11, 12) are on the cold side and combustion takes place in a hot ceramic combustion chamber. The position and nature of the circuit means that a minimun of NOx is generated, with the greatest possible thermodynamic gradient.

Description

Process for converting heat into power after

the Stirling principle with internal combustion

In the past 200 years, numerous thermal power processes with internal and external combustion have been developed, tested and built.

The majority of the processes are based on a constant improvement in the performance-weight ratio and the price-performance ratio.

In the context of the current environmental discussion, this one-dimensional direction of development is no longer sufficient. A modern and future-oriented thermal power process must have the following properties: quiet, high thermodynamic efficiency, good exhaust gas analysis, if possible without constant oil changes, modest pressures, no exotic materials, suitable for combined heat and power, long service life, easy maintenance.

According to the current state of the art, some of these parameters are initially mutually exclusive. For a long time, experts hoped for the decisive breakthrough from the Stirling principle. But Fig.l (TS-Diagra m) shows the crucial handicap of the Stirling process.

You have to run through a metal wall with the entire heating power at high pressure and high temperature. In this respect, the diesel _^ or Otto principle with the explosion of the fuel ^* directly above the piston "thermodynamically intelligent".

On the other hand, better exhaust analysis, low noise and conceivable limit efficiency clearly speak for the Stirling principle. For clarification:

The starting niche for the new process is primarily engine power plants (combined heat and power plants) for environmentally friendly and decentralized heat and power coupling, which today operate almost exclusively according to the diesel or gas-Otto process.

The high level of noise caused by the explosion of the fuel requires extensive noise protection measures, which in turn make maintenance and cooling more difficult. Furthermore, thorough maintenance and regular oil changes with dioxin problems in the recycling of used oils must be accepted at regular and short intervals.

In addition, there are considerable corrosion and material problems with the exhaust gas heat exchanger, the exhaust gas analysis is terrifying with and without a catalytic converter.

As a promising compromise solution, some researchers such as Naotsugu Isshiki, Shinji Moriya, fktβs, Paveletic and Miwa have now combined the advantages of internal combustion with the advantages of the Stirling process. Briefly called "ICSE" (Internal Combustion Stirling Engine) procedure.

The results have so far been disappointing, they should be significantly improved by the process described as the ^"new method.

Fig. 2 (TS diagram) schematically shows the solution: An exhaust gas-air mixture goes through a cycle from state 1 to 2, 3,, 5, 6 to 1. A counter-current cooling brings the exhaust gas-air mixture from state 6 to state 1. Between 1 and 2, a fraction of the circulating gas quantity is removed and through the same amount of combustion air replaced.

From 2 to 3 the exhaust air mixture is compressed, from 3 to - \ from a heater. memory (regenerator) preheated.

From - \ to 5, the fuel is added and burned during work performance and expansion.

The heat accumulator (regenerator) is recharged from 5 to 6.

Then the cycle starts again.

The previously known geworde ^no n A process for the conversion of heat into force after de .. Jtirling principle with internal combustion have the drawback that an attempt was made to compress from 6 to 3 isothermally, at the limit, large infinitely slowly, or with infinitely Exchange area.

Furthermore, most processes work with stoichiometric air quantities or small excess air numbers.

The result is extremely high end temperatures, which require exotic materials, and a "dirty" exhaust gas analysis for NOx.

On the other hand, if one wants to enter and exit with a multiple excess of air between 1 and 2 and the entire amount of reaction gas, the valve cross sections are much too large or there is too much residual energy in the exhaust gas. The heat-power process according to the invention avoids these disadvantages in that counter-flow or cross-flow cooling with acceptable areas or temperature differences is placed before the adiabatic or polytropic compression from 2 to 3.

Then the C0 ₂ content of the exhaust gases is extremely high, the exhaust gas temperature is low and thus the exhaust gas loss is also very small.

The method includes a deliberate constant exhaust gas recirculation up to the ignition limit, so that the NOx content remains a minimum, with full utilization of the thermodynamic gradient.

The proposed method is an ecological optimization of efficiency, exhaust gas analysis and noise.

To clarify, use a concrete numerical value for an exhaust gas-air mixture with natural gas (or heating oil), with on average e.g. 100 ° C lower and 1200 ° C upper temperature, 40-50% practical thermodynamic efficiency, CO values of 0-10 ppm and NOx values of 150 ppm can be achieved without catalyst at the correct speeds and combustion chamber geometries.

The noise level of the process is 0-50 decibels ^* without a sound insulation hood.

The low-temperature heat still has the level of 60-90 degrees with approx. 40-50% energy which is interesting for heating purposes, the exhaust gas loss and the machine space losses are below 10%. The low final pressure at 7-8 bar is particularly interesting, so that the hot parts can be built with tolerable materials.

The following is used to explain the practical implementation of the method described in FIG. 2:

A piston (1) with crank drive and usually without oil lubrication works in a cylinder (2). It compresses the enclosed air / exhaust gas mixture when going up.

Then the displacer (3) shifts the compressed air / exhaust gas mixture via the check valve (4) and the regenerator (5) to the hot side of the system. On whether ^r ~ s exit from the regenerator is supplied to the fuel (gas or oil).

Now the displacer (3) and piston (1) move downwards in the same sense and convert the work of expansion into mechanical work.

If the piston (1) is then in the bottom dead center area, the displacer (3) is moved upwards, the hot gas is displaced into the work space via the regenerator (5) and the cooler (6). The cycle then begins again.

Between the end of the last shift and the start of the new compression, the exhaust gas valve (11) is opened and with the air metering device (9) with inlet valve (12) a quantity of fresh combustion air precisely assigned to the fuel metering device (10) is inserted.

To start the system, the hot part of the system can be brought to ignition and working temperature via heating device (8). In order to work out the advantages of the invention more clearly, as already mentioned, can be seen in FIGS. 1 and 2 (TS diagram).

Fig.l shows in the arrow diagram a Stirling process with 100 ° C lower and 1200 ° C upper temperature. The oval curve is the real process that normally actually takes place.

Such a process would have a relatively high degree of efficiency, but either extremely large heating surfaces, exotic working media, an extremely hot fire and / or very high filling pressures.

2 shows the desired thermodynamic course of the method according to the invention with internal combustion:

From working point 2 with e.g. 50 ° C and 1 bar gas condition, compress to operating point 3 (e.g. 120 ° C and 2 bar pressure).

Then move from 3 to 4 (e.g. 1200 ° C, then controlled combustion and expansion with end point 5 (e.g. 1300 ° C) and move to 6 (e.g. approx. 250 ° C).

Depending on the choice of regenerator surfaces, structure, pressure loss and mass, the thermodynamic optimum can be selected for every speed and desired power density. e.g. 10, 20 or 50 k temperature difference for the regenerator and not approx. 100 k as in the example.

The elementary calculation in the order of magnitude of the example results in a feed and discharge of air and exhaust gas with approximately 10% of the process gas quantity per cycle. The advantages of the described method compared to the pure diesel / Otto or pure Stirling principle result directly from the course of the process _-, _

- Since the combustion takes place only in the hot part, there are no molecular fragments and, with the correct dimensions, almost complete combustion.

- Since no lubricating oil residues can get into the hot part, the usual oil change problem on internal combustion engines is eliminated.

- Depending on the choice of fresh air fed in per cycle, there is a strong NOx suppression up to the limit of ignitability, a constant exhaust gas recirculation, since many molecules pass through the cycle several times.

The relatively low combustion temperature also has a strong NOx-preventing effect. Here the NOx can be reduced to a minimum shortly before the CO increases.

- Due to the large temperature gradient, efficiencies of over 50% can be achieved on the other shaft, and this with optimum exhaust gas analysis at the same time.

- Since the working piston is in the cold area, dry running with straight guidance and thus low-oil or oil-free operation can be designed.

- The valves are also unproblematic in the cold area.

- The process continues to work extremely quietly since there are no explosions.

- The maximum final pressure at operating point 4 is very modest in the example, so the requirements on the material are considerably lower than in the case of pure stirring, diesel or Otto processes. - The price for the many advantages is to be paid with a moderate speed, a relatively large displacement per kW and a relatively high power to weight ratio

The environmental emergency, which is already officially documented in all statistics, justifies and justifies the necessary effort.

The ecological age ahead requires completely new construction principles.

Since the main purpose of use is initially stationary systems, the higher power-to-weight ratio of the machine is not critical.

However, light snow-running systems based on the new principle can also be implemented, however the quality of combustion decreases with increasing speed.

This method can also be implemented with any number of cylinders, so that the flywheel weights and the non-uniformity of the movement improve with higher outputs.

Claims

Claims: 1.) Process for converting heat into power according to the Stirling principle with internal combustion, characterized in that an exhaust gas / air mixture according to FIG. 2 is cooled from (6) to (1) in countercurrent or crossflow, between ( 1) and (2) emits a fraction of exhaust gas and the same amount of fresh air is added, compressed from (2) to (3), stored heat from a regenerator from (3) to (4), from (4) to (5) Fuel is added during expansion and work performance and from (5) to (6) gives heat to the regenerator. 2.) Method according to claim 1, characterized in that according to Figure 3 to force the Gegeπstro it close the valves (4) when the displacer (3) goes up. 3.) Method according to claim l, characterized in that the displacer (3) is controlled directly via a cam disk of the main shaft. 4.) Method according to claim 1, characterized in that the outlet valve (11) and inlet valve (12) with cam disk of the main shaft are controlled directly or via rocker arm. 5.) Method according to claim 1, characterized in that the fuel metering (10) and the Luft¬ amount metering (9) are adjustable, positively controlled, for regulating speed and power. 6.) Method according to claim 1, characterized gekeπnzeichent that the cooling of Fig.2 between (6) and (1) or equivalent in Fig. (6) is omitted and the exhaust gas at point (6) Fig.2 is released to the outside .