Neat fuel influence on biodiesel blend emissions

Abstract

Abstract

The emissions of oxides of nitrogen (NO _x ) from biodiesel blended fuels reported in the literature vary from an NO _x increase to an NO _x decrease relative to the neat petroleum diesel fuel (PDF). To explain these NO _x differences, three PDFs with varying fuel properties were admixed with a neat soy-derived biodiesel at 10 per cent and 20 per cent volume ratios and evaluated using a heavy-duty diesel engine exercised over transient and steady-state cycles. The PDFs with ‘low’ and ‘medium’ cetane numbers led to a change in combustion phasing when blended with the neat biodiesel, resulting in reduced NO _x emissions at low engine power. The B100 blended with the ‘high’-cetane-number PDF showed minimal change in combustion phasing and resulted in an NO _x increase at all engine loads. The derived peak in-cylinder gas temperature variation correlated with the brake-specific NO _x emissions indicating that the thermal NO _x formation responds to the addition of biodiesel. The biodiesel blends had an NO _x —particulate matter trade-off, also suggesting a thermal NO _x effect. The increase in NO _x emissions of the biodiesel blends also had a strong correlation with the level of saturated hydrocarbons at high engine power.