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801.
High performance liquid rocket engines are often characterized by rectangular cooling channels with high aspect ratio (channel height-to-width ratio) because of their proven superior cooling efficiency with respect to a conventional design. However, the identification of the optimum aspect ratio is not a trivial task. In the present study a trade-off analysis is performed on a cooling channel system that can be of interest for rocket engines. This analysis requires multiple cooling channel flow calculations and thus cannot be efficiently performed by CFD solvers. Therefore, a proper numerical approach, referred to as quasi-2D model, is used to have fast and accurate predictions of cooling system properties. This approach relies on its capability of describing the thermal stratification that occurs in the coolant and in the wall structure, as well as the coolant warming and pressure drop along the channel length. Validation of the model is carried out by comparison with solutions obtained with a validated CFD solver. Results of the analysis show the existence of an optimum channel aspect ratio that minimizes the requested pump power needed to overcome losses in the cooling circuit. 相似文献
802.
A semi‐implicit scheme is presented for large eddy simulation of turbulent reactive flow and combustion in reciprocating piston engines. First, the governing equations in a deforming coordinate system are formulated to accommodate the moving piston. The numerical scheme is made up of a fourth‐order central difference for the diffusion terms in the transport equations and a fifth‐order weighted essentially nonoscillatory (WENO) scheme for the convective terms. A second‐ order Adams–Bashforth scheme is used for time integration. For higher density ratios, it is combined with a predictor–corrector scheme. The numerical scheme is explicit for time integration of the transport equations, except for the continuity equation which is used together with the momentum equation to determine the pressure field and velocity field by using a Poisson equation for the pressure correction field. The scheme is aimed at the simulation of low Mach number flows typically found in piston engines. An efficient multigrid method that can handle high grid aspect ratio is presented for solving the pressure correction equation. The numerical scheme is evaluated on two test engines, a laboratory four‐stroke engine with rectangular‐shaped engine geometry where detailed velocity measurements are available, and a modified truck engine with practical cylinder geometry where lean ethanol/air mixture is combusted under a homogeneous charge compression ignition (HCCI) condition. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
803.
804.
Quasioptimal and numerical solutions of the exact equations of optimal low-thrust motion in a Newtonian central gravity field
are compared. The main properties of the optimal solutions are confirmed. It is established that the characteristic velocity
is independent of the spacecraft or constant-thrust engine parameters
Translated from Prikladnaya Mekhanika, Vol. 44, No. 9, pp. 115–122, September 2008. 相似文献
805.
B. Bougie A.P. van Vliet J.J. ter Meulen 《Proceedings of the Combustion Institute》2007,31(1):685-691
Time-resolved laser-induced incandescence was used to estimate primary particle size distributions inside the combustion chamber of a heavy-duty diesel engine as a function of the crank angle, for two different engine loads at two different probe locations. Assuming a log-normal particle size distribution, an increase of the mean primary particle size was seen during the first stages of the combustion cycle, followed by a decrease later on during the combustion process. 相似文献
806.
热声发动机驱动的脉管制冷机是一种完全无运动部件的低温制冷机,具有非常好的应用前景,本文介绍了本实验室在这方面取得的最新进展。首先我们对驻波热声发动机进行了改进设计,提高了其驱动压比,用氦气作为工质最大压比达到了1.15。在此基础上我们用其驱动同轴双向进气小孔型脉管制冷机,通过调整热声发动机的振荡频率,使之与脉管达到匹配,最终达到了84.3K的最低制冷温度,这也是目前用驻波热声发动机驱动脉管所达到的最低制冷温度。同时,在此实验过程中,一些抑制跳频的方法也得到了实验验证。 相似文献
807.
利用 INCA 标定系统工具,在一台 CA6DL2-35E3 高压共轨重型柴油机原预、主喷欧 3 喷油 MAP 上进行了基于单次喷射(去除预喷)及三段喷射(增设后喷)两种模式的喷油参数对发动机性能影响规律试验研究.单喷试验结果表明,提高喷油压力可以改善除 NOx 外其余发动机性能参数,结合喷油正时的延迟可确定一个优化整机性能的折衷点.增设后喷后,改变主后喷间隔(主喷结束到后喷开始)NOx 及碳烟排放均存在拐点,而随着后喷油量的增加(从主喷油量给出)碳烟及 NOx 排放均降低;根据对动力性/经济性影响小及尾气排放降低或不恶化为优化原则对工况点进行优化后,可以认为优化后喷参数能够较好地改善发动机各项性能. 相似文献
808.
809.
Treating the black hole molecules as working substance and considering its phase structure, we study the black hole heat engine by a charged anti-de Sitter black hole. In the reduced temperature-entropy chart, it is found that the work, heat, and efficiency of the engine are free of the black hole charge. Applying the Rankine cycle with or without a back pressure mechanism to the black hole heat engine, the compact formula for the efficiency is obtained. And the heat, work and efficiency are worked out. The result shows that the black hole engine working along the Rankine cycle with a back pressure mechanism has a higher efficiency. This provides a novel and efficient mechanism to produce the useful mechanical work, and such black hole heat engine may act as a possible energy source for the high energy astrophysical phenomena near the black hole. 相似文献
810.
Critical condition of inner cylinder radius for sustaining rotating detonation waves in rotating detonation engine thruster 总被引:1,自引:0,他引:1
Akira Kawasaki Tomoya Inakawa Jiro Kasahara Keisuke Goto Ken Matsuoka Akiko Matsuo Ikkoh Funaki 《Proceedings of the Combustion Institute》2019,37(3):3461-3469
We describe the critical condition necessary for the inner cylinder radius of a rotating detonation engine (RDE) used for in-space rocket propulsion to sustain adequate thruster performance. Using gaseous C2H4 and O2 as the propellant, we measured thrust and impulse of the RDE experimentally, varying in the inner cylinder radius ri from 31 mm (typical annular configuration) to 0 (no-inner-cylinder configuration), while keeping the outer cylinder radius (ro = 39 mm) and propellant injector position (rinj = 35 mm) constant. In the experiments, we also performed high-speed imaging of self-luminescence in the combustion chamber and engine plume. In the case of relatively large inner cylinder radii (ri = 23 and 31 mm), rotating detonation waves in the combustion chamber attached to the inner cylinder surface, whereas for relatively small inner cylinder radii (ri = 0, 9, and 15 mm), rotating detonation waves were observed to detach from the inner cylinder surface. In these small inner radii cases, strong chemical luminescence was observed in the plume, probably due to the existence of soot. On the other hand, for cases where ri = 15, 23, and 31 mm, the specific impulses were greater than 80% of the ideal value at correct expansion. Meanwhile, for cases ri = 0 and 9 mm, the specific impulses were below 80% of the ideal expansion value. This was considered to be due to the imperfect detonation combustion (deflagration combustion) observed in small inner cylinder radius cases. Our results suggest that in our experimental conditions, ri = 15 mm was close to the critical condition for sustaining rotating detonation in a suitable state for efficient thrust generation. This condition in the inner cylinder radius corresponds to a condition in the reduced unburned layer height of 4.5–6.5. 相似文献