Experimental Study On Combustion And Emission Characteristics Of Multi-cylinder HCCI Engine

Faced with increasingly serious energy and environmental problems, how to further improve the thermal efficiency of internal combustion engine and reduce harmful emissions is an important issue in today’s international vehicle dynamics research.we must save energy and reduce emissions. HCCI combustion and hybrid have good prospects for development.HCCI is realized on a 4 cylinder gasoline engine based on OKP(optimized kinetic process) technology, which increased compression ratio and redesigned intake and exhaust systems. To combine the HCCI engine and hybrid system effectively, we expand the load range by increasing the compression ratio. Then we study the effect of compression ratio on HCCI combustion and emission characteristics. We delve into the effect of the intake temperature, coolant temperature, EGR, intake air pressure on combustion and emission to improve HCCI combustion. Then we combine HCCI gasoline engine with the series hybrid to build a new bench to compare the fuel consumption. So we can explore a more effective and cleaner mode.Results show that, increasing the compression ratio can effectively expand the load range of HCCI engine. The maximum pressure rise rate limits to expand the high-load, while combustion cyclic variations limites its expansion of low load. The power performance and economy of engine optimize because of the higher compression ratio. And we can relize the HCCI mode in lower intake temperature. But high compression ratio brings the combustion knock which need better reliability of engine. The high compression ratio leads to lower HC, NOx and higher CO emission in HCCI combustion mode.When the coolant and intake temperature increased, the cylinder pressure and temperature rose, the CO and HC declined, the cyclic variations also declined. The excessive coolant and intake temperature may cause combustion knock, but the low temperature may cause misfire. Therefore, suitable coolant and intake temperature are very important to combustion stability. The higher intake pressure brings the engine better power, but the excessive intake pressure makes the engine explosion. It can expand the high load together with EGR. When the EGR rate increases, the pressure, temperature and the pressure rise rate in cylinder decline and the combustion duration extends to avoid the knock of engine. Meantime it significantly reduces NOx emissions. But when the EGR rate increases, the increased cyclical variation is corrupted to the stable operation. The cyclic variation between cylinders in HCCI mode is large, especially the 1st,4th cylinder variations is greater than 2nd,3rd cylinder variations.We focus on using switch-mode control strategy and selects NEDC working condition to do experiment on the hybrid &HCCI test bench. Result shows that, there is a large potential for energy saving and emission reduction. It can achieve economy of 5.56 L/100 km in the NEDC conditions, which is 11.3% and 22% lower compared to the SI&hybrid system and the original engine. It can achieve economy of 5.85 L/100 km in the ECE conditions, which is 16.3% lower compared to the SI mode of 6.99 L/100 km. This shows that combining HCCI combustion and hybrid systems can further improve economy and reduce emissions.