Investigating the role of atomization on flame stability of liquid fuels in an annular spray burner

Atomization, vaporization, turbulent mixing, and the chemical kinetics of a liquid fuel impact the combustion efficiency, stability, and emissions within IC engines. When fuels with varying physical properties are used in the same fuel injection system, they can exhibit very different atomization, represented by droplet size (SMD) and spray droplet distribution (SDD), which can then potentially influence the flame stability. In the current paper, the effect of the atomization process on flame stability is investigated by using a single nozzle size with three different hydrocarbon fuels, i.e., n-heptane, n-dodecane, and toluene. This study also investigates the flame stability for the same fuels using a unique approach in which nozzle sizes are selectively varied for each fuel to control the atomization process and minimize differences in the spray characteristics. The results show that the atomization process plays a major role in the flame liftoff heights and blowout limits. n-Dodecane, which produces the largest droplets and exhibits the lowest volatility, experiences highest flame liftoff heights and the greatest resistance to flame blowout compared to the other tested fuels. When the atomization process is controlled, more similar liftoff heights and blowout limits for all fuels were observed. The differences in liftoff height was shown to be a result of two-phase (spray) flame speed (i.e., pre-vaporized fuel reactivity (SL), and time scales associated with droplet evaporation). Differences in blowout was shown to be largely tied to fuel volatility, droplet size (i.e., the liquid loading into the flame), and the heat of combustion.