Neat fuel influence on biodiesel blend emissions

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.