|
The staged combustion cycle, also called topping cycle or preburner cycle,〔 〕 is a thermodynamic cycle used in some bipropellant rocket engines. In staged combustion, one propellant is sent through a preburner and partially burned using a small portion of the second propellant. The resulting hot gas is used to power the engine's turbines and pumps, then injected into the main combustion chamber along with the remainder of the second propellant to complete combustion. There are two main variants of the cycle depending on which propellant is sent through the preburner: oxidizer-rich staged combustion (ORSC) and fuel-rich staged combustion (FRSC). The advantage of staged, or "closed", combustion is that all of the cycle's gases and heat go through the combustion chamber. (An alternative design, called the gas-generator cycle, is an "open" cycle where the gas used to drive the turbopumps is exhausted overboard without passing through the main combustion chamber, reducing efficiency.) Since no propellant is dumped overboard, staged combustion allows for high power turbopumps which permit very high chamber pressures, allowing the use of high expansion ratio nozzles at low altitude for better performance. Disadvantages of staged combustion include harsh turbine conditions, exotic plumbing to carry the hot gases, and complicated feedback and control. In particular, ORSC requires advanced metallurgy due to extremely corrosive oxidizer-rich gas, while FRSC requires use of a fuel that will not coke, such as liquid hydrogen. ==History== Staged combustion (''Замкнутая схема'') was first proposed by Alexey Isaev in 1949. The first staged combustion engine was the S1.5400 (11D33) used in the Soviet planetary rocket, designed by Melnikov, a former assistant to Isaev.〔George Sutton, "History of Liquid Propellant Rocket Engines", 2006〕 About the same time (1959), Nikolai Kuznetsov began work on the closed cycle engine NK-9 for Korolev's orbital ICBM, GR-1. Kuznetsov later evolved that design into the NK-15 and NK-33 engines for the unsuccessful Lunar N1 rocket. The non-cryogenic N2O4/UDMH engine RD-253 using staged combustion were developed by Valentin Glushko around 1963 for the Proton rocket. After the failure of the N-1, Kuznetsov had been ordered to destroy the NK-33 technology, but instead he warehoused dozens of the engines. In the 1990s, Aerojet was contacted and eventually visited Kuznetsov's plant. Upon meeting initial skepticism about the high specific impulse and other specifications, Kuznetsov shipped an engine to the US for testing. Oxidizer-rich staged combustion had been considered by American engineers, but deemed impossible.〔''Cosmodrome'' History Channel, interviews with Aerojet and Kuznetsov engineers about the history of staged combustion〕 The Russian RD-180 engine, purchased by Lockheed Martin (subsequently by United Launch Alliance) for the Atlas III and V rockets, also employs this technique. In the West, the first laboratory staged-combustion test engine was built in Germany in 1963, by Ludwig Boelkow. Hydrogen peroxide/kerosene fueled engines such as the British Gamma of the 1950s may use a closed-cycle process (arguably not ''staged combustion'', but that's mostly a question of semantics) by catalytically decomposing the peroxide to drive turbines ''before'' combustion with the kerosene in the combustion chamber proper. This gives the efficiency advantages of staged combustion, whilst avoiding the major engineering problems. The Space Shuttle Main Engine is another example of a staged combustion engine, and the first to use liquid oxygen and liquid hydrogen. Its counterpart in the Soviet shuttle was the RD-0120, similar in specific impulse, thrust, and chamber pressure specification to the SSME, but with some differences that reduced complexity and cost at the expense of increased engine weight. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「staged combustion cycle」の詳細全文を読む スポンサード リンク
|