Shock tube combustion of liquid hydrocarbon sprays of toluene

Abstract

The liquid spray combustion of toluene has been studied in shock waves at temperatures between 900 and 2000 K and pressures up to 20 bar in oxygen–argon mixtures. The ignition delays were found to be dependent on the pressure and or fuel/oxygen ratio and the presence of up to 10% of additive. Two types of combustion were found: Type I occurred at lower temperatures and gave a steady combustion where the pressure rose steadily. Type II was detected at higher temperatures and in the presence of certain additives and gave a very sharp ‘spiked’ pressure rise. This phenomenon may be due to the occurrence of small droplet explosions or microcombustions and is similar to that of ‘knock’ in engines. The effect of additives on the ignition delay time depended on both the additive used and the concentration. 1% DTBP (di-tert-butyl peroxide) in the toluene has little effect on the ignition delay but 10% DTBP reduced it a little. 5% IPN (isopropyl nitrate) and EHN (ethyl hexyl nitrate) both had a neglible effect on the ignition time in this temperature region. IPN was also found to affect the type of combustion, changing it from Type I to Type II.