A new expansion cycle scheme of the scramjet engine system including a hydrocarbon-fuel-based(kerosene)regenerative cooling system and supercritical/cracking kerosene-based turbo-pump was proposed in this paper.In this cycle scbeme,the supercritical/cracking kerosene with high pressure and high temperature is formed through the cooling channel.And then,in order to make better use of the high energy of the supercritical/cracking fuel,the supercritical/cracking kerosene fuel was used to drive the turbo-pump to obtain a high pressure of the cold kerosene fuel at the entrance of the cooling channel.In the end,the supercritical/cracking kerosene from the turbine exit is injected into the scramjet combustor.Such supercritical/cracking kerosene fuel can decrease the fuel-air mixing length and increase the combustion efficiency,due to the gas state and low molecular weight of the cracking fuel.In order to ignite the cold kerosene in the start-up stage,the ethylene-assisted ignition subsystem was applied.In the present paper,operating modes and characteristics of the expansion cycle system are first described.And then,the overall design of the system and the characterisitics of the start-up process are analyzed numerically to investigate effects of the system parameters on the scramjet start-up performance.The results show that the expansion cycle system proposed in this paper can work well under typical conditions.The research work in this paper can help to make a solid foundation for the research on the coupling characteristics between the dynamics and thermodynamics of the scramjet expansion cycle system. A new expansion cycle scheme of the scramjet engine system including a hydrocarbon-fuel-based (kerosene) regenerative cooling system and supercritical / cracking kerosene-based turbo-pump was proposed in this paper. In this cycle scbeme, the supercritical / cracking kerosene with high pressure and high temperature is formed through the cooling channel. And then, in order to make better use of the high energy of the supercritical / cracking fuel, the supercritical / cracking kerosene fuel was used to drive the turbo-pump to obtain a high pressure of the cold kerosene fuel at the entrance of the cooling channel. In the end, the supercritical / cracking kerosene from the turbine exit is injected into the scramjet combustor.Such supercritical / cracking kerosene fuel can decrease the fuel-air mixing length and increase the combustion efficiency, due to the gas state and low molecular weight of the cracking fuel. order to ignite the cold kerosene in the start-up stage, the ethylene-assisted ignition subsystem w as applied.In the present paper, operating modes and characteristics of the expansion cycle system are first described. And then, the overall design of the system and the characterisitics of the start-up process are analyzed numerically to investigate effects of the system parameters on the scramjet start-up performance. The results show that the expansion cycle system proposed in this paper can work well under typical conditions. the research work in this paper can help to make a solid foundation for the research on the coupling characteristics between the dynamics and thermodynamics of the scramjet expansion cycle system.