Autoignition-assisted flame regime of sustainable aviation fuel, ammonia and dimethyl ether blends

This project aims to study the combustion behavior of a new class of sustainable and environmentally friendly fuels for energy applications. Such new fuels will help reduce carbon emissions in the energy, transportation, and industrial sectors. One of the critical components of the new fuel is ammonia (NH3), a fuel with high hydrogen content. While ammonia can be stored and transported more safely than hydrogen, ammonia combustion differs from traditional fossil fuels like gasoline, diesel, and aviation fuels. Therefore, this research project aims to investigate a combination of ammonia and a highly reactive and biomass derived Dimethyl Ether (DME) to replicate the practical combustion behavior of traditional fossil fuels. Flame speed and ignition delay are two fundamental fuel mixture characteristics that play significant roles in the combustion process. Both characteristics have been studied extensively for their importance in designing and developing advanced combustion systems. However, the combustion regime in which the flame and autoignition simultaneously affect the combustion process is not well understood. This combustion regime is called autoignition-assisted flame and has a different morphology and characteristics with respect to traditional laminar premised or diffusion flames. In this combustion regime, the flame propagates over a pool of intermediate species, which are produced due to the low-temperature chemistry of the mixture. The research objective here is to understand and quantify the autoignition-assisted premixed laminar flame of ammonia and DME blends at elevated gas temperatures and pressures. The flame regimes across various gas temperatures, pressures, equivalence ratios, and Damkӧhler numbers will be investigated experimentally and numerically. The Rapid Compression Machine–Flame (RCM-FLAME) apparatus is used to study the flame regime with several optical diagnostic techniques. The proposed project has four transformative aspects: (1) quantification of flame propagation speed over a wide range of physico-chemical conditions, (2) experimental investigation of the effects of first-stage and second-stage autoignition on flame propagation speed, (3) the effect of stretch on outwardly propagating spherical autoignition-assisted flames, and (4) accuracy of kinetic models developed in simulating the combustion of ammonia-DME mixtures. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.