May 20 2011

What is the difference between regular gas and diesel fuel?

Category: Energy & Fuel

Answer:

Gas vs DieselWhen crude oil is refined it typically goes through a distillation process where various compounds are separated based on their distinct vaporization temperatures. Gasoline is separated at 104° F – 401° F, diesel gets separated at 482° F – 662° F. In 2009, diesel fuel accounted for roughly 7% of all energy used in the US and 17% of all petroleum products, the 2nd largest petroleum product after gasoline. Here is how the different fuels and their corresponding engines stack up based upon a head to head comparison.

Fuel Economy – Diesel fuel has a higher inherent energy concentration than gasoline making it more efficient per unit of volume. Diesel engines are also more efficient in the way they use the fuel. An idle diesel engine will typically use 1/3 as much energy as a gas based model.

Fuel Cost – Since September 2004, the price of regular gasoline has typically been lower than the price of diesel fuel even though diesel fuel is easier to refine. There are a few theories/reasons why diesel has become more expensive.

  • Worldwide demand for diesel fuel and other distillate fuel oils is up.
  • The use of ultra-low sulfur diesel fuel has affected production and distribution costs.
  • Federal and state taxes on diesel fuel are higher than on regular gasoline.

Diesel fuel supporters have indicated that if demand were higher, the price would drop considerably with the benefits of economies of scale.

PowerGas engines provide more horsepower giving them the ability to reach higher RPMs. Diesel engines provide more torque and are better suited for pulling or towing heavier loads.

Fuel Availability – Since only 2% of the cars in the US are diesel powered and the demand is lower, the numbers and locations of diesel fuel stations are also lower.

Emissions – The primary determinant of carbon dioxide emissions is the amount of carbon in the fuel. The Code of Federal Regulations (40 CFR 600.113) gives values for carbon content per gallon of gasoline and diesel fuel which EPA uses in calculating the fuel economy of vehicles:

  • Gasoline carbon content per gallon: 2,421 grams
  • Diesel carbon content per gallon: 2,778 grams

In the US, new emission standards have been approved for a shift to an ultra-low sulfur diesel (USLD). In 2006, the EPA effectively cut the allowable level of sulfur in highway diesel fuel by 97%, as part of a program to reduce emissions from larger vehicles like trucks and buses. The same standard was phased into effect in 2010 for non-road diesel fueled vehicles as well.

Choosing between a gas and diesel engine ultimately comes down to utility and cost. Cars with gas engines are cheaper, run smoother, and fuel is easier to find. Cars and trucks with diesel engines, however, are good for towing and have better fuel economy over the long haul. A new study was done recently that found that diesels were a better value.


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