Niagara Gazette — A few weeks back I wrote an article on the major differences between gas and diesel vehicles entitled “Diesel 101.” This week, in my ongoing effort to educate you on diesel vehicles I will cover the topic of the fuel such vehicles use ... Diesel fuel! Read on.
Diesel fuel energy density and rating at the pump
When crude oil is processed at refineries, it is separated into several different kinds of fuel. At U.S. refineries in 2012, a 42-gallon barrel of oil typically delivered 19 gallons of gasoline, 11 gallons of diesel fuel, and lesser quantities of jet fuel, home heating oil, kerosene, liquefied petroleum gas and other distillates. Diesel fuel produced for vehicle use is sometimes called “diesel oil” or No. 2 diesel. Kerosene, which is chemically similar but more highly refined and less viscous, may also be referred to as No. 1 diesel.
Diesel fuel is heavier and oilier than gasoline, and it supports compression ignition with an auto ignition temperature (the temperature at which a substance will burn without exposure to an external flame or spark) of just 410° F compared to 536° F for gasoline. Diesel fuel also has a higher energy density than gasoline. One gallon of diesel contains approximately 17.6 percent more energy – 147,000 British Thermal Units (BTUs) compared to 125,000 BTUs for gasoline. This additional fuel energy is one of several reasons that diesel engines get better fuel economy than their gasoline counterparts.
Diesel fuel is normally sold in a single grade whose quality is identified by a cetane number that expresses the fuel’s ability to ignite when sprayed into hot compressed air. Higher cetane diesel fuel typically provides smoother operation and a reduction in engine noise. On-road diesel fuel in the U.S. must have a minimum cetane number of 40, although most pump diesel is in the 42 to 45 range. “Premium” diesel fuels with higher cetane numbers and a variety of special additives are sold in some markets. Diesel fuel in California typically has a higher cetane number due to some unique fuel blending requirements in that state.