Abstract In this study a heat exchanger is designed for cooling exhaust gas and an experiment is carried out to investigate the effect of Exhaust Gas Recirculation (EGR) temperature on destruction of the fuel’s availability due to combustion processes in IDI diesel engine cylinder. To serve this aim an exergy analysis is conducted on the engine cylinder which provides all the availability terms by which the evaluation of in-cylinder irreversibilities is possible. The availability terms including heat transfer, inlet and exhaust gases and work output are presented during the engine operation at different load and speeds. To clarify the effect of using EGR in each case, EGR is introduced to the cylinder at various ratios and temperature during the tests. The results show about 60 to 70 % of fuel’s availability is destroyed by irreversibilites. Also, the results reveal that the increase of EGR temperature leads to reduce of combustion irreversibility. On the other hand the increase of EGR temperature leads to heat and availability are dissipated of the wall and exhaust gas. So depend on the engine operation at different loads and speeds, the increase of EGR temperature could be lead to a positive or negative effect on the engine performance.

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