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#11
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Max Kallio wrote:
2-stroke diesels need compressed air for starting the engine, so the turbo (exhaust driven centrifugal supercharger) is out of a guestion and it produces very little boost at low rpm anyhow. Modern large 2-stroke Diesels (EMD 710 series for example) have a mechanical drive to the turbocharger which spins it at low power settings and it acts as a mechanical blower. As power settings come up and exhaust volume increases, the turbine takes over and operates the supercharger. Much more efficient than converting mechanical power to electrical then back to mechanical again. |
#12
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Don Stauffer wrote:
Why not just have a small compressed air pump driven by gears from crankshaft or camshaft, with a tank to store a few "starts" full of compressed air? Seems like an easier fix than an electric driven compressor. People should really study up on some of the things that have been done with turbo- and super-chargers for the past 60 years before getting carried away. For the last 20 years, for example, virtually all EMD locomotive engines (2-stroke diesels) have used a hybrid mechanical/turbo supercharger. At low power settings and during starting, a sprag (overrunning clutch) spins the turbocharger from the engine's own gear train, just like the old Roots blowers used to be turned. But when the power is increased, the turbine takes over and spins the compressor faster than the engine's drive, so the overrunning sprag releases and the turbo is fully powered by exhaust. Proven, simple, no silly mechanical-electrical-mechanical conversions to go through. But the 2-stroke diesel is dead anyway. Conventional 4-stroke turbo-diesels are the present (except for ever-decreasing production of EMD 710 engines) and the future of diesel power. |
#13
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#14
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#15
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Why is the 2 stroke diesel dead?
I know little about diesels, just the obvious, like no sparkplug. Bob |
#16
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Bob wrote:
Why is the 2 stroke diesel dead? I know little about diesels, just the obvious, like no sparkplug. Bob High emissions and lower fuel efficiency compared with competitive 4-stroke diesels In order to get emissions down, a 2-stroke diesel engine has to be "overblown" so that an excess of fresh air is pushed through the cylinder to drive out the exhaust gasses fully, but doing that wastes mechanical power. So solving the emissions problem aggravates the efficiency problem and vice-versa. And also, 2-stroke diesels have a lot higher lubricating oil consumption rate than similar 4-strokes, and that aggravates emissions too. The EMD 710 is the only remaining locomotive 2-stroke, and is being phased out by the EMD 4-stroke "H-series" engine. Detroit Diesel was the biggest maker of 2-strokes for trucks, earthmovers, yachts, etc. and they stopped 2-stroke production several years ago. And its been over 20 years since many 18-wheelers used Detroit 2-strokes anyway. Fairbanks-Morse still builds their opposed-piston 2-strokes for a few Navy applications and for stationary applications (flood control pumps, backup generators, etc.) and will probably continue to do so, but that's a pretty small market segment. Since 2 NGs are aviation related, that is one area where the 2-stroke *might* hang on longer because of its weight savings, but its ultimately probably doomed there also. |
#17
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Steve wrote in :
Bob wrote: Why is the 2 stroke diesel dead? I know little about diesels, just the obvious, like no sparkplug. Bob High emissions and lower fuel efficiency compared with competitive 4-stroke diesels In order to get emissions down, a 2-stroke diesel engine has to be "overblown" so that an excess of fresh air is pushed through the cylinder to drive out the exhaust gasses fully, but doing that wastes mechanical power. So solving the emissions problem aggravates the efficiency problem and vice-versa. And also, 2-stroke diesels have a lot higher lubricating oil consumption rate than similar 4-strokes, and that aggravates emissions too. The EMD 710 is the only remaining locomotive 2-stroke, and is being phased out by the EMD 4-stroke "H-series" engine. Detroit Diesel was the biggest maker of 2-strokes for trucks, earthmovers, yachts, etc. and they stopped 2-stroke production several years ago. And its been over 20 years since many 18-wheelers used Detroit 2-strokes anyway. Fairbanks-Morse still builds their opposed-piston 2-strokes for a few Navy applications and for stationary applications (flood control pumps, backup generators, etc.) and will probably continue to do so, but that's a pretty small market segment. Since 2 NGs are aviation related, that is one area where the 2-stroke *might* hang on longer because of its weight savings, but its ultimately probably doomed there also. exspecially since they are testing at least one rotary diesel, very much lighter and quieter for unmaned small reconasinst planes. KB -- ThunderSnake #9 Warn once, shoot twice 460 in the pkup, 460 on the stand for another pkup and one in the shed for a fun project to yet be decided on |
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