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2-stroke engines seem to offer a massive advantage over 4-stroke engines. In the case of gasoline engines, there is a need for forced induction, but in the case of large diesels (which invariably have forced induction anyway) it seems that their advantages outweigh the disadvantages.

So why is it that all newly developed diesels (not counting large ship engines and research designs such as Achates Power) are 4-stroke?

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2 Answers 2

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There have been smaller two stroke diesels produced (the Comma TS3 or the Detroit Diesels - very popular) but to make the TS3 work successfully they need forced induction -a Rootes blower was used.

The 4-stroke tends to be used as their the fuel consumption is generally better while there are more components, another consideration is the ancillary component layout - a 4 stroke may be easier.

The are questions on other stack exchanges with more / different information : you could start with this one : https://mechanics.stackexchange.com/questions/24213/two-stroke-diesel-engine-do-they-use-forced-induction-on-them?rq=1

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  • $\begingroup$ Why is the fuel consumption better for 4 stroke engines? $\endgroup$
    – Demi
    Jun 9, 2017 at 5:23
  • $\begingroup$ Simply because the induction / compression / power / exhaust strokes are separated better $\endgroup$
    – Solar Mike
    Jun 9, 2017 at 5:28
  • $\begingroup$ Is that because part of the power stroke isn't being stolen for exhaust and intake? $\endgroup$
    – Demi
    Jun 9, 2017 at 5:30
  • $\begingroup$ Do you know the 2 and 4 stroke cycles ? Have you checked out the other post? $\endgroup$
    – Solar Mike
    Jun 9, 2017 at 5:33
  • $\begingroup$ Yes, I do. I understand what you are saying. $\endgroup$
    – Demi
    Jun 9, 2017 at 5:34
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It's all about what comes out

Two-stroke, forced-induction diesels have been a mainstay of heavy industry for quite some time (Detroit Diesel 71 series, EMD 567/645/715, never mind ship engines). However, they aren't as amenable to precise emissions control as their four-stroke counterparts. This can be shown by EMD's switch to the four-stroke J (EMD 1010) engine for the SD70ACe-T4 locomotive, as they were unable to get the EMD 715 to meet EPA Tier 4 without eating an unacceptable weight penalty or using SCR (which is a logistical problem for railroads, having to deal with large quantities of yet another consumable).

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