Effects of Cetane Number on High-Pressure Fuel Spray Characteristics with a Hot Surface Ignition Source

The concept of multi-fuel capable compression ignition (CI) engines aims to reduce the logistical burden of fuel sourcing efforts in the military supply chain. Achieving reliable performance when utilizing low quality fuels in unmanned aerial vehicle (UAV) CI engines involves many challenges and requires the development of novel ignition devices for long-term operation. In designing these devices, the limitations of existing hot-surface heating elements must be evaluated. An experimental study using a rapid compression machine (RCM) investigated the effects of cetane number on high-pressure spray ignition with a hot surface energy addition device. Three kerosene-based fuels were formulated by the Army Research Laboratory (ARL) to have nearly identical physical properties but variable auto-ignition behavior. The experiments were performed at conditions relevant to light-duty CI engines for UAVs at increased elevation. Results demonstrate that unassisted spray ignition results in two-stage ignition after the injector has closed. In contrast, at high heating element surface temperatures the ignition behavior is dominated by high temperature chemical pathways, and the effect of fuel reactivity on combustion heat release is reduced.