NOx emissions from low-temperature combustion of biodiesel made of various feedstocks and blends

• Qualitative analysis of various biodiesel feedstocks by using FTIR.
• Ignition delay increased when the portion of biodiesel increased.
• Ignition temperature decreased when the portion of biodiesel increased.
• Ignition delay and ignition temperature are related to the degree of unsaturation.
• For biodiesel, NOx emitted from highly unsaturated feedstock at LTC.

Nitrogen oxides (NOx) are one of the major hazardous emissions from biodiesel-fueled engines that need to be regulated stringently. In this paper, NOx emissions from different types of biodiesel were studied using a laboratory combustion chamber. Biodiesel fuels with various portion of fatty acid methyl esters (FAMEs) from soybean methyl ester (SME), tallow oil (TO), and waste cooking oil (WCO) were combusted at 330–420 °C simulating low-temperature combustion (LTC). Combustion analysis results show that neat biodiesel fuels had longer ignition delay and lower ignition temperatures compared to ultra-low sulfur diesel (ULSD). The unsaturation of biodiesel samples and their blends with ULSD was analyzed for its effects on NOx emissions. The results showed that biodiesel with more unsaturated fatty acids emitted more NOx compared to biodiesel with more saturated fatty acids. A paired t-test showed that neat TO, WCO, and WCO B50 had significant reduction in the formation of NOx compared with ULSD and SME B20. It is concluded that less unsaturated FAME fuels would be preferable when reduction of NOx emissions is a critical issue.