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Significant advancements have been made in recent years in the development of combustion system for spark-ignition direct-injection engine (SIDI) engine, which have resulted in fuel economy saving, low exhaust emission and a significant power advantage under homogeneous fuel operation, compared to equivalent PFI (Port Fuel Injection) engines. Key challenge for small-displacement SIDI engine, which has short path lengths between the injector and piston and is therefore prone to increase wall wetting, is minimizing or eliminating the amount of wall wetting to reduce smoke emission. A side-injection system also requires sufficient spray penetration to fully transport fuel to the centrally mounted spark plug at the desired injection timing event.

We have developed a small-displacement gasoline direct-injection engine (1.3L). Gasoline direct-injection engines rely on ultra-lean stratified combustion to deliver significantly better fuel economy, and are already used in many practical applications. When gasoline direct-injection is applied to a small-displacement engine, however, the amount of wall wetting of fuel on the piston surface will increase because the traveled length of the fuel spray is short. This may result in problems such as smoke production, high emissions of unburned HC, and poor combustion efficiency.

It is very important for the control of particulate emissions in diesel engines to reduce oil consumption. In order to control oil consumption in diesel engines, the mechanism by which sliding surface profiles of piston top rings are changed during endurance testing and the effect of the profiles on oil consumption were determined. The results obtained indicate that oil consumption depends largely upon the ratio of barrel face drop (e) to effective sliding surface width(B) of top ring profiles after endurance testing. The results also indicate that when the e/B is less than 6 /1000, oil consumption increases greatly. A technique is proposed for reducing oil consumption by controlling the e/B ratio through optimizing the top ring design.