Investigation on sea-level thrust gain in ejector mode of rocket-based combined cycle engine

One of the principal research subjects within the field of rocket-based combined cycle (RBCC) engines has been the ejector mode, which has been the focus of research for a considerable period of time. The objective of this paper is to present a detailed analysis to the ejector mode of kerosene-fueled RBCC engine. The matching mechanism of the diffusion and afterburning (DAB) mode was obtained through a combination of experiment, theoretical modeling, and numerical simulation. The thrust gain of the sea-level ejector mode was subsequently analyzed. The findings indicate that: (1) In the DAB mode, the requirement of the thermal or geometric throat area ratio is small. The difficulty in organizing the thermal throat has led to the use of a geometric throat to achieve choking on the engine. The results of the model calculation indicate that a thrust gain of 25.2 % for a sea-level ejector mode can be achieved by employing a throat area ratio of 1.83. (2) For the sea-level ejector mode, the mixing requirement can be satisfied when the length of the mixing section reaches 4 times the hydraulic diameter of the rocket nozzle outlet's section. The use of a throat area ratio of 1.8 allows for a thrust gain of 15.9 % in the sea-level ejector mode. The presence of fuel pylons has been observed to reduce thrust gain. (3) The matching mechanism of sea-level ejector mode is revealed. When the rocket flow rate, bypass ratio, combustion organization and throat area ratio match, the maximum thrust gain can be achieved.