Overview of the key technologies of combined cycle engine precooling systems and the advanced applications of micro-channel heat transfer

A review of the key technologies of air-breathing engine precooling system and the use of micro-channel heat transfer is presented. A survey on various types of air-breathing engine cycles is presented, highlighting the characteristics of the energy cycles and the corresponding key technologies. The existing precooling schemes are classified into four types, i.e. Fuel Precooling (FPC), Mass Injection and Precompressor Cooling (MIPCC), combination of FPC and MIPCC, and Third-Fluid Cooling (TFC). Precoolers with micro-channel structures are found to have high heat dissipation capacity and high compactness. In detail, the applications of microchannel flow heat transfer like in the SABRE engine of the British Skylon spaceplane were introduced. Fundamental investigations on the microchannel heat transfer enhancement are essential for the development of the precooling technique. In order to better understand the micro-channel heat transfer mechanisms, experimental studies on single phase gaseous flow heat transfer in small flow passages are briefly overviewed, revealing some controversial conclusions on microscale flow and heat transfer characteristics. The limited experimental data on microchannel gaseous flow heat transfer largely hinders the theoretical development. Since the air precooling technique is at its infancy in China, experimental investigations are essential to overcome the gap.