NO<inf>x</inf>Mitigation Strategy for Oxidized Biodiesel in a Heavy-Duty Truck Diesel Engine

Unsaturated methyl esters in biodiesel make it susceptible to oxidation and fuel quality degradation upon long-term storage. It is almost impossible to use biodiesel for commercial applications immediately after production. The lead time between biodiesel production and usage is generally high, causing auto-oxidation and fuel quality degradation. Hence any onsite improvement in fuel quality should be tested with aged biodiesel. To avoid the food versus fuel debate, non-edible oil feedstocks are preferable for producing biodiesel. However, biodiesel from non-edible oil sources has more unsaturated methyl ester constituents. The traditional trade-off between oxides of nitrogen (NOx) and soot emissions in conventional diesel combustion is reduced to a more severe NOx problem with biodiesel. In the present study, NOx mitigation through fuel modifications is studied for oxidized biodiesel produced from a non-edible oil, Karanja. The effects of blending ethanol and butanol with oxidized Karanja biodiesel for NOx mitigation are studied through experimental investigations in a heavy-duty truck diesel engine. The Karanja biodiesel is stored for one year in a 200-litre steel barrel at room conditions to mimic commercial storage conditions. 5% alcohol blended with biodiesel is used for analysis, and results are compared with diesel and oxidized biodiesel. The results show that alcohol blending to biodiesel advances fuel injection timings and decreases ignition delay. Even though the NOx emissions of oxidized biodiesel are higher than that of diesel, a 5% blend with ethanol helps bring down NOx close to the level of diesel. Ethanol is a better choice than butanol for NOx mitigation due to its higher latent heat of vaporization and associated cooling effect. It is also observed that blending with alcohol reduces smoke and NOx emissions of oxidized biodiesel.