Investigations were conducted to determine the carbon—forming characteristics of MIL-F-5624 and MIL-F-5161 type fuels in a single combustor from a J33 turbojet engine and of a MIL-F-5161 fuel in a J35 full-scale engine. Single-combustor simulated engine conditions were 20,000-foot altitude, 90-percent rated engine speed, and zero ram. Full-scale engine operation was at sea-level, zero-ram conditions.nThe carbon deposition of MIL-F-5624 and MIL-F-5161 fuels obtained in the single combustor could be estimated from a previously estab¬lished empirical correlation with volumetric average boiling tempera¬ture and hydrogen-carbon ratio. The carbon deposition in the full-scale engine using MIL-F-5161 fuel was greater than the deposition normally obtained with MIL-F-5624 fuels. This trend, also noted in other types of turbo-jet engine, was concluded to be the result of fuel characteristics rather than combustion-chamber configuration. The results obtained in these investigations, together with other available full-scale-engine operational information, indicate that MIL-F-5161 fuels form more carbon than most MIL-F-5624 fuels, as predicted by the correlation, and may result in marginal operation in several turbojet engines.
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