Internal-combustion engines – Two-cycle – Whirl through piston-controlled ports
Patent
1989-06-26
1990-07-03
Okonsky, David A.
Internal-combustion engines
Two-cycle
Whirl through piston-controlled ports
123302, F01N 328
Patent
active
049381784
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the controlling of exhaust gas emissions from two stroke cycle internal combustion engines by the use of catalysts to treat the undesirable components of the engine exhaust gas.
Environment protection authorities in various countries prescribe limits to the emissions in the exhaust gases of motor vehicles and usually the limits placed on emissions from private cars, motor cycles and light commercial vehicles are progressively becoming more strict. In most countries the permissible levels of emissions for automotive vehicles are stipulated on the basis of the weight of various components of the exhaust gas per mile or kilometer travelled, the limits applyomg irrespective of the weight of the vehicle or the size of the engine thereof. Accordingly, there has been a trend towards the production of small motor vehicles of relatively light weight whereby the rate of consumption of fuel can be reduced with a corresponding reduction in the weight of the various exhaust gas components generated per unit distance travelled.
The three major components of the exhaust gas which must be controlled are hydrocarbons (HC) oxides of nitrogen (NOx) and carbon monoxide (CO). NOx is normally treated by a catalyst that requires the establishment of a reducing environment to separate the oxygen from the nitrogen, whereas an oxidising atmosphere is required to treat the HC and CO.
The use of catalysts in the exhaust systems of vehicle internal combustion engines is widely known and practised in the control of exhaust emissions. It is customary to locate the catalyst in the exhaust system, somewhat downstream from the actual exhaust ports of the cylinder or cylinders of the engine, where the exhaust gases from any one cylinder or from a number of cylinders have been subject to a degree of mixing between the time of leaving the cylinder and reaching the catalyst. As a result of the mixing the distribution of the various components of the exhaust gas is approaching a homogeneous mixture when presented to the catalysts. Accordingly a catalyst system must be used that is able to treat the HC NOx and CO components of the generally homogeneous exhaust gas mixture.
It is known, as shown in SAE Paper 872098 relating to investigations by the Toyota Central Research and Development Laboratories, Inc., that the efficiency of conversion of a three-way catalyst system applied to an automotive type four stroke cycle engine is substantially dependent upon the air/fuel ratio of the exhaust gas presented to the catalyst. In particular it is known that the efficiency dramatically changes as the air/fuel ratio transits the stoichiometric ratio. As can be seen from the graph constituting FIG. 1 of the accompanying drawings, the efficiency of conversion of HC and CO increases as the air/fuel ratio of the exhaust gas increases, that is as the mixture gets leaner. In contrast, the efficiency of the conversion of NOx is high, whilst the air/fuel ratio is low, that is, with a rich exhaust gas mixture, but drops most dramatically as the air/fuel ratio passes through stoichiometric from a rich to a lean mixture.
Engines operating on the two stroke cycle have presented a substantial problem in the control of the level of exhaust emissions, particularly in engines where fuel is entrained in the air charge when it enters the engine cylinder, as part of that fuel passes unburnt through the exhaust port during the conventional scavenging process. This escape of unburnt fuel, that contributes to HC and CO in the exhaust gas, can be reduced by modern electronically controlled fuel injection systems that inject the fuel directly into the engine cylinder rather than the fuel being carried into the cylinder with the incoming air charge. However, the direct injection of the fuel does not in itself contribute significantly to the control of the generation of NOx, particularly as the rate of fuel consumption increases with the increase in size of the vehicle resulting in a corresponding increase in the level of NOx emissions when measured on a
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Lear Mark
Schlunke Christopher K.
Okonsky David A.
Orbital Engine Company Proprietary Limited
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