WO1994010439A1

WO1994010439A1 - Mixing/metering unit

Info

Publication number: WO1994010439A1
Application number: PCT/NL1993/000219
Authority: WO
Inventors: Paul Eugene Cornelia Krieckaert; Servatius Alfons Maria Jaasma
Original assignee: Gentec BV
Current assignee: Gentec BV
Priority date: 1992-11-03
Filing date: 1993-10-29
Publication date: 1994-05-11
Anticipated expiration: 1995-05-03
Also published as: AU5576694A; EP0774065A1; NL9201918A; JPH08502569A; CA2146996A1

Abstract

Mixing/metering unit (2) for introducing a fluid into an intake air stream of a combustion device, which fluid vaporises on introduction. The mixing/metering device (2) comprises an annular shield (3) fitted in the intake channel (1). A slit is defined between the shield (3) and the intake channel (1), the fluid entering said slit by means of one or more introduction channels. At the downstream end the slit is provided with an opening (7) through which the fluid is able to enter the intake channel (1). An opening (9) for the ingress of air is optionally present at the upstream side.

Description

Mixing/metering unit

The present invention relates to a mixing/metering unit for introducing a fluid into an intake air stream of a combustion device, which fluid is at least partially liquid prior to introduction and at least partially vaporised following introduction, comprising an at least partially annular shield fitted in the intake channel for the air stream, the fluid being supplied via an introduction device into the slit-shaped chamber between the shield and the wall of the intake channel.

A mixing/metering unit of this type has already been disclosed in the prior art. Mixing/metering units of this type are used for diverse types of apparatus in which, for example, gas which is liquid under pressure is burned in vapour form with air. An example of an apparatus of this type is a combustion engine. In this context the aim in the prior art is to inject a fluid of said type, such as LPG, in liquid state into the intake channel. Injecting in the liquid state has the advantage that a smaller and therefore better controllable amount can be introduced per injection. However, with this arrangement problems arise because moisture present in the air freezes and leads to deposits as a result of the heat withdrawn by the vaporising fluid. Such deposits can vaporise again at a later stage, but this leads to inaccurate metering and obstruction of.the flawless functioning of the device. An attempt has been made to solve problems relating to freezing by fitting heated walls opposite injectors in the intake channel. Although heating of this type is satisfactory under certain operating conditions there remain circumstances under which freezing still occurs with all the associated disadvantages. Specifically in the case of combustion engines which are used in non-stationary applications, very rapidly fluctuating conditions prevail and under all of these conditions correct metering of the fluid must take place in order, on the one hand, to consume as little fuel as possible and, on the other hand, to comply with all current environmental requirements. The aim of the present invention is to provide a mixing/metering unit which does not have the disadvantages described above.

This aim is achieved in the case of a mixing/metering unit described above in that the introduction device is arranged in such a way that the fluid introduced into the slit-shaped gap has a component of movement perpendicular to the direction of movement of the air and the shield is open at the downstream end thereof and wherein the ratio between the surface area of the slit-shaped chamber at the downstream end thereof and the surface area of the outlet orifice of the introduction device being such that the fluid is accelerated in the slit-shaped chamber. By means of a mixing/metering unit of this type the fluid introduced is subjected to an increase in speed on issue, as a result of which it is possible to feed said fluid in a controlled manner over a larger wall surface area. This results in a larger wall surface area is available for the heat transfer, which being able to proceed more rapidly and more effectively. Moreover it is possible for a rotary motion to be imparted using the device according to the present invention. As a consequence a drop of fluid, which is not exposed to the air stream in the intake channel, is moved over a relatively large wall surface area, as a result of which heat exchange with the environment is able to take place distributed over a large surface area. By this means it is possible effectively to prevent freezing. According to an advantageous embodiment of the invention the upstream side of the shield is open for ingress of air into the slit-shaped chamber. An additional air supply of this type is important especially in the case of larger amounts of air. By this means not only is better mixing achieved but the heat transfer is also improved. The fluid will describe a spiral-shaped path.

According to a further advantageous embodiment the opening at the upstream side of the shield has a smaller surface area than the opening at the downstream side. On the one hand this is necessary because of the additional amount of vaporising fluid, which is supplied in the slit-shaped chamber, and on the other hand this is important to enable expansion of the fluid in a controlled manner.

The construction described above is preferably designed as a Laval nozzle. In this case Laval flow occurs in the slit-shaped chamber on emergence into the intake channel.

In order to achieve optimum vaporisation it is possible to provide either the channel wall or the shield with heating. Several introduction devices for fluid can be fitted in order further to increase the capacity. Optimum functioning is achieved if said devices have outlets directed in opposing directions and are actuated alternately. This results in a rapidly fluctuating flow, as a result of which an optimum quantity of fluid can be vaporised.

The invention will be explained in more detail below with the aid of an illustrative embodiment shown in the drawing. In the drawing:

Fig. 1 shows, partly in cross-section, a mixing/metering device according to the invention, fitted in an intake channel; Fig. 2 shows a section along line II-II in Fig. 1; and

Fig. 3 shows a section along line III-III in Fig. 2, regulating means also being indicated diagrammatically.

In an intake channel 1 (Fig. 1) air flows in the direction of arrow 15. A mixing/metering unit 2 is installed in said intake channel 1. Said mixing/metering unit comprises a shield 3, which is attached to wall 5 of the mixing/metering unit and to the intake channel 1 with the aid of hollow stubs 16. There is an.annular tapered chamber 4 between shield 3 and wall 5. With this arrangement the outlet orifice 7 of the annular chamber is considerably larger than the inlet orifice 9. The outlet orifice 8 of introduction device 6 for fluid opens into the annular chamber 4. Said outlet orifice 8 is indicated in the drawing perpendicular to the direction of flow 15 of the air. Wall 5 adjoins a heating channel 10, whilst a heating channel 11 is fitted in shield 3. The heating channel 11 is provided with heating medium, such as coolant, via the stubs 16. It can be seen from Fig. 2 that a second introduction device 13 is present in addition to introduction device 6. The direction of flow of. the fluid entering through said devices is indicated by arrows 18 and 17 respectively. A coolant feed 19 and coolant discharge 20 are also indicated in Fig. 2. Fig. 3 shows lines 21 and 22 which are connected to a control valve 14, which is shown diagrammatically and is controlled by an electric lead 23, in a manner which is not shown in more detail, in order to supply fluid originating from supply line 24 alternately to introduction device 6 or 13. The device described above functions as follows:

When there is a prevailing air flow from orifice 9 to orifice 7 fluid, such as LPG which is in vapour form, is injected into the slit-shaped chamber 4. With this arrangement the surface area of the orifice 8 of the introduction device 6 is dimensioned with respect to the surface area of the outlet orifice 7 in such a way that a jet flow results extending spirally in the downstream direction. As a result of the so-called "Laval" effect the emerging fluid will be accelerated, so that the time available for heat transfer can be reduced, or more heat can be transferred within a given time. Said jet flow consists of the vaporising fluid. Said fluid will move over a relatively large surface area of the wall of shield 3 or the wall 5 of the intake channel. Because both walls are heated, optimum vaporisation of the fluid will be able to take place without there being a risk of deposition of the moisture particles frozen in the air. In Fig. 2 the spiral flow for introduction device 6 is shown by means of arrow 17. An alternating flow of fluid through introduction device 6 and introduction device 13 can be achieved with the aid of control valve 14. As can be seen from arrows 17 and 18, the fluid jets generated in this way are in opposite directions.

It has been found that an appreciably increased fluid discharge speed can be achieved using the mixing/metering unit according to the invention. Whereas a value of 60 m/s was customary in the prior art, a value of 200 m/s and more can now be obtained. As a result of the large heat exchange surface area, it is also possible to extract a very large amount of heat from the heating medium. Values of 2 kwh have been achieved in tests. The mixing/metering unit can react particularly quickly to fluctuating conditions, which is particularly important under non-stationary conditions. With the construction now proposed it is always guaranteed that the fluid reaches a heated wall. This is in contrast to the prior art, where a fluid jet was injected towards an opposite wall but in the case of high air speeds never reached said wall, with the result that problems still arose with the moisture present in the air.

Although the invention has been described above with reference to a preferred embodiment, and more particularly with respect to the use of LPG in an internal combustion engine, it must be understood that a mixing/metering unit of this type can be of a different design depending on the specific application. Thus, it is possible to use the mixing/metering unit for burners and similar installations. The sole important factor is that, using the construction now proposed, it is possible, by rapid reaction to fluctuating conditions to be able to extract a large amount of heat within a relatively short time.

Claims

1. Mixing/metering unit (2) for introducing a fluid into an intake air stream of a combustion device, which fluid is at least partially liquid prior to introduction and at least partially vaporised following introduction, comprising an at least partially annular shield (3) fitted in the intake channel (1) for the air stream, the fluid being supplied via an introduction device (6) into the slit-shaped chamber (4) between the shield and the wall (5) of the intake channel, characterised in that the introduction device (6) is arranged in such a way that the fluid introduced into the slit-shaped chamber has a component of movement to the direction of movement of the air and the shield is open (7) at the downstream end thereof and wherein the ratio between the surface area of the slit-shaped chamber at the downstream end thereof and the surface area of the outlet orifice (8) of the introduction device (6) being such that the fluid is accelerated in the slit-shaped chamber.

2. Mixing/metering unit according to Claim 1, wherein the shield is open at the upstream side (9) for ingress of air into the slit-shaped chamber.

3. Mixing/metering unit according to one of the preceding claims, wherein the surface area of the opening (9) at the upstream side of the shield is smaller than at the downstream side.

4. Mixing/metering unit according to one of the preceding claims, wherein the intake channel and the shield are designed as a Laval nozzle.

5. Mixing/metering unit according to one of the preceding claims, wherein the intake channel is provided with heating means (10) at the location of the shield.

6. Mixing/metering unit according to one of the preceding claims, wherein the shield is provided with heating means (11).

7. Mixing/metering device wherein at least two introduction devices (6, 13) for fluid are present having outlets facing in opposite directions.

8. Mixing/metering device according to Claim 7, wherein means (14) are present for alternately supplying fluid to the one and the other introduction device.