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In year 2000, Taiwan EPA will implement a regulation for a 2% of mandatory sales of electric scooters to reduce the motorcycle emission. In order to cope with this regulation, Industrial Technology Research Institute (ITRI) and local motorcycle makers have carried out an electric scooter development which involves developing from the electric propulsion system development to the prototyping scooter to run a series fleet tests. By installing the lead-acid battery into the scooter, the maximum speed can be reached to 50 km per hour, the cruise mileage per charging is 60 km. In addition to these, the preliminary test results show that the scooter can satisfy most of the target customers. This article will describe the development of the zero emission scooter from the electric propulsion system to a small scale of fleet test.

Five systems, fuel injection, ignition modulation, intake port flow control, exhaust after-treatment, and electric propulsion systems, are discussed here in terms of engine design modifications and new systems retrofitted to the motorcycle to reduce the exhaust emission. A fuel injection system has been implemented to a 125cc air-cool four-stroke engine, and the results show that the improvement on the fuel economy, reduction of emission on HC and CO, and the fuel economy are 20%, 68%, and 10% respectively. By implementing the electrical ignition system into the target engine, the fuel economy and emission have slightly improved. The application of the inlet air flow control to a target engine also obtains 75% on CO reduction. The effectiveness of the exhaust after-treatment on a 80cc 2-stroke engine has demonstrated that the emission can be reduced up to 75%.

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.

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.