Measuring the soot onset temperature in high-pressure n-dodecane spray pyrolysis

Soot formation in pyrolyzing sprays of n-dodecane is visualized and quantified in a high-pressure, high-temperature, constant-volume spray chamber at 38  bar, 76 bar, and 114 bar. Sprays of n-dodecane are injected at 500 bar from a single-hole, 186-µm orifice diameter fuel injector. We quantify the temporal evolution of the soot optical thickness and the total soot mass formed in the pyrolyzing sprays using a high-speed extinction imaging diagnostic. The vessel ambient temperature and pressure are varied independently to identify the soot onset temperature for n-dodecane pyrolysis. Linear extrapolation of the maximum soot formation rates as a function of ambient temperature reveals a soot onset temperature near 1450 K. The onset temperature determined here for n-dodecane is within 50 K of those previously measured along the centerline of atmospheric pressure coflow diffusion flames for smaller alkane fuels.