How Does a Diesel Engine Work

How are diesel engines different from gas engines and why should you think about buying a diesel-powered vehicle? Efficiency and cleanliness are compared.

diesel engineSommai Damrongpanich/Shutterstock

Less than 5% of the cars and light trucks operating on American roads today are powered by diesel engines. Contrast that to the rest of the world, especially Europe, where half or more of the passenger vehicles run on diesel. The discrepancy raises many questions.

How a diesel engine works:

What is the difference between diesel and gasoline engines?

Diesel engines have existed since the late 19th century. Invented by Rudolf Diesel, who was born in France but pursued his career in Germany, diesel engines differ from gas engines mostly by the manner in which fuel combustion occurs. Otherwise, the mechanicals are indistinguishable. While gasoline engines rely on spark plugs to ignite a gasoline and air mixture in the combustion chamber, diesel engines super-heat air by compressing it to the point that the hot air causes the fuel to combust on contact. This type of combustion is 25- to 35% more efficient, which translates into better gasoline mileage. A four-door diesel-powered sedan can routinely get more than 50 or even 60 miles per gallon of fuel, easily eclipsing their gasoline-powered counterparts.

What are the advantages of diesel engines?

In addition to better mileage, diesel engines last roughly twice as long as gasoline engines on average. This longevity is due largely to the fact that diesel fuel contains more natural lubricants than gasoline, reducing engine wear. Most over-the-road commercial trucks and many home standby generators run on diesel for this reason.

Diesel engines also pollute less per mile than gasoline-powered engines, especially in more recent years, as new diesel technology has greatly reduced emissions. The telltale puffs of black smoke from diesel exhausts have essentially been eliminated. However, diesel does produce more particulate matter in its exhaust, as well as more nitrogen dioxide, so the question of which fuel is better for the environment is still under debate. If you make mostly short trips in your car, it seems pretty clear that gasoline is the more environmentally friendly option. But, if you drive longer distances, diesel is the green way to go.

Technological advances have also addressed the other primary knock on diesel engines, which is that they are slower to accelerate. Modern diesel engines post 0 to 60 mph output that is comparable to gasoline-powered cars.

Why haven’t diesel cars caught on in the U.S.?

There are many reasons diesel is still not a significant player in the American passenger car market and most of these reasons are economic. Because diesel engines are costlier to build, sticker prices are higher—you can expect to pay at least a $2,000 premium. Diesel engines also cost more to repair, and diesel cars usually cost more to insure. Plus, even though the refining process used to create diesel fuel is simpler than that for gasoline, diesel is more expensive, offsetting the gains from better mileage. Federal fuel taxes are around 25% higher on diesel than on gasoline: currently 24.4 cents per gallon for diesel compared to 18.4 cents for gasoline.

Mark Johanson
Mark Johanson is an experienced home and garden writer/editor/publisher. He has written several books and hundreds of magazine articles. He has edited and directed more than 400 DIY and gardening books, including the BLACK+DECKER® Home Improvement Library series and two of the best-selling gardening books in North America. He is an experienced DIYer and enthusiastic gardener.