Glow-plug-assisted combustion of nitromethane sprays in a constant volume chamber

Experimental investigations on spray combustion of nitromethane in air within a constant volume chamber are presented. The sprays produced by a commercial gasoline injector, were ignited by using a pair of glow plugs, while the initial chamber pressure was varied from 1 bar to 7 bar. The nature of the combustion processes at various initial pressures was elucidated by measuring the pressure rise as well as using FTIR spectroscopy of the combustion products, and high speed photography. The maximum differential pressures reached during combustion were found to increase with chamber pressure up to 4 bar, and decrease thereafter while the ignition delays were found to be in the order of 10 ms for all pressures. The global equivalence ratio was found to vary from 0.43 at an initial pressure of 1 bar to 0.06 at an initial pressure of 7 bar, thus reducing the flame temperatures achieved within the chamber with increasing chamber pressures. The trends observed in the calculated heat release rates, cumulative heat released, and rate of heat loss from the chamber were found to provide key insights into the combustion process, which was concluded to be occurring through three distinct processes – turbulent premixed combustion, turbulent spray combustion, and turbulent film combustion. The effects of decreasing flame temperatures on the three processes were discussed in detail.