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This study aims at improving understanding of the relation between smoke-reduction effect of post injection and design and operating conditions in small diesel engines. A series of experiments was conducted using a single-cylinder diesel engine under a fixed NOx emission condition to investigate the smoke reduction effect of post injection varying the number of injection nozzle orifice and piston bowl diameter, which would influence the interaction between main spray flames and post sprays. The results indicate that the larger number of nozzle orifice with smaller diameter reduces smoke emissions under late post injection conditions. Advanced post injection reduces smoke emissions for the smaller piston bowl diameter; while retarded post injection reduces smoke emissions for the larger piston bowl diameter. Explanations for these trends were attempted paying attention to the influence of the main spray flames on post sprays., 単気筒ディーゼル機関においてアフター噴射を採用し，メイン噴霧火炎とアフター噴霧の干渉の強さに関連の深い噴射ノズル仕様(噴孔径×数)，噴射圧力，燃焼室形状を変更した実験を行った．その結果にもとづき，アフター噴射の効果と設計条件との関係について考察を行った．

This study aims at obtaining the after-injection strategy to reduce smoke emissions in a diesel engine, where after injection is employed in combination with pilot injection. The experiments were performed using a single-cylinder diesel engine under various conditions of pilot and after injection at a fixed load. The results show that small after-injection quantity with short interval offers reduced smoke emission. Larger pilot-injection quantity provides larger smoke reduction from the level in the case without after injection. The smoke-reduction effect is scarcely affected by pilot-injection timing in the case of a larger pilot-injection quantity. These tendencies are explained with attention to the interaction between main-spray flame and after-injection spray., 単気筒ディーゼル機関を用いて，パイロット噴射量や時期を変えながらアフター噴射条件を変化させて実験を行い，その結果を，アフター噴射を行わない場合と比較し，メイン噴霧火炎とアフター噴霧の干渉を考慮した考察を加えることにより，アフター噴射による黒煙低減効果が得られる条件について検討を行った．, 2012年5月25日自動車技術会春季学術講演会において発表.

This study aims to investigate the spray development process of diesel spray under small-quantity injection condition. The effects of injection pressure and injection quantity on spray tip penetrations were analyzed using a rapid compression and expansion machine, and the effects of injection-rate pattern on spray development process were simulated using a one-dimensional spray model. The results show that the spray tip penetration is dependent on time with exponent more than one just after injection start, and the exponent turns to one and one half as time elapses. With small-quantity spray the exponent is one forth after the end of injection. The simulation results show that the penetration dependence on time to the power of more than one during beginning of injection is caused by increasing momentum flux by rising injection rate, and the penetration rapidly decelerates as reducing momentum flux at the spray tip by decline of injection rate., 日本機械学会2015年度年次大会 2015.9.13-16

Numerical study using a CFD simulation is carried out in order to better understand the mixture formation processes in a diesel engine with post injection. The effects of post injection timing, nozzle specifications, and combustion chamber shape on mixture formation process were investigated by CFD simulations for past experimental engine conditions. The results show that if post injection spray penetrates into high mixture fraction region in simulation, smoke reduction effect by post injection is not obtained in experiments.