Precooled jet engine
A precooled jet engine is a concept for high speed jet engines that features a cryogenic fuel-cooled heat exchanger immediately after the air intake to precool the air entering the engine. After gaining heat and vapourising in the heat exchanger system, the fuel (e.g. H2) burns in the combustor. Precooled jet engines have never flown but are predicted to have much higher thrust and efficiency at speeds up to Mach 5.5. Precooled jet engines were described by Robert P. Carmichael in 1955.
Pre-cooled engines avoid needing an air condenser because, unlike Liquid air cycle engines (LACE), pre-cooled engines cool the air without liquefying it.
A pre-cooled engine could be in the power-plant for a space launcher vehicle or for a very long range, very high speed aircraft.
One main advantage of pre-cooling is that, for a given overall pressure ratio, there is a significant reduction in compressor delivery temperature (T3), which delays the onset of the T3 limit as flight speed increases. Consequently, sea-level conditions (corrected flow) can be maintained after the pre-cooler over a very wide range of flight speeds, thus maximizing net thrust even at high speeds.
Precoolers have never flown.[update]
Precoolers were first proposed as part of the research in America on Project Suntan- a liquid hydrogen fuelled aircraft. Robert P. Carmichael in 1955 devised several engine cycles that could be used with hydrogen fuel, and this was one.
Interest in precooled engines saw a brief emergence in the UK in 1982, when Alan Bond (formerly of the Blue Streak missile project) created a LACE-like design he called SATAN. The primary difference of these systems is that the air is only cooled, rather than liquified, and thus the gases are not actually separated, apparently giving significantly greater overall performance, due to a reduction in the amount of hydrogen used for cooling.
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