Enhancing diesel engine compatibility of wheat germ-based biodiesel through preheating: combustion, emission, and thermal insights

Abstract

The growing demand for sustainable and environmentally responsible energy systems has intensified research on renewable fuels and their thermal behavior during energy conversion processes. In this study, wheat methyl ester (WME), synthesized from wheat germ oil via transesterification, was experimentally investigated with an emphasis on its thermal and combustion-related characteristics in compression ignition engines. Owing to its oxygenated molecular structure, WME exhibits distinct combustion-related pressure behavior compared to conventional diesel fuel. To improve its physicochemical and thermal response prior to injection, WME was preheated to 80 degrees C. Fuel blends containing 20%, 60%, and 100% WME by volume were tested under both unheated and preheated conditions using a single-cylinder, air-cooled diesel engine. The analysis focused on thermal and energy-related parameters, including brake thermal efficiency, in-cylinder pressure evolution, exhaust gas temperature, infrared-based spatial thermal distributions, and emission characteristics. The results show that fuel preheating improves the fuel flow and combustion response of WME-containing fuels, leading to relatively higher brake thermal efficiency compared with their non-preheated counterparts, accompanied by reductions in brake specific fuel consumption, carbon monoxide, unburned hydrocarbons, and smoke emissions. Conversely, increased exhaust gas temperatures, in-cylinder pressure levels, and nitrogen oxide emissions were observed, reflecting intensified thermal activity during combustion. Overall, the findings demonstrate that thermally assisted fuel preparation is a practical and effective approach for improving the thermal performance and energy conversion behavior of renewable biodiesel fuels without requiring any mechanical modification to conventional diesel engines.