Natural gas vehicle fuel vapor delivery system

Apparatus for delivering natural gas within an optimal pressure range to a system outlet connection for ultimate delivery for combustion in an engine comprising:

• an insulated tank for holding liquid natural gas and having first and second sets of port pairs, one port of said first set opening into the upper portion of the interior of said tank and the other port of said first set opening into the lower portion of the interior of said tank;
• a first heat exchanger means coupled between said ports of said second set of ports for establishing a gas flow path within said tank to thermally couple said gas flow path and the contents within said tank;
• gas flow path means connecting the outlet of said heat exchanger to the system outlet connection;
• second heat exchanger means coupled between said second port of said first set and a common junction for converting liquid fuel passing therethrough into vapor;
• fluid flow switching means including first and second control valves having their inputs coupled to said common junction and each responsive to the pressure within the upper portion of said tank, said first valve coupling fuel from said common junction to the system outlet connection when tank pressure is above a certain level while remaining closed for pressure below said certain level, and said second valve constructed to introduce fuel to said first heat exchanger means when the tank pressure is below said certain level while remaining closed when the pressure is above said certain level;
• and
• a regulator valve coupled between said second heat exchanger output and said port opening into said tank upper portion with said regulator valve closing in response to a drop in internal pressure of said tank below a predetermined level
• whereby the delivery pressure in said tank is maintained relatively constant independent of vapor flow requirements of the engine independently of the level of liquid natural gas in said tank.

The method of maintaining and controlling delivery pressure from a liquid natural gas storage tank independently of vapor flow requirements by an engine fueled by gas from said tank and independently of the liquid level in said tank which tank has an internal gas flow path in thermally conducting relation with the interior of said tank with the output of said flow path being coupled to the engine comprising the steps of:

• sensing a demand for gas fuel by said engine;
• responding to said sensing step by converting liquid natural gas to vapor;
• comparing the level of the pressure within said tank to a predetermined pressure level;
• switching the fluidic communication of said vapor in response to said comparing step between a direct connection to said engine when said pressure within said tank exceeds said predetermined level and to said tank internal flow path whenever said pressure within said tank is less than said predetermined level;
• and
• regulating said tank pressure including the steps of
• recognizing that the pressure within said tank has dropped below a predetermined level while no fuel demand is present from said engine;
• converting liquid natural gas from said tank into vapor;
• and
• introducing said vapor to said tank interior.

Apparatus for delivering natural gas within an optimal pressure range to a system outlet connection for ultimate delivery to an engine comprising:

• an insulated tank for holding liquid natural gas and having first and second sets of port pairs, one port of said first set opening into the upper portion of the interior of said tank and the other port of said first set opening into the lower portion of the interior of said tank;
• a first heat exchanger means coupled between said ports of said second set of ports for establishing a gas flow path within said tank to thermally couple said gas flow path and the contents within said tank, said first heat exchanger including a tube formed in a tortuous path within said tank and arranged for thermal coupling with the liquid remaining in said tank at any level;
• said first heat exchanger further including a thermally conductive plate having said tube mounted thereon with said plate extending between the lower and upper portions of said tank interior;
• gas flow path means connecting the outlet of said heat exchanger to the system outlet connection;
• second heat exchanger means coupled between said second port of said first set and said common junction of said control valves for converting liquid fuel passing therethrough into vapor;
• and
• fluid flow switching means including first and second control valves having their inputs coupled to a common junction and each responsive to the pressure within said tank, said first valve coupling fuel from said common junction to the system outlet connection when tank pressure is above a certain level while remaining closed for pressure below said certain level, and said second valve constructed to introduce fuel to said first heat exchanger means when the tank pressure is below said certain level while remaining closed when the pressure is above said certain level;
• whereby the delivery pressure in said tank is maintained relatively constant independent of vapor flow requirements of the engine independently of the level of liquid natural gas in said tank.