Assessment of the Ignition and Lift-off Characteristics of a Diesel Spray with a Transient Spreading Angle

Multi-hole diesel fuel injectors have shown significant transients in spreading angle during injections, different than past fundamental research using single-hole injectors. We investigated the effect of a this transient spreading angle on combustion parameters such as ignition delay and lift-off length by comparing a three-hole nozzle (Spray B) and single-hole nozzle (Spray A) with holes of the same size and shape as targets for the Engine Combustion Network (ECN). With the temperature distribution for a target plume of Spray B characterized extensively in a constant-volume combustion chamber, the ignition delay and lift-off length were measured and compared. Results show that the lift-off length of Spray B increases and grows by approximately 1.5 mm after the initial stages of ignition, in an opposite trend compared to Spray A where the lift-off length decreases with time. The Spray B lift-off length increase is consistent with a transition to from wide to narrow spreading angle that would tend to increase lift-off length, but lift-off is stabilized for a substantial period of time by a wide annular region of combustion products formed when the plume was initially wide.