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In this paper options for on-board storage and home refueling of natural gas vehicles are presented and discussed. The on-board natural gas storage options considered are: storage at 2.2 MPa (300 psig) in activated carbon-filled cylinders, and 7.0 MPa (1000 psig) and 16.7 MPa (2400 psig) in hollow cylinders. Information is presented on small home refueling compressors designed to compress the natural gas to the above mentioned storage pressures. Also shown are data on the density and energy density of natural gas at pressures up to 21 MPa (3000 psig), It is found that to achieve a range of 160 km (100 miles), a 12.7 km/L (30 mpg) vehicle requires 232, 170 and 62 liters (8.2, 6.0 and 2.2 ft3), respectively, of natural gas storage volume at the three pressures considered. A preliminary comparison of the three storage options suggests that storage above 7.0 MPa is preferred.

Natural gas is a good fuel for internal combustion engines, but its low energy density is a significant drawback. The energy density can be increased by adsorption on a high surface area activated carbon. But with usage, some of the constituents in the natural gas composition accumulate on the carbon and reduce its adsorptivity. The adsorption-desorption of natural gas on 9LXC activated carbon was investigated to 100 cycles at 21 °C and pressures of up to 12 MPa. The decrease in the capacity, G, as a function of the number of cycles, N, was found to follow the empirical correlation:G/Go = 1 − 0.085Log (N). Analysis of the activated carbon after 100 cycles showed accumulation of C4. and higher hydrocarbons but not of C2 and C3. For automotive applications, activated carbon appears practical in a narrow pressure range, centering around 7 MPa (1000 psig). The preferred storage is at a pressure of 17 MPa or higher, without the use of activated carbons.

Natural gas can be used as a vehicular fuel, but its low energy density is a significant drawback. The energy density can be increased by adsorption of the natural gas on high surface area sorbents. The adsorption of methane on activated carbons and molecular sieves was investigated at pressures up to 16 MPa (2300 psig). The improvement in methane storage capacity over empty cylinders is appreciable at low pressures but diminishes as the pressure increases. When adsorbed, for example, on 9LXC activated carbon at 3, 7, and 14 MPa the energy density increased by 245%, 100%, and 53%, respectively. Less improvement was observed with molecular sieves.