Research On Emission Characteristics Of Direct Injection Gasoline Engine With Multistage Injection

The number of particles of GDI gasoline engine produced are significantlymore than diesel engines with particle trap and the traditional port fuelinjection gasoline engine, and these particles are generally less than100nm. Recentmedicine studies show that ultrafine particle with size less than100nm do much largerharm to human health than large particles with the size of more than100nm. So theresearch of GDI particulate emissions, and attempts to improve the technology toreduce particulate emissions quantity and quality is of great significance. The PFIinjection mode has a larger advantage in particulate emissions than the GDI gasolineengine. While the GDI gasoline engine is with higher intake efficiency in the coldstart and high load. This paper uses PFI combined GDI injection mode in themedium and small load, and contrastively study combustion and emissioncharacteristics of combined injection mode and simple GDI injection mode.The research results show that:1) In homogeneous mode:a) According to the cylinder pressure, cylinder temperature and heat release ratecurve, injection time in300°(CA BTDC) and320°(CA BTDC) is the bestunder the fuel injection ratio of0:10in cylinder. When fuel injection advanceangle changes from260o(CA BTDC) to the340o(CA BTDC), CO andTHC emission is overall decreasing trend with injection timing advance. Withthe early injection timing, NOx emissions shows a trend of increase.The number and mass concentration of particles showed aunimodal distributionunder different injection time. There is minimum total number concentration ofparticles when the injection time changes under all the same injection ratio and320o(CA BTDC) is considering the optimal injection time.b) The overall trend in cylinder pressure curve is the peak cylinder pressure increasesand the peak positions around the front with the increase in the proportion of SPI accounted for injection. The peak heat release rate increases more and more withPFI/cylinder injection proportion enlarging, and the peak position is more andmore close to the front. The average temperature in the peak cylinder with singlepoint fuel injection in cylinder/proportion increased more and more, and thepeak position is more and more close to the front. Emissions of CO, THC arein overall decreasing trend decreasing trend. Emissions of NOx showed anincreasing trend. Particulate emissions peak decreases with the proportion ofsingle point/cylinder to increase. The peak of particle number concentrationmove to the direction of size decrease with the proportion increase. The particlemass concentration distribution was unimodal distribution, and particle masspeak fall on the state of aggregation size range. Under all the same injectiontime, the total number concentration of particles is a decreasing trend with singlepoint fuel injection to increasing. The best ratio of injection is7:3. The total massconcentration of particles under various injection ratios transform complex withthe injection time. The total mass concentration of particles under5:5and7:3injection ratio is significantly lower than other injection ratio.2) Under lean burn mode:a) Combustion condition changes better with increasing of fuel ratio, cylinderpressure, heat release rate and the cylinder temperature peak value has promotion.The THC, CO emission integrally decrease with fuel injection ratioincreasing, NOx emission increases with the injection ratio increased; Both theinitial nucleation particles number concentrations and the particle size slightlylarger are the overall decreasing trend with fuel proportion to increase.b) In two cases of the fuel injection ratio both3:7and7:3, the peak of cylinderpressure, heat release rate, in cylinder temperature all showed an increasingtendency with the fuel injection advance angle from110o(CA BTDC) is delayeduntil80o (CA BTDC). With the injection delay, CO emissions of two ratio willincrease, THC emissions is to reduce, NOx emissions will increase. The emissionsof particles will increase with fuel to postpone under3:7fuelinjection ratio (in cylinder injector based), and emissions of particles is the overall decreasing trend with fuel to postpone under the fuel injection ratio of7:3(single point injection mainly).c) With the advance of ignition time, the peak of pressure in the cylinder, the heatrelease rate, and temperature in the cylinder are gradual increase in variousinjection ratio and injection time. But in the fuel injection ratio of0:10,80o(CA BTDC), the peak of the cylinder pressure, heat release rate, andcylinder temperature decline when the injection timing advance to25o(CA BTDC).The particle number and mass concentration showed a unimodaldistribution, and the peak value increased with the ignition advance.