Table 4-27, emissions from vehicle fueling are several grams per gallon.
Table 4-29: Fuel from LPG Fuel Delivery
Liquid Spill Volume
Transfer tank outage
Bulk tank outage
Truck fill outagea
Truck fill hose
Local tank hose
Local tank outage
Vehicle tank outage
aBetter vapor management could eliminate this emissions source by the year 2010.
Many LPG tanks are already equipped with automatic stop-fill devices that could eliminate fuel tank vapor venting; however, Titles 8 and 13 of the California Administrative Code require the use of the outage valve. Other countries, including the Netherlands where many LPG vehicles operate, do not use the outage valve for fueling. One might expect that many LPG vehicles in California are fueled without using the outage valve if they are equipped with automatic stop fill devices.
A committee of NFPA, CHP, NPGA, and WLPGA representatives are working to set standards that will allow LPG vehicles to be fueled without leaking LPG to the atmosphere. Equipment that will minimize the fuel released from transfer fittings is also being approved (Wheeler 1994). EPA regulations on evaporative emissions from vehicles will also eliminate outage valve emissions.
Emission estimates for LPG fueling are based on the following conditions:
1391 cc loss from fuel couplings on 10,000 gal delivery trucks. Fluid loss is equivalent to 18 " of 1.25" (inner diameter) hose (Lowi 1992)
Current vehicle hose coupling liquid losses are 7.57 cc (Lowi 1992) for a 12 gallon fuel transfer. Dry-break couplings would have less than 5 percent of the trapped volume of current LPG nozzles of the same capacity. The use of these nozzles is expected beyond the year 2000.
Current fuel tank vapor displacement is based on sonic flow through a 1.5 mm orifice, 70F tank temperature with a fuel pressure of 105 psig. Assuming an orifice discharge coefficient of 0.5 results in 2 g/s of vapor flow. With an 8 gal/min flow rate, vapor displacement is 15 g/gal.