Abstract Reducing exhaust emissions and, consequently, recovering wasted energy and exergy of an engine are the primary purposes of engine research. In previous studies, improving the combustion efficiency and reducing the exhaust emissions by homogeneous combustion, and the recovery of engine wasted energy (especially exhaust wasted energy) to use in the downstream cycles have been researched. In the present study, the feasibility of recovering exhaust energy to evaporate diesel fuel and the effects of adding diesel vapor on combustion efficiency, exhaust emissions, and overall engine efficiency have been investigated. To achieve these purposes, an experimental investigation on the effects of adding diesel vapor was performed. And, the numerical analysis was used to investigate the feasibility of the diesel evaporation by recovering exhaust energy. The experimental tests were performed at a constant speed (1000 rpm) and three amounts of fuel injection. In each amount of fuel injection, the amount of diesel vapor increased in three steps up to the knock threshold. In the experimental investigation, the share of the indicated work, combustion irreversibilities, heat transfer loss, and exhaust gas from the inlet exergy have been shown. Also, the effects of adding diesel vapor on exhaust emissions (PM, NO, CO and HC) and the cycle variation were investigated. Furthermore, the chemical exergy of each one of the species in the exhaust stream was investigated in detail. In the numerical investigation, the following results were investigated: the available exhaust gas exergy up to the dew point, the share of the exhaust recoverable energy from the diesel evaporation energy, the improvement of the second law efficiency by recovering exhaust gas energy, the reduction of exhaust gas temperature, and the required length of heat exchanger for increasing the diesel temperature from ambient temperature up to the exhaust gas temperature. According to the achieved results, adding diesel vapor reduces combustion irreversibility and heat transfer loss; also, the second law efficiency improves from 30% to 44%. Using a heat exchanger can recover 20-45% of the required evaporation heat of diesel. The reduction of exhaust gas temperature after the heat exchanger is less than 2%. The maximum required heat exchanger length for increasing the diesel temperature from ambient temperature up to the exhaust gas temperature is 50 cm. The addition of diesel vapor decreases NO and soot emissions and, simultaneously, increases CO and HC emissions. The addition of diesel vapor decreases the cycle variation, especially in low-load conditions. According to the chemical exergy of the various species in the exhaust gas mixture, the CO2 and H2O emissions have the most destructive effect on the environment; also, the detrimental environmental impact of CO emission is more than NO until being oxidated by a catalyst.

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