To study the performance, emission and combustion characteristics of a single cylinder constant speed direct injection diesel engine using Watermelon Seed oil – the output diesel which fuses on various loads and additive nbutanol. An experiment underwent with combinations of different fusions of watermelon seed oil with diesel such as B20, B40 on various loads, and the result of which was compared with pure diesel fuel. The result showed that the Brake Thermal Efficiency (BTE) for watermelon seed oil with additive n-Butanol and its fusion has low BTE that of the diesel. There were a notice of Carbon Monoxide (CO), Hydrocarbon (HC) and NOx emission. There were also a tangible amount of smoke emission and decrease of combustion properties such as high pressure and heat frequency for watermelon seed oil and diesel fusion on full load. The conclusions were likely that the lower blends of watermelon seed oil can be used in diesel engine without any alterations. © 2019 Elsevier B.V., All rights reserved.