Understanding the spray ignition process is of utmost importance due to the fact that modern combustors in aircraft need to be (re)-ignited under a wide range of (sometimes extreme) operating conditions. Since in many of these combustors spark ignition systems are installed, the amount of spark energy required for successful ignition over a range of operating conditions must be known. In addition, the desire to prevent unwanted explosions in transportation and storage of combustibles motivates exploring the mechanisms at play during the process of ignition. The presence of liquid fuel in the form of a multi-sized spray of droplets that must be ignited only serves to increase the difficulty of ignition.
A new mathematical analysis is presented of the ignition of a spray/air mixture by an infinite heated surface. In contrast to previous work in the literature the entire history of the ignition process is accounted for starting from the flame embryo progenitor stage, through the thermal runaway stage to the final flame propagation stage. For tractability at the current stage the chemical kinetics is taken to be that of a single global reaction. The spray is modeled using the sectional approach and the influence of fuel spray characteristics on ignition is determined. Delay in ignition due to the build-up of vapour from the fuel droplets as well as heat loss to the droplets for evaporation are found to play a role.
