Impact of biodiesel application at various blending ratios on passenger cars of different fueling technologies

The effect of biodiesel on emissions of diesel passenger cars is a combination of the fuel properties, the blending ratio, and the vehicle technology. In this study, saturated and unsaturated biodiesel fuels were tested neat (B100) and in 30% blend with fossil diesel (B30) on two Euro 3 diesel passenger cars of different engine technologies, namely common rail and unit injector. The measured dataset is enlarged by introducing B10 results from an earlier study [15] in order to produce generalized conclusions over a wider range of blends. None of these vehicles was equipped with a particle filter and different conclusions might be reached for filter-equipped vehicles. The results indicate that the influence of biodiesel on pollutant emissions primarily depends on the blending ratio and secondly on the level of unsaturation and engine technology. Tailpipe CO2, NOx and PM emissions with biodiesel varied from −1% to +3%, −1% to 14%, and −18% to −35%, respectively, compared to fossil diesel. The difference over fossil diesel generally increased with an increasing blending ratio. CO and HC emissions increased over the fossil diesel but remained at low levels and did not threaten the compliance of the vehicles with their respective emission limits. Use of biodiesel on the common rail vehicle led to a smaller NOx increase and a higher PM reduction than in the unit-injector case. The unsaturated fuel generally led to higher NOx emissions from both engine technologies. However, the maximum blending ratio of saturated biodiesel is limited to around B30 due to cold-flow limitations. Hence, the saturated vs. unsaturated species ratio should be carefully designed in market fuels in order to optimize environmental and operational benefits. Overall, it appears that blends up to 10% v/v may be introduced with limited urban air quality implications.

► The impact of biodiesel fuels on regulated pollutants increases with concentration of the biodiesel in the fuel.
► Straight biodiesel at passenger cars increases NOx emissions up to 16% while it decreases PM by 70%.
► The common rail technology compared to unit injector is more compatible with the use of biodiesel due to lower emissions.
► Unsaturated biodiesels favor NOx formation. Saturated biodiesels are limited by low temperature behavior.