Impact of n-butanol addition to hydrogenated catalytic biodiesel fueled a constant volume combustion chamber; a computational study

Abstract

ABSTRACT The continuous quest for renewable, efficient, and clean energy sources has led to significant advances in the field of biodiesel production. Hydrogenated catalytic biodiesel (HCB) seems to be a promising option among various renewable biodiesel fuels which can be obtained from waste cooking oil. However, its extreme ignitability limits its application in existing engines. Therefore, a blend of n-butanol and HCB has been proposed in the present study, aiming to explore the spray combustion and soot formation behavior of these blends as a step toward the best possible utilization of this blend in engine. The objective was to examine the impact of adding n-butanol to HCB fuel on spray combustion and soot particles. A new skeletal chemical kinetic model of HCB/n-butanol blend was introduced and validated through measured data reported in the literature. Numerical studies have been performed in a constant volume combustion chamber under reactive spray environments. The simulation results concluded that, blending 20%, 40%, and 60% n-butanol with HCB fuel increased the heat release rates by 31.6%, 47.8%, and 87%, respectively. Furthermore, introducing a 20% of n-butanol into HCB fuel resulted in a 35.7% increase in ignition delay time and a 35.3% increase in flame liftoff length. These results demonstrated the reactivity of n-butanol/HCB mixture experienced a decrease when increasing the n-butanol fraction in the blend, while the fuel atomization was improved. The simulation results also demonstrated a notable reduction in the equivalence ratio when the n-butanol addition ratio was increased, which was a result of the entrainment effect that enhanced the mixing of fuel spray and surrounding fresh air. The simulation results also demonstrated that, adding 20%, 40%, and 60% n-butanol to HCB fuel resulted in a 25%, 43%, and 50% reduction in soot mass of HCB, respectively. This was mainly attributed to the less amount of C2H2, A1, and A4 species with n-butanol addition. Consequently, this sequential reduction leads to suppression of PAHs growth, nucleation, surface growth, and soot coagulation. Besides, a longer flame length resulting from the increased blending ratio of n-butanol could also have an additional soot suppression effect by improving air-fuel mixing and thus suppressing the overall soot mass.