Spray and combustion characteristics of neat acetone-butanol-ethanol, n-butanol, and diesel in a constant volume chamber

Intermediate product of biobutanol production, acetone-butanol-ethanol (ABE) as an alternative fuel has drawn increasing attention in recent years due to its potential to eliminate various production costs. In this work, neat acetone-butanol-ethanol (ABE) with a component volumetric ratio of 3:6:1, n-butanol, and neat diesel were studied in a preburn type constant volume chamber with optical access. The ambient temperature and oxygen ranged from 800 to 1200 K and 21% to 11%, respectively, covering both conventional and low temperature combustion (LTC) regimes. Time resolved images of the spray and natural flame luminosity (indicator of soot) were captured by a high speed camera coupled with a copper vapor laser beam. The images show that the flame lift-off length and liquid penetration of n-butanol and ABE are much longer and shorter, respectively, than that of diesel under all tested conditions. This results in a longer "gap" between the liquid spray and the flame in ABE and n-butanol combustion that provides more space and time for the droplets to evaporate and mix with the ambient air, which is expected to decrease the local equivalence ratio at the combustion region. Indeed, the natural flame luminosity of ABE and n-butanol is reduced significantly under all tested conditions compared to that of diesel. For all the tested fuels, especially ABE, the combustion duration decreases with the reduction of ambient temperature due to a stronger premixed combustion, while it increases with the reduction of oxygen concentration due to the dilution effect. Therefore, ABE has a high potential to reduce soot emissions when used in diesel engines, but it would also suffer from combustion phasing retardation like butanol under LTC conditions with high EGR.