Characteristics of ethylene and methane combustion in a range of high temperature and low oxygen environments

New understanding of turbulent jet flames of natural gas, and blends of natural gas with ethylene (C2H4), issuing into a range of preheated coflowing oxidisers with reduced oxygen (O2) concentrations are reported. Comparisons are made for coflow O2 concentrations of 3 %, 4 %, 5 %, 6 %, 9 % and 11 % and coflow temperatures of 1250 K, 1315 K and 1385 K. Instantaneous and simultaneously planar imaging measurements of temperature, hydroxyl radicals (OH) and formaldehyde (CH2O) were taken at eight locations ranging from 9 mm to 75 mm downstream of the jet exit plane. The experimental data is supplemented with chemical reaction modelling. It is shown that increasing the proportion of C2H4 in the fuel supply resulted in an increase in the flame front temperature. At 3 % O2, CH2O signal did not very between the three fuels containing C2H4, whilst at 9 %, the signal increased with increasing C2H4. OH number density was highest for a blend of 66 % NG and 33 % C2H4. The fuel composition made little effect on the jet spread rate. Reaction modelling found evidence of changes in the reaction process, both in the suppression of reactions with different fuels, and in the suppression of reactions, and the locations they occur, with reducing O2 concentrations. Reaction modelling also found a significant decrease in ignition delay when C2H4 was present in the fuel mixture, and an increase in ignition delay as all four fuels transition to MILD combustion.