Abstract For the purpose of reducing NOx which is a serious pollutant of diesel engine caused by high temperature of diesel combustion, application of recirculated exhaust gas (EGR) is widely used in vehicle industries. Besides, it has been proven that the second law of thermodynamics (the concept of exergy) contributes to the better understanding of the engine inefficiencies and finding the sources of irreversibilities or exergy loss. In this experimental investigation, the second law analysis is applied to an EGR implemented, IDI naturally aspirated diesel engine. The aim of this study is to find how different exergy terms of the engine cylinder are affected by EGR induction. To serve this aim various exergy terms crossing the engine cylinders as a control volume are illustrated. In order to cover the main operating condition of the engine, three different speeds of 1500, 2000 and 3000 rpm and the corresponding loads of 25, 50 and 75% of maximum achievable load for each speed were tested. In each case four EGR mass ratios ranging from 0% to 20% are introduced to the engine intake to cover EGR conventions. It was concluded that using EGR mostly increases the cylinder total irreversibility mainly because of extending the premixed combustion region and consequently the decrease of maximum temperature of the cycle. This effect is more significant as engine is approaching full load.

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