I am not well versed in diesel engines. To prove my point, I've learned in the last month that a two-stroke diesel engine actually exists.

My Question.

What kind of diesel engine (four-stroke or two-stroke) is most commonly used in heavy vehicles that we all see roaming about the surface of the planet?


What is the reason a two-stroke or four-stroke engine would be the most used in a particular application?

I would imagine that a two-stroke diesel engine would have a higher emissions footprint, regarding hydrocarbons, than a four-stroke diesel engine due to the way that two-strokes function but this is an assumption on my part.

  • 1
    The last point about emissions is interesting. Gasoline 2S motors burn oil (-> smoke) and fuel/air ratio isn't always perfect (-> partially burned fuel). When with carburetor, they also spill unburned fuel. But Diesels don't use the crank case for compression (-> no oil), the fuel is injected (->no unburned fuel), and run with excess of air (->always enough oxygen, not much partially burned fuel). So it seems 2S Diesel could be as clean as 4S in theory. But what's about reality?
    – sweber
    Jan 5, 2016 at 9:18

1 Answer 1


Most small(ish) diesel engines in cars, diggers, generators etc are 4-stroke.

The main reason being efficiency - Although a 2-stroke engine is technically capable of more power output, a 4-stroke engine uses less fuel to produce the same power output.

Many VERY large diesel engines (EG Super-Tankers) are 2-stroke, This is because they are direct drive (propeller shaft attached directly to the crank with no gearing or clutch) these are classed a Low speed engines, and can burn much cheaper Heavy Fuel Oil.

  • Where is your reference (the yellowish section) from? Any other information? Jan 5, 2016 at 22:13
  • It's worth noting that there are an awful lot of Detroit Diesel engines in trucks, boats, and stationary applications. The Detroits are two-stroke and range in size from a 2-51 that was probably under 50 HP to the 16V149 which would easily put out 1000 HP (and took up as much space as a VW bus).
    – dlu
    Sep 7, 2016 at 4:40
  • Detroit Diesel switched to four-stroke in the 1990s.
    – Hobbes
    Dec 16, 2016 at 10:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.