Comprehensive experimental study on the performance and emission behavior of biodiesel–methanol dual-fuel in compression ignition engines

Biodiesel, a renewable and biodegradable alternative fuel, is derived from vegetable, animal, or waste oils through transesterification with short-chain alcohols. Its high oxygen content, sulfur-free composition, and lubricity-enhancing properties offer significant advantages in terms of engine performance and emission reduction. In this study, cold-pressed linseed oil obtained from Kunduz region of Afghanistan was converted into fatty acid methyl esters by transesterification method. The resulting linseed methyl ester was blended with conventional diesel at mass ratios of 10%, 20%, and 30% to obtain B10, B20, and B30 fuel mixtures. Additionally, to enhance combustion and emission characteristics, 5% and 7.5% methanol were introduced into the B20 blend, resulting in B20M5 and B20M7.5 variants. Experimental investigations were conducted on a single-cylinder diesel engine at a constant speed of 1800 rpm under varying load conditions. As a result of the study, optimum results were obtained in terms of engine performance and emission values ​​in B20 blend fuel. The B20 blend containing 20% linseed methyl ester demonstrated the most balanced performance–emission profile, achieving a 15–28% increase in brake thermal efficiency and reductions of approximately 22% in CO and 19% in HC emissions compared to pure diesel. Moreover, the addition of methanol to the B20 blend further improved combustion dynamics and led to a notable reduction in NO x emissions, highlighting its potential as an effective strategy for cleaner diesel combustion. B20M5 and B20M7.5 blends with 5% and 7.5% methanol addition provided additional emission benefits at 75–100% load, reducing CO and NO x emissions by 7–18%.