Gasoline's volatility is better described as its tendency to evaporate at a specific temperature and measured by the Reid Vapor Pressure (RVP) in units of psi. The more volatile gasoline is, the higher the evaporation rate, and the higher the RVP. Most gasoline blends need their RVP to stay below 14.7 psi, which is the normal average atmospheric pressure. Anything higher than that would boil off into a gas. However, there are some regions that are so cold, refiners blend their winter formulas up to an RVP of 15 psi.
During the winter, refiners adjust their blends by mixing in more butane, which itself has an RVP of 52 psi. The blend will have a higher RVP than the summer blend and ignite more easily in cold weather. During the summer months, the use of butane is reduced, lowering the RVP and preventing it from boiling off in warmer weather. If we used a winter blend during the summer, the effects of gasoline evaporating would lead to increased emissions and the formation of smog. At the federal level, refineries must produce their summer blend no later than April 1, although states can mandate an earlier date. Gasoline travels from refineries to terminals and storage locations through pipelines at a rate of 4 miles per hour, or about 100 miles per day. It can take several weeks for gasoline refined in the Gulf Coast region to reach terminals and storage facilities throughout the country. For this reason, terminals and storage facilities aren't required to stock the summer blend until May 1.
Butane is relatively inexpensive and plentiful. All other things being equal, it is the reduction in butane that causes the summer increase at the pump. The good news is that according to the EPA, summer blend gasoline has 1.7-percent more energy than its winter counterpart, which will give you better gas mileage in the summer.
The switch between summer and winter blends is complicated at the refinery level and takes place twice a year, once in the fall (to winter blend) and once in the spring (to summer blend). During the switch, refineries take advantage of the downtime and perform routine maintenance.
The EPA has set the minimum RVP for summer blends to be 9 psi. The wide range of temperatures and different environmental standards throughout the country necessitate the need for up to 14 unique blends to be used nationwide. The EPA can also make exceptions. For example, because of fuel shortages caused by Hurricane Harvey, some areas of Texas could sell gasoline with an RVP as high as 11.5 through late September 2018.
Occasionally, we experience unusually warm weather before the refineries switch over to their summer blends. The warmer weather causes the gasoline to evaporate, and your vehicle may experience a condition known as "vapor lock." To combat this, automotive manufacturers have moved the fuel pump to the inside of the fuel tank so that it is always submerged. However, older vehicles and some vessels with outboard motors may still experience vapor lock in this situation.
A lot of work goes into the nation's fuel system. Not only do we need to manufacture enough gasoline to feed our nation's love for the automobile and wide roads, but we also have to have the right fuel at the right place and at the right time.
For more information, visit www.suncoastresources.com or call (800) 677-FUEL [3835].
