Effect of Biodiesel Blending on Emission Characteristics of Modern Diesel Engine 2008-01-2384

The use of biodiesel fuels as an alternative fuel for petroleum diesel fuel is very effective for the reduction of CO₂ emission, because biodiesel is produced from renewable biomass resources. Biodiesel is usually blended to conventional diesel fuel in various proportions. It is possible that this biodiesel blending causes the problems on emission characteristics of modern diesel engine, because it could be confirmed that the application of neat biodiesel to modern diesel engines whose control parameters were optimized for conventional diesel fuel deteriorated the emission performances. It is necessary to clarify the effect of biodiesel blending on exhaust emissions of modern diesel engine.

Rapeseed oil methyl ester (RME) was selected as a biodiesel used in this study. Biodiesel blended fuels were applied to the multi-cylinder light-duty diesel engine which included the various latest technologies for low emission (e.g. common-rail injection system, cooled-EGR system, variable geometry turbocharger (VGT), and aftertreatment systems).

RME blending increased in engine-out NOx emission, as mentioned by many researchers. The main reason for that is a decrease in EGR rate with blending RME. In addition, an increase in NOx emission by RME blending was clarified more at tail-pipe, because the rich spike blended with RME for lean NOx trap (LNT) degraded the NOx reduction performance of LNT. An increase in oxygen content in the fuel with blending RME caused the drastic reduction of engine-out smoke emission, but high blending rate of RME increased tail-pipe PM emission. This is caused by an increase in soluble organic fraction (SOF) emission derived from poor volatility of rich spike which contains the large amount of RME. The results of JE05 transient mode test showed the same tendency of tail-pipe emissions at steady-state operation as mentioned above.

These test results denoted that biodiesel blending led to a simultaneous increase in NOx and PM emissions of modern diesel engine without engine modifications. However, the optimizations of intake air and rich spike injection conditions according to blending rate of biodiesel will make it possible to meet the future emission regulations.