Fuel Temperature Effects on Soot Formation in Jet A and HEFA-SPK High-Pressure Flames

Abstract

The impact of fuel temperature and composition on flame structure and in situ soot formation is investigated at 1.0 MPa using spatially resolved laser-induced incandescence (LII) measurements. Concurrent OH* chemiluminescence measurements are used to correlate soot formation and retention with flame heat release. Experiments were conducted over a range of fuel temperatures spanning from 300 K to 575 K, and two liquid hydrocarbon fuels (Jet A and HEFA-SPK). Operating conditions are selected to correspond to mission-relevant low power pilot-only operation for taxiing and approach, and high power operation for cruise. During pilot-and-main operation, fuel aromatic content is vital for the production of soot regardless of fuel temperature. Without aromatics in the fuel, soot production is drastically reduced. For fuels with aromatic content, increasing fuel temperature results in a shift in soot formation structure from small, high-intensity pockets to more frequent, less intense dispersed fields. Pilot-only operation operates locally at an equivalence ratio well above critical sooting limits, resulting in soot formation for Jet A as well as HEFA-SPK. LII signal intensity is ~3.5 times more intense with aromatics present in the fuel at this condition, indicating their importance in soot formation. The inclusion of aromatics in the fuel results in more rapid soot formation and shifts the location of peak signal intensity upstream. Elevated fuel temperatures for pilot-only operating conditions result in more rapid soot consumption in the downstream region of the combustor only when aromatics are present.