As has been mentioned here a few times, new 2-stroke engines with fuel injection are much cleaner (hydrocarbons were the old 2-strokers' sin, iirc). You can find them in some snowmobiles, and Peugeot makes a scooter with a FI'ed 2-stroke (diesel?).
As for the large, slow-turning diesels' efficiency, my guess is that two things are a helping factor:
- Low rpms -> lower friction losses,
- Very large displacement -> less surface area (per volume) through which heat can escape.
Does anyone have any idea at how hot those engine run? I mean, what are the typical coolant and exhaust gas temperatures?
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e·co·mod·ding: the art of turning vehicles into what they should be
What matters is
where you're going, not
how fast.
"... we humans tend to screw up everything that's good enough as it is...or everything that we're attracted to, we love to go and defile it." - Chris Cornell
[Old] Piwoslaw's Peugeot 307sw modding thread