Research on Gasoline Homogeneous Charge Induced Ignition (HCII) by Diesel in a Light-Duty Engine

摘要

Gasoline engines suffer low thermal efficiency and diesel engines have the emission problem of the trade-off between NO_x and soot emissions. Homogeneous Charge Induced Ignition (HCII) is introduced using a port injection of gasoline to form a homogeneous charge and using a direct injection of diesel fuel to ignite. HCII has the potential to achieve high thermal efficiency and low emission combustion. However, HCII combustion mode still has problems of high THC emissions at low load and high pressure rise rate at high load. In order to improve the gasoline reactivity and reduce THC emissions, double injection of diesel was applied in HCII mode. In order to reduce peak pressure rise rate (PPRR), a two-staged high-temperature heat release is achieved at suitable engine condition. The effects of HCII mode on combustion and emission characteristics are studied in a light-duty engine. The results show that HCII achieved similar or even higher thermal efficiency than conventional diesel combustion under moderate peak pressure rise rate at 0.5 MPa and 0.8 MPa indicated mean effective pressure (IMEP), with extremely low NO_x and smoke emissions. In HCII, compared with single injection of diesel, the THC and CO emissions of double injection was significantly lower, with a biggest CO reduction of 35% and with a largest THC reduction of 26%, and the combustion efficiency was improved, with a biggest increase of 2%, but the indicated thermal efficiency was slightly lower. In HCII, compared with single injection of diesel, the NO_x emissions of double injection was lower. When Start of Injection (SOI) was earlier than certain crank angle, smoke emissions of diesel single injection increased apparently. However, the smoke emissions of diesel double injection remained at a low level over the whole SOI2 sweep in HCII. In HCII, the peak pressure rise rate of diesel double injection was lower than single injection, and the combustion duration of double injection was shorter. In HCII, a two-staged high-temperature heat release rate is achieved under suitable gasoline ratio and diesel injection timing. The heat release rate was apparently divided into two peaks, the initial premixed combustion of diesel and the combustion of the ignited gasoline. Compared with conventional diesel combustion, the peak pressure rise rate of two-staged HCII was significantly reduced. The diesel injection timing can be effectively used to control the start of combustion and combustion phasing of HCII.