Effects of fuel components and combustion parameters on the formation mechanism and emission characteristics of aldehydes from biodiesel combustion

The effect of fuel components and combustion parameters on the emission characteristics of aldehydes from biodiesel combustion is investigated, and the formation mechanism of aldehydes is revealed. The results show that CH2O and CH3CHO are the main aldehydes produced during biodiesel combustion. The rise in initial temperature and pressure reduces the formation of aldehydes, which accelerates the generation of reactive radicals to promote the oxidation of aldehydes. As the equivalence ratio decreases from 2.0 to 0.5, the concentrations of formaldehyde and acetaldehyde decrease from 444.58 to 438.19 mu g/m3 to 164.72 and 6.71 mu g/m3, respectively, due to the oxidation and dilution effect of air on aldehydes. In addition, when the number of C--C bonds in biodiesel is increased from 0 to 1, the concentrations of formaldehyde and acetaldehyde are enhanced by 117.89 % and 12.74 %, respectively, because of the reduction in the content of reactive radical H. The main formation pathway of aldehydes is as follows: Biodiesel is initially consumed via H-abstraction reactions by reactive radicals (OH, H, etc.) to produce primary fuel radicals, which mainly undergo beta-decomposition to form key oxidation intermediates (C4H6, C2H4, C2H3, etc.). Consequently, these small molecular intermediates will be converted to aldehydes by oxidation and dehydrogenation reactions.