Effect of Exhaust Gas Recirculation on Exhaust Emissions from Diesel Engines Fuelled with Biodiesel

Application of biodiesel fuel (BDF) to diesel engine is very effective to reduce CO₂ emission, because bio-diesel is carbon neutral in principle. However, when biodiesel was applied to conventional diesel engines without modification for biodiesel, NOx emission was increased by the change in fuel characteristics. It is necessary to introduce some strategies into diesel engines fuelled with biodiesel for lower NOx emission than conventional diesel fuel case. The purpose of this study is to reveal that exhaust gas recirculation (EGR) is one of the solutions for the reduction of NOx emission and meeting the future emission regulations when using biodiesel.

Neat Rapeseed oil methyl ester (RME) as a biodiesel (B100) was applied to diesel engines equipped with high pressure loop (HPL) EGR system and low pressure loop (LPL) EGR system. Cooled HPL EGR was increased during steady-state operations and JE05 transient mode tests. An increase in HPL EGR rate drastically reduced NOx emission, and did not increase PM emission, because soot formation was suppressed by the oxygen in RME. It could be confirmed that an increase in EGR rate made it possible to achieve low emission meeting 2009 regulation in Japan.

Engine-out emissions measurements were made to develop a comparison between HPL and LPL EGR in steady-state operation test. LPL EGR improved CO and NOx emissions, compared with the case of HPL EGR. An increase in the rate of LPL EGR caused simultaneous reduction of NOx and smoke emissions.