Arrangement for return of exhaust gases in supercharged engines

Details Arrangement for return of exhaust gases in supercharged engines Arrangement for return of exhaust gases in supercharged engines

1997-06-05

1998-08-11

Koczo, Michael

Power plants

Fluid motor means driven by waste heat or by exhaust energy...

With supercharging means for engine

F02M 2507

Patent

active

057911460

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to an arrangement for return of exhaust gases in combustion engines.
One method for reducing releases of nitrogen oxides, NO.sub.x, is to return part of the exhaust gases to the engine before the next combustion. Part of the exhaust gases will remain in the combustion chamber after the scavenging stroke has been completed, i.e. after the exhaust valve has closed, and this feedback is called natural EGR (exhaust gas recirculation). This natural EGR is difficult to control in conventional engines without variable valve times.
In addition, a partial quantity of exhaust gases is usually returned via external EGR ducts to the inlet system of the combustion engine, thereby enabling feedback of exhaust gases to take place in a more controlled manner by means of control of an EGR valve. In certain operating situations, e.g. idling, no EGR is desired, since the engine may begin to misfire and possibly stop. On Otto engines, EGR systems have frequently come to be used for the purpose of reducing releases of nitrogen oxides, which primarily form at very high combustion temperatures.
In order to be able to return exhaust gases to the inlet side of the engine. it is necessary that the pressure on the exhaust gases be greater than the pressure on the inlet air on the inlet side of the engine. On supercharged combustion engines, particularly on supercharged diesel engines in which combustion takes place with air excess, however, the pressure on the inlet side is substantially greater than the exhaust pressure, which is obviously greatest at high engine speeds and high engine loads. This means that the pressure on the partial quantity of exhaust gases which is to be returned has first to be increased in order to make it possible for a flow of exhaust gases to be returned to the inlet side of the combustion engine even in extreme load situations.
On supercharged combustion engines it would be possible to achieve a developed flow of exhaust gases to the inlet side of the engine if the exhaust gases were returned to a point in the inlet system before the compressor stage, but this is not desirable in that the compressor would be fouled by the exhaust gases and its efficiency would also be reduced.
There are a multiplicity of different solutions for making it possible to return exhaust gases on supercharged combustion engines.
For example, U.S. Pat. No. 4,250,711 indicates a solution whereby exhaust gases are returned from the exhaust side to the inlet side after the compressor stage by means of the EGR duct connecting to the compressor diffuser entirely after the compressor blades. It also indicates that an extra compressor for the exhaust gas flow may be incorporated in the EGR duct. The disadvantage involved is that this solution for a practical and economic application makes it impossible to incorporate an exhaust gas cooler after the compressor stage, since the exhaust gas cooler would be obstructed by the returned exhaust gases and reduce its efficiency.
U.S. Pat. No. 4,231,225 indicates another solution whereby when a partial flow of exhaust gases from the engine, in this case the exhaust gases from one bank of cylinders in a V-engine. has passed through a first exhaust turbine in a first supercharger unit, it is returned to a second compressor in a second supercharger unit. New clean combustion air is compressed in the compressor stage of the first supercharger unit and remaining exhaust gases from the other cylinders of the engine pass through the exhaust turbine of the second supercharger unit. In this case the recirculating exhaust gases pass first through a turbine, thereby reducing the pressure in the exhaust gases. In that system a fixed quantity of exhaust gases is thus recirculated to the inlet side of the engine whatever the operating conditions at the time, which is to the detriment of vehicle handling during, for example, idling, since very uneven engine running may occur. In that system the controllability of the EGR flow is very bad, since the exh

REFERENCES:
patent: 4231225 (1980-11-01), Aya
patent: 4250711 (1981-02-01), Zehnder
patent: 4756285 (1988-07-01), Pischinger
Patent Abstracts of Japan, vol. 17, No. 604, M-1506, abstract of JP, A, 51-80089 (Hino Motors Ltd), 20 Jul. 1993.

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