Improve Combustion During Cold Start of DI Diesel Engine by EGR Under Normal Ambient Temperature

During cold start of DI diesel engine, exhaust gas comprises a great deal of unburned hydrocarbon, fuel vapor, and product of partial oxidation reaction. If these compositions are reintroduced into cylinder by EGR, the positive effects may shorten ignition delay, and thus promote ignition. Furthermore, considering thermal effect of EGR and its minor dilution effect during cold start, the combustion performance of cold start could also be promoted through introducing EGR. Through experiments conducted on a 135 single cylinder DI diesel engine, effects of EGR on combustion and emission performance during cold start process were investigated. Comparison of combustion performance between cold start processes with and without EGR suggested that it is an effective measure to improve cold startability of DI diesel engine by controlling EGR system during cold start. Furthermore, opacity during cold start was also investigated, and the results suggested that opacity during the initial phase of cold start could also be significantly improved through controlling EGR system.