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Supersonic Combustion

Introduction

Supersonic Combustion Ramjet Engine (SCRam jet) is the propulsion system of future hypersonic transporter. This engine is also a candidate of the Rocket Based Combined Cycle which uses different kinds of engines during flight. During low mach number phase, RBCC operates in rocket mode (or ejector rocket mode). At mach 3, the operating mode will be switched to Ramjet mode and it operates in continues to accelerate. When the flight speed is sufficiently fast, the engine will operate in scramjet mode. In a SCRam jet engine, it is quite difficult to achieve the stable combustion and flame stabilization because the combustion occurs under supersonic condition. Therefore, the fuel selection and the injection system key design parameters for this engine. And the geometrical design of the combustor is also quite important for flame stabilization and stable combustion.

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Research Target of Supersonic Combustion

We focus on hydrocarbon fuels as a candidate of SCRam jet engine because of its high density. Hydrogen has been thought to be the best fuel for SCRam jet for a long time because it has high reactivity and good performance as coolant. These characteristics are quite suitable for SCRam jet because the stable combustion will be easily achieved due to high reactivity and the vehicle under hypersonic flight must be equipped with some cooling system. However, one of the largest drawbacks of hydrogen is its low density and it is inevitable for the vehicle to be large enough for fuel storage. Therefore, hydrocarbon fuel is a promising candidate. It is difficult to achieve stable combustion using hydrocarbon fuel because which has lower reactivity compared with hydrogen and we focus on the improvement of ignition characteristics by spark assist and fuel reformation by thermal decomposition. The experimental research is conducted with supersonic wind tunnel at Hongo campus to establish the optimal injection system and to estimate the effects of fuel reformation.

Experimental setup

The vitiated wind tunnel and cavity based combustor is used in this experiment. The effects of various parameters such as the inlet total enthalpy and fuel equivalence ratio are researched. The optical measurements are conducted through the side equipped observation windows.

scram1

scram2

Under Hot Condition

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