The Department of Energy has a fuel efficiency goal of 10 miles per gallon for heavy-duty trucks fueled by liquefied natural gas; present-day trucks fueled by diesel average only 6 miles per gallon. To achieve this goal, high-pressure injection of natural gas in diesel engines is essential, but the systems available today that are supposed to prevent the natural gas from venting from the fuel tanks to the atmosphere are ineffective for high-pressure fuel-delivery systems. Combining a thermodynamic vent system with a Ranque-Hilsh tube may be an effective method to reduce the boil-off of vent gas. This new device is attractive because it is simple, has few moving parts, and could reduce the boil-off vent rate by up to 96 percent. This vent system also ensures that only gaseous natural gas is vented, and that any liquid phase in the vent line is filtered and retained in the tank. In Phase I, the proof of concept for the venting device will be conducted using a test rig that simulates vent conditions in trucks fueled by liquefied natural gas. A Ranque-Hilsh tube for high-pressure methane and a heat exchanger will also be designed and fabricated. In Phase II the concept will be further refined, optimized, and tested in an operational tank system for liquefied natural gas.
Commercial Applications and Other Benefits as described by the awardee:According to the Energy Policy Act of 1992, 75 percent of all new vehicles in fleets used by Federal and State governments are required to be fueled with alternative fuels. Heavy-duty trucks are also now required to meet strict 1994 State and Federal clean air standards. Using liquefied natural gas as a fuel reduces visible smoke, nitrogen oxides, and particulate emissions while allowing heavy-duty trucks to achieve ranges found on conventional diesel trucks.
