Power plants – Combustion products used as motive fluid
Reexamination Certificate
1997-12-19
2001-04-03
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
C417S295000, C417S505000, C417S279000, C137S487500, C137S565110
Reexamination Certificate
active
06209309
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to the art of fluid controls and, more particularly, to fuel controls for combustion engines such as gas turbine engines that provide primary or secondary power to a vehicle.
BACKGROUND OF THE INVENTION
Cost and size of engine components are of constant concern in vehicular engine applications. This is particularly true for small turbojet engines that are designed for use in missiles and other short-life/disposable applications.
It is known to use a pulse width modulated valve (PWM valve) on the high pressure side of a fuel pump to meter the fuel flow to a gas turbine engine by cycling the PWM valve between an on and off position. Fuel flow is determined by the time period that the valve is open during each cycle and by the cycle frequency. Typically, such systems utilize a regulator valve to control the inlet pressure to the PWM valve by bypassing fuel flow from the high pressure side of the fuel pump back to the fuel tank. Examples of such systems are shown in U.S. Pat. Nos. 3,568,495 to Fehler et al.; 3,936,551 to Linebrink et al.; and 4,015,326 to Hobo et al.
Two disadvantages associated with these systems are the size and cost of the PWM valve components which must be designed to withstand the output pressure of the fuel pump, which commonly is in the range of 100-200 psig to provide adequate fuel injection pressure to the combustor.
Another disadvantage associated with these systems is the wasted power input into the pressurized fuel flow that is bypassed by the regulator valve from the high pressure side of the fuel pump back to the fuel tank. The wasted power is particularly critical in missiles and other vehicles having a limited fuel capacity and a mission profile that may be determined by the time required to deplete the stored fuel.
Yet another disadvantage associated with these systems is the pulsating flow generated by the PWM valve as it cycles between its open and closed positions. Such pulsating flow can result in combustor flameout and/or deleteriously affect the combustor stability. Accordingly, depending on the engine and combustor parameters, these systems typically require some form of accumulator/damper in the high pressure fuel line connecting the PWM valve to the combustor to dampen the pulses in the fuel flow to the combustor. The accumulator/damper is an additional component that adds cost, complexity and weight to the system and introduces a potential failure point in the system.
Thus, it can be seen that there is a need for a small, low-cost, and efficient fuel control system for gas turbine engines and, in particular, for small turbojet engines.
SUMMARY OF THE INVENTION
It is the principal object of the invention to provide a new and improved fluid flow control system.
More specifically, it is an object to provide a small, low cost fluid flow control, and particularly a small, low-cost fuel control system for a gas turbine engine and, in particular, for small turbojet engines.
It is a further object of the invention to provide a fluid flow control system that utilizes a PWM valve to meter the fluid flow without requiring any additional components dedicated to damping pulses in the fluid flow generated by the PWM valve.
It is a further object of the invention to provide a fuel control system that reduces or eliminates the energy wasted in bypassing pressurized fuel flow from a pump outlet back to a fuel tank.
These and other objects of the present invention are attained in a fluid flow control in the form of a fuel control system that utilizes a PWM valve to meter a fuel flow to the inlet of a fuel pump that pumps the metered fuel flow to an engine. By virtue of this construction, the PWM valve is not subjected to the output pressure of the fuel pump. This allows the fuel control system to utilize a small, low-cost PWM valve, such as is commonly used in connection with automotive fuel injectors. Further, because the fuel is metered prior to entering the fuel pump, the fuel pump only pumps the precise amount of fuel required for the engine and no energy is wasted in pumping a fuel flow that must be bypassed back to a fuel tank. Additionally, because the PWM valve is on the inlet side of the fuel pump, the fuel pump can be utilized to dampen the PWM valve generated pulses in the fuel flow by operating with a vapor core wherein fuel is vaporized at the pump inlet and reformed back to liquid at the pump outlet, thereby damping the pulses.
According to one aspect of the invention, a method for controlling a fluid flow rate from a pump is provided and includes the steps of providing a pump having a pump inlet and a pump outlet, and a fluid flow path to the pump inlet. The fluid flow path is cyclically restricted to achieve a fuel flow to the pump inlet that cycles between a first flow rate for a time period T
1
and a second flow rate for a time period T
2
, with the second flow rate T
2
being greater than the first flow rate. The fluid flow to the pump inlet is pumped by the pump from the pump inlet to the pump outlet.
According to another aspect of the invention, the method further includes the steps of vaporizing at least a portion of the fluid flow at the pump inlet for at least a portion of the time period T
1
and reforming the vaporized fluid flow back to liquid at the pump outlet.
According to another aspect of the invention, an improvement is provided in a method for controlling the fluid flow rate from a pump including the steps of providing a pump having a pump inlet and a pump outlet, providing a substantially liquid fluid flow to the pump inlet, pumping the fluid flow with the pump from the pump inlet to the pump outlet while creating a pressure at the pump outlet that is above the vapor pressure of the fluid flow at the outlet. The improvement includes repetitively reducing the pressure at the pump inlet to a value below the vapor pressure of the fluid flowing into the pump inlet to provide a vapor core within the pump sufficient to dampen pulses in the fluid flow.
Other objects, advantages and novel features of the present invention will be apparent to those skilled in the art upon consideration of the following drawing and detailed description of the preferred embodiments.
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Hamilton Sundstrand Corporation
Kim Ted
Wood Phillips VanSanten Clark & Mortimer
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