Evaluation of Biodiesel Blends on the Performance and Emissions of a Common-Rail Light-Duty Engine and Vehicle

Today most of the European member states offer diesel fuel which contains fatty acid methylesters (biodiesel) at a range between 0.5 to 5% vol. In order to meet longer term objectives, the mixing ratio is expected to rise up to 10% vol. in the years to come. The question therefore arises, how current engine technologies, which were not originally designed to operate on biodiesel blends, perform at this relatively high mixing ratio. A number of experiments were therefore performed over several steady-state operation modes, using a 10% vol. biodiesel blend (palm oil feedstock) on a light-duty common-rail Euro 3 engine. The experiments included measurement of the in-cylinder pressure during combustion, regulated pollutants emissions and fuel consumption. The analysis showed that the blends tested present good fuel characteristics. Combustion effects were limited but changes in the start of ignition and heat release rate could still be identified. The palm-oil biodiesel resulted in both higher and lower smoke and NOx emissions over the engine map, depending on the operation point. This was attributed to effects of both the chemistry and the physical properties of the biodiesel. The detailed results collected on the engine bench were then compared against a Euro 3 common-rail light-duty vehicle driven on the chassis dynamometer, to also include the effect of typical diesel emission control system (EGR and oxidation catalyst). In addition to the palm biodiesel, an RME-diesel blend was also tested to examine the effects of a fuel with different characteristics. When used on the vehicle under transient engine operation, both biodiesel blends reduced PM emissions. Marginal effects on NOx over the certification test could be identified, while the palm-oil biodiesel gave higher NOx emissions over more transient driving cycles. The results of this study show that up to 10% biodiesels could be used on current diesel vehicles, without expecting much difference on their emission performance. Of course long-term effects of biodiesel use still need to be considered, further to the direct effects on diesel emissions.