The Effects of Biodiesel Blending on Regulated and Unregulated Emissions from a Single-Cylinder Compression Ignition Engine

Increased industrialization and world population have caused a steep growth in petroleum fuels demand and corresponding concerns about their environmental impact. One alternative to petroleum diesel is biodiesel, a renewable oxygenated liquid fuel made from fatty acid methyl or ethyl esters. Biodiesel can form blends with petroleum diesel fuel at any ratio and, thus has the potential to partially, or totally, replace petroleum diesel for compression ignition (CI) engines. Although biodiesel has similar physical properties as petroleum diesel, its chemical nature affects the engine performance and exhaust emissions.;In this study, the effect of biodiesel fuel properties on emissions of regulated and unregulated (but hazardous) exhaust constituents were examined for four biodiesels, produced from palm, jatropha, soybean, and beef tallow oil. These fuels were blended with Ultra Low Sulfur Diesel at proportions of 5%, 10%, 20%, 50%, and 100% (v biodiesel/v diesel). The engine utilized was a single-cylinder Yanmar L100V, 0.435L, CI engine that has been upgraded to utilize a high-pressure common-rail fuel injection system. In addition to examining the emissions of criteria pollutants (NOx, CO, and PM), data was collected on the emissions of individual hydrocarbon species, particularly formaldehyde. Formaldehyde is usually the most abundant carbonyl in engine exhaust and ambient air and is also classified as human carcinogen by the International Agency for Research on Cancer.;Results of this study show a decreasing trend for brake specific NO x emissions with both increasing biodiesel content and increasing load which is probably due to engine injection optimization to account for differences in cetane number, fuel viscosity, and energy content between ULSD and biodiesel blends. Decreasing trends of carbon monoxide and total hydrocarbon emissions were observed with both increasing biodiesel content and increasing load. The reduction was assumed to be associated with a hotter combustion environment and the presence of oxygen in the fuel structure. The results also showed a non-linear increase in PM with biodiesel content with the peak emissions at B50 for all biodiesel feedstocks. This finding is contrary to most of the existing literature; therefore, a more extensive investigation into PM emissions was suggested. Results of formaldehyde emissions differed for the various biodiesels, with jatropha and soybean showing higher levels of formaldehyde emissions while beef tallow and palm showed lower levels. Viscosity and energy content were the two fuel properties most closely correlated with this behavior. Overall, formaldehyde emissions decreased substantially less than total hydrocarbon emissions. It means that the use of biodiesel does not reduce emissions of individual harmful combustion products as much as it reduces total hydrocarbon emissions.