Power plants – Reaction motor – Liquid oxidizer
Reexamination Certificate
2002-08-09
2004-06-22
Yu, Justine R. (Department: 3746)
Power plants
Reaction motor
Liquid oxidizer
C060S257000
Reexamination Certificate
active
06751945
ABSTRACT:
BACKGROUND
Rocket engines require propellants to be fed to them at very high pressures. This has historically been accomplished in two general ways: first, with the use of a pressurized fluid, such as high pressure helium; and second, with the use of a pump.
In the first way (i.e., a “blowdown” system), a pressurized fluid is added directly to the propellant tank and exerts a force on the propellant. Nitrogen and helium, both inert gases, pressurized to a pressure as high as 50,000 PSI, have been used successfully in the past. As they are inert, there need be no barrier (e.g., membrane or piston) placed between these pressurized fluids and the propellant. The problem with this method, however, is that the pressurized fluid also exerts a force on the propellant tank. Because of the extremely high pressures required of the pressurized fluid, the walls of the propellant tank must be thick enough to withstand the pressure. The propellant tank is therefore very heavy. Rockets employing the pressurized fluid must use a greater proportion of their thrust lifting this extra weight, and therefore they are not as efficient as rockets that do not require this added weight.
Historically, one way to solve the above weight problem is to employ the use of a pump. Pumps (e.g., reciprocating, centrifugal, or radial pumps) are generally very complex and expensive and require their own driving means, such as an engine. Further, the engine driving the pump burns a significant percentage of the total propellant. For small rocket engine systems, since a pump is too complicated, too heavy, and too expensive pressurized fluids are generally used to pressurize the propellant. However, for large rocket engine systems, pumps have the advantage that the walls of the propellant tank need not be thick, since there is little or no pressure in the tank. Therefore, the propellant tank is much lighter, and the added weight of the pump is more than offset by the reduction in propellant tank weight.
Another problem with both the blowdown and pump pressurizing systems is the pressure limitation. Current rocket engine combustion pressures are generally limited to 3,000 PSI or less, because most rocket engine turbopumps cannot create an outlet pressure higher than about 7,000 PSI, and because in most blowdown systems, pressurizing propellant tanks above around 1,000 PSI requires tanks whose wall thicknesses and weights are prohibitive.
U.S. Pat. No. 3,213,804 to Sobey (“Sobey”) discloses fluid pressure accumulators that are connected to sources of low and high pressure by means of butterfly valves. Essentially, the pressurized fluid exerts force on the propellant in small, designated containers. While the walls of these containers must be thick in order to withstand the high pressure of the pressurized fluid, the walls of the propellant tank need not be. Therefore, the total weight of the rocket engine system employing Sobey's invention may be less than that of the previously discussed rocket engine system because these containers (fluid pressure accumulators) are small in comparison to the propellant tank.
U.S. Pat. No. 6,314,978 to Lanning, et al. (“Lanning”) discloses a reciprocating feed system for fluids having storage tanks
1
,
2
,
3
that are similar in purpose to the fluid pressure accumulators disclosed in Sobey. Instead of valves
50
,
52
,
54
disclosed in Sobey, Lanning discloses four valves for each storage tank
1
,
2
,
3
. For example, associated with storage tank
1
are: valve
13
between storage tank
1
and low pressure fluid
5
; valve
16
between storage tank
1
and high pressure discharge
7
; valve
20
between storage tank
1
and vent manifold
18
; and valve
24
between storage tank
1
and pressurized gas supply
8
. Each valve must be accurately and reliably controlled by a controller
11
. Further, each valve may have associated with it a sensor
11
a.
SUMMARY OF THE INVENTION
A problem with Sobey's invention, however, is its complicated use of valves. In order to reduce the weight of Sobey's invention further, the sizes of the fluid pressure accumulators must decrease (thus reducing their weight). However, as they decrease, the rotation speed and precision of the butterfly valves must increase in order to accommodate the same propellant flow rate to the rocket engine. This places great stresses on the valves, and eventually a point is reached (in reducing the size of the fluid pressure accumulators) at which the valves cannot reliably rotate fast enough to provide the required timing.
Lanning has problems that are similar to the problems of Sobey. For example, Lanning requires a trade-off between reducing the size and weight of storage tanks
1
,
2
,
3
, and increasing the speed, reliability, and working pressure of the valves. In other words, in order to reduce the size and weight of storage tanks
1
,
2
,
3
, the valves must be able to reliably and accurately open and close at a faster rate. This puts great stresses on the valves. Further, the control system must be more complicated.
In a preferred embodiment, the present invention provides for pressurizer for pressurizing a fluid, comprising: a pressurant entrance configured for the introduction of a pressurant; a fluid entrance configured for the introduction of said fluid; a fluid exit configured for the expulsion of said fluid; and at least one transfer chamber movable in a cycle with respect to at least one of said pressurant entrance, said fluid entrance, and said fluid exit, wherein said pressurizer is configured so that for a portion of a cycle said pressurant exerts a force on said fluid inside said transfer chamber, and wherein said transfer chamber is configured to receive said pressurant via said pressurant entrance, receive said fluid via said fluid entrance, and expel said fluid via said fluid exit by the force exerted by said pressurant upon said fluid inside said transfer chamber.
In a preferred aspect, the pressurizer comprises at least three transfer chambers, configured so that while at least one transfer chamber is in fluid connection with said fluid entrance, at least one other transfer chamber is in fluid connection with said fluid exit and said pressurant entrance. In another preferred aspect, at least one transfer chamber comprises: a movable piston configured to substantially separate said pressurant from said fluid inside said transfer chamber; and a limiter configured to prevent said piston from moving beyond a certain point inside said transfer chamber. In another preferred aspect, the pressurizer further comprises: a motor configured to move said transfer chamber at a cycle speed; a sensor configured to sense a quantity of propellant inside said transfer chamber; and a controller connected to said sensor and said motor, configured to adjust said cycle speed at least as a function of said quantity sensed by said sensor.
In another preferred aspect, a cross sectional area of said transfer chamber is less than {fraction (1/10)} a cross sectional area of said fluid exit. In another preferred aspect, the pressurizer further comprises a rotatable spindle housing a plurality of transfer chambers, wherein, in a cross section of said spindle, a distance between corresponding points of two transfer chambers is less than ½ a maximum characteristic length of said fluid exit along a direction of rotation of said spindle. In another aspect, in a cross section of said spindle, a dimension of said transfer chamber along a path taken by said transfer chamber is less than a minimum distance between said pressurant entrance and said pressurant exit along a path taken by said transfer chamber. In another aspect, in a cross section of said spindle, a maximum characteristic length of said fluid exit along a direction of rotation of said spindle is less than ½ of a minimum distance between said pressurant entrance and said pressurant exit along a path taken by at least one transfer chamber.
In another preferred aspect, the pressurizer further comprises a pressurant exit configured f
Rodriguez William H.
Yu Justine R.
LandOfFree
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