Investigating the Effect of a Diesel–Refined Crude Palm Oil Methyl Ester–Hydrous Ethanol Blend on the Performance and Emissions of an Unmodified Direct Injection Diesel Engine

[Image: see text] In this research, the optimum condition for the production of refined crude palm oil methyl ester from refined crude palm oil was investigated using the response surface method via the transesterification reaction in a batch process. The refined crude palm oil was obtained by vacuum distillation of crude palm oil to extract some of the free fatty acids from the oil, providing nutritional benefits and reducing the chemical consumption of the production process. The purity of methyl ester in the refined crude palm oil methyl ester was studied to adjust four independent variables: methanol content (11–23 vol %), concentration of potassium hydroxide (4–12 g/L), stirrer speed (100–500 rpm), and reaction time (9–45 min). The results showed that methyl ester had a purity of 96.91 wt % when synthesized under optimal conditions of 18.2 vol % methanol, a potassium hydroxide concentration of 10.0 g/L, a stirring speed of 380 rpm, and a reaction time of 36.4 min at 60 °C. Refined crude palm oil methyl ester was blended with diesel and ethanol to study the feasibility of using the diesel–refined crude palm oil methyl ester–hydrous ethanol blend in an unmodified diesel engine. A comparative study of fuel properties, emissions, and performance of the diesel–refined crude palm oil methyl ester–ethanol blend was used to assess the feasibility of fuel blends (D40RM50E10, D30RM60E10, D20RM70E10, and D10RM80E10) in diesel engines at various engine speeds and loads. The results showed that the D40RM50E10 blend provided the closest performance to diesel and was environmentally friendly, as it provided nitrogen oxide and carbon monoxide emissions 32 and 55% lower than those with diesel, respectively. The test results indicated that the diesel–refined crude palm oil methyl ester–hydrous ethanol blend is an attractive alternative fuel in agricultural engines that reduces diesel consumption and benefits farmers and rural communities.