Study on the Design Criteria of the Coaxial Injector for a LOX/Hydrogen Rocket Engine —Evaluation of Design for Injectors of the LE-5 Engine and Its Derivatives—

Abstract

Based on the author's recent study on detailed modeling of the atomization characteristics of a liquid/gas phase coaxial injector, an improved computation model for predicting the combustion performance of a LOX/hydrogen engine is proposed. The features of this model are that it allows calculation of the local rate of atomization of the LOX jet and deals with droplet size distribution of the LOX spray. Additionally the model applies the burning rate constant of LOX/hydrogen combustion derived by the author's former experiment. Using this model, evaluations of the design criteria for the LE-5 engine, which was equipped on the H-2 launcher, and its derivative engines, which have been used with the H-2A launcher, were conducted. Furthermore, optimization of the derivative engine's injector design to improve combustion stability and combustion performance was discussed.

Establishment of Design Method for Liquid Hydrogen Regenerative Cooling Combustor of LOX/Hydrogen Rocket Engine

“…The following presents an optimizing design procedure for the combustor of the LE-5B engine (CASE-D), the prototype of which with a candidate injector was pointed out to be marginally stable for low frequency combustion instability in the range of 80-100 Hz in the former study. 4) Figure 10 shows a schematic for the design optimizing procedure. Here, we adopt an engine cycle whereby all injecting hydrogen is fed to combustion directly after being used as regenerative coolant to obtain a higher hydrogen injection temperature.…”

“…(3), where the combustion gas properties are calculated along the axial position of x using the former calculation model for combustion. 4) h g ðxÞ ¼ 0:023k t ReðxÞ 0:8 Pr 0:4 =DcðxÞ ð 3Þ…”

“…Clearly the correlations are satisfactory. As to combustion stability of low frequency instability, the calculated combustion time lags, which are tabulated in Table 2, were substituted into the stability equations 4) to evaluate the stability margin. The results are shown in Fig.…”

“…8; CASE-G (HM-7 þ ) shows marginal stable combustion like that of the LE-5B with candidate injector (CASE-D) shown formerly. 4) This marginal stable combustion is due to a longer combustion time lag for the LOX side as shown in Table 2. Figure 9 shows the heat flux distributions; CASE-A (LE-5) has the highest heat flux because heat flux is proportional to combustion pressure.…”

“…3) Additionally, applying the atomization model to calculation of the combustion process in the LOX/hydrogen combustor gave a detailed calculation model for predicting combustion performance. 4) Using that model, the design criteria for the LE-5 engine, which was used as the second stage of the H-2 launcher, and its derivatives were evaluated, and the author proposed an alternate design for the prototype injector to improve combustion stability and combustion performance. In the present study, the latest model for predicting combustion performance is extended to deal with the heat load on the combustor and the cooling characteristics of the liquid hydrogen.…”