Internal-combustion engines – Two-cycle – Whirl through piston-controlled ports
Patent
1989-07-05
1990-05-15
Okonsky, David A.
Internal-combustion engines
Two-cycle
Whirl through piston-controlled ports
60302, F01N 328
Patent
active
049248200
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the controlling of exhaust gas emissions from internal combustion engines by the use of catalysts to convert 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 places on emissions from private cars, motor cycles and light commercial vehicles are more strict than those applicable to trucks and other heavy commercial vehicles. 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 kilometre travelled, the limits apply 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 the 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 within it to separate the oxygen from the nitrogen.
The use of catalysts in the exhaust systems of vehicle internal combustion engines is widely known and practised in the control of exhaust gas emissions. It is customary to locate the catalyst elements in the exhaust system somewhat downstream from the actual exhaust port of the cylinder or cylinders of the engine where the exhaust gases from any one cylinder or from a number of cylinders will have been subject to a degree of mixing between the time of leaving the cylinder and reaching the catalyst. Accordingly, the distribution of the various components of the exhaust gas is approaching a homogeneous mixture when presented to the catalysts.
It is known, 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 and in particular 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 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.
The above referred to SAE Paper discusses the results of an experiment carried out on a manifold injected six cylinder four stroke cycle engine, wherein the air/fuel ratio was artificially cycled at a frequency of 1 Hz and it was found that this cyclic variation of the air/fuel ratio had some detrimental effects on the NOx conversion efficiency with rich mixtures and an improvement in the conversion with lean mixtures. More importantly, it was shown that the cycling of the mixture ratio reduced the sensitivity of the conversion efficiency to air/fuel ratios so that there was a decrease in the rate of change in NOx conversion efficiency as the air/fuel ratio transits the stoichiometric value. This improvement in the conversion of NOx is shown in FIG. 2 of the accompanying drawings. The results represented in the SAE Paper were achieved by an artificial cycling of the air/fuel ratio by an adaption of the fuelling rate control programme of the fuel injection system for the purpose of the experiments. The adaption of the fuelling rate was arranged to achieve the desired air/fuel ratio in the exhaust gas immedia
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Lear Mark
Schlunke Christopher K.
Seeber Kenneth P.
Okonsky David A.
Orbital Engine Company Proprietary Limited
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