A laboratory investigation on the effects of unsaturated bonds and chain lengths of different biodiesel feedstocks on carbon dioxide, carbon monoxide, and methane emissions under low-temperature combustion

Abstract

Biodiesel fuel is produced from various types of feedstock and as a result, its chemical composition and exhaust emissions may vary depending on the feedstock type. In this study, combustion of three biodiesel fuels derived from soybean methyl ester (SME), waste cooking oil (WCO), and tallow oil (TO) was carried out separately in a combustion chamber to better understand the effects of feedstock type on carbon dioxide (CO2), carbon monoxide (CO), and methane (CH4) emissions under low-temperature combustion (LTC) and fuel-rich conditions. Additionally, blended biodiesel fuels, B20 and B50, with ultra-low sulfur diesel (ULSD) of these biodiesel fuels were examined. From the impact of different biodiesel feedstocks on combustion parameters, linear relationships were observed between the fuels and the peak combustion temperature and pressure (R2 values ranging from 0.82 to 0.98). ULSD showed the highest emission of CO and the lowest emissions of CO2 and CH4 among the other fuels. Compared to ULSD, it was found that the use of pure biodiesel fuels reduced the CO and enhanced CO2 emissions by a factor of 1/3 and 3, respectively. Biodiesel fuel with a high degree of unsaturation and high portion of long methyl esters such as SME appeared to produce more CO and less CO2 emissions than those with low degrees of unsaturation and short chain lengths (WCO and TO). It is thought that the length of fatty acid methyl esters (FAMEs) affects the emissions because shorter chains, which contain less unsaturated structures, have the high oxygen-to-carbon ratio.