An investigation of the carbon-forming characteristics of MTL-F-5624B, grades JP-3 and JP-4, jet-engine fuels varying in smoke-volatility index was conducted in a single-tubular combustor.. Combustion-chamber carbon deposits and exhaust-gas smoke densities were determined at two combus¬tor operating conditions simulating (A) a 4-pressure-ratio engine at a 20,000-foot altitude and Zero flight speed, and (B) a 7-pressure-ratio engine at sea level and a flight Mach number of 0.87.nAt the lower-pressure condition (condition A), carbon deposits and exhaust-gas smoke densities correlated with three empirical fuel factors: smoke-volatility index, smoke point, and NACA K factor (function of dis-tillation characteristics and hydrogen-carbon ratio). The best correla-tions of carbon deposits were obtained with the NACA K factor and the smoke point, however. At the higher-pressure condition (condition B), the deposits and smoke densities did not satisfactorily correlate with any of the fuel factors considered.
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