Effect of fuel air equivalence ratio on the flameless combustion of liquid hydrocarbon

A laboratory scale model combustor was designed based on flameless combustion of liquid spray in a microturbine atmosphere. The effects of fuel (0# diesel)/air equivalence ratio Φ on the flow field, combustion regime, range of flameless mode, temperature and pollution emissions of the model combustor were studied mainly through experiments and supplementally numerical computation. The results indicate that there is an obvious ring vortex in the flow field, which provides a basis of fluid dynamics for the recirculation of high-temperature exhaust gases. The mixture of species around the fuel nozzle is significant to the conversion of the combustion regime. The operation range of the flameless mode in the model combustor is 025≤Φ≤050, and in which the combustion temperature is homogeneous. The average chamber temperature Tavg and pollutant emissions are impacted by Φ and the thermal input. At the same thermal input conditions, Tavg increases and the emissions of CO and NOx drop with increasing Φ in the experimental range. At the same Φ condition, Tavg drops and the emissions of CO and NOx increase with the decrease in thermal input. The lower the thermal input, the faster the growth in CO emission amount, while NOx is affected much less. It can be concluded from the analysis that appropriate preheating of combustion air is an effective way to enhance the lean combustion stability with low chamber heat density and expand lean flammability.