Daily Fuel Economy Tip

What is the Difference Between Diesel and Gasoline?

Gasoline and diesel fuel are the two main sources of energy for today’s cars.  Although they are both derived from the same source (oil) they certainly aren’t interchangeable, have different chemical properties and are burned in two different ways.  Below is a quick overview of the differences between the two fuels and the pros and cons of each.

First off, there are very long winded, scientific answers to this question, and if you’ve come here for that you’re not going to find it.  This is going to be a very quick and dirty breakdown of the two fuels with minimal chemistry and jargon.

Both gasoline and diesel fuel are derivatives of crude oil, however they each consist of very different molecular structures.  This happens due to each fuel being derived at different temperatures within the crude oil refining process.

Aside from the chemical differences, the diesel fuel and gasoline differ in how they are burned and used to create energy for your car:

Gasoline Engines: Cars that use gasoline have to use spark plugs in order to ignite the fuel, which is due to the fact gasoline engines have a relatively low compression ratio.  Here is what a typical stroke cycle looks like for a gasoline powered engine:

1. Gasoline and air are combined and forced into the cylinder
2. Gas/air mixture is compressed.
3. Spark plug fires causing the mixture to ignite and explode, forcing the piston up and giving your car power.
4. Burned mixture is forced out as exhaust.

Diesel Engines: Because diesel engines have much higher compression ratios, a diesel engine doesn’t utilize spark plugs.  As I’m sure you remember from chemistry class, as gases are compressed, their temperature will increase, and diesel engines have such a high compression ratio that the heat produced by the compression is enough to ignite the fuel/air mixture.  Here is what the typical stroke cycle looks like for a diesel powered engine:

1. Air is forced into the cylinder, and is compressed.
2. As this is going on, diesel fuel is sprayed into the cylinder.
3. The compression causes the diesel fuel to ignite, causing the piston upwards, which gives the car energy.
4. Burned mixture forced out as exhaust.

Of the two fuels, diesel tends to get better gas mileage than gasoline because it has a higher density, which leads more energy per each explosion within the cylinder.  Also, diesel engines tend to be more efficient by nature.

Despite the better fuel economy from diesel fuel, gasoline is the cleaner burning of the two, and is one of the main reasons why diesel cars aren’t as popular in the United States.

So, that’s the quick and dirty look at the differences between gasoline and diesel fuel.  If you would like a more in-depth breakdown, there are plenty of resources online that will be able to help you.

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