Abstract:
A flow control system for a fuel includes an adjustable speed control valve configured to control a flow of fuel. A variable area orifice is arranged upstream of the speed control valve and is configured to control the flow of the fuel to the speed control valve. A flow control system for a turbine fuel and a method of controlling fuel flow are also disclosed.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to a variable area orifice for an engine. 
         [0002]    An engine includes a turbopump, a nozzle, and a turbine. Liquid hydrogen fuel entering the turbopump is compressed and delivered through a nozzle, which vaporizes the liquid hydrogen into a high-pressure hydrogen gas. The high-pressure hydrogen gas expands through the turbine section and exits the engine through an exhaust. 
         [0003]    Engines generally operate at or below a certain maximum speed. The speed of the turbines can be modulated by a speed control valve, which controls the flow of fuel to the turbine, so as not to exceed the maximum. 
         [0004]    In some instances, the engine is required to operate at speeds approaching the maximum speed. This requires very high flowrates of fuel to be fed to the turbine. When the engine is signaled to slow down, the speed control valve must respond quickly enough to adequately control the very high flowrate in order to prevent overspeeding. 
       SUMMARY OF THE INVENTION 
       [0005]    A flow control system for fuel includes an adjustable speed control valve configured to control a flow of fuel. A variable area orifice is arranged upstream of the speed control valve and is configured to control the flow of the fuel to the speed control valve. A method is also described. 
         [0006]    These and other features may be best understood from the following drawings and specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  schematically shows an engine with a flow control system. 
           [0008]      FIG. 2A  shows a side view of a variable area orifice of the flow control system of  FIG. 1 . 
           [0009]      FIG. 2B  shows an opposite side view of the variable area orifice of  FIG. 2A . 
           [0010]      FIG. 3  shows a phantom view of the variable area orifice of the flow control system of  FIGS. 1-2B  in a housing. 
           [0011]      FIG. 4  shows a section view of the variable area orifice of the flow control system of  FIGS. 1-3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1  schematically shows an engine  8 . The engine includes a fuel tank  9 , a turbopump  10 , a nozzle  11 , and a turbine  12 . Liquid hydrogen entering the turbopump  10  from the fuel tank  9  is pressurized and vaporized through the nozzle  11  to generate a high-pressure hydrogen gas flow. The hydrogen gas flow (“fuel”) is then passed through the turbine  12 . A controller such as an auxiliary control unit  13  controls the flow of liquid hydrogen from the fuel tank  9 . In one example, the auxiliary control unit  13  provides a pulsed flow of liquid hydrogen to the turbopump  10 . 
         [0013]    The turbine  12  may include a fixed area nozzle (not shown). In this case, the auxiliary control unit  13  is the sole modulator of fuel pressure throughout the engine  8  by modulating the flowrate of liquid hydrogen that is vaporized. That is, the pressure differential on either side of the turbine  12  depends only on the amount of fuel exiting the nozzle  11 . 
         [0014]    A flow control system  15  for the engine  8  fuel includes a speed control valve  14  and a variable area orifice  16 . The speed control valve  14  is in this example an on/off type, so that the speed control valve  14  is only capable of being in an open position and a closed position, with no intermediate positions. The speed control valve  14  can be controlled by, for instance, a mechanical governor or an electrical controller. In this example, the variable area orifice  16  is upstream from the speed control valve  14 . Thus the variable area orifice  16  controls the flow of fuel from the nozzle  11  to the on-off type speed control valve  14 . 
         [0015]    When the flowrate of the fuel flowing to the turbine  12  is very high, the variable area orifice  16  provides an extra measure of protection (in addition to the speed control valve  14 ) to ensure that the engine  8  does not over-speed. For example, there may be a period of operation where the flowrate of fuel to the engine  8  is required to be high so that the engine  8  operates at a speed approaching its maximum speed. The auxiliary control unit  13  may determine that the engine  8  should operate at a slower speed. 
         [0016]    At some point, the auxiliary control unit  13  sends the speed control valve  14  a signal to slow the speed of the turbine  12  by reducing the flowrate of fuel. The auxiliary control unit  13  may also send such a signal to the turbopump  10 . The engine  8  may operate at an undesirably high speed for a period of time if the speed control valve  14  is not able to respond quickly enough. The variable area orifice  16  modulates flow of fuel to the speed control valve  14  so that a slow response time of the speed control valve  14  does not lead to over-speeding of the engine  8 . 
         [0017]      FIGS. 2A and 2B  show opposite sides of the variable area orifice  16 . The variable area orifice  16  incudes a housing  18 , an inlet  20  receiving fuel from the nozzle  11  ( FIG. 1 ), an outlet  22  sending fluid to the turbine  12 , and vents  24 . 
         [0018]      FIG. 3  shows a view of the variable area orifice  16  with the housing  18  shown in phantom. 
         [0019]      FIG. 4  shows a section view of the variable area orifice  16 . The variable area orifice  16  includes a spring-loaded piston  26  in fluid communication with the vents  24  via an orifice  28  at a first end  29   a  of the piston  26  adjacent a spring  31 . Thus the piston  26  is vented to low pressure outside the housing  18 . 
         [0020]    The piston  26  further includes an arm  30  extending perpendicular to the piston  26  from an opposite end  29   b . The arm  30  includes a conical pintle  32  extending parallel to the piston  26  toward the spring end  29   a . An orifice  34  is adjacent the pintle  32  and in fluid communication with the outlet  22 . 
         [0021]    In operation, the piston  26  moves in response to the pressure of fuel in the housing  18  along its axis P by the spring  31 . The pressure of fuel entering the housing  18  is modulated by the auxiliary control unit  13 . That is, forces generated by the flow of fuel through the housing  18  with respect to the forces generated by the spring  31  on the piston  26  determine the positioning of the piston  26  and consequently the arm  30  and pintle  32 . At a pre-determined fuel pressure in the housing  18  (depending on the flow of fuel from the nozzle  11  to the variable area orifice  16 ), the pressure on the piston  26  surface exceeds the piston spring  31  preload and moves the piston  26 , depending on the rate and/or preload of the spring  31 . 
         [0022]    As the arm  30  and pintle  32  move towards the orifice  34 , the pintle  32  moves into and incrementally blocks the orifice  34  such that the area through which fuel can flow through the outlet  22  decreases. As the arm  30  and pintle  32  move away from the orifice  34 , the pintle  30  moves out of and incrementally opens the orifice  34  such that the area through which fuel can flow through the outlet  22  increases. Thus the variable area orifice  16  modulates the flow of fuel before it reaches the speed control valve  14  ( FIG. 1 ) to ensure that the engine  8  does not over-speed. 
         [0023]    When the auxiliary control unit  13  sends a signal to slow down the engine  8 , the flow of liquid hydrogen from the fuel tank  9  through the turbopump  10  and nozzle  11  is reduced, and the speed control valve  14  is signaled to reduce the flow of fuel to the turbine  12 . There may be a time delay after the auxiliary control unit  13  reduced the flow of liquid hydrogen to the turbopump  10  and before the flow of fuel to the turbine  12  is reduced. If the speed control valve  14  does not respond quickly enough in this interim time, the engine  8  may over-speed. The variable area orifice  16  upstream from the speed control valve  14  is configured to modulate flow of fuel from the nozzle  11  to the speed control valve  14  such that even a slow response time of the speed control valve  14  does not cause the engine  8  to over-speed, as was described above. 
         [0024]    Variables including the orifice  34  area, the pintle  32  geometry (including shape and/or dimensions), the spring  31  rate and preload, and the ratio of the orifice  34  area to the inlet  20  and/or outlet  22  area can be designed to match the required fuel inlet pressure range and fuel flow rate requirements to the turbine  12 . 
         [0025]    Although embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.