Research On Particle Emission During Start Up Period Of GDI Engine

GDI engine wildly used in vehicle currently in virtue of higher compression ratio,accurate oil supply,fast response,low pumping loss and many other advantages.However,compared with PFI engine,GDI engine has higher particle emissions.In all operating conditions,the number concentration of particle emissions during starting period is even one order of magnitude higher.This research focus on physical and chemical properties,morphology characteristics also particle mass via gravimetric method to study start-up period of particle emission based on two GDI engine testing bench,in view of different cooling water temperature and different blended oxygen fuel measurement analysis.And in idling condition,study on different control parameters impact on particle size distribution and particle number concentrations of particulate emissions via using ECU with open loop control.Based on the characteristics and microstructure of particle emission during starting period also under different starting conditions of GDI engine,this research establish formation model of particle and simulate process of primary particles accumulate into particle,and go deep into mechanism of particle generation:1.Establish particles sample and analysis system,design secondary dilution system to dilute start-up period exhaust,use particle size analyzer to measure particle size distribution,particle number concentration measure total mass of particle emissions under 20 ? and 40 ?,60 ?,80 ? cooling water and different fuels.Study affect by adjusting control parameters of physical and chemical properties.Distribution of particle size is single-peaked by using gasoline under start-up period with different temperatures of cooling water,the peak value appears in 20 nm,the number concentration peak value of 20? is 1.75x1010/cm3.The nuclear mode particle number concentrations at different cooling water temperatures during start-up period dominant more than 90% of total amount.Compared with gasoline,four oxygen-blended fuels including E10,E20,M5 and M15 were used to obtain rules that the number concentration of particles in each particle size section was reduced.The effects of control parameters such as injection time,ignition time,excess air ratio and speed during idling condition were studied via adjusting ECU.Setting idle speed is 1200 r/min,excess air ratio is 1.0,ignition time 5°,10 °,15 °,and 20 ° CA BTDC under 230 °,250 °,270 °,290 ° and 310 ° CA BTDC injection time measure the particle size distribution,it is concluded that all conditions are in single-peaked distribution.In addition,the particulates emission characteristics of GDI engine at three typical idling speeds of 800,1000 and 1200r/min and excess air ratio of 0.85,1.0 and 1.1 were selected for start-up period were studied.2.Analyzing chemical characteristics of GDI engine start-up period particles by using particle sampling and chemical analysis system,including chemical element,SOF carbon numbers after Soxhlet extraction,PAHs contents under different cooling water temperature and different blended fuel,and evaluating toxicity of PAHs in particles under each condition.Elementary analysis of uniform primary particle size,non-uniform primary particle size particles and atypical flocculent particles via energy spectrum analysis,found the u uniform primary particle size,non-uniform primary particle size particles mainly consist of C,O and trace amounts of Si,whereas flocculent particles also consist of Co,Cr,Fe and other metal elements besides C,O.GDI engine using gasoline during transient start-up period PAHs emissions were 8160.36 ug/ug/L and 4982.15 L under 20? and 80 ? cooling water,occupy 65.1% and 65.6% of total PAHs emissions respectively;using E10 fuel at 20? and 80? compared with gasoline were reduced by 39.0% and 39.0% respectively;using M15 fuel at 20? and 80? compared with gasoline were reduced by 30.2% and 30.2% respectively.Therefore,reducing PAHs emission during transition period by effectively shortening heating time of cooling water in start-up period and applying oxygenblended fuel can improve the mixture quality in-cylinder,and achieve to reduce PAHs emission during the entire start-up period of GDI engine.3.Establish TEM sampling and analyzing system for observing particle morphology and measuring under different sampling time and cooling water temperature by using transmission electron microscope(TEM)and energy spectrometer(EDX),and other measuring instruments,based on measuring data to make statistics and analysis,combining with the GDI engine start-up period particulate emissions' physical and chemical properties to study on impact of particle formation process and mechanism.Via observing particles with TEM under 20? and 40?,60?,80? cooling water and starting the 0 s and 30 s sampling timing,it can be concluded that 20? cooling water sampling particles mostly are long chains,tree branchs which have fractal-like structure,the primary particles have equally size,size distribution range smaller;particle structure under 80? cooling water has no obvious variation.Using Canny edge extraction method and Hough transform method batched process TEM images of 19283 primary particles,mainly distributed in the range of 5-30 nm,and the number concentration peak distribute in range of 10-20 nm.Design pure carbon particles experiment method,according to empirical formula to establish relationship between carbon particle size distribution and the mass calculation and verified,use empirical formula to calculate particle emissions real-time mass distribution according to particle number concentration and size distribution of GDI engine start-up period,provide suggestion of lowering particulate emissions based on mass calculation results.4.Establish motion model of primary particles in finite space via using Langevin's equation,and establish aggregation collision model by combining Langevin's equation and on lattice DLCA model.The simulation boundary condition is calculated according to primary particle size distribution during the start-up period from GDI gasoline engine.Four aggregation models are simulated with 50,100,200,300 and 400 primary particles,equally sized primary particle aggregation with no sintering,equally sized primary particle aggregation with sintering,unequally sized primary particle aggregation with no sintering and unequally sized primary particle aggregation with sintering.Combined with primary particles distribution from GDI engine startup period,it is concluded that the equally sized primary particles mostly generated during early of start-up period and aggregate into small clusters which classified into nuclear particles,unequally sized primary particles mostly generated during middle and late of start-up period and aggregate into larger agglomerates and furthermore have chemical adsorption become even larger accumulation mode particles.