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An adaptive cycle engine is an evolutional aero-engine that can achieve low fuel consumption and high efficiency by adjusting the thermodynamic cycle; however, few studies have been conducted on adaptive cycle engine performance at low speeds. A high-fidelity ground starting model of an adaptive cycle engine is established by correcting the low speed characteristics of the components, while considering the effects of rotor inertia, volume, combustion efficiency, and the thermal inertia of the combustor and turbine. By employing a physically enhanced prediction method, three operating states of the compressor at low speeds are obtained: compressor, stirrer, and turbine state. The matching mechanism of the adaptive cycle engine and the detailed influence of the variable geometries on the engine's performance during the starting process are explored. The study shows that the third bypass duct has little effect on the engine starting time, and opening the mode select valve can reduce the starting time. Compared with the initial settings, the starting time decreases by 3.98 s after optimization with the variable geometries. The detailed impact of the variable geometries on the engine's starting performance provides an engineering reference value for the control strategies. • A high-fidelity ground starting model of an adaptive cycle engine is established by correcting the low speed characteristics of the components, while considering the effects of rotor inertia, volume, combustion efficiency, and the thermal inertia of the combustor and turbine. • A physically enhanced prediction method based on PSO-SVR for extrapolating the low-speed characteristics of compressors is proposed to solve the problems of low accuracy and discontinuous isentropic efficiency at low-speeds. • The detailed impact of the variable geometries on the adaptive cycle engine's starting performance provides engineering reference value for the optimum designing of adaptive cycle engine start control strategies. [ABSTRACT FROM AUTHOR]

Adaptive cycle engines (ACEs) represent a sophisticated class of power units, embodying numerous variable geometry components, marking them as pivotal for the advancement of next-generation high-speed civil and military engines. Nonetheless, this variability introduces substantial complexity into the engineering of control laws. Contemporary research predominantly relies on either manual methodologies or global optimization algorithms. The former rarely achieves peak performance, while the latter incurs substantial computational expenses. This research introduces an accelerated methodology by using variable-step gradient with boundary constraints (VGB) algorithm tailored for the nuanced optimization challenges posed by multi-variable, multi-constraint nonlinearities inherent in ACEs. Recognizing that ACE's peak performance is typically boundary-constrained, the algorithm strategically manipulates variable geometries to widen the operational gap from the most disadvantageous boundary (MDB), thereby inching closer to the engine's ideal operational nexus. This strategy culminates in a decease in computational overhead, diverging significantly from conventional global optimization approaches. Empirical findings represent the method's efficacy, with a maximal performance deviation of just 3.78 % across three steady-state missions. Post transient control law refinement, engine's starting time contracted by 5.93 s via VGB algorithm, opposed to baseline design point configurations. Collectively, this approach serves as a versatile and efficient blueprint for designing control laws. [ABSTRACT FROM AUTHOR]

Abstract: Road transportation using air as a fuel has attracted much attention over the past decade. The fuel (air) can be in two forms, compressed gas form and cryogenic liquid form and engines based on both forms of air have been investigated. Prototypes of air powered road vehicles are expected to emerge over the next few years. However, there have been debates over the advantages and disadvantages of the two technologies. This paper aims to compare the two technologies from the technological point of view. Engines for a typical small scale passenger car are used for the analyses and the comparison is based on the shaft work, coolth, efficiency and energy density. It is shown that the shaft work outputs and the coolth available to engines powered by both fuels increase with increasing working pressure and temperature. Given the working pressure and temperature, liquid air powered engines have a slightly lower specific work outputs than compressed air powered engines. The volumetric energy density of liquid air, however, is much higher than that of compressed air, and liquid air has much higher coolth than compressed air. On the other hand, the efficiency of the compressed air powered engines is higher than that of liquid air powered engines mainly because of the higher energy consumption of liquefaction plants. The analyses also suggest that an effective use of coolth be a key to improve the overall efficiency of liquid air powered engines. [ABSTRACT FROM AUTHOR]