VEHICLE AND STORAGE LNG SYSTEMS
LNG, for use as a motor vehicle fuel, is stored in a manner that does not require massive tanks, eliminates evaporative loss and reduces refrigeration energy consumption. A Stirling cryocooler extends through a wall of a highly insulated, relatively low pressure container to its cold end located in the vapor phase above the liquid surface. The pressure or temperature of the LNG is sensed and applied to a feedback control that modulates the heat transfer rate of the Stirling cryocooler so that LNG vapor is liquefied at a rate to maintain a desired pressure and temperature within the container. Maintaining a superatmospheric pressure in the container reduces the energy consumption required for re-liquefaction of the LNG vapor. The apparatus is also usable for liquefaction of natural gas for refueling vehicles from the ubiquitous consumer level domestic gas distribution system.
1 . An apparatus for storing a liquefied combustible gas in a thermally insulated container that is sealable from the atmosphere and capable of superatmospheric pressurization, the gas including a liquid phase and a vapor phase above the liquid phase and separated by a surface of the liquid, the apparatus comprising:
(a) a Stirling cycle cooler mounted to the container and extending through a wall of the container to a cold end of the cooler, the cold end of the cooler being located in the vapor phase above the liquid surface, the Stirling cycle cooler being driven by a prime mover that has a variable power output and is controllable at a control input for varying the heat transfer rate of the Stirling cycle cooler from the cold end to a heat rejector that is external to the container;
(b) a temperature or pressure sensor positioned to sense the temperature or pressure within the container and having an output for communicating its sensed temperature or pressure;
(c) a Stirling cycle cooler feedback control for controlling the temperature or pressure within the container, the control having an input connected to the output of the sensor and an output connected to the control input of the prime mover and adapted for variably controlling the temperature or pressure within the container.
2 . An apparatus in accordance with claim 1 wherein the sensor is a temperature sensor positioned in the liquid phase.
3 . An apparatus in accordance with claim 1 wherein the sensor is a pressure sensor positioned in the vapor phase.
4 . An apparatus in accordance with claim 1 wherein a heater is mounted within the container, the heat output of the heater being variably controllable at a heater control input connected to an output of the Stirling cycle cooler feedback control, the control adapted to transfer heat to the liquefied gas in the container for increasing the gas pressure within the container.
5 . An apparatus in accordance with claim 1 wherein the prime mover comprises an electromagnetic linear motor mechanically linked to drive the Stirling cooler and a Stirling engine also mechanically linked to drive the Stirling cooler and connected to receive combustible gas from the container for powering the Stirling engine
6 . An apparatus in accordance with claim 1 wherein the control modulates the Stirling cooler's rate of heat transfer from the vapor phase and thereby maintains the pressure within the container at a desired pressure above atmospheric pressure.
7 . An apparatus in accordance with claim 6 wherein the control maintains the pressure within the container in the range from above atmospheric pressure to 20 bar absolute for storing the combustible liquefied gas.
8 . An apparatus in accordance with claim 6 wherein the control maintains the pressure within the container in the range from above atmospheric pressure to 2 bar absolute for transporting the LNG out of the container.
9 . An apparatus in accordance with claim 1 and further comprising a fuel pumping apparatus mounted to the container, the pump having a vaporizing chamber, a heater mounted for supplying heat to the vaporizing chamber, an inlet check valve and an outlet check valve arranged to allow flow of liquid phase into the chamber and from the chamber through an outlet conduit to a vehicle engine, the outlet conduit being located at a position for contacting contained LNG in its liquid phase.
10 . A method for maintaining a liquefied combustible gas in an insulated container, the gas including a liquid phase and a vapor phase above the liquid phase that are separated by a surface of the liquid phase, the method comprising:
(a) condensing vapor phase by transferring heat from a location in the vapor phase to outside the container, the transfer including cooling a surface in contact with the vapor phase to a temperature below the temperature of the vapor phase;
(b) sensing the temperature or pressure within the container; and
(c) modulating the rate of transferring heat from the vapor phase in response to the sensed temperature or pressure to maintain the pressure within the container at a desired pressure above atmospheric pressure.
11 . A method in accordance with claim 10 and more particularly comprising modulating the rate of transferring heat from the vapor phase at a rate that maintains the pressure within the container at a maximum safe pressure for the container in order to store the combustible gas at the warmest safe temperature and thereby minimize power required for transferring heat from the vapor phase to outside the container.
12 . A method in accordance with claim 11 wherein the pressure maintained within the container is in the range from above atmospheric pressure to 20 bar absolute for storing the combustible liquefied gas.
13 . A method in accordance with claim 10 and more particularly comprising modulating the rate of transferring heat from the vapor phase at a rate that maintains the pressure within the container at desired pressure for driving the gas out of the container.
14 . A method in accordance with claim 13 wherein the pressure is maintained in the range from above atmospheric pressure to 2 bar absolute.
15 . A method in accordance with claim 13 and further comprising heating the gas within the container for elevating the pressure to the desired pressure.
16 . An apparatus for compressing combustion-supporting air flowing into an internal combustion engine through an air intake plenum, the engine being fueled by a supply of liquefied combustible gas that is conveyed through a conduit network into engine combustion chambers, the apparatus comprising:
a combustible gas vaporizer physically located within the air intake plenum and having gas-conveying passages that are part of the conduit network, the gas-conveying passages being interposed between the gas supply and the engine combustion chambers, the vaporizer being adapted to allow expansion within the gas-conveying passages of the liquefied combustible gas, the vaporizer having heat exchanger fins on the exterior of the vaporizer, the fins being longitudinally aligned along the air flow plenum for transferring heat from incoming air through the air intake plenum to the combustible gas vaporizing in the vaporizer.