Simulation of EGR Stratification on Timing-Sequential Regionalized Diesel Combustion

In this paper, the influences of EGR distribution on timing-sequential regionalized diesel combustion characters and emissions have been investigated numerically. Timing-sequential regionalized diesel combustion described in previous paper is realized by post injection and proper in-cylinder chemical atmosphere transport to keep post injection fuel injecting to high oxygen concentration region. Cases with EGR stratification have similar heat release rate character compare to uniform EGR case while lower soot emissions and identical NO emissions as local EGR rate equal to uniform case, similarly, lower NO emissions and identical soot emissions as EGR mass equal to uniform case. Axial and radical EGR stratification that defined artificially in cylinder under the condition of 1,650 r/min and 50 % load have been numerically analysed by commercial STAR-CD code. It is indicated that both axial and radical distribution of EGR stratification make NO and soot emissions decrease simultaneously, however, radical EGR distribution works better. NO emissions decrease while soot emissions keep constant under the case of EGR stratification with post injection using main injection timing advance and higher local EGR rate; it is also found that cyclic net work per cylinder is improved at some extent. Intake port shape and swirl rate also have been investigated to analyse in-cylinder gradient of EGR distribution to achieve EGR stratification. EGR gas distributes by gradient in cylinder as air and air-EGR mixture flow through two intake valve that connected to tangential and spiral intake port respectively.