Numerical combustion of aviation fuel part I: a cross-model comparison of n-heptane premixed flame

Four different n-heptane mechanisms were used to simulate a fuel rich n-heptane premixed flame and their results were compared with experimental measurements. In addition to discussion of the numerical performance of each mechanism, flux analysis coupled with the atomic distribution technique was used to find the major reaction pathways for fuel consumption, product formation, and the evolution of olefins and other intermediates. Hydrogen abstraction followed by B scission is the major fuel consumption route overtaken by unimolecular decomposition only at 1400-1500K. At that high temperature, however, not much fuel remains so that unimolecular decomposition reactions contribute insignificantly toward the overall fuel decomposition process. Low temperature chemistry of peroxy radicals forms a minor fuel consumption route in this premixed flame. Olefins are formed by B scission and consumed by direct decomposition, radical addition, and hydrogen abstraction reactions. The techniques and pitfalls of flux analysis were also discussed in order to map out a methodology that can be used to identify the true nature of the combustion chemistry. The results obtained from this study for n-heptane is critical to build practical combustion mechanisms for large paraffins, which are major components of liquid aviation transportation fuels. It should be recognized that the conclusions derived here arc for premixed flames, and may not apply to diffusion flames.