Pollutant Emissions from Biodiesels in Diesel Engine Tests and On-road Tests

Abstract

Interest in biodiesel use is increasing due to concerns over the availability and environmental impact of petroleum fuels. In this study, we analyzed biodiesels prepared from seven different feedstocks: waste cooking oil, rapeseed oil, olive oil, palm oil, coconut oil, canola oil, and soybean oil. Exhaust emissions of gas-phase compounds (CO2, CO, NO2, NO, THC) and particulate matter were measured for each biodiesel and Ultra Low Sulfur Diesel (ULSD) during combustion in a diesel generator operating under different engine loads (0, 25, 50, 75, 100%). The composition of each biodiesel was also analyzed using a variety of chemical and physical tests to investigate the relationship between fuel properties and pollutant emissions. The results showed that both engine performance and biodiesel composition affected emissions levels. All brake-specific emissions decreased with increased of engine load because of high fuel efficiency at high loads. All of the biodiesels except coconut oil produced less THC emissions than ULSD, and soybean oil, palm oil, olive oil produced less CO than ULSD. Particulate matter emissions were reduced for all biodiesel fuels compared to ULSD. However, CO2 emissions from biodiesels were higher than ULSD. NO emissions from biodiesels were higher than ULSD at low load, but some of them started (ex. Palm oil) to perform better with increased load, and finally produced less NO than ULSD. All biodiesel produced less NO2 than ULSD. Considering NOx emissions in unit of g/kg fuel, NO increased and NO2 decreased with increased engine loads, resulting in highest total NOx emissions at 50% to 75% load, depending on the fuel. NO was the majority of total NOx emission. Biodiesel oxygen content was strongly correlated to PM and HC emissions. The H: C ratio, ratio of saturated fatty acids and degree of unsaturation of biodiesels all had a substantial effect on NO emissions. Density measurement was an easy way to predict total NOx from biodiesels. Methods of running on-road biodiesel truck tests and data analysis were developed. Both road condition and engine performance affected the formation of emissions. Vehicle specific power (VSP) was calculated to present real power required in on-road tests. Tests data of highways showed that CO and HC emissions (g/kg/fuel) decreased with the increase of VSP.