Effects Of Control Parameters On GDI Engine’s Start And Idle Operations

Starting and idling process is very important for automotive engines. This papermainly studies the starting and idling process of the gasoline direct injection engine.In order to start the engine quickly, more fuel is injected to the cylinder to formationthicker mixture which makes the engine emit large amounts of unburned HC. And thestarting performance would be very difference with different control parameters. GDIengine starting process is very fast which it just needs two cycles to reach1000r/min.This paper mainly studies the first two cycles of the starting process. Starting processcontrol parameters mainly concludes: ignition timing, injection timing, injection pulsewidth, the bypass valve opening degree. Idling is a common condition for automobileengines. As the urban traffic becomes crowded, the idling condition is taking moreand more proportion of the engine conditions. Idling belongs to steady–statecondition. As the control parameters changes, the idling performance would bedifference. This paper mainly studies the control parameters effects on the speed andHC emissions. The control parameters mainly conclude: ignition timing, injectiontiming, excess air ratio, the bypass valve opening degree.To the first cycle of the starting process:(1) The best fuel injection pulse-widthrange reduces with the increase of cooling water temperature. Reasonable injectionpulse-width range is8,6,5,4ms which is lessening when the temperature of thecooling water is20,30,50,80℃.(2) Ignition timing is corresponding to a rotationalspeed is higher, the HC less ignition timing range. The better ignition timing is15,5,0,0°BTDC when the water temperature is20,30,50,80℃. The higher thetemperature of cooling water, delay the ignition timing is more advantageous to thefirst cycle of combustion.(3) Injection timing appears the highest speed at90°BTDCwhen the temperature of cooling water is20,30,50,80℃.For the second cycle in starting process:(1) When the first cycle controlparameters in the same conditions, with the increase of the fuel injection pulsewidth, the speed of the second cycle will first increase then stay around a certainspeed. When fuel injection pulse-width is in8ms, the speed is high relatively and theHC emission is less.(2) For the ignition timing, when the first cycle controlparameters in the same conditions, and the ignition timing is between20to25°BTDC, the speed is high relatively and the emissions of HC is less.(3) For the injection timing, when it is90°BTDC, the speed is the highest and the emissionsof HC is least.(4) The by-pass valve has a little influence on the second cycle. Forthe first five cycles in starting process, with the increase of the number of cycles, thefuel injection pulse-width will decrease.For the injection timing is90,140,210°BTDC in the experiment, fuel injectionpulse-width is least when the injection timing is90°BTDC. For the emissions ofHC, when injection timing is90°BTDC in the first four cycles, the emissions ofHC is the least, but for the fifth cycle,140°BTDC is the least.The following conclusion could be got from the test of adjusting the idle speedcontrol parameters:(1) According to the different ignition timing, cylinder pressure and HCemission speed in contrast, fuel injection pulse width and other parameters conditionskeep unchanged. Along with the delay of ignition timing, cylinder pressure andmaximum speed increased, causing HC emissions increased.(2) Through the comparison of the opening speed and HC emissions of differentbypass valve, in order to change the air coefficient, speed increase with the bypassvalve opening increases, the emission of HC with height.(3) Through the comparison of speed and HC emissions with different fuelinjection timing, while maintaining the same excess air coefficient and otherparameters under the condition that the injection timing at50°BTDC speed to be30，100°BTDC higher, but HC emission is less.(4)Through the comparison of different excess air coefficient of speed and HCspeed, excess air coefficient, the highest in the0.85.(5) Through the comparison of speed and HC within different cooling watertemperature, while keeping the excess air coefficient and other parameters unchangedcircumstances, along with the cooling water temperature from20-90℃.speedincreased, fuel injection pulse width required to reduce, the emissions of HC reduced.