Precooled jet engine
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A Precooled jet engine is a concept for high speed jet engines that features a cryogenic fuel-cooled heat exchanger between the air intake and the (LP) compressor, to precool the air entering the compressor. After gaining heat and vapourising in the heat exchanger, the fuel (e.g. H2) is burnt in the combustor.
A potential application for a precooled turbojet is as part of the powerplant for a space launch vehicle, or for a very long range, very high speed aircraft.
Precooled jet engines have never flown, but are predicted to have much higher thrust and efficiency at speeds up to Mach 5.5.
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[edit] Advantages of precoolers
One main advantage of precooling is that, for a given Overall Pressure Ratio, there is a significant reduction in compressor delivery temperature (T3), which delays the onset of the T3limit as flight speed increases. Consequently corrected flow can be maintained constant over a wide range of flight speeds thus maximizing net thrust at high speeds.
Another advantage is that the compressor and ducting after the inlet is subject to much lower temperatures, and hence may be made of light alloys. This greatly reduces the weight of the engine, which further improves the thrust/weight ratio.
[edit] Applications
A potential application for a precooled turbojet is as part of the powerplant for a space launcher vehicle, or for a very long range, very high speed aircraft.
[edit] History
Precooled jet engines were described by Robert P. Carmichael in 1955.[1]
[edit] Fuel
The fuel typically proposed for precooled jet engines is usually hydrogen, since liquid hydrogen is liquid at deeply cryogenic temperatures, and has a very high total specific heat capacity, including the latent heat of vapourisation, higher than water, over its useful range.
However, the low density of liquid hydrogen has negative effects on the rest of the vehicle, and the vehicle physically becomes very large, although the weight on the undercarriage and wing loading may remain low.
