A new combustion system of a heat-insulated natural gas engine with a pre-chamber having a throat valve

Abstract

A ceramic heat-insulated natural gas engine has been developed which incorporates a pre-chamber and a throat valve to the main chamber. Low-pressure natural gas is supplied into the pre-chamber to form fuel-rich mixtures in the pre-chamber during the intake stroke while the throat valve is closed, while natural gas and exhaust gas recirculation (EGR) gas are charged in the intake port to form a homogeneous mixture in the main chamber. Experiments showed that spontaneous ignition took place near top dead centre (TDC) in the pre-chamber immediately after the throat valve was opened, followed by homogeneous charge compression ignition (HCCI) combustion in the main chamber, featuring very fast combustion and extremely low NO_X emission. Effects of engine parameters including compression ratio, throat valve opening timing, the fuel fraction injected into the pre-chamber and the EGR ratio were investigated. It was found from the experiment that 85 per cent of the fuel supplied could be successfully burned in HCCI combustion in the main chamber being triggered by the spontaneous ignition in the pre-chamber, and the HCCI combustion could be controlled if the engine parameters mentioned above could be well optimized.