Abstract
The hybrid electric motorcycle (HEM), which combines an internal combustion engine and an electric motor, offers the greatest potential to reduce the exhaust emissions and energy consumption. Since the engine is the main source of emissions and fuel consumption, its efficiency is necessary to be improved. The purpose of this paper is to design a lean burn engine for HEM. A traditional 250cc spark-ignition engine was modified to be a lean burn engine by redesigning the inlet port, fuel supply system, and ignition system. A pilot inlet port was designed to enhance tumble air motion, which improved the lean combustion. The increased charge motion, enlarged gap of spark plug, and advanced spark timing enabled the engine to run leaner mixture. The experimental results showed that the lean limit of the original engine at minimum BSFC was about 16 of air-fuel-ratio. The lean limit of the modified port system was extended to 18 due to higher air motion. A HEM simulation model using Matlab/Simulink was employed to evaluate the fuel economy and exhaust emissions. The simulated results show that the fuel economy of lean burn HEM compared with the traditional motorcycle is increased by 102%. For the exhaust emissions, the CO and HC are reduced by 77.4% and 77.3%, respectively. Nevertheless, NOx emission is increased by 177%.
Keywords: Lean burn; Hybrid electric motorcycle; Spark-ignition engine; Swirl ratio.