Effect Of First Cycle Combustion In GDI Engine On Hot Start

As energy and pollution questions being more seriously, more and more people focuson them. Canceling idling is helpful for reducing emissions and fuel consumption, especiallyin city conditions. GDI is one of best supporters for canceling idling technology becauseGDI engine can began to work in one cycle. Based on this, expansion cylinder auxiliarystarting technology has been created which means fuels will be injected into expansioncylinder and ignited to push the engine working, except normal starting. In this way, GDIengine can start more easily. However, chamber temperature and combustion in this way areobviously different from normal combustion; especially combustion process in expansioncylinder can be considered as constant volume combustion. Additionally, air mass in both oftwo cylinders is changing with different piston positions. Therefore, the effects ofcombustion boundary conditions about expansion cylinder and compression cylinder onexperiments and simulation. Based on this, the proper starting strategy has been createdthrough analyzing effects of both cylinders combustion on starting rate, electricalconsumption and starter load.Based on4G15-GDI experiment platform and simulation platform, the conclusionshave been shown as the following:In expansion cylinder auxiliary starting technology, for expansion cylinder combustion,combustion process can be considered as constant volume combustion. Increasing injectionpressure would be obviously helpful for combustion under lean mixture condition. Differentpiston positions and cooling liquid temperature influence combustion quality seriously. Thecombustion area is largest when the position is in the middle of stroke and cooling liquidtemperature is90°C；for compression cylinder combustion, both of spontaneous combustionand misfire exists in the process. When the piston of compression cylinder is before90BTDC and cooling liquid temperature is100°C, only moderate mixture concentration areacan be ignited.. Spontaneous combustion phenomenon appears after120BTDC and becomesseriously as position moving down. The strategy of injection timing in60°~90°CA BTDCcan eliminate spontaneous combustion. Moreover, cooling liquid temperature playssignificant influence on combustion which enlarging spontaneous combustion range asraising.For mixture being ignited normally, ignition timing has little effect on staring andstarter connecting timing has obviously effect on strati in the strategy of injecting fuelsfirstly in expansion chamber. It should be connected in the early period of combustion.Injecting fuels has little effect on staring when the piston is far away from TDC. Based onthis, the strategy of no fuel injecting into cylinder can save40%starting time. Additionally,in other positions, expansion cylinder auxiliary starting technology can save starting 20%~40%time and electrical power, especially using the strategy of injecting fuels firstly inexpansion chamber.