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
    Commented 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? Commented 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
    Commented Sep 7, 2016 at 4:40
  • Detroit Diesel switched to four-stroke in the 1990s.
    – Hobbes
    Commented Dec 16, 2016 at 10:45

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