Improvement of Exhaust Emissions from a Two-Stroke Engine by Direct Injection System

The in-cylinder direct-injection systems have been developed and incorporated in the small two-stroke motorcycle engines for the purpose of reducing the HC emissions. The fuel systems under assessment include the solid-fuel cylinder-wall, air-assisted cylinder-wall and air-assisted cylinder-head injection systems. Through the chassis dynamometer tests carried out, these injection systems were investigated and compared. The results show that adopting the injection approach could achieve significantly lower HC emissions than the carburetor version of the same engine. The maximum reduction in HC emissions was accomplished by air-assisted cylinder-head injection, and the reduction percentage was around 46%. However, it was also found that, due to the occurring of the irregular combustion at light load, very high engine-out HC emissions still existed in spite of the adopted injection type. To improve that, a skip-injection control strategy at idling was then developed. The test results show that the engine-out HC emissions could be further reduced to 1.6 g/km if the cylinder-head injection with skip-injection control is used.