The effects of nitrogen-containing compounds on PAH and soot across a suite of laboratory devices

The effect of nitrogen-bearing fuel additives on soot and PAH emissions formation has been investigated in a collaborative university, industrial and governmental effort. The overall objective of this program was to obtain fundamental understanding of how changes in fuel composition can effect soot and PAH emissions from military aircraft combustors. Six different laboratory burners, including a premixed flat flame, an opposed-flow diffusion flame, a well-stirred reactor, a turbulent spray flame, a shock tube, and a high pressure turbulent combustor were used to investigate the impact of additives covering a wide range of combustion conditions. The additives included various nitroalkanes (nitromethane, nitroethane, and nitropropane), i-propylnitrate, nitrogen dioxide, pyridine and quinoline. Fuels included ethylene, a heptane/toluene blend and JP8. The effects of many of the additives were examined in most experimental facilities and the results were contrasted and compared. The experimental results were also modeled using a variety of modeling packages and mechanisms. Reductions in soot were as large as 70%, although in some cases no change was detected; in others, increases were observed. Modeling failed to offer explanations for all of the experimental observations. This paper will summarize the key results, our interpretations, and suggest some needs for future research.