Diesel engines for locomotives

[Anonymous]

QUOTE: Originally posted by jruppert

EMD's "H" engine is a four stroke. Like Detroit, EMD now makes a four stroke. Many other places home to two stroke engines are now four stroke clubs. I suspect the two stroke engine in the near future will become only a history.

And the reason being is that the 2 cycle engine is getting more difficult to meet the smog laws due to oil burning. EMD 710's never got their oil changed, just the filters. They would burn about 50gals. of oil to 4000gals. of fuel.

[jchnhtfd]

QUOTE: Originally posted by drailed1999

QUOTE: Originally posted by jruppert

EMD's "H" engine is a four stroke. Like Detroit, EMD now makes a four stroke. Many other places home to two stroke engines are now four stroke clubs. I suspect the two stroke engine in the near future will become only a history.

And the reason being is that the 2 cycle engine is getting more difficult to meet the smog laws due to oil burning. EMD 710's never got their oil changed, just the filters. They would burn about 50gals. of oil to 4000gals. of fuel.

also, it is very difficult to get adequate scavenging of exhaust gasses and control of valve timing in a 2 stroke engine, which doesn't help the emissions thing at all...

[Overmod]

Actually, if you think about it, "inadequate scavenging" on a two-stroke diesel is indistinguishable in its effects from EGR. All it implies is that you have relatively less oxygen in the compressed charge, and in turn can inject relatively less fuel for burning.

Valve timing, likewise, is not a difficult thing to control in a two-stroke, in fact it's easier because EMDs only have valve gear on the exhaust of their two-strokes. If what you meant is that there is no explicit variable control over the intake timing (because it's essentially set by scavenge-port geometry and piston configuration) you'd be right, but that's different from what was said.

A more important source of emissions trouble for two-strokes has to do with the way the physics of scavenge emission work -- you are losing heat in the cylinder walls when the "intake" air in the pressurized crankcase expands through the scavenge ports, and this will have a quenching effect on the late burn in the cylinder (remember that we're talking about VERY small relative amounts of pollutants here). You could get around this by preheating the charge air (the opposite of intercooling), but two ugly things happen: the effective charge density goes down (rapidly getting into Unsustainable Levels Of Boost) and the added heat in the crankcase both degrades and vaporizes the lube oil more quickly.

If lube oil were nothing but heavy-chain paraffins, there would be relatively little consequence (other than premature quenching or partial ignition of the less volatile fractions) on engine operation -- but engine lube oil even for two-stroke diesels usually contains ingredients to make it more effective as a lubricant, or to hold up better in extreme conditions (e.g. keeping piston cooling spray effective). Combusting these ingredients will almost certainly hurt emissions, and in some cases (e.g. detergents) can form ionic nuclei in the exhaust that serve as seeds for particulate formation.

I believe some of the research in progress in this area involves pairs of hard coatings for bores and rings that do not require explicit lubrication by combustible oil, and in the provision of insulated separation between crank (and other lubricated joints) and intake air around the scavenge porting in the cylinders. It may not be enough.