Ejector ramjet

#The present invention relates generally to ramjet propulsion devices, more particularly to ramjets having secondary fluid induction systems, such as ejectors.

#A "ramjet" is a jet engine in which a fuel is combusted, having in its forward end a continuous inlet of air that depends on the speed of flight rather than on a mechanical compressor, for the compressing effect produced on the air. In ramjet powered missiles and other high performance systems, the need is to accelerate the vehicle from 0 or low velocity to a velocity where a ramjet will begin to operate on its own (Mach number about 2-3). The problem with the conventional ramjet is its inability to produce thrust at low speed. One solution is to use a turbojet or other conventional jet to get the vehicle moving initially; however, once the vehicle is moving at a velocity sufficient for the ramjet to operate, the turbojet is simply dead weight for the rest of the mission (unless it is discarded). Therefore, most ramjet-powered missiles use a rocket to accelerate to the initial velocity, although the use of rockets is very inefficient. Because it is small and compact, the rocket is attractive for use because it can be discarded. This is acceptable for some missions; however, for missions where the vehicle has other constraints such as internal stowage on the launcher the size and weight of the rocket motor becomes disadvantageous. If the rocket is integrated into the system and made to operate more like a jet engine (i.e., made so that it works with a secondary fluid (i.e., air)) the propulsion efficiency of the entire system can increase. The air-breathing action in low velocity flight is typically considered as augmentation to the rocket thrust, and is referred to as an ejector rocket or air-augmented rocket.

#An "ejector" is a jet pump for withdrawing a secondary fluid from a space by movement of a primary fluid. When an ejector is combined with a ramjet as shown in FIG. 1, an "ejector ramjet" 10 is produced. Shown are a rocket 12, ejector 14, diffuser 16, combustor 18, and nozzle 19. The rocket 12 produces a primary exhaust jet 20, inducing secondary fluid 22 (typically air) into the ejector ramjet engine 10. A frictional shear boundary is shown at 24 between primary and secondary fluids.

#FIG. 1 shows a schematic sectional view of a conventional ejector ramjet;

#FIGS. 2a-b illustrate wave dynamic pressure exchange between fast- and slow-moving fluids;

#FIG. 3 shows a schematic of the oscillating external driver embodiment of the present invention;

#The improved ejector ramjet of the present invention will now be described with reference to FIGS. 3-6. When comparing the fluid processes of these embodiments with a conventional ejector ramjet as shown in FIG. 1, one will observe the same velocity at the exit of the mixing section but the static pressure at exit will range from about two times to about four times as great as that of the conventional ejector ramjet. This can result in a significant thrust increase at static conditions, and, at high speeds, the improved ejector ramjet engine can produce significant mixing improvements over conventional ramjet and scramjet engines.

#Referring now specifically to the embodiment shown in FIG. 3, an oscillating external primary jet 20 is shown exiting the primary nozzle 26. Nozzle 26 is preferably a two-dimensional nozzle, having side panels which include fluid injectors 28 and 30, respectively. Fluid injectors 28 and 30 operate to alternately separate the primary jet 20 from opposite sides of nozzle 26. The fluid used to drive the primary jet back and forth can be any fluid, for example, liquid or gaseous fuels, or ram air. Any fluid having a higher pressure than the local nozzle pressure may be utilized for producing the oscillation of the primary jet. The fluid injectors or deflectors 28 and 30 are preferably controlled by a feedback control system which senses engine exhaust pressure as well as inlet pressure, and informs the deflecters of the frequency for alternating the primary jet from side to side. The frequency of primary jet oscillations may vary over a broad range depending on duct geometry, vehicle speed, etc. The frequency of primary jet oscillation may range from about 1 Hertz up to 100 Hertz or more depending on the engine size.

#Sidewalls 32 and 34 of the propulsion duct direct alternating slugs of primary and secondary fluid into separate downstream channels or tubes created by partition 36. Thus, as shown in FIG. 3, primary fluid 20 is shown entering the upper duct section bounded by wall 32 and barrier 36, while secondary air 22 is shown entering the lower duct bounded by wall 34 and barrier 36. Shown at 38 is a preceding slug of secondary fluid while shown at 40 is a preceding slug of primary fluid. Primary fluid 40 draws secondary fluid slug 44 into the lower duct by creating a partial vacuum behind it while primary fluid slug 42 pushes secondary flow slug 38 into the upper portion of the propulsion duct. By alternating the separation of the primary jet 20 from the two-dimensional nozzle via the fluid injectors 28 and 30, the primary and secondary fluids may contact each other in the respective ducts in such fashion as to transfer energy in a nonviscous, substantially frictionless manner (wave dynamic pressure exchange).