Preliminary Evaluation of Heat Exchanger for LACE

An experimental study on cooling the heat exchanger by liquid hydrogen was conducted to establish a method of estimating the heat exchanger performance for LACE. Based on the test results, an analytical method of estimating the liquefaction ratio, a!, and the hydrogen outlet temperature, THout of the heat exchanger is proposed to evaluate the performance of the heat exchanger. According to comparison of the specific impulse, Isp, obtained from this method of estimating a! and THout with that obtained by using the coolant-side temperature efficiencies, 4 L and r$ =, in the liquefaction section and the precooler section of the heat exchanger, it was found that selecting the values of d L and r$ c as performance indexes of the heat exchanger is one of the simplest and most effective ways for estimating the I,, value of the basic LACE. Based on this method of estimating the Isp value, the effect of the flight trajectory on the basic LACE performance was investigated. The results show that the I, value of the basic LACE has a low value iu the low flight Mach number range regardless of the difference of the flight trajectories. Therefore, the tank return feeding system using subcooled hydrogen is discussed as a way to improve the performance of the basic LACE. reulace the stored oxidizer for rocket engines by ut&ing the large cooling capacity of liquid hydrogen to liquefy atmospheric air. Moreover, LACE is greatly advantageous for application in RBCC engines because many engine components can be commonly used under both modes of operation, i.e., the LACE mode and the pure rocket mode. Various investigators'g) have discussed typical LACE technology, namely, using liquid hydrogen to liquefy inlet air. The air liquefaction ratio ranges from 3.0 to 5.0, which is much lower than the stoichiometric ratio. As a result, the specific impulse of such a LACE is not significantly higher than that of a pure LH&02 rocket engine. Various methods4' to improve the performance of LACE have been discussed, for example, the use of slush hydrogen,') the use of a vortex-tube,5) the use of a high-pressure hydrogen-expansion liquefied engine,@ and so on. However, the key technologies needed to realize improvements have not been sufficiently investigated making it diflicult to, evaluate their feasibility, Therefore, it is necessary to clarify the required criteria for realizing the basic LACE.