GB2025517A - Petrol engine with steam injection - Google Patents

Abstract

A carburettor 5 is connected through pipe means 7 to the inlet port of the engine and means are provided for introducing steam into the pipe means. In operation, the engine is started on an air/petrol mixture from the carburettor and, while the engine is running, steam is introduced between the carburettor and the inlet port of the engine to mix with the air/petrol mixture entering the inlet port. Water is preheated in a pipe 17 wrapped around exhaust pipe 15 and is converted into steam in a boiler 13 heated by unspecified means. The amount of water is up to 40% by weight of the amount of fuel. <IMAGE>

Description

SPECIFICATION Petrol engine and a method of operation thereof This invention relates to petrol engines and to a method of operating the engines to bring about a reduction in some of the noxious gases present in the exhaust.

A long-term development programme of petrol engines has enabled the performance and fuel economy of the engine to be increased particularly by the use of higher compression ratios. The high compression ratios have however meant that, to avoid knocking in the engine, it has been necessary to introduce additives into the petrol. One of the most important additives which reduces knocking is tetraethyl lead. The use of this material has meant that pollution of the environment may result and various studies have been made concerning pollution and exhaust emissions from petrol engines.

The emissions from petrol engines consist largely of unburnt hydrocarbons, carbon monoxide, oxides of nitrogen (now), oxides of sulphur and lead compounds. While carbon monoxide is itself toxic, the oxides of nitrogen and the unburnt hydrocarbons are converted fairly rapidly in sunny conditions to various substances which cause eye irritation and respiration problems. When lead alkyls are added to petrol, organic halogen compounds are also added and the lead is present in the combustion chiefly as an aerosol containing inorganic salts, for example the chlorobromide. Not only are lead compounds toxic to human beings but they also have a very harmful effect on various catalytic devices developed for the conversion of CO and unburnt hydrocarbons in exhaust gases to harmless CO2 and water.

It is desirable therefore that ways should be developed of avoiding the use of leaded petrol.

Over the years various proposals for the use of water as an additive to the fuel/air mixture fed to petrol engines have been put forward.

In fact, during the Second World War, methanol/water mixtures were used in high performance aircraft engines, with the object of permitting higher knock-limited overall compression ratio for a given grade of fuel.

According to a first aspect of the present invention, in a method of operating a petrol engine, the operation of the engine is started on an air/petrol mixture from a carburettor and, while the engine is running, steam is introduced between the carburettor and the inlet port of the engine to mix with the air/stroke petrol mixture entering the inlet port.

The mass ratio of water injected to petrol used (W/F) may be up to 40%, although between 20 and 35% is a suitable proportion.

It has been found that, when the steam is being mixed with the air/petrol mixture, a reduction in NOX and CO in the exhaust gases from the engine is obtained.

According to a second aspect of the present invention, a petrol engine has a carburettor connected through pipe means to the inlet port of the engine and means for introducing steam into the pipe means.

The steam may be generated in a boiler associated with the exhaust pipe of the engine, such that water supplied to the boiler is converted to steam by heat from the exhaust pipe.

In order that the invention may be more readily understood it will now be described, by way of example only, with reference to Fig.

1 of the accompanying drawings which is a diagrammatic view of a petrol engine in accordance with the present invention.

A multi-cylinder petrol engine 1 has an inlet manifold 3 connecting the inlet ports of the cylinders. A carburettor 5 is connected to the inlet manifold through a pipe 7. The pipe 7 has a further pipe 9 leading in to it and this pipe 9 is connected through a valve 11 to a boiler 13. The exhaust pipe 15 of the engine has a tube 1 7 wrapped around part of it and the tube is connected at one end to a water tank (not shown) and at the other end to the boiler 13.

In use, the engine is started with the valve means 11 closed and a petrol/air mixture is fed in the usual way from the carburettor into the engine by way of the inlet manifold 3.

The waste gases from the engine are passed to the atmosphere through the exhaust pipe 1 5. The heat developed by the exhaust gases heats water circulating through the tube 1 7 and the temperature of the exhaust gases may be sufficient to convert the water into steam, in which case the steam can be supplied directly to the inlet side of the valve 11.

Usually however the water supplied to the tube 1 7 is heated in the tube and it then passes to the boiler 1 3 where it is converted into steam by some heating means (not shown). When a quantity of steam has been generated, the valve 11 is opened to introduce this steam into the pipe 7 between the carburettor and the inlet manifold so that the steam mixes with the petrol/air mixture and is drawn into the engine. The ratio of the steam to the petrol is controlled by the valve means 11.

Fig. 2 of the accompanying drawings shows in graphical form the results of tests carried out on such an engine with a substantially constant engine speed of 3000 r.p.m. with various proportions of steam introduced downstream of the carburettor.

It can be seen that, with a 14% water/fuel mass ratio, there is a reduction of 1 1% in NOx, a 16% decrease in CO and very slight changes in brake horsepower and brake specific fuel consumption (B.S.F.C.).

Higher W/F ratios, for examples about 37%, lead to a 30% decrease in NOx, a 33% decrease in CO but there was a 6% increase in HC. The exhaust temperature ET curve followed the same pattern as the HC curve.

It was found that with a 37% W/F ratio, there was a drop of about 5% in the maximum pressure inside the combustion chamber.

Fig. 3 of the accompanying drawings shows in graphical form the effect of varying the W/F mass ratio on a petrol engine operating at a constant speed of 2500 r.p.m. For example, it can be seen that at a 27% W/F ratio, there is a 40% decrease in NOX, an 8% decrease in CO and only a 1.2% decrease in brake horsepower and a 0.4% decrease in the B.S.F.C. By increasing the W/F ratio to 41%, the NOX was decreased by 47% and the CO by 10%. There was a drop of 3% in the maximum pressure at 14% W/F ratio and 11% drop in pressure at 41 % W/F ratio.

Fig. 4 shows in a similar manner the results of tests carried out on a petrol engine operating at a constant speed of 2000 r.p.m. while the W/F ratio was adjusted. With a W/F ratio of 34%, there resulted a 2% decrease in B.S.F.C., a 34% decrease in NOx, 13% decrease in CO and a 6% increase in HC.

It can be seen therefore that, by injecting steam into the inlet manifold of the engine, it can be an effective way of controlling the emission of nitric oxides from petrol engines.

The experimental results which have been carried out show that by injecting up to 40% of water resulted in a 30 to 50% reduction in nitric oxide without appreciable loss in brake horsepower. The dissociation of the injected water led to a 10 to 20% decrease in CO.

The reduction in combustion temperature due to water injection might have resulted in a decrease in the dissociation of combustion products. The efficiency of the expansion process is slightly improved and the fuel consumption is reduced.

Water injection has a great retarding influence on flame propagation for lean mixtures but under rich mixture conditions a slight increase in flame speed was observed.

With the engine running using unleaded petrol, water injection served as a very effective diluent for inhibiting detonation. This is partly because of the inter-cooling it provides and partly because of the influence of steam as an anti-detonant.

As shown in Figs. 2, 3 and 4, an increase in the W/F mass ratio brings about a rise in the engine exhaust temperature (E.T.).

Claims (9)

1. A method of operating a petrol engine, in which operation of the engine is started on an air/petrol mixture from a carburettor and, while the engine is running, steam is introduced between the carburettor and the inlet port of the engine to mix with the air/petrol mixture entering the inlet port.

2. A method of operating a petrol engine as claimed in claim 1, in which the mass ratio of water to petrol entering the inlet port is up to 40%.

3. A method of operating a petrol engine as claimed in claim 2, in which the mass ratio of water to petrol entering the inlet port is between 20 and 35%.

4. A method of operating a petrol engine as claimed in any preceding claim, wherein the steam is formed using heat from the exhaust pipe of the engine.

5. A petrol engine having a carburettor connected through pipe means to the inlet port of the engine and means for introducing steam into the pipe means.

6. A petrol engine as claimed in claim 5, in which the engine has a pluraiity of cylinders and the pipe means includes an inlet manifold to the cylinders.

7. A petrol engine as claimed in claim 5 or 6, wherein the steam is generated in a boiler associated with the exhaust pipe of the engine such that water supplied to the boiler is converted to steam by heat from the exhaust pipe.

8. A petrol engine as claimed in claim 5 or 6, in which the steam is generated in a boiler fed with water which is preheated in a heater associated with the exhaust pipe of the engine.

9. A petrol engine substantially as hereinbefore described and operated with reference to the accompanying drawings.