Research On The Mixture Formation And Combustion Characteristics Of Lateral Swirl Combustion System For Diesel Engines

To increase the air utilization efficiency, optimize the fuel/air mixture formation and improve the economic & environmental effect of direct injection(DI) diesel engines, a new lateral swirl combustion system(LSCS) was proposed concerned on unique design of the geometric shape of the combustion chamber. The key idea of the LSCS was the creation of a special structure named as the ’convex edge’, which was distributed around the wall of combustion chamber. When the fuel spray impinged with the convex edge, the fuel would be divided into two parts and two lateral swirl would be formed on both sides of the convex edge. As a result, the fuel diffusion area would be enhanced and the fuel/air formation would be promoted. To verify the improvement of fuel/air mixture formation and economic & environmental performance of LSCS, a serious of researches such as optical diagnose experiment, numerical simulation analysis and single cylinder test concerned on LSCS were carried out.For attaining a general understanding of the fuel diffusion and air utilization of LSCS, the optical experiments were designed and conducted in constant volume vessels and the fuel spray and diffusive flame formation images of LSCS and omega combustion system(OMECS) were captured by a high speed camera. It was shown that after the impingement between fuel and the convex edge, two obvious fuel swirling were achieved in LSCS. As a result, the fuel spread rate and area were increased owning to the swirling mechanism. Obvious difference was also caught by comparing flame formation between LSCS and OMECS. In the LSCS, the diffusion flame was separated to both side of the convex edge expectedly. As the resistance of the wall on fuel spread was lower, the flame in LSCS chamber spread faster and two swirls were observed. The flame thinness around the chamber wall was very thin and most of the fuel was burned without constraints by the chamber wall. Nevertheless, all the flame was nearly tiled on the OMECS chamber wall and the thinness of the flame also increased with the mixing of unburned fuel.Numerical simulation was conducted to verify the combustion and emission characteristics of the engines with LSCS. It was the influence of LSCS that were investigated to evaluate the performance of the engines with the new system on fuel/air diffusion, in-cylinder fuel and velocity distribution, heat release rate and emissions. By the simulation results, the effect of the lateral swirling on the fuel/air mixture formation and combustion characteristics of diesel engine was revealed and the ’three stages’ combustion process of LSCS was proposed.On the basis of the research of fuel/air mixture formation and combustion mechanism of LSCS, the influence of the key parameters of LSCS chamber such as the chamber diameter, height of convex edge and radius of convex edge arc on the combustion and emission characteristics were analyzed by numerical method. A optimal value of chamber diameter was determined by comparing the dynamic and Soot emission performance. The results shown that the height of convex edge was a key parameter controlling the air motion and fuel/air mixture formation effectively. The variation of the radius of convex edge arc would lead a obvious change on the steering angle of convex edge and a smaller steering angle could achieve a better combustion and emission characteristic of LSCS.Then, practical economic and emission performance of LSCS were tested in a single cylinder engine to evaluate its application in diesel combustion system. The evaluation was based on the experimental performance of a advanced combustion system-double swirl combustion system(DSCS). Test results shown that the LSCS could achieve a better fuel consumption and less soot emission than DSCS. As it had been affirmed that the application of DSCS could obtain a lower fuel consumption and soot emission, the comparison results between LSCS and DSCS supported that both of the fuel/air mixing and engine performance could be promoted owning to the introduction of lateral swirling combustion and the application of LSCS were significant and promising.