1995-09-01

A Review of Technological Approaches for Reducing Exhaust Emissions from Two-Stroke Cycle Engine with In-Cylinder Injection System 951775

From the investigations carried out in the two-stroke cycle engine with in-cylinder injection system, it was found that the level of hydrocarbon emissions from the engine was still too high if compared to that of an ordinary four-stroke cycle engine. For such high level of hydrocarbon emissions, it could be identified as coming from the mixture misfiring during the combustion process rather than the mixture short-circuiting during the scavenging process. The reasons for inducing the occurrence of mixture misfiring were also under investigation and could be further classified into five major categories: poor atomization of fuel spray, excessive amount of residual gas, instability of in-cylinder air flow, wall-wetting of the injected fuel spray and phenomena of secondary fuel injection. To overcome the above problems, respective new approaches have been therefore developed. According to the experimental investigation, performed at ITRI, for assessing the effects of these technological approaches, the following statements could be drawn: (a) an air-assisted fuel injection system is to improve the fuel atomization; (b) the approach of skip injection control could effectively resolve the problem of mixture misfiring at idling, which is originally due to the existence of the excessive amount of residual gas within the cylinder; (c) through the control of the in-cylinder air flow by using a exhaust charge control valve, the irregularity of combustion could be substantially improved through the light load range; (d) increasing the temperature of the combustion chamber seems to be a necessary technology approach in order to assist the evaporation of wall-wetted fuel in the light load range; (e) while the design modification of injection nozzle is to resolve the problem of the secondary injection which is usually associated with the air-assisted injection system, especially at higher loads.

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