GB2233037A

GB2233037A - Coanda pump powered by engine exhaust gases

Info

Publication number: GB2233037A
Application number: GB8926709A
Authority: GB
Inventors: James David Coleman; Anthony Gregory Smith; Michael Kopmells
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-11-26
Filing date: 1989-11-27
Publication date: 1991-01-02
Anticipated expiration: 2009-11-27
Also published as: GB2233037B; GB8926709D0

Abstract

The flow of exhaust gas over the surface 11, from the surrounding chamber, and through the diffuser 12 induces the flow of air through an inlet 15 to mix with the exhaust gas. Part of the mixed flow may be recirculated through the duct 14. Additional fluids, e.g. fuel and water, may be induced by the exhaust gas flow. The surfaces over which fluid flows may be coated with precious metal catalyst for exhaust gas treatment. The flows of exhaust gas and air may be controlled dependent upon an engine throttle control or management system. The induced air flow may provide engine cooling and the mixed gas may be used for surface heating, e.g. de-icing. <IMAGE>

Description

COMBUSTION ENGINES This invention relates to combustion engines, particularly to engines including Coanda effect devices driven by engine exhaust gases for the purpose of entrainment of a secondary fluid, which may be air.

As a by-product of their operation, engines, which might be operating on the internal combustion principle, produce excess heat and exhaust gases.

The excessive heat of such engines is removed by a cooling system. This usually involves passing a cooler ambient fluid over a surface where heat transfer can occur. Sometimes air is passed directly over the engine, through a cowling.

Alternatively, a fluid such as water, is used for direct cooling of the engine parts and heat is extracted from the water in a heat exchanger. Many water-cooled systems make use of a fan, driven either by an electric motor which may be designed to cut in when the temperature of the coolant fluid exceeds a certain level, or by a fan belt which is in turn driven by the engine 5 rotational motion. Both of these methods make demands upon the engines power which are additional to the main driving power that is required. The belt driven cooling fan is reliable but takes energy from the engine whether or not it is required and affects cooling even when this may not be desirable. The electrically driven cutin fan only uses power when required, but can be unreliable.

In addition, some cooling systems make use of engine oil as a coolant. This requires the use of an oil pump and many complex seals to prevent leakage of the oil. It has been found advantageous in certain cases to replace the oil cooling by drawing ambient air through the engine cooling passages.

As discussed above, the second by-product is that of an exhaust gas flow. Conventional exhaust systems found typically on road vehicles perform the following functions: 1) They duct the gases to a convenient point of discharge.

2) They silence the otherwise noisy engine.

3) They create a desirable back-pressure on the exhaust ports to overcome the effect of valve overlap.

The exhaust apparatus in most systems does not "process the exhaust gases, it merely takes them away to discharge through one or more box-type silencers.

There is a considerable amount of energy in the exhaust gases, so much so in fact, that they are used in some engines to drive a turbocharger. This turbine device extracts the energy and uses it to charge the inlet gases to the engine.

The pollution of the environment with noxious exhaust gases has been of concern for some time. More recently, pressure has been exerted on motor vehicle manufacturers to "clean up" internal combustion engine emissions. The government now intends that from 1993 all new vehicles will be fitted with a catalytic convertor.

This requirement will affect Britain's eighteen million motorists who will be required to pay for the convertor to be installed.

In general, the internal combustion generated products are considered to take the following form.

a) Smoke - visible to the naked eye b) Carbon monoxide c) Carbon dioxide d) Unburned hydrocarbons e) sulphur oxides f) nitrogen oxides Virtually all of these pollutants have a harmful effect on the ecosystem. It is said that in the U.K., 40% of nitrous oxide emission is from motor vehicles. One final pollutant is noise.

Particulate emission, smoke, is now receiving a lot of attention. Diesel engines are considered to be especially prone to soot emission. Impending exhaust emission laws in Europe and the USA have prompted motor manufacturers to investigate particulate trap filters. These are used to reduce the particulate content in the exhaust flow but are prone to blocking. Some designs use a system whereby twin traps are required. In systems of this nature when one trap becomes excessively full, the other trap comes into action by means of a switching process.

New traps are being developed in order to make the cleansing process a more continuous one. It is understood that these use heated air to burn off the clogging materials before they reach the trap. Existing systems appear to use a convenient source of air on the vehicle, such as an air brake reservoir.

The catalytic convertor is at present the only device which can cut noxious exhaust emissions to a reasonable extent.

Present full three way convertors can cut carbon dioxide levels by nearly 20% and change most of the other harmful gases into harmless water and nitrogen. The noxious gases are forced to pass through the ceramic honeycomb structure of the convertor coated with a thin layer of platinum and other precious metals. The convertors can only be used with unleaded fuel and can become blocked by particulate material.

Research has shown that the performance of catalytic convertors can be improved by injection of air such that the catalysis occurs in an oxidising environment. At present, systems which make use of this principle, require air to be supplied by an air pump, which draws energy from the engine.

A draw back with existing catalytic convertors, whether or not they use air injection, is that they reduce engine power by about 10%. This means that more fuel is burnt achieving the same performance.

It is essential that pollution from combustion engines is reduced. At present the engine performance degrading catalytic convertor appears to be the only solution on offer.

Coanda entrainment devices are used when it is desired to entrain one fluid with another. Typically, a high pressure primary fluid is fed through the Coanda device. By means of the Coanda effect this is able to induce a secondary flow.

The purpose of this invention is to apply the use of Coanda effect devices to the exhaust / cooling / emission control system of a combustion engine. In this invention it is envisaged that all or part of the high energy exhaust gases will be the primary flow of a device which embodies the Coanda effect. A secondary flow, which may be multi-phase, will be entrained by the unit.

It is envisaged that the secondary flow will principally be air. It may however be advantageous to induce more fuel, a liquid such as water or another fluid.

A combustion engine, including a Coanda effect device may offer one or more of the following benefits: a) Generation of a flow of ambient air for use in engine cooling. The air may be drawn through an engine, over a heated engine surface or through a heat exchanger containing a sealed engine coolant.

b) A reduction in the noise emission of the exhaust flow brought about by the action of the shear layers in the Coanda flow and the shielding effect of the nozzle and possibly a further tertiary flow.

c) A reduction of certain noxious pollutants brought about by the mixing between the primary exhaust flow and the entrained fluid, particularly at the initially high temperature of the exhaust gases. Coanda devices are renowned for their ability to achieve excellent mixing between the primary and secondary flows. It is envisaged that the detrimental contents of the exhaust gases may be reduced by this mixing process.

d) It is recognised that Catalytic conversion takes place more effectively in an oxidising atmosphere and some systems make use of either engine management systems to alter fuel/air mixture ratios or an external pump to inject atmospheric air which may have been pre-heated.

It is hoped that the system will allow injection of variable quantities of air, which may have been pre heated, as required to affect this purpose. The pre heating of the entrained air could occur electrically or by means of a heat exchanger which could be part of the engine's cooling system.

e) For improvement of existing particulate traps, it is to be hoped that an external source of compressed air, could become surplus to requirement. Clean air could be drawn through the system and heated by the exhaust gases during entrainment. If necessary, the air could be pre heated in a heat exchanger before mixing with the exhaust gases. In this way a near continuous cleaning mode might become possible.

f) A convenient means by which a suction force can be generated whilst the engine is operating. Some road going tankers require the on-board vessel to be evacuated. It may be desirable to use the available suction force of the Coanda device to achieve this evacuation.

The Coanda device could be placed very near to the exhaust ports on the internal combustion engine, to make use of as much of the surplus energy as possible which is normally thrown away. It is envisaged that the surfaces of the Coanda device could possibly be coated in the same precious metals as those found in the present catalytic convertors.

In the present designs of convertors, it is necessary to force the gases through a honeycomb of material coated with precious metals for the conversion to take place. One inherent feature of a Coanda device is that the primary flow will attach very closely to the curved "Coanda" surface. The turbulence in the primary, exhaust, flow will be very high.

Surface reaction may be enhanced. The use of small multiple Coanda effect devices could maximise surface area for catalysis. The exhaust system could become shorter, more robust, and lightweight. This is because unlike a conventional exhaust, ducting downstream of the nozzle may not be subjected to such high pressures or temperatures.

As the nozzle operating pressure can be matched to the engine's optimum back pressure, there is potentially no deterioration of performance caused by such a device. The nozzle's ability to entrain depends upon the exhaust flow which is in turn dependent on engine speed. Thus when the engine is turning faster and therefore doing more work, the secondary flowrate could be increased which might be desirable in the cooling context. Furthermore, the back pressure could be matched to the engine performance requirements by linking the setting of the Coanda effect device to an engine control. This might be a direct throttle linkage or a full engine management control system.

If necessary, the blended exhaust flows from such a device could be blown onto surfaces to achieve heating which would not be too excessive. For example, the blown air could be used to form a de-icing system for items such as windows and lamps and aircraft carburettors One presently preferred construction according to the invention is more particularly described with reference to the accompanying drawing wherein: Figure 1 is a sectional elevation of an exhaust driven Coanda nozzle; and Figure 2 is a like view of a second form of exhaust driven Coanda nozzle.

Referring now to the drawing Figure 1, a schematic section is shown of an axisymmetric version of an exhaust powered Coanda effect nozzle which comprises three main parts; these being the exhaust supply pipe 1, the nozzle outer body 2, and the nozzle inner body 3. The high pressure, high temperature exhaust from a combustion engine flows into the settling chamber 4, formed between the outer body and the inner body.

The exhaust is accelerated as it leaves the settling chamber via the primary flow exit 5.

The primary flow of exhaust gases forms a peripheral annular jet which attaches to the Coanda surface 6. As the jet flows over this Coanda surface and into the diffuser section 7, it entrains and mixes with a secondary flow of fluid thus creating a depression at the nozzle entry 8. The depression causes further fluid or fluids to be drawn through the nozzle. The internal surfaces of the Coanda nozzle 9 could be coated with precious metals to perform some catalytic conversion of the exhaust gases. Furthermore, the flow surfaces could be heated to affect particulate burn off, and or reaction rate if desired. Flow exit occurs at 10.

Figure 2 shows another form of a Coanda nozzle. In this case, the nozzle is mounted within an external casing. In this form, it is also envisaged that some of the internal passageways may be coated with catalytic materials. Primary exhaust gases will issue from the primary flow exit 11.

According to the Coanda effect the flow will attach closely to the Coanda surface 12. Some flow will exit at 13, the remainder will recirculate into the duct 14. Entrainment of additional fluid or fluids can be achieved through 15 if desired.

Various modifications may be made within the scope of this invention. It may be preferable to use a number of nozzles as opposed to a single nozzle. The nozzle, or nozzles may be of different cross-section. For example, the nozzle may be rectangular in shape in order to fit into the available space within a vehicle. The nozzle may make use of a serrated edge at the primary flow exit in order to increase the turbulence of the primary flow and hence increase the mixing rate with the secondary flow still further. For multi-cylinder engines, the nozzle or nozzles may have more than one inlet for the exhaust supply in order to take the flow from each engine cylinder. The Coanda surface may make use of an external rather than internal profile. The Coanda device or devices may be mounted within an external casing for the purpose of ducting a tertiary flow.

Claims

Claims:

What we claim is: 1) A combustion engine having an exhaust flow and a Coanda flow device arranged to receive all or part of the exhaust flow to act as its primary flow in order to entrain a secondary flow.
2) An engine according to Claim 1 wherein the Coanda flow device comprises a hollow body which is provided with a) an annular nozzle arranged to direct the primary flow from a point adjacent one end of the hollow body to the other end thereof; b) a converging convex Coanda surface immediately downstream of said nozzle; and c) a diverging section immediately downstream of the Coanda surface, the arrangement being such that the primary flow along the Coanda surface and diverging section entrains a secondary flow.
3) An engine according to Claim 2 in which there exists a parallel mixing region between the converging convex Coanda surface and the diverging section.
4) An engine according to Claim 2 or 3 wherein the Coanda flow device has more than one outlet for the primary flow.
5) An engine according to Claim 2,3 or 4 wherein the hollow body of the Coanda flow device is of an annular crosssection.
6) An engine according to Claim 2,3 or 4 wherein the hollow body of the Coanda flow device is of a non-annular cross-section.
7) An engine according to Claim 1 in which, in use, the primary flow is directed over an external Coanda body, said body being contained within a housing such that the primary flow and entrained secondary flow are ducted within the constraints of the housing.
8) An engine according to Claim 1 in which the primary flow is made to pass over a combination of internal and external Coanda surfaces, of the types described in any of the Claims 2 to 7.
9) An engine according to Claim 1 which comprises more than one Coanda ejector of the type described in any of Claims 2 to 7.
10) An engine according to Claim 1 having means by which the primary and or secondary flows can be regulated.
11) An engine according to 10 in which the regulation is controlled by an engine management system.
12) An engine according to 10 in which the regulation is controlled by a linkage to the engine throttle control.
13) An engine according to any of the preceding claims in which all or part of the secondary flow is caused to flow through the engine's cooling system.
14) An engine according to Claim 13 in which all or part of the secondary flow effects direct cooling on the engine's surfaces.
15) An engine according to Claim 13 in which all or part of the secondary flows are passed through one or more heat exchangers.
16) An engine according to any preceding claim wherein the Coanda flow device is positioned within the exhaust system such that the mixed primary and secondary flows are made to entrain tertiary flow in such a way as to reduce noise emission from the primary flow.
17) An engine according to any preceding claim arranged to entrain secondary flows into the primary flow for the purpose of chemical pollutant reduction.
18) An engine according to any preceding claim in which a secondary flow is induced into the exhaust gas flow before the combined flow enters a Catalytic convertor.
19) An engine according to any preceding claims in which, in use, Catalytic conversion is partially or wholly brought about within the Coanda effect device.
20) An engine according to any preceding claim wherein the Coanda flow device forms part of an exhaust particle reduction system.
21) An engine according to Claim 20 having components arranged to be heated for the purpose of burning off particulate materials.
22) An engine according to any of the preceding claims wherein the Coanda flow device is arranged to cool the exhaust gases as they exit from the engine.
23) An engine according to any of the preceding claims wherein the Coanda flow device is arranged so that the combined primary and secondary flows exiting from it are made to form an aerodynamic shield around the remaining, unmixed exhaust flows.
24) An engine according to any preceding claim in which the secondary flow and or mixed primary flows from the Coanda flow device are made to flow through or around other components for the purpose of heating.
25) An engine according to any preceding claim in which the secondary flow is passed through a heat exchanger before entering the Coanda flow device, so that the secondary flow may be heated before mixing with the primary flow.
26) An engine substantially as hereinbefore described with reference to and as shown by Figure 1.
27) An engine substantially as hereinbefore described with reference to and as shown by Figure 2.
28) An exhaust assembly for an engine according to any preceding claim comprising an exhaust duct for conveying a said exhaust flow, and a Coanda flow device coupled to the duct to receive all or part of said flow as its primary flow.
29) A Coanda flow device adapted for connection to an exhaust assembly of an engine to produce an engine according to any of Claims 1-27.
30) A method of constructing an engine according to any of Claims 1-27 comprising the step of coupling a Coanda flow device to an exhaust flow duct of an engine.
31) An engine, according to any of the preceding claims in which the Coanda flow device produces a suction force as well as or instead of secondary flow.
32) A Coanda flow device which is part of the exhaust system of an engine so that all or part of the exhaust flow is made to be the primary flow in order to entrain a secondary flow.