星用490 N发动机偏工况工作特性试验

准确掌握液体火箭发动机不同参数下的工作特性及裕度对其使用可靠性至关重要。对第二代490 N发动机开展偏工况高空模拟和地面热试车，研究了推力和混合比变化对发动机工作特性的影响。结果表明:高空模拟环境下发动机能在混合比1.54～1.80及真空推力372～584 N的较宽包络范围内正常工作。随着推力的增加，真空比冲和喉部温度均提高，燃烧室效率依次呈增大、平稳、下降的趋势，喷管效率小幅增大。随着混合比的增大，真空比冲和喉部温度也提高，燃烧室效率未发生明显变化，喷管效率微降低。额定混合比下，室压在0.61～1.56 MPa区间内波动平稳，具备真空推力345～900 N工作能力，但在0.51 MPa时产生与输送系统耦合的中低频（207 Hz）燃烧振荡。高工况引起喉部热流冲刷加剧以及温度升高会加速涂层的损失，使得发动机长程工作寿命下降，但在一定的偏离范围及单次点火时长内仍能满足卫星25000 s鉴定级寿命要求。 

Test on working characteristics of 490 N engine for satellites under off-rated conditions

Accurately mastering the working characteristics and margin of liquid rocket engine under different parameters is crucial to its reliability. High-altitude simulation and ground hot fire tests of the second generation 490 N engine under off-rated conditions were carried out, and the influence of thrust and mixing ratio changes on the engine working characteristics was studied. Results indicated that, the engine can work normally within the wide envelope scope of mixing ratio 1.54—1.80 and vacuum thrust 372—584 N under high-altitude simulation environment. With the increase of thrust, the vacuum specific impulse and throat temperature both rose, the combustion chamber efficiency increased, kept stable and decreased in turns, and the nozzle efficiency increased slightly. As the mixing ratio increased, the vacuum specific impulse and throat temperature also increased, the combustion chamber efficiency did not change obviously, and the nozzle efficiency decreased slightly. For the rated mixing ratio, the combustion chamber pressure fluctuated smoothly within the range of 0.61—1.56 MPa, enabling to work with the vacuum thrust of 345—900 N. However, it produced combustion oscillation of low/middle frequency (207 Hz) coupled with the feed system at 0.51 MPa. The intensifying erosion of hot flow and increasing temperature in the throat under high working conditions accelerated the loss of coating, which reduced the long-term working life of engine. Nonetheless, it can still meet the working life requirements of 25 000 s for satellite identification within a certain off-rated range and single ignition duration.