Diesel-fuelled homogeneous charge compression ignition engine with optimized premixing strategies

Abstract

The operation of a diesel-fuelled homogeneous charge compression ignition (HCCI) engine was studied in a single-cylinder, direct-injection diesel engine with regard to three key parameters: Spray penetration, time for premixing, and dilution of the premixed charge. The relationships between these parameters were clarified through spray measurements, flame imaging, and combustion analysis. The spray penetration was optimized by a small included angle to avoid wall impingement at low pressure and temperature in the cylinder. However, the hole diameter did not affect spray penetration. Sufficient time for premixing was realized by advanced injections earlier than 100 crank angle degrees (CAD) before top dead centre (BTDC) at 800 r/min. Dilution of the premixed charge to control ignition timing was investigated by adopting exhaust gas recirculation (EGR). The optimized premixing strategies of two-stage injection, with a small amount of the ignition-promoting fuel (1.5 mm3) - which was injected near TDC to assist the combustion of a premixed charge (10 mm3) - resulted in an indicated mean effective pressure of up to 250 kPa within 3 per cent fluctuation, along with a significant reduction in particle matter and nitrogen oxides emissions, while 46 per cent EGR rate was applied to the premixed charge with preheated intake air at 433 K.