Search Results

In order to enhance the thermal efficiency of gasoline engines, a combustion mode namely Homogeneous Charge Induced Ignition (HCII) was introduced and examined in this paper. Port-injected gasoline was used as the main fuel and formed a homogeneous charge in the cylinder. Diesel was used as the pilot fuel, directly injected into the cylinder, and self-ignited and this induced the ignition of the premixed gasoline-air charge. The images of HCII combustion process were taken on an optical engine through a high-speed CMOS camera. The multi-point induced ignition phenomena were observed and the parameters like flame luminance, ignition delay and combustion duration were analyzed by image analysis. The result shows that as the gasoline/diesel ratio increases with a fixed low pilot amount, the ignition delay increases, the initial ignition area extends from the center towards the periphery of the combustion chamber, and the combustion velocity increased.

Gasoline Direct Injection (GDI) engines developed at nineties of the twentieth century can greatly improve the fuel economy. But the combustion chamber design and mixture control of the engines are very complex compared with Port Fuel Injection (PFI) gasoline engines. A two-stage gasoline direct injection (TSGDI) combustion system is developed and aimed to solve the problem of the complexity. Two-stage fuel injection and flexible injection timings are adopted as main means to form reasonable stratified mixture in the cylinder. A simple combustion chamber and helical intake port are designed to assist the mixture's stable combustion, which reduces the difficulties of the combustion system design. Systematical simulation and experimental studies of the effects of injection strategies such as different first,second injection timings and injection ratios, on the mixture formation processes and engine performanc are made in detail.

HCCI combustion was studied in a 4-stroke gasoline engine with a direct injection system. The electronically controlled two-stage gasoline injection and spark ignition system were adopted to control the mixture formation, ignition timing and combustion rate in HCCI engine. The engine could be operated in HCCI combustion mode in a range of load from 1 to 5 bar IMEP and operated in SI combustion mode up to load of 8 bar IMEP. The HCCI combustion characteristics were investigated under different A/F ratios, engine speeds, starts of injection, as well as spark ignition enabled or not. The test results reveal the HCCI combustion features as a high-pressure gradient after ignition and has advantages in high thermal efficiency and low NOx emissions over SI combustion. At the part load of 1400rpm and IMEP of 3.5bar, ISFC in HCCI mode is 25% lower and NOx emissions is 95% lower than that in SI mode.