Influence of methyl and ethyl esters-based biodiesel synthesized from safflower oil on the performance, combustion, and exhaust emissions

Abstract Methanol production relies mainly on fossil resources, while ethanol is largely produced from renewable feedstocks. This distinction supports transitioning biodiesel production from fossil-based methanol to bio-based ethanol. While safflower methyl ester has undergone extensive investigation as an alternative fuel source, research exploring safflower ethyl ester remains limited. This experimental study aims to reveal the effects of safflower oil-derived ethyl ester blends on diesel engine performance, combustion, and emission characteristics. The research compared pure ethyl and methyl esters, ester blended fuels, and ultra-low sulfur diesel under various engine loads at a constant speed of 1500 rpm. All fuels exhibited similar cylinder pressure curves, with pressure increasing proportionally to engine load. Ethyl ester fuels showed the earliest combustion start, while pure methyl ester and diesel had retarded ignition timing. Ester blends generally showed lower brake thermal efficiency up to an average of 8.49%. However, this was followed by ethyl ester–diesel blends with a slight decrease up to 1.8%. Ethyl ester fuels had lower mass fuel consumption at low loads. The blends of ethyl esters with 20% diesel showed the second lowest brake-specific fuel consumption but it showed an average reduction of 8.2%, while diesel had the lowest value throughout experiments. Ester fuels generally produced lower carbon monoxide emissions up to an average value of 13.4% compared to diesel. Methyl ester with 20% diesel blend showed lower carbon dioxide emissions by 2% compared to other fuels. Pure biodiesels showed significantly increased hydrocarbons emissions up to 50.8% on average. Ester fuels produced lower nitrogen oxides emissions up to an average of 17.8% relative to diesel fuel. The study concludes that safflower-based biodiesel, particularly with ethyl and methyl esters, is a viable alternative fuel. Graphical abstract