Study Of Particulate Emission Characteristics On A Gasoline Direct Injection Engine Under Steady Condition

The combination of gasoline direct injection and turbocharging have become the direction of gasoline engine at present and in the future,but the number of particle emission of GDI engine is higher than the PFI engine,and the particle size is smaller,the smaller the particle effective diameter,greater damage on human body.In addition,benzo(a)pyrene and dibenzo(a,n)anthracene,which is contained in engine particulate emissions,have strong toxicity to human cancer.From the national six emission limits,the gasoline engine vehicle has to be carried out the exhaust particulate mass and nunmber emission test under cold start at room temperature.In this paper,the effects of ignition timing,injection time,excess air coefficient and exhaust gas recirculation on the particle number concentration,mass concentration and PAHs composition of GDI engine are studied by EA111 engine bench test.The main research contents are as follows:1.Advancing ignition timing will cause the mixing time of fuel and air shortened,the uneven degree of mixture increased,the rise of maximum cylinder pressure and maximum temperature will increase the formation of carbon ions by cracking dehydrogenation,the particulate emissions increased.The effect of injection timing on the particle concentration is mainly determined by the formation of mixed gas.Early fuel injection will cause fuel impinging on piston top,local rich leads to the increase of particulate emissions,late injection can not use the flow of intake process to improve quality of the mixed gas,it will also cause the increase of particulate emissions.Increasing excess air coefficient,fuel and air can be better mixed,while the maximum cylinder pressure and the maximum temperature will be reduced,reducing the formation of initial carbon particles,the particle concentration decreased obviously.If the excess air coefficient is too large,too thin mixture is not conducive to the spread of the flame,resulting in incomplete combustion of mixed gas,it will lead to particulate emissions increased again.Introducing gas into the cylinder can improve the temperature of the working fluid is conducive to better fuel atomization,while reducing the maximum cylinder pressure and maximum temperature also inhibited the formation of carbon particles,All the factors maked the emission concentration decrease with the increase of EGR rate.2.Converted the particle number concentration into mass concentration and analyzed the effects of ignition timing,injection time,excess air coefficient and exhaust gas recirculation on the mass concentration of GDI engine particulate emissions.The results show that under the condition of small load,ignition timing advance makes the total mass concentration of particulate matter increased.Under the condition of moderate load,ignition timing advance leads to the total mass concentration of the particulate emission decreased first and then increased.When inject fuel at 30 CA ATDC,the impact of fuel and the piston caused a higher concentration of particulate emissions,if fuel injection time is delayed,the impact of fuel and the piston is reduced,which decreases the total mass concentration of particulate emissions.With the increase of excess air coefficient,the emissions of the total particle mass concentration decreased,continue to increase the excess air coefficient,larger effective diameter accumulation mode particle concentrations increased rapidly,so the total particle mass concentration increased.If the excess air coefficient is too large,too thin mixture is not conducive to combustion,and it leads to the formation of a larger effective diameter of the accumulation of particles,so that the mass concentration of particulate emissions increased dramatically.With the increase of the EGR rate,the introduction of the exhaust gas is helpful to the atomization of the fuel oil,which reduces the total mass concentration of the emission particles.3.Using the particle flow dilution sampling system,the exhaust particles was collected by glass fiber filter.Use the Soxhelt extraction to handle the filter paper samples and concentrate samples` to 1ml.Use gas chromatography mass spectrometry to assay the concentrations of sixteen polycyclic aromatic hydrocarbons concentrationed in the samples.Results show that under the condition of 2000r/min,75 Nm,concentrations of fluorene and benzo(k)fluoranthene,dibenzo(a,h)anthracene remain low,and the concentration did not change with the change of control parameters,phenanthrene,anthracene,fluoranthene,pyrene,benzo(a)anthracene,benzo(a)pyrene usually have higher concentration and the concentrations change a lot with the change of control parameters.Concentration of 2 rings,5 rings and 6rings PAHs is usually lower than 20 ppm,however 3 ring,4 ring PAHs concentration is high,and the influence of the control parameters is great.Although the Concentrationof fluoranthene and pyrene in the particles is high,the carcinogenic equivalence factors are all 0.001,which could not significantly affect the total carcinogenic toxicity of particle.Benzo(a)pyrene,Dibenzo(a,h)anthracene carcinogenic toxic equivalency factors are both 1,the Dibenzo(a,h)anthracene concentration usually is lower in particles,therefore,the total car-cinogenic equivalent concentration of particle emissions mainly depends on the concentration of benzo(a)pyrene.