DE2-3: In-cylinder Stratification of External EGR Gas for Diesel Combustion(DE: Diesel Engine Combustion,General Session Papers)

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A technique for in-cylinder stratification of external EGR gas for Direct Injection (DI) diesel engines was developed in order to reduce toxic exhaust emissions. EGR gas is supplied from one of the two intake ports which make upper swirl flow and lower swirl flow during the intake stroke. After the intake stroke, the vertical stratification of EGR gas is formed. In the final stage of compression stroke, a squish flow brings the vertically stratified gas into the piston cavity, and EGR gas is radially stratified in the piston cavity at the end of the compression stroke. This technique for stratification was developed by using unsteady computational fluid dynamics (CFD) simulation. Prior to exhaust emission tests, the accuracy of the simulation was evaluated by in-cylinder visualization using Laser Induced Fluorescence (LIF) imaging. Exhaust emission tests showed smoke reduction effect under medium load condition, when the EGR gas delivered to the inner part of the piston cavity. This smoke reduction effect was investigated by CFD simulation using a series calculation methodology from the injector nozzle internal flow to the in-cylinder fuel spray, mixture formation and combustion. At the beginning of the combustion, the higher concentration of EGR gas in the inner part of the cavity lowered combustion temperature and reduced the soot formation rate. The fresh air, which existed in the outer part of the cavity at the injection timing, accelerated the oxidization of the soot cloud at the latter period of the combustion.
一般社団法人日本機械学会の論文
2008-07-28

DE2-3: In-cylinder Stratification of External EGR Gas for Diesel Combustion(DE: Diesel Engine Combustion,General Session Papers)

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