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Abstract Design study of the precooling heat exchanger specified for high speed airbreathing propulsion was carried out from the perspective of overall engine performance. The precooler proposed for the SABRE engine was adopted as the representative configuration for evaluation. Design procedure of the precooler was developed and incorporated into a cycle analysis model such that the variation in engine performance can be assessed as the design inputs is altered. By means of the differential-evolution algorithm, the design characteristics of the precooler were clarified through the idea of Pareto-Optimality. Precooler total mass and axial length, together with engine specific impulse, was included as optimization objectives on account of the results of parametric analysis. Pareto-optimal-fronts were obtained with the influence of some key design parameters such as the precooling temperature and the intake efficiency was analyzed. The results show that precooler design is a tradeoff between the optimization objectives considered. Selection of a larger precooling temperature helps to increase engine specific impulse and reduce the mass of precooler, although engine specific thrust is decreased slightly, whereas larger intake efficiency is extremely preferred for precooled cycles from not only the performance side of the engine, but more importantly, the geometry side of the precooler. Highlights • Design study of precooler is presented from the perspective of Pareto optimality. • Tradeoff feature is observed between the selected optimization objectives. • Significant increase in specific impulse can only be made within a certain range. • Adoption of larger precooling temperature benefits both the precooler and cycle. • Developing high performance intake is extremely important for precooled engines. [ABSTRACT FROM AUTHOR]

The demanding of a holistic view for the engines in the fuel direct precooled family was clarified. A unified cycle model was proposed so as to provide a consistent thread of insight for the engine family. The model indicates that the engines in the fuel direct precooled family are not collections of different cycles, but essentially the same cycle operating under different conditions. Theoretical analysis of the unified cycle was carried out to make clear the dependencies of the engine performance parameters. Numerical model was developed also to take into account the actual conditions including the real fluid properties, the mass addition effects, etc. Performance evaluation and optimization based on the numerical model were completed for three typical cycles under the flight condition of Mach 5.0 with the dynamic pressure q 0 = 45 kPa. The results show that the PC-RT cycle possesses superiority on both the geometry and performance sides among the cycles evaluated. The selection of precooling temperature is a tradeoff between the specific thrust and the specific impulse. Compared to the conventional ramjet engine, the precooled cycles have the potential to provide both high specific thrust and high specific impulse. [ABSTRACT FROM AUTHOR]

Precooling technology is an effective way to improve the flight Mach number for turbojet engine. To solve the problem of engine performance degradation caused by excessive fuel consumption, a multi-stage precooling-compression cycle is newly proposed, in which the secondary cooling capacity of fuel is reused by transfer the heat energy from fuel to the mechanical work. To evaluate the engine performance, several new performance parameters are defined and a thermodynamic model is established, in which the optimum distribution of pressure ratio for each stage of turbine/compressor and the performance limit of engine are derived in theory. By calculation, it is found that the heat absorption capacity of fuel and the engine performance could be improved with the increase of stage number. Further, the lower and upper performance boundaries of engine could be obtained when the stage number is set to one and infinity respectively. Moreover, considering the engineering application, the two-stage precooling-compression cycle will be regarded as the best design, and when the engine performance is improved by about 8.15%, the heat transfer area of pre-cooler will be increased by 88.19%, as well as the mass of compressor and turbine will be increased by 30.33% and 11.18% respectively. • A multi-stage precooling-compression cycle (MPC) is proposed for precooled engine. • The distribution strategy of pressure ratio for each stage of compressor is reveled. • The performance boundaries of MPC and their influencing factors are analyzed. • The best stage number of MPC is two. • The engine performance of 2-MPC is improved by about 8.15%. [ABSTRACT FROM AUTHOR]

To solve the problem of engine performance degradation caused by excessive fuel consumption in the precooled engine cycle, a new optimization method based on the cascade utilization of cold source is proposed, in which the cold sources with different temperature ranges and different working fluids are reasonably matched and adequately utilized. Based on this method, two new optimization cycles are put forward, i.e., the air reheat precooling cycle (ARPC) and the hydrogen reheat precooling cycle (HRPC). To evaluate the performances of these two cycles, a unified model is established. According to the simulation results, the fuel consumption of the HRPC could be reduced by 0–21.04% compared with the traditional precooled engine. Besides, the specific impulse of the HRPC, which can be raised by 16.78% when the heat transfer effectiveness is set to 0.9, is higher than that of the ARPC, which can be increased by 12.64% at most. Moreover, considering the operating constraints, the reduction of the minimum temperature difference of the regenerator and the increase of the pressure recovery coefficient of intake are effective ways to expand the performance boundaries. The results in this paper are beneficial for the performance optimization of the precooled engine cycle. • Cascade using of cold source is proposed to improve performance of precooled cycle. • Two new cycles are put forward based on the proposed optimization method. • The optimized cycles can dramatically improve specific impulse of precooled engine. • The optimized cycles can greatly reduce synthesis difficulty of precooled engine. • Future research directions and potential applications are summarized. [ABSTRACT FROM AUTHOR]

Fuel direct precooled engines are proposed to propel hypersonic cruise and acceleration vehicles. The engine branch includes a variety of cycle configurations. It is realized that based on a series view modeling concept, the different configurations can be parameterized via a unified thermodynamic model through which the issues concerning cycle synthesis and design can be converted to a parameter/configuration optimization problem. With the proposed model, analysis for representative cycles characterized by different turbine-compressor coupling schemes is carried out to reveal how the cycle performances are determined by its arrangements. The results indicate that the engine using fuel turbine possesses a high comprehensive performance, and the one using gas turbine can achieve larger air pressure ratio — which is beneficial for component level synthesis with rocket engines. Besides, the optimum performances for the cycles evaluated are obtained when the fuel flow required for precooling is equal to that permitted for stoichiometric combustion. Moreover, the engine performance seems more sensitive to air side pressure loss of precooler for the design with smaller air pressure ratio, and for engines with larger pressure ratio, the efficiencies of air compressor and gas turbine are the dominant factors. • Fuel direct precooled engines are proposed for hypersonic transportation vehicles. • Unified thermodynamic model is developed for the engines using series view method. • Performance of engines with typical turbine-compressor coupling schemes evaluated. • Engines use fuel turbine show better performance than that using gas turbine only. • Optimum choice of precooling depth and sensitivity of engine thrust are revealed. [ABSTRACT FROM AUTHOR]

Fuel indirect precooled cycles (IPC) are attractive candidate to enable next generation reusable launch vehicle. Thermodynamic analysis was carried out to bound the performance of this innovative propulsion concept. A unified model which can represent the core working principle of the whole engine family was proposed to make the analysis possible, with which the conditions in determining the performance boundaries of the family were derived, and new efficiency figure (i.e., EoP) for the precooling-compression sub-cycle (PCS) was defined. Numerical method for the model was developed also to perform the parametric analysis. The results show that the cycle performance is bounded by two extremes, with the upper and lower of which are defined by the EoP of 100% and 0 respectively. For real engines, the state of the art design practice gives an EoP level of 10–30%. Moreover, it indicates that fuel properties possess remarkable effects on the PCS, whereas hydrogen shows the best application potential. From the standpoint of system overall design, optimum choice for the EoP and fuel equivalence ratio are proposed, with the performance superiority of the IPC over the Brayton cycles is revealed, and the impacts of the intake and combustor performance on the extremes are clarified. • A unified model is developed from thermodynamic generalization of precooled cycles. • Performance of the cycle family is evaluated from a "series view" perspective. • Relations and factors crucial to engine performance and the extremes are derived. • Performance boundaries and superiority of the cycles to Brayton engines revealed. • Impact of material temperature limit on use of precooling benefits is clarified. [ABSTRACT FROM AUTHOR]

Indirect precooled engine (IPE) is a promising power for single-stage-to-orbit (SSTO) and the booster stage of a two-stage-to-orbit (TSTO) vehicles. Thrust of IPE is realized the most decisive factor that affects vehicle mission performance; therefore it is particularly critical to ensure that the engine can fully exert its thrust performance through active control since the flight parameters will change substantially alongside the trajectory. On account of this, control law of maximizing thrust for a single branch IPE is developed in current study. To this end, a high-fidelity off-design model of IPE is constructed to evaluate how engine performance is regulated by the various changeable parameters. The results indicate that engine thrust and specific impulse are functions of total fuel mass flow, nozzle throat area and the temperatures of preburner and main combustor, which can be conveniently controlled in real engines by actuators or changing the related fuel mass flow through fuel valves. Based on the influence characteristics revealed, the maximum thrust control law of the engine is synthetized, with the range of engine thrust can be regulated along a representative flying trajectory is evaluated. The results may provide some useful guidance about performance control of IPE with complex multi-branch intermediate cycles. • High-fidelity off-design model for single branch IPC engine developed for analysis. • Main characteristics of IPC engine under off-design conditions are revealed. • Control strategy of maximum thrust state of the engine is designed. • Thrust adjustment boundary and performance in typical mission trajectory evaluated. [ABSTRACT FROM AUTHOR]