Method for measuring compressed natural gas

• US 5,970,786 A
• Filed: 09/25/1997
• Issued: 10/26/1999
• Est. Priority Date: 09/25/1997
• Status: Expired due to Fees

• Current Assignee: Igor Krasnov, Robert S. Smith
• Original Assignee: Igor Krasnov, Robert S. Smith
• Inventors: Smith, Robert S., Krasnov, Igor
• Primary Examiner(s): Noori, Max
• Assistant Examiner(s): AW MUSSE, ABDULLAHI H
• Application Number:
  US08/937,866
• Time in Patent Office: 761 Days
• Field of Search: 73/149, 73/861.01, 73/861.02, 73/708, 137/7, 137/12, 222/1, 141/4
• US Class Current: 73/149
• CPC Class Codes: F17C 2205/0326 electrically actuated
• CPC Class Codes: F17C 2205/0364 flexible or articulated, e.g. a hose
• CPC Class Codes: F17C 2221/033 Methane, e.g. natural gas, CNG, LNG, GNL, GNC, PLNG
• CPC Class Codes: F17C 2250/043 Pressure
• CPC Class Codes: F17C 2250/0439 Temperature
• CPC Class Codes: F17C 2250/0621 Volume
• CPC Class Codes: F17C 2260/024 Improving metering
• CPC Class Codes: F17C 2260/026 by calculation
• CPC Class Codes: F17C 2270/0139 Fuel stations
• CPC Class Codes: F17C 2270/0168 by vehicles
• CPC Class Codes: F17C 2270/0171 Trucks
• CPC Class Codes: F17C 5/007 for individual gas tanks or containers, e.g. in vehicles filling with liquid fuel not under pressure, B60S5/02, B67D7/00
• CPC Class Codes: G01F 17/00 Methods or apparatus for determining the capacity of containers or cavities, or the volume of solid bodies measuring linear dimensions to determine volume G01B
• CPC Class Codes: G01F 23/14 by measurement of pressure

Abstract

A compressed natural gas (CNG) vehicle refueling system is designed for refueling fleets of vehicles with identical fuel tanks. The amount of CNG dispensed into the tanks may be closely approximated without the use of a flow meter. An initial standardized volume is calculated based upon the ambient temperature, the initial pressure level and an approximate compressibility of the gas. Gas is dispensed into the fuel tank to a desired pressure which is confirmed with a pressure gage. A final standardized volume of gas contained within the fuel tank is calculated based upon the final pressure level and assuming no change in the compressibility of the gas. The initial standardized volume of gas is subtracted from the final standardized volume of gas to yield an actual volume of gas dispensed from the storage vessel. Empirically derived temperature correction factors may be used to generate an even more accurate approximation of CNG dispensed. The temperature correction factors compensate for the difference in temperature between operating temperatures and the standardized temperature of zero degrees celsius.

Claims

1. A method for approximating a volume of compressed natural gas dispensed from a pressurized storage vessel into a fuel tank wherein the water volume of the fuel tank is known, comprising:

(a) measuring an ambient temperature surrounding the fuel tank;

(b) measuring an initial pressure level of the fuel tank;

(c) calculating an initial standardized volume of gas contained within the fuel tank based upon the ambient temperature, the initial pressure level and an approximate compressibility of the gas, and multiplying the initial standardized volume of gas by a temperature correction factor to compensate for the difference in temperature between the ambient temperature and a standardized temperature, wherein the temperature correction factor comprises multiplying the initial standardized volume of gas by an empirically-derived temperature-to-pressure relationship for the gas and the fuel tanks;

(d) dispensing the gas into the fuel tank to a desired final pressure level;

(e) calculating a final standardized volume of gas contained within the fuel tank based upon the final pressure level and assuming no change in the compressibility of the gas; and

then

(f) subtracting the initial standardized volume of gas from the final standardized volume of gas to yield an actual volume of gas dispensed from the storage vessel.

2. A method for approximating a volume of compressed natural gas dispensed from a pressurized storage vessel into a fuel tank wherein the water volume of the fuel tank is known, comprising:

(a) measuring an ambient temperature surrounding the fuel tank;

(b) measuring an initial pressure level of the fuel tank;

(c) calculating an initial standardized volume of gas contained within the fuel tank based upon the ambient temperature, the initial pressure level and an approximate compressibility of the gas;

(d) dispensing the gas into the fuel tank to a desired final pressure level;

(e) calculating a final standardized volume of gas contained within the fuel tank based upon the final pressure level and assuming no change in the compressibility of the gas, and approximating an increase in temperature of the gas during step (d) based upon the final pressure level and an empirically derived temperature-to-pressure relationship for the gas and the fuel tank; and

then

multiplying the final standardized volume of gas by a temperature correction factor to compensate for the difference in temperature between the approximate increased temperature and a standardized temperature; and

then

(f) subtracting the initial standardized volume of gas from the final standardized volume of gas to yield an actual volume of gas dispensed from the storage vessel.

3. The method of claim 2 wherein the temperature correction factor comprises multiplying the final standardized volume of gas by an empirically-derived temperature-to-pressure relationship for the gas and the fuel tank.

4. A method for approximating the volume of compressed natural gas dispensed from a pressurized storage vessel into a fuel tank wherein the water volume of the fuel tank is known, comprising:

(a) measuring an ambient temperature surrounding the fuel tank;

(b) measuring an initial pressure level of the fuel tank;

(c) calculating an initial standardized volume of gas contained within the fuel tank by dividing the initial pressure by standard sea level pressure, multiplying by the water volume of the fuel tank, multiplying by a compressibility factor of the gas at standard sea level pressure, and then dividing by a compressibility factor of the gas at the initial pressure;

(d) multiplying the initial standardized volume of gas by an empirically-derived temperature-to-pressure relationship for the gas and the fuel tank to compensate for the difference in temperature between the ambient temperature and a standardized temperature;

(e) dispensing the gas into the fuel tank to a desired final pressure level;

(f) approximating an increase in temperature of the gas during step (e) based upon the final pressure level and an empirically derived temperature-to-pressure relationship for the gas and the fuel tank;

(g) calculating a final standardized volume of gas contained within the fuel tank by dividing the final pressure level by standard sea level pressure and then multiplying by the water volume of the fuel tank;

(h) multiplying the final standardized volume of gas by an empirically-derived temperature-to-pressure relationship for the gas and the fuel tank to compensate for the difference in temperature between the approximate increased temperature and a standardized temperature; and

then

(i) subtracting the initial standardized volume of gas from step (d) from the final standardized volume from step of gas from step (g) to yield an actual volume of gas dispensed from the storage vessel.