In recent years, numerous studies have been carried out on the effect of biodiesel fuels on engine performance and exhaust emissions. But in those studies, no attention has been paid to the thermo-economic analysis of engines while using biodiesel and its blends with diesel fuel. For this aim, various blends of waste cooking oil biodiesel with diesel fuel were tested in a four-cylinder direct-injection diesel engine. The experiments were carried out at a constant engine speed and load and four different biodiesel–diesel blends. The combustion reactions were determined using experimental data and, finally, the thermo-economic analysis was performed for steady-state control volume of the engine by using and solving energy, exergy and economic balances. First law, second law and combustion efficiencies, specific fuel consumption and the rate of exergy destruction were the results of thermodynamic analysis. The economic analysis also leads to some results such as the cost rates of power generation, fuel consumption and losses. The results showed that the best thermodynamic condition of the engine was achieved when using pure diesel. The most economical and costly operating conditions occurred when using 50% and 10% biodiesel–diesel by volume.

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