Design and control of semi-direct injection spark ignition engine fuelled by LPG

摘要

This paper designs a lean-burn system and its control strategies to retrofit the motorcycle engine as a semi-direct injection (SDI) engine. The lean-burn system of the SDI engine consists of a high-swirl charge, fuel injection during intake-valve opening, and liquefied petroleum gas (LPG) as the fuel. The high-swirl charge motion is generated by the new intake port with a controllable plate which is designed using the computational fluid dynamics software. The lean limit is therefore extended due to the stratified charge by higher in-cylinder swirl motion. By controlling the controllable plate, the SDI engine can be operated in stratified mode with leaner air-fuel ratio (AFR) at lower load and engine speed. The SDI engine can be switched to homogeneous mode with stoichiometric AFR for higher load and engine speed. Therefore, the proposed control strategies consist of an engine management system, adaptive intake manifold pressure control, adaptive torque control in stratified mode, adaptive torque control in homogeneous mode, and switching strategies for switching between stratified and homogeneous modes. The SDI engine and its control strategies are verified with the motorcycle test on a chassis dynamometer. The tests including driving cycle and constant speed test are executed to investigate the fuel economy of SDI engine as compared with original engine. The raw emissions of idle operation between SDI and original engines are investigated as well. Experimental results show that the SDI engine can reduce the exhaust emissions and fuel consumption as compared with original engine.