Abstract:
A heater for gas fuel mounted to a pressure reducing regulator to warm the gas after the temperature is reduced by the pressure reduction. The heater receives the fuel from the regulator through an external pipe and has separate gas and coolant passages therein. The coolant passage receives liquid engine coolant that heats both the gas and the regulator. A heater core has a plurality of radially extending fins around which the gas passes with the coolant passing through the interior of the core. Coolant flow is regulated by a thermostat that is responsive to the temperature of the gas to open and close the coolant passage.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a gas fuel heater and in particular to a heater mounted to a pressure regulator and having a thermostatic control that is responsive to the gas temperature to control the flow of engine coolant through the heater. 
     2. Description of Related Art 
     Compressed natural gas, when used as a vehicle fuel, is stored at very high pressures, typically greater than 3000 psi. The vehicle engine cannot utilize the fuel at this high pressure. Thus, a pressure reducing regulator is needed to lower the gas fuel pressure. A single stage regulator is more desirable than a multiple stage regulator due to the simplicity of the design. During the pressure reduction, as the gas expands, the temperature of the gas decreases. This expansion of gas can yield gas temperatures near or below −100° C. This cooling effect of the gas is most notable in the preferred single-stage regulator design. The single-stage regulator manufactured by ITT Conoflow is designed to expand the gas outside the body of the regulator so that the regulator itself is not subjected to the extreme cold of the expanding gas. 
     The gas fuel metering valve on the engine, however, must have gas at a temperature above 40° C. and preferably above 0° C. to avoid freezing of any moisture in the fuel line. When this pressure reducing regulator is used in close proximity to the engine, there is insufficient ambient heating of the gas in the fuel line connecting the regulator to the metering valve, on the engine to warm the fuel to the desire temperature. A heater is needed to raise the temperature of the expanded gas above the minimum temperature required by the fuel metering valve. 
     SUMMARY OF THE INVENTION 
     The present invention provides a natural gas heater that is thermostatically controlled. The heater housing is coupled to the body of the regulator. The heater is connected to the engine cooling system and receives engine coolant that flows through a coolant passage in the heater. The heater has a gas passage therein with a gas inlet and outlet. The heater gas inlet is in communication with the gas outlet of the regulator via an external pipe. 
     The heater housing is cylindrical and has a core therein that separates the gas and coolant passages. The core includes a cylindrical wall having radially outwardly extending fins in the gas passage and radially inward extending fins in the coolant passage. The outwardly extending fins are truncated at alternating axial ends, forming a serpentine gas passage around the fins. The cylindrical housing has a gas inlet and a gas outlet circumferentially spaced apart from one another. A pair of fins separate the gas inlet from the gas outlet, providing a insulating air space between the inlet and the outlet. 
     Engine coolant flows through the center of the core to provide heat to the core and the radially outward extending fins in the gas passage. A thermostat is provided to close the coolant passage when the gas is overheated. The thermostat is controlled by a wax reservoir located in the gas passage adjacent the gas outlet. The thermostat thus responds to the gas temperature to open and close the coolant passage. 
     Since the heater is attached externally to the regulator body as opposed to being integrally formed with the regulator body, if the regulator is used in a vehicle configuration where sufficient ambient heating of the gas fuel is available between the regulator and the engine, the heater can simply be eliminated and the fuel line to the engine coupled to the gas outlet of the regulator body. 
     In preferred embodiments, the gas fuel is regulated to 110 psi or 120 psi and is warmed to about 90° F. The heater of the present invention can be used with gaseous fuels other than natural gas that are stored at high pressures and are excessively cooled when the pressure is reduced in a single stage regulator. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of the natural gas fuel system. 
     FIG. 2 is a perspective view of the regulator and gas heater of the present invention. 
     FIG. 3 is an exploded perspective view of the regulator and gas heater shown in FIG.  1 . 
     FIG. 4 is a sectional view as seen from the line  4 — 4  of FIG.  2 . 
     FIG. 5 is a sectional view as seen from the line  5 — 5  of FIG.  2 . 
     FIG. 6 is a cut-away perspective view of the heater housing end cap. 
     FIG. 7 is an enlarged perspective view of the heater core. 
     FIG. 8 is a sectional view of the heater core with the fins removed. 
     FIGS. 9 and 10 are side and end views of a fin of the heater core. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The heater  10  of the present invention is shown in FIG. 1 in a vehicle fuel system. The fuel system includes a fuel tank  12 , a pressure regulator  18  and the heater  10  to supply gas fuel, such as natural gas to an engine  14 . The engine  14  has a cooling system that includes a radiator  16  connected to the engine by hoses  19  and  21  in a conventional manner for a liquid cooled engine. The heater  10  is mounted to the body  36  of the pressure regulator  18 . The regulator  18  receives high-pressure gas fuel from the tank  12  via a fuel line  20 . The Regulator  18  reduces the pressure of the gas that exits the regulator  18 . As a result of the drop in pressure of the gas, the gas temperature is reduced. The cooled gas travels through an external pipe  22  from the regulator outlet to the gas inlet of the heater  10 . After being heated in the heater  10 , the gas travels through the fuel line  24  to a metering valve  26  on the engine  14 . A fuel line  28  directs the fuel from the valve  26  to the engine. Coolant from the engine cooling system is provided to the heater through a coolant line  30  and is returned to the engine cooling system through a coolant line  32 . 
     With reference to FIGS. 2-5, the heater  10  is shown in greater detail. The heater  10  is shown attached to the regulator  18 . The regulator  18  includes a body  36  having a gas inlet  38  and a gas outlet  40 . The regulator is preferably a regulator from ITT Conoflow from its High Pressure Natural Gas Vehicle series of regulators and is designed to expand the gas primarily outside the body of the regulator, beyond the outlet  40 . As a result, the regulator is not subjected to the extreme cold of the expanding gas. The external pipe  22  directs the cold, low-pressure gas from the outlet  40  to the gas inlet  42  of the heater  10 . 
     The heater  10  includes a housing  43  with three main sections, a cylindrical portion  44 , an extension  46  and an end cap  48 . The cylindrical portion, the extension and the end cap  44  are held together by a threaded stud  50  that is threaded into the housing extension  46  and extends through the housing cylindrical portion  44  and end cap  48 . A nut  52  at the end of the heater retains the stud  50 . A pair of bolts  54  secures the housing extension to the regulator body  36 . An O-ring  57  provides a seal between the housing extension and the regulator body  36 . Bolts  55  couple the end cap  48  to the cylindrical portion  44  with an O-ring seal  59  therebetween. 
     The coolant inlet  56  to the heater is provided in the extension  46 . The housing extension is cup shaped having a radial end wall  62  and forms a hollow chamber  58 . The chamber  58  is open to the end of the heater that faces the regulator  18 . When the heater is attached to the regulator, the regulator body  36  closes the chamber  58 . The coolant inlet  56  admits the liquid coolant into the chamber  58 , whereby the coolant engages the regulator body  36  to heat the regulator. The housing extension has an aperture  60  through the radial end wall  62  to allow coolant flow from the chamber  58 . The aperture  60  is positioned opposite from the coolant inlet  56  such that coolant entering the chamber  58  must flow across the regulator body to the aperture  60 . 
     The cylindrical portion  44  has a bottom wall  64  at one end and is open at the opposite end that is sealed against the extension with an O-ring seal  65 . A core  66  is placed within the cylindrical portion  44 . The core has a tubular or cylindrical wall  68  with a plurality inwardly extending fins  70  and outwardly extending fins  72 . The stud  50  extends through the core inside the tubular wall  68 . An end cover  74 , similar to a washer, is placed at the open end of the cylindrical portion and seats on the ends of the outer fins  72 . The cover  74  extends radially between the tubular wall  68  of the core and the inside surface of the housing cylindrical portion  44 . The tubular wall  68  of the core  66  divides the interior of the housing cylindrical portion  44  into separated gas and coolant passages. The gas passage is radially outside of the tubular wall  68  while the coolant passage  78  is inside the tubular wall  68 . The cover  74  is spaced from the end wall  62  of the extension to provide a gap  79  for coolant flow from the aperture  60  to the center of the core where the coolant flows through the tubular wall, over the surface of the inner fins  70 . The coolant heats the tubular wall  68  and the outer fins  72 . 
     The coolant flows to the well  80  formed in the end cap  48 . From the well  80 , coolant flows through sump  82  to a cross bore  84  leading to the coolant outlet  86 . The sump  82  forms a ledge  83  and a seat  85  for a thermostat  90 . The thermostat  90  has a fitting  92  that is threaded in the bottom wall  64  of the housing cylindrical portion  44 . The thermostat  90  includes a plunger  91  that engages the seat  85  to close the sump  82 , stopping the flow of coolant through the heater. The plunger  91  is biased away from the seat  85  by a spring  93  that engages the ledge  83  and the lip  95  of the plunger. A rod  97  is connected to the plunger  91  and extends into a wax reservoir  94 . The wax reservoir is disposed in the gas passage adjacent the gas outlet  96 . If the gas fuel temperature rises too high, the wax melts and increases in volume, causing the rod and plunger to move against the spring until the plunger engages the seat  85  to stop the flow of coolant. When the gas temperature later drops, the wax solidifies and contracts, allowing the plunger to move away from the seat by the spring force and allow coolant flow to resume. The thermostat wax reservoir  94  is disposed in the housing cylindrical portion  44  in the gas passage adjacent to the heater gas outlet  96  so that the thermostat is responsive to the gas temperature, not the coolant temperature, in regulating the flow of coolant through the heater. As a result, the gas is maintained at a constant or near constant temperature while the regulator body temperature will vary somewhat depending on the flow of the coolant through the housing extension  46  necessary to maintain the desired gas temperature. 
     The core  66  is shown in greater detail with reference to FIGS. 7-10. The core includes an extrusion forming the tubular wall  68  and the inwardly directed fins  70 . The exterior of the wall  68  is formed with a plurality of circumferentially spaced T-shaped slots  98 . The slots  98  receive individual fins  72 . The fins have an enlarged edge  104  that is T-shaped in cross section as shown in FIG.  10 . The fins are truncated at one end by a cutout portion  102 . The fins are mounted to the wall  68  by sliding the T-shaped edge  104  lengthwise in the slots  98 . The fins  70  are arranged with the cutout portion  102  at alternating ends of the core  66 , forming a serpentine path for the gas flow over the surface of the fins  70  as shown by the arrows  110  in FIG.  7 . 
     With specific reference to FIG. 8, the core wall  68  is shown with a larger space  106  adjacent the T-slots and another larger space  108  between adjacent T-slots. Two closely spaced T-slots  98  separate the spaces  106  and  108 . The space  106  is provided adjacent to the gas flow outlet  96  in the housing cylindrical portion  44  while the space  108  is positioned adjacent the gas inlet  42 . The two slots  98  between the spaces  106 ,  108  are provided for two full length fins  112  that are like the fins  72  without the cutout portions  102 . The fins  112  provide an air space therebetween creating an insulating layer between gas inlet  42  and gas outlet  96  so that the inlet gas does not cool the outlet gas. 
     The external connection between the regulator outlet and the heater gas inlet by the pipe  22  enables the regulator to be easily used without the heater  10  if the application provides sufficient fuel line length between the regulator and the engine metering valve for ambient heating of the fuel. The heater is not mounted to the regulator, and the fuel line  24  to the engine is connected directly to the regulator outlet  40 . 
     While it is preferred to mount the heater to the regulator such that the regulator is also warmed by the coolant, the heater can be used as a stand alone heater. In this case, there would not be an open chamber  58  for the coolant to heat the regulator. Rather, the coolant would flow through an inlet into the core area of the heater for flow through the inside of the tubular wall  68  to heat the core  66 . The heater still has the advantage of regulating coolant flow as a function of the gas temperature, not the coolant temperature. The invention should not be limited to the above-described embodiment, but should be limited solely by the claims that follow.