Assessment of engine characteristics in dual-fuel mode using post-mixed biodiesel and coconut shell producer gas

• Dual-fuel CI engine tested with mahua–karanja biodiesel and coconut shell gas. • MBD20 + producer gas reduced NOₓ by 18.95 % and smoke by 16.48 % at full load. • Brake thermal efficiency dropped moderately in biodiesel dual-fuel configurations. • Peak pressure and HRR decreased due to lower cetane rating of producer gas. • Supports SDGs by promoting clean, renewable fuels in diesel engine applications. This study presents a detailed evaluation of a four-stroke compression ignition engine operating in a dual-fuel mode using biodiesel blends and producer gas. The biodiesel blends were formulated from mahua and karanja oil methyl esters, while the producer gas was derived from coconut shells. A Kirloskar TAF1 diesel engine was employed to analyze performance, combustion characteristics, and emission behavior under various load conditions, with a constant producer gas flow rate ensuring test consistency. The research compared the dual-fuel performance of biodiesel blends against conventional diesel. Among the tested configurations, the MBD20 blend (20 % biodiesel) with 1.6 kg/h of producer gas exhibited specific operational patterns. At higher engine loads, this combination led to a 13.95 % increase in brake-specific fuel consumption (BSFC) and a 20.89 % decrease in brake thermal efficiency (BTE) relative to neat diesel, indicating a trade-off in thermal performance and fuel economy. However, emission characteristics showed marked improvements. Smoke opacity decreased by 16.48 %, and nitrogen oxide (NOₓ) emissions dropped by 18.95 %, highlighting the potential of cleaner combustion. Conversely, emissions of carbon monoxide (CO) and unburnt hydrocarbons (HC) rose by 44.45 % and 45.09 %, respectively, due to partial combustion under dual-fuel conditions. The integration of renewable biodiesel with producer gas in diesel engines demonstrates promising environmental benefits. While some compromises in efficiency exist, this dual-fuel strategy presents a sustainable and cleaner alternative to fossil diesel, aligning with energy diversification and emission reduction goals.