Analysis of combustion instability and complexity in diesel-biodiesel blends: Effects on performance, emissions, energy, and exergy

Diesel engines are a major source of nitrogen oxides, carbon dioxide, and particulate matter emissions. While biodiesel blends offer potential emission reductions, challenges remain in viscosity, flash point, cold weather performance, and combustion characteristics. This study examines the performance and emission behavior of biodiesel–diesel blends to enhance efficiency and reduce environmental impact. Multiscale entropy analysis was employed to assess combustion instability and complexity, focusing on the influence of fuel composition and engine speed at full load. Experimental investigations were conducted using biodiesel derived from tomato, papaya, and apricot, blended with diesel. The tested fuels included binary and ternary biodiesel–diesel blends with varying levels of complexity. Results indicate that at optimal operating conditions, biodiesel blends enhance energy and exergy efficiency while exhibiting higher carbon dioxide and nitrogen oxide emissions compared to pure diesel. Hydrocarbon emissions decreased under optimized conditions, while fuels with lower chemical complexity demonstrated improved torque output. Diesel, characterized by greater combustion complexity, resulted in lower exergy and useful work. These findings contribute to the understanding of biodiesel application in compression ignition engines, providing insights into performance optimization and emission control strategies. Keywords: Biodiesel blends; combustion stability; engine emissions; energy efficiency; exergy analysis.