A Review on the Effects of Biodiesel Blends on Compression Ignition Engine NOx Emissions

Abstract

Biodiesels are produced by the transesterification of corresponding triglyceride feedstocks of vegetable (example: soybean, canola, palm, karanja) or animal fat sources. Currently, the leading feedstocks are soybean oil in the U.S., canola oil and rapeseed oil in Canada and Europe, and palm, karanja, jatropha and other oils in Asia. Due to the cost and production considerations of these biodiesels, blending biodiesels with the petroleum fuels appears to be a prudent option in the near-term. The use of biodiesels in compression ignition engines results generally in a reduction in the emissions of carbon monoxide (CO), hydrocarbons (HC), and particulate matter (PM), but a slight increase in the oxides of nitrogen (NOx ) emission. The reported NOx emissions do not exhibit definitive trends and the results are significantly influenced by many factors, including engine type and design, test cycle, start of injection, ignition delay, fuel composition, adiabatic flame temperature, radiative heat transfer, fluid dynamics and combustion phasing. Due to appreciable variations in the physical properties and the highly nonlinear nature of the combustion process, the NOx emission with biodiesel blends does not vary monotonically with the percentage of biodiesel in the blend. Hence, the intricate dependence of NOx on biodiesel and its blending effect cannot be completely explained under all engine type and operating conditions. Although the literature contains several studies on the performance and emissions of compression ignition engines fueled with neat biodiesels, the information on the effects of blends is scattered and has not yet achieved a definitive status to explain the blending effect on NOx . Hence, this work was motivated to review the available data with respect to the NOx emission from engines fueled with the petroleum diesel/biodiesel blends.