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An air-assisted direct injection system has been developed and applied to a two-stroke spark-ignited motorcycle engine of 82 c.c. displacement to reduce exhaust emissions, particularly unburnt hydrocarbons. The injection system, which induces a small amount of compressed air and metered fuel from electronic-control valve, delivers the air/fuel mixture into the cylinder. This paper shows the preliminary results of engine dynamometer tests. Also investigated are the improvement of combustion and reduction of unburnt HC emission by the use of dual spark plugs and skip injection techniques at light load engine condition.

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.

A 125c.c. motorcycle is retrofitted with catalytic converter in order to demonstrate the emission reduction technology applied to the widely used vehicles in Taiwan. The retrofitting process minimizes the vehicle modifications while maintains the engine performance characteristics and accomplishes the maximal emission reduction results. Parameters of installation locations, substrate materials, cell density, precious metal composition/loading and catalytic converter size are all investigated in the chassis dynamometer test cell. Results of the motorcycle tested in ECE40 cycle show that significant reduction in HC emission can be achieved. But the reduction of CO emission is moderately low with the catalytic converter. The exhaust smoke is also decreased to certain extent. Use of secondary air improves the conversion efficiency of HC and CO very much effectively by supplying adequate oxygen from a reed valve system.

A low-pressure air-assisted fuel injection system had been applied to a 2-stroke motorcycle to reduce the fuel consumption and emissions. This system injected atomized fuel into cylinder through a nozzle located in cylinder wall and resulted in fuel economy and emission improvements. In the ECE40 test, the average fuel consumption and hydrocarbon emission of the fuel-injected motorcycle were reduced by 27.5% and 38.3% compared to the carburetor version.