Experimental Investigation On Combiustion Control Of Multi-Cylinder HCCI Gasoline Engine

With the increase of vehicle population, one key problem in energy and environmental fields is to develop an engine with high efficiency and ultra-low emissions. Optimized kinetic process (OKP) technology uses the waste thermal energy in the coolant and exhaust gases for intake air heating to realize HCCI combustion in a multi-cylinder gasoline engine. According to combustion control concept, this paper explores potential of combustion and emission improvement of multi-cylinder OKP-HCCI engine and ignition and combustion phase control of HCCI combustion. The effects of spark assisted HCCI, external EGR and other operational parameters on HCCI combustion and emissions were investigated.The results show that utilization of spark assisted HCCI was found to increase Indicate mean effective pressure(IMEP), pmax, (dp/dθ) max and reduce cycle-to-cycle variation so as to improve the stability of HCCI combustion in critical state of HCCI. Under lower-limit boundary conditions of HCCI combustion, spark assisted HCCI combustion had higher Cycle to cycle variation and cylinder to cylinder variation. Spark assisted HCCI could achieve a Two-stage combustion. When increasing the spark advance angle, the heat release rate peak value increased. The introduction of spark significantly advanced the combustion to top dead center (TDC) and lowered the NOx and HC emissions at low load operating on low speed (1200rpm～1600rpm).Moreover, effects of external EGR, inlet charge temperature, coolant temperature, and engine speed on HCCI combustion and emissions were examined. The results show that external EGR can retard the beginning of HCCI combustion and slow the rate of heat release. When increasing the EGR rate, the duration of combustion extended, the pmax and (dp/dθ) max decreased. The NOx emissions decreased and it maintained at a low level (50×10-6). But the CO and HC emissions deteriorated at lower engine loads.The change in inlet charge temperature and coolant temperature will affect a visible change of HCCI combustion. What's more, gasoline HCCI engine is sensitive to engine speed. With the engine speed increasing, the beginning of combustion (CA10) retarded, CA50 and the duration of combustion has a phasic variation.