While exploring ways of producing better fuels for propulsion of a spacecraft on the Mars sample return mission, a researcher at Johnson Space Center (JSC) devised a way of blending fuel by combining methane or natural gas with a second fuel to produce a fuel that can be maintained in liquid form at ambient temperature and under moderate pressure. The use of such a blended fuel would be a departure for both spacecraft engines and terrestrial internal combustion engines. For spacecraft, it would enable reduction of weights on long flights. For the automotive industry on Earth, such a fuel could be easily distributed and could be a less expensive, more efficient, and cleaner-burning alternative to conventional fossil fuels.
The concept of blending fuels is not new: For example, the production of gasoline includes the addition of liquid octane enhancers. For the future, it has been commonly suggested to substitute methane or compressed natural gas for octane-enhanced gasoline as a fuel for internal-combustion engines. Unfortunately, methane or natural gas must be stored either as a compressed gas (if kept at ambient temperature) or as a cryogenic liquid. The ranges of automobiles would be reduced from their present values because of limitations on the capacities for storage of these fuels. Moreover, technical challenges are posed by the need to develop equipment to handle these fuels and, especially, to fill tanks acceptably rapidly. The JSC alternative — to provide a blended fuel that can be maintained in liquid form at moderate pressure at ambient temperature — has not been previously tried.
A blended automotive fuel according to this approach would be made by dissolving natural gas in gasoline. The autogenous pressure of this fuel would eliminate the need for a vehicle fuel pump, but a pressure and/or flow regulator would be needed to moderate the effects of temperature and to respond to changing engine power demands. Because the fuel would flash as it entered engine cylinders, relative to gasoline, it would disperse more readily and therefore would mix with air more nearly com- pletely. As a consequence, this fuel would burn more nearly completely (and, hence, more cleanly) than gasoline does.
The storage density of this fuel would be similar to that of gasoline, but its energy density would be such that the mileage (more precisely, the distance traveled per unit volume of fuel) would be greater than that of either gasoline or compressed natural gas. Because the pressure needed to maintain the fuel in liquid form would be more nearly constant and generally lower than that needed to maintain compressed natural gas in liquid form, the pressure rating of a tank used to hold this fuel could be lower than that of a tank used to hold compressed natural gas.
A mixture of natural gas and gasoline could be distributed more easily than could some alternative fuels. A massive investment in new equipment would not be necessary: One could utilize the present fuel-distribution infrastructure and could blend the gasoline and natural gas at almost any place in the production or distribution process — perhaps even at the retail fuel pump. Yet another advantage afforded by use of a blend of gasoline and natural gas would be a reduction in the amount of gasoline consumed. Because natural gas costs less than gasoline does and is in abundant supply in the United States, the cost of automotive fuel and the demand for imported oil could be reduced.
This work was done by Thomas A. Sullivan of Johnson Space Center. For further information, contact the Johnson Commercial Technology Office at (281) 483-3809. Refer to MSC-22873.