Diesel/methanol dual-fuel combustion: An assessment of soot nanostructure and oxidation reactivity

The use of renewable methanol partly substituting diesel fuel can support the transition to low-carbon engines, in the form of diesel/methanol dual-fuel combustion. Particulate filters are still required for diesel/methanol dual-fuel combustion engines to meet the emission standard. Their periodical regeneration depends on the soot oxidation reactivity and nanostructure. We therefore assessed the influences of premixing methanol on soot oxidation reactivity and nanostructure at both engine loads. The results showed that increasing methanol substitution ratio shifted thermogravimetric profiles towards low temperature direction. The average activation energies of M20 and M40 samples (the methanol substitutions of 20% and 40%) dropped by 41.1-43.9 kJ/mol and 53.2-99.7 kJ/mol compared to diesel one at both engine loads, respectively. With an increase in methanol substitution ratio, a notable reduction in primary particle size was observed, with the shorter and more tortuous fringes as well as larger separation distance between the stacked fringes. The increasing trend in soot oxidation reactivity with methanol addition correlated well with the changes in primary particle size and fringe parameters, which means that soot oxidation reactivity highly depends on its morphology and nanostructure. It can be expected from the results that diesel/methanol dual-fuel operation has the advantages in engine fuel economy improvement regarding the regeneration of particulate filters.