Energy outputs and emissions of biodiesels as a function of coolant temperature and composition

Strict emission legislation forced engine manufacturers to replace fossil diesel with sustainable biofuels. Biodiesel combustion produced lower thermal efficiency and higher nitric oxide (NO) emissions. The NO gas emissions depend on the saturated fatty acid (SFA) and unsaturated fatty acid (USFA) levels present in the plant oil. To overcome biodiesel combustion challenges, effective utilisation of engine waste heat could help in achieving high thermal efficiency and low emissions. Effects of biodiesel SFA and USFA levels, and engine coolant temperature on four different biodiesel types are studied. Lamb fat biodiesel (LFB), chicken fat biodiesel (CFB), waste cooking oil biodiesel (WCOB), and Karanja biodiesel (KB) were used. LFB and CFB have higher SFA%, whereas WCOB and KB have higher USFA%. The coolant temperature was varied from 65 °C to 85 °C at different engine loads. It was observed that with increased coolant temperatures, the brake thermal efficiency of the engine was increased by 4–5% with LFB and CFB compared to diesel, due to reduced heat losses and better oxy-fuel combustion. The NO and CO2 emissions for high SFA fuel (LFB and CFB) were reduced by 19–22% and 0.2–6%, respectively, as compared to USFA rich fuel (WCOB and KB) and diesel fuel. However, smoke emissions were found to be higher for CFB, WCOB, and KB than diesel, but LFB produced 4–6% less smoke than USFA (WCOB and KB) and diesel fuel. The study concludes that coolant temperature influences engine performance and pollutants, but use of appropriate SFA-level biodiesel could reduce emissions without compromising thermal efficiency.