The Mineta National Transit Research Consortium at San José State University recently released a study on the generation of various pollutants during low-temperature combustion (LTC) of several types of biodiesel in comparison to ultra-low sulfur diesel (ULSD).

The results of the peer-reviewed report showed that certain sources (feedstocks) of biodiesel produced less pollution than others under certain combustion conditions.

In addition to being a renewable energy source for the transportation sector and reducing exhaust emissions, biodiesel may have the advantage of reducing the size and number of soot particles emitted. The resulting recommendation is that energy policies and environmental regulations leverage the proper choice of biodiesel feedstocks and blending ratios to optimize combustion efficiency and environmental sustainability.

The Mineta study focused on generation of nitrogen oxides (NOx), particulate matter (PM) and carbon emissions from LTC of different grades of biodiesel from three different feedstocks: soybean methyl ester (SME), tallow oil (TO), and waste cooking oil (WCO). Biodiesel containing more unsaturated fatty acids emitted higher levels of NOx than the biodiesel with more saturated fatty acids. Thus, biodiesel with fewer unsaturated fatty acid methyl esters such as TO and WCO would be preferable when reduction of NOx emissions is desired. The performance of a bus that ran on blended biodiesel was found to be very similar to that of one that ran on ULSD, and drivability was not an issue with blended biodiesel.

“Biodiesel is being industrialized as one of the potential sources of sustainable energy for transportation in the future,” said Dr. Ashok Kuma, the study’s principal investigator. “This study provides additional justification for the use of biodiesel as an alternative fuel compared to regular diesel.”

The study recommends that governments consider using particular blends of biodiesel in urban and commercial vehicles to enhance the quality of air and to promote healthy living. Meanwhile, agriculture departments should publish guidelines for farmers for growing environmentally friendly biodiesel feedstock.