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:The characteristic velocity C * is derived from the assumption of one-dimensional flow in a uniform pressure field, and is usually evaluated using a combustion chamber pressure measured on the chamber wall. In the swirlingoxidizer-flow-type hybrid rocket engines, the C * efficiency in excess of 1.0 was sometimes measured due to an increased wall pressure in the centrifugal force field of the swirling flow. It was induced that the specific impulse efficiency was useful to evaluate the C * efficiency accurately without using the combustion chamber pressure when the CF efficiency was given. This evaluation method of the C * efficiency was confirmed to be appropriate and available by the burning tests using the swirling-oxidizer-flow-type hybrid rocket engines with optimum expanding nozzles.

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Expander bleed (EB) cycle is a unique engine cycle developed inJapan which is used for LE-5B, MB-XX and LE-X. MHI evaluated starting transient behavior and steady state performance of idle mode operation of EB cycle by comparing with full expander (FE) cycle. As a result, transient behavior prediction showed EB cycle is robust against changing some engine parameters and valve timing. In idle mode operation, EB cycle can have high specific impulse by changing valves position. The sensitivity against disturbances is not so different from FE cycle. Nomenclature Isp = Specific Impulse MRC = Chamber Mixture Ratio MRE = Engine Mixture Ratio PF ∆ = Fuel Injection Pressure Drop PO ∆ = Oxidizer Injection Pressure Drop Pc = Combustion Chamber Pressure