Rocket

About: Rocket is a research topic. Over the lifetime, 14018 publications have been published within this topic receiving 95852 citations. The topic is also known as: rockets.

Experimental status of high frequency liquid rocket combustion instability

Abstract: A necessary criterion for any self-sustained vibrating system, including unstable rocket combustion, is that enough energy must be supplied to the system at the proper frequency and phase relationship to overcome that lost by damping. However, there is no one unique sustaining combustion process, and there are several kinds of damping, and several different kinds of vibration. When one adds to this picture the fact that two or more kinds of vibration can coexist, the subject becomes complex. There are several kinds of combustion instability. When the chamber pressure changes slowly enough so that wave motion in the chamber is not a factor, the resultant instability, usually driven by fluctuations in the propellant flow rate and sustained by a “combustion time delay,” is called “chugging.” At higher frequencies, one can have longitudinal wave motion in the chamber (also sustained by flow fluctuation or by “time delay”), and then cylindrical wave motion. The most important cylindrical modes are the first transverse and first radial. They have a very nonlinear characteristic-may exist only at very low amplitude unless “triggered” to a critical amplitude-whereupon the amplitude grows enormously and the thrust chamber may experience heavy thermal and mechanical damage. The stable combustion field in a liquid rocket consists of liquid streams impinging and forming liquid fans, these breaking into ligaments and blobs and finally into a dense cloud of droplets. All of this liquid burns on its surface at a rate controlled by its surface area and turbulent heat and mass transfer. Some 70%–90% of the product gas is formed by droplet combustion but this plays little part in the instability. The other 30%–10% of the gas is formed from fans, ligaments, and blobs near the injector, and these burn slowly, probably because their specific area is small and because of the low gas-phase concentration of oxidizer species around fuel fans and fuel species around oxidizer fans. When high-frequency instability occurs the most dramatic change takes place in this poorly atomized and mixed region as is shown in high speed motion pictures. The high transverse gas velocity shatters the liquid, and particle displacement causes gas-liquid mixing, both resulting in intense gas generation. At low amplitudes these effects damp as well as drive, but at high amplitude the net effect occurs at the proper phase relationship to sustain the high-frequency instability. Other processes may also be important, especially the fact that the feed system must respond to the local chamber pressure changes caused by the instability. Until recently, the most effective way to avoid destructive high-frequency instability was the empirical selection of injector styles that had a relatively high triggering threshold, and avoiding the triggering by careful control of engine starting and operating procedures. More recently it has become possible to arrive at empirical stabilization systems, described below, such that the instability initiated by a trigger will die out, and stable combustion will be resumed promptly. This characteristic has been termed “Dynamic Stability.” High speed movies and pressure-time traces are presented, showing in a two=dimensional combustion apparatus processes similar to those occurring in full size chambers. These data include: o 1. Stable and unstable combustion with alcohol-liquid oxygen. A backlight-filter arrangement provides for silhouetting the liquid droplets and observing their behavior. 2. Stable and unstable combustion with liquid oxygen-jet fuel. The processes are probably similar to the above, but are difficult to observe because of optically dense hot soot in the combustion gas. 3. A combination of variable-amplitude, transverse high-frequency instability, with a feed-system chug. The pressure records are difficult to interpret without photographic support. 4. High-pressure, dense, liquid oxygen-RP combustion showing heavy damping of the pressure waves, except in the injection region where the amplitude is high. 5. Stable and unstable combustion with liquid oxygen-hydrogen. When the hydrogen is injected as a high-velocity gas, the system is generally stable. With liquid hydrogen injection the characteristics are similar to liquid oxygen-jet fuel. 6. Stable and unstable combustion with nitrogen tetroxide-unsymmetrical dimethylhy-drazine. These “storable” propellants exhibit a sustaining mechanism like liquid oxygen-jet fuel, but their “sensitive region” is more widespread, and their hypergolicity gives rise to kinds of “triggers” not present with nonhypergolic propellants. The processes observed in the movies are discussed briefly relative to the various sustaining processes that have been advanced for this kind of instability. These include: loss of ignition, chemical preparation time or time delay; detonation waves; pressure- or temperature-sensitive chemical kinetics; the “exploding” of droplets burning at pressures above their critical pressure; and the shattering and mixing of the streams, fans, and drops by the gas “particle” motion. Methods of control of high-frequency instability for practical engines include the use of baffles that interfere with the unwanted gas motion, “pre-mix” schemes that rapidly disinte-grate the unmixed and poorly atomized portion of the spray, and other designs that may combine these processes with effective damping of the wave motion. The application of the baffle principle to the H-1 (Saturn) engine injector is discussed.

Aerodynamic control mechanism for thrust vector control

Abstract: A rocket thrust vector control system including jet tabs and aerodynamic control surfaces is disclosed The control system removes roll information present in commands to the aerodynamic surfaces and provides only pitch and yaw information to the jet tabs for the thrust vector control The roll information is removed by a geared summing mechanism The resulting pitch and yaw output is used to drive the thrust vector control jet tabs The same powered actuators are used for both the aerodynamic control surfaces and the jet tabs

Mixed pod rocket release system

Abstract: A rocket release system, for an aircraft, having rocket pods randomly loaded with mixed rocket types and having provisions for selecting the type, release mode and quantity of rockets to be released. The rocket release is programmed so that the weapons remain balanced on each side of the aircraft and only safe combinations of rockets may be released. A continuous display of rocket inventory is provided along with a warning when the inventory of a particular type of rocket is depleted.