A numerical study on the laminar diffusion and premixed flames for methane−air and methane−ethanol with ozone at atmospheric and elevated pressures

Abstract

This work elucidated the laminar diffusion and premixed flames for methane–air and methane–ethanol (20 % and 40 %) with ozone concentrations of 100 ppm and 5000 ppm from 1 bar to 10 bar. The predicted diffusion flames were sensitive to ozone but depended on the fuels and pressures. At 1 bar, ozone induced higher peak flame temperatures and acetylene (C2H2) but with lower flame heights and soot. At higher pressures, the soot yields predicted for methane were increased by ozone whereas those for methane–ethanol were varied non-linearly. Meanwhile, C2H2 and soot formation were raised with ethanol while the maximum flame temperatures behaved non-monotonically. Besides, ethanol extended the flames with ozone at 1 bar but shortened these flames from 2 bar onwards whereas this trend was opposite for the flames without ozone. Owing to the higher pressures, the diffusion flame heights, temperatures and soot were raised. C2H2 for methane was unchanged while those for methane–ethanol flames were declined by 30 %. For the laminar premixed flames, ozone encouraged fuel decomposition and hence increased the laminar burning velocities for methane–air and methane–ethanol flames at all pressures by 11 % (maximum deviation). At 1 bar, the consumption of intermediate species concentrations i.e. formaldehyde (CH2O), hydroxyl (OH) and the formation of benzene (A1) and naphthalene (A2) were raised by ozone. At 2 bar and above, ozone generally produced lower intermediate species whereas inconsistent trends were found for the soot/polycyclic aromatic hydrocarbon (PAH) species. Separately, the effect of ethanol was only predicted at 1 bar, where the intermediate and soot/PAH species were promoted. As pressure increased from 1 bar to 10 bar, the laminar burning velocities and intermediate species for methane and methane–ethanol were decreased but with higher soot/PAH species.