Power plants – Internal combustion engine with treatment or handling of... – Material from exhaust structure fed to engine intake
Reexamination Certificate
1999-04-08
2001-04-03
Freay, Charles G. (Department: 3746)
Power plants
Internal combustion engine with treatment or handling of...
Material from exhaust structure fed to engine intake
C239S265110
Reexamination Certificate
active
06209312
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a rocket motor nozzle assembly designed to reduce nozzle recession, especially for rocket motor nozzle assemblies comprising carbon-based materials.
2. Description of the Related Art
One factor taken into consideration in nozzle design is the configuration of the divergent/convergent pathway defined by the nozzle, and the restrictive orifice or throat area of the nozzle. Mass flow through the nozzle produces the force or thrust produced by the rocket motor. The proportions of the mass flow pathway, particularly the ratio of area at the exit plane to area at the throat, establish how efficiently the nozzle converts pressure in the mass flow stream to thrust produced by the motor. It is within the purview of those skilled in the art to design a nozzle to optimize the ratio of exit area to throat area.
Another factor taken into consideration in nozzle design is the weight penalty imparted to the rocket motor by the nozzle assembly. Intuitively, a lesser weight nozzle assembly is desirable because the lesser the weight of the nozzle assembly, the farther the rocket motor assembly can travel. For this reason, carbon-based materials are highly advantageous for use as nozzle insulation due to their low weight. As referred to herein, carbon-based materials include, but are not limited to, carbon or graphite bulk and composite materials with constituents previously subject to carbonization or graphitization, known as carbon/carbon, graphite/carbon, and cloth, fiber, or powder-filled phenolic composites, and also a large array of metal or silicon carbides.
It is widely acknowledged in the industry, however, that carbon-based nozzle throats tend to recede, especially at high operating temperatures and pressures. Studies have identified several reasons for nozzle throat recession. One among several reasons involves oxidation reactions between the carbon-based nozzle material and oxygen-containing constituents of the combustion products. As the propellant in the rocket motor burns, the carbon-based nozzle is exposed to the hot combustion gases, such as O
2
, H
2
O, CO
2
, and NO. These gases, especially water and carbon dioxide, tend to react with the carbon-based nozzle materials to produce carbon monoxide gas, which is carried off with the discharged combustion products. Another reason for nozzle throat erosion is the abrasive impact of high velocity particles in the gas stream against the nozzle throat. Still another reason for nozzle throat recession involves pyrolysis of the throat material itself, particularly when volatile decomposition products form.
The recession of the nozzle throat inner surface during motor operation is a source of several problems in rocket operation. As the nozzle throat material recedes, the exit area to throat area ratio (or expansion ratio) diminishes, thereby decreasing the efficiency of the nozzle. Additionally, rough nozzle surfaces, which tend to form during nozzle recession, have been shown to undergo recession at faster rates than smooth surfaces. Thus, the nozzle throat recession process can be characterized as a self-perpetuating phenomenon. Another problem attributable to nozzle recession is a loss of predictability. Calculations for determining acceptable payloads and requisite propellant grain stocks must be accurate to ensure that the rocket will reach its intended target. The calculations necessary for ascertaining rocket dimensions and payloads are dependent upon many variables, including nozzle throat dimension. In-flight variations of nozzle throat dimension due to recession can significantly complicate, if not render impossible, precise motor performance calculations.
To address the shortcomings of carbon-based nozzle throats, refractory metal and metal alloys are occasionally used in spite of their high specific gravities. Examples of such materials are tungsten and its alloys.
However, the weight penalty and expense associated with the presence of the tungsten and other refractory metals often make these refractory materials impractical and uneconomical for applications involving bulky throat insert cross-section sizes. Additionally, such cross sections are subject to tensile and compressive stresses due to thermal shock early in motor burn when thermal expansions near the rapidly heated exposed surfaces are restrained by cooler regions of the cross section farther from the exposed surfaces. Indeed, surface heating can be so intense that temperature gradients of thousands of degrees per inch are possible. Such thermal stresses in both the axial and tangential (or hoop) directions can produce thermal fractures in the nozzle component, and potentially ejection from the motor.
Refractory ceramic materials have also occasionally been used in an attempt to address the shortcomings of carbon-based nozzles. Refractory ceramics present lesser weight penalties than refractory metals, but thermal shock penalties may be greater than in refractory metals.
To address the problem of restrained thermal deformations, U.S. Pat. No. 3,200,585 to Climent et al., the complete disclosure of which is incorporated herein by reference, discloses the use of a plurality of tungsten washers as constituting the throat portion of a nozzle, with the washers being stacked to form a cylindrical structure. The washers include radially extending slits to permit expansion and contraction of the washers in response to thermal stresses. However, the tubular structure disclosed by Climent et al. has several drawbacks. For example, the tubular structure is disposed only in the throat region of the nozzle pathway, leaving other portions of the pathway, such as the nosetip, entrance, and susceptible exit regions of the pathway, unprotected. Additionally, tungsten is chemically reactive with carbon-based insulation or substrate. As a consequence, the tungsten and carbon-based portions are prone to recession. Finally, the mounting of the tungsten washers and their support member can be a laborious and time-consuming process.
It would, therefore, be a significant advancement in the art to provide a nozzle assembly that takes advantage of the low weight of carbon-based materials and the erosion resistance of metals and alloys, yet does not impose an undue weight penalty to the rocket motor assembly and avoids nozzle recession and its associated problems.
SUMMARY OF THE INVENTION
It is, therefore, an object of this invention to provide a rocket motor assembly that accomplishes the above-mentioned improvement in the art.
In accordance with the principles of this invention, these and other objects are attained by the provision of a nozzle assembly mountable to a rocket motor body to form part of a rocket motor assembly for receiving and discharging high temperature combustion products from a combustion chamber of the rocket motor body. In accordance with an embodiment of this invention, the nozzle assembly includes at least a mount structure adapted for mounting of the nozzle assembly to the rocket motor body, a converging-diverging nozzle structure associated with the mount structure and comprised of at least one carbon-based material, and one or more erosion-resistant liners. The nozzle structure comprises a nose tip region, a restricted cross-sectional throat region, and an exit cone region that collectively provide an interior surface configured to define a converging-diverging flow path through which the combustion products pass during operation of the rocket motor assembly. Each of the liners comprises at least one leg portion and a corresponding body portion angled relative to the leg portion. Each of the leg portions of the liners protrudes into an edge or groove of the nozzle structure to engage the liner to the nozzle structure. The body portions of the liners collectively cover the throat region and optionally the nose tip region of the nozzle structure along the flow path, as well as the exit cone region along sections of the flow path that are prone to more than negligible amounts of recessio
Carr, Jr. Clyde E.
Singer Victor
Cordant Technologies Inc
Freay Charles G.
Sullivan Law Group
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