Fuel and Diluent Effects on Diesel Odor Species in a Premixed Flat Flame

As a group of diesel engine exhaust products, oxygenated hydrocarbons have been found to be responsible for the characteristic diesel odor. Contadictory effects of fuel properties on the emission levels of these species in both diesel engines and spray burner experiments have been reported. In the present study, a prevaporized premixed flat flame was used to investigate the fuel and diluent effects on these species. The results suggest a definite fuel effect on formation rates of oxygenates. In general, aromatic fuels produced higher concentration levels of oxygenates than paraffins, and the oxygenate concentration increases as the carbon number increases for the straight chain compounds. GC/MS analysis of the oxygenate fraction of the samples indicated a similar oxidation mechanism for all alkanes. Branching of alkanes was found to lead to more cyclization, but not always higher oxygenate levels. The addition of CO₂ as a diluent in the combustion air increased the levels of oxygenates in the flame and post flame zones. However, diffusivity of the mixture was found to have no such effect. GC/MS analysis of the CO₂ diluted samples indicated a suppression of ring formation relative to air only samples.