Experimental and Modeling Investigation of NO Formation Mechanism for Biodiesel and its Blend with Methanol 2019-01-0217
Biodiesel makes an attractive option to replace fossil diesel owing to its applicability in diesel
engines without major modifications. An increase in oxides of nitrogen (NOx) emissions with
biodiesel compared to diesel is a major concern for its wider use. Blending alcohols, such as
methanol, with biodiesel is a potential remedy to mitigate NOx formation. Several experiments
have been performed so far in different engine types to confirm this effect. However, computa-
tional investigations studying the effects of biodiesel-methanol blends on NO formation are scarce. A combined experimental and computational approach is adopted here to investigate the NO formation mechanisms with neat biodiesel and biodiesel-methanol blend fueled light duty diesel engine. Firstly, a new compact kinetic model is utilized consisting of oxidation reactions for methyl butanoate and n-dodecane as a surrogate for biodiesel. A surrogate is defined to represent biodiesel based on a combined property and functional group based approach. This kinetic scheme is comprehensively validated for its component kinetics and available fundamental combustion experiments for biodiesel. Later, the suitability of the surrogate is examined by comparing the predicted 3D CFD engine simulations with experiments for combustion and emission characteristics of neat biodiesel. The simulations performed using the surrogate show a good agreement with the experiments. Finally, a methanol sub-mechanism is incorporated in the biodiesel surrogate to investigate the effects of biodiesel-methanol blend. Again, a comparison has been made between the biodiesel-methanol blend engine experiments and computations. The results obtained from the present work and the discussions provided therein provide better understanding of the NOx formation mechanism and its mitigation in biodiesel fueled diesel engines.