Optical Diagnostic Analysis Of Pollutants In Cylinder With EGR Stratification

In view of the trade-off relation between soot and NOx in the process of diesel engine combustion,researchers have proposed EGR-stratified intake system.By introducing high-concentration EGR into the NOx generation region,low-concentration EGR is introduced into the soot formation region,achieving simultaneous reduction of NOx and soot.In addition,with the progress of optical test technology,more and more optical test methods are applied to the engine.In this paper,the laser induced incandescent(LII)combined with the two-color method to measure the volume fraction of in-cylinder soot under EGR stratification,which has the advantages of real-time on-line calibration,simple optical path,easy operation and so on.This study is based on a four-valve high-pressure common-rail single-cylinder compression ignition optical engine,combined with two independently developed EGR layering devices.The laser-induced light emission method was used to measure the soot volume fraction,and the effect of different EGR stratification modes on the soot volume fraction was studied.In this paper,a LII optical test platform is set up.At the same time,the high-speed camera and ICCD are used to record the combustion process in the cylinder.Through the combination of laser-induced light and two-color method,the quantitative measurement of the soot volume fraction in the cylinder is achieved.The image processing is programmed by MATLAB.The software integrates the image output of the numerical calculation process and the calculation results,and performs a verification experiment on the LII test system on a stable flame.The experimental results show that the LII test system has the ability to measure the soot volume fraction.Experimental studies on optical engines were conducted to analyze the effects of different EGR rates and EGR stratification schemes on the soot volume fraction in the cylinder.The original field distribution of pollutants in the cylinder obtained by simulation shows that the NOx generation area is mainly located near the center of the combustion chamber,and the soot formation area is mainly distributed near the wall surface.Based on the above results,it is necessary to introduce high concentrations into the center of the combustion chamber.EGR suppresses the generation of NOX,introduces low-concentration EGR in the surrounding area of the combustion chamber to reduce the formation of soot at the early stage and promotes the oxidation of the soot in the later stage.Therefore,the adoption of “middle and four weeks of dilute” radial EGR layering is conducive to the simultaneous reduction of NOx and soot.The goal.Comparison and analysis of the effects of different EGR stratification schemes on soot generation results show that,under the experimental conditions of EGR rate of 25%,the spiral EGR introduction method under the conduit layering scheme is lower than the spiral EGR introduction method under the double airway stratification scheme.The reduction of 0.91% is due to the fact that the EGR introduction position is closer to the valve under the ducting scheme,reducing the mixing of the exhaust gas with the fresh air before entering the cylinder and ensuring a higher delamination at the same EGR rate.Under the two layered schemes,the spiral EGR introduction method has better effect on soot reduction than the tangential EGR introduction method,indicating that the spiral EGR introduction method under the layered scheme of the catheter has the best delamination effect.Under the helical EGR stratification scheme,the influence of different EGR rates on the ER stratification effect was analyzed by changing the EGR rate.The results showed that compared with the homogeneous EGR intake method,the soot volume fraction decreased when the EGR rate was 15%.3.31%,when the EGR rate is 25%,the soot volume fraction is reduced by 4.34%.When the EGR rate is 30%,the soot volume fraction is reduced by 2.70%.It can be seen that under different experimental conditions,due to the air flow in the cylinder Inconsistent,there is an optimal EGR rate for each specific operating condition,which makes the stratification within the cylinder high and achieves an ideal stratification method.