A feasibility study of an atrex engine at approved technology levels

A new ATREX (Air-Turbo-Ram Expander cycle) engine configuration has been proposed to show that the engine can be developed in about 10 years, if the development project has started under enough resources. The novel tip-turbine of the original engine is replaced by a conventional aft-turbine configuration. Also, the turbine inlet temperature (TIT) is reduced to 1200K. The engine has been shown to perform well even under a relaxed configuration which uses only approved metal technologies for modern jet engines. The performance can be improved to that of the original ATREX engine after the oxidation problem of carbon/carbon composite is solved. Some technical issues on developing the new ATREX engine have been addressed. The most important issue would come from the transient total temperature change due to the rapid acceleration from sea level static (SLS) condition (288K) to Mach 6 at 30km of altitude (1680K) in 6 minutes. The change of the fan rotor radius due to this large temperature change have been assessed to be 1.1% of the fan blade height, at the trailing edge of the first stage rotor. If this corresponds to the tip clearance, this will result in 3% of fan efficiency reduction per stage, and 13% of the surge margin reduction. Although these are important technical issues, the issues are less critical for ATREX engine which only has a two-stage fan, than for a turbo jet. The relative tip clearance will become larger toward the exit of the compressor. Therefore, it is less risky to start developing the air-breathing engine for Two-Stage To Orbit (TSTO) space transportation system by setting the ATREX engine as the baseline.