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#21
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Don Stauffer wrote:
Don Stauffer wrote: A 4-stroke diesel is still an Otto engine. An Otto cycle engine is one with four strokes, intake, compression, power, and exhaust. Doesn't care whether SI or CI. Whoops Before everyone jumps on me, I left off an important qualification. I was specifically talking about cars, airplanes and highway trucks. Large Diesels, (stationary, large ship, etc) do run a different cycle- the true Diesel cycle. However, even the true Diesel cycle of larger engines is not the true cycle Diesel really wanted. He couldn't develop the true cycle he wanted (constant enthalpy), and a large Diesel comes somewhat close. A high speed (vehicle) engine doesn't even come close with even today's technology. It is pretty close to an Otto cycle, though still not exactly. Otto cycle has infinitesmal fraction of cycle for ignition and burn, while even a high speed Diesel (and even the SI engine) still ignites and burns over a finite angle of crank rotation. Still, the result, as I say is MUCH closer to Otto than the cycle Rudy had intended. Still makes a good engine, however :-) I pretty much agree, although today's high-speed diesels are doing a lot better at approchin the constant-enthalpy cycle than they used to, thanks to being able to divorce the injection profile from crankshaft position via electronically-controlled injection systems. |
#22
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"Steve" wrote in message ... I pretty much agree, although today's high-speed diesels are doing a lot better at approchin the constant-enthalpy cycle than they used to, thanks to being able to divorce the injection profile from crankshaft position via electronically-controlled injection systems. Now that you mentioned it, what sort of rpm ranges are the high speed diesels capable of? You may remember that some years ago (just after the Arabs shut off the oil) AVCO showed a rather smallish (V8?) diesel that you could swap into just about any American car of the time. Cost was about $5000, estimated. They claimed some rather high RPM capabilities for this engine. |
#23
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Don Stauffer wrote: Bryan Martin wrote: Not so. In the Otto cycle, the fuel and air are introduced to the cylinder during the intake stroke. In the Diesel cycle only the air is introduce to the cylinder during the intake stroke, the fuel in injected at the end of the compression stroke. in article , Don Stauffer at wrote on 5/13/05 10:47 AM: A 4-stroke diesel is still an Otto engine. An Otto cycle engine is one with four strokes, intake, compression, power, and exhaust. Doesn't care whether SI or CI. In terms of the thermodynamics the fuel is immaterial. It is only a source of heat for raising temp and pressure. The AIR is the true Carnot working fluid with either a CI or SI engine. In an indicator diagram of the SI engine, one would be hard pressed to see the difference even if fuel were shut off during the induction stroke. The reason a Diesel is not a true (though close) Otto cycle is that in the true Otto cycle the burning is instantaneous (or at least an infinitesmal number of degrees of crank rotation or percentage piston motion. The Diesel is not an Otto cycle it is a completly differant cycle. The Diesel is a constant pressure cycle where the presure is constant through the expansion phase. |
#24
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karel wrote: "Sport Pilot" wrote in message oups.com... Sooo. I oftern transpose letters, I don't proofread something as triavil as usenet messages. If you consider your messages trivial, why post them? Anyway, I won't see them anymore. Ploink! Only a fool assumes that someone who has trouble spelling or pronuciation. |
#25
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Don Stauffer wrote: Don Stauffer wrote: A 4-stroke diesel is still an Otto engine. An Otto cycle engine is one with four strokes, intake, compression, power, and exhaust. Doesn't care whether SI or CI. Whoops Before everyone jumps on me, I left off an important qualification. I was specifically talking about cars, airplanes and highway trucks. Large Diesels, (stationary, large ship, etc) do run a different cycle- the true Diesel cycle. However, even the true Diesel cycle of larger engines is not the true cycle Diesel really wanted. He couldn't develop the true cycle he wanted (constant enthalpy), and a large Diesel comes somewhat close. A high speed (vehicle) engine doesn't even come close with even today's technology. It is pretty close to an Otto cycle, though still not exactly. Otto cycle has infinitesmal fraction of cycle for ignition and burn, while even a high speed Diesel (and even the SI engine) still ignites and burns over a finite angle of crank rotation. Still, the result, as I say is MUCH closer to Otto than the cycle Rudy had intended. Still makes a good engine, however :-) You can only get so much speed when you inject the fuel through the combustion or expansion cycle. High speed diesels get more speed by injecting more of the fuel early. But an aircraft engine doesn't need to turn more than 2500 RPM so we should be able to get the benifit of the longer burn time. |
#26
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"Sport Pilot" wrote ...
Only a fool assumes that someone who has trouble spelling or pronuciation. Isn't able to complete a sentence either? Rich |
#27
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Got cut off some how.
Actually I thought I had decided not to send it, and came back and some how hit the enter key. |
#28
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Sport Pilot wrote:
karel wrote: "Sport Pilot" wrote in message groups.com... Sooo. I oftern transpose letters, I don't proofread something as triavil as usenet messages. If you consider your messages trivial, why post them? Anyway, I won't see them anymore. Ploink! Only a fool assumes that someone who has trouble spelling or pronuciation. ......... what? I'm waiting for the rest. And its "pronuNciation." Its one thing to have the occasional typo, but typing a constant run-on of misspelled and non-punctuated text just screams "I'm a moron!" to the world. |
#29
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#30
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"Steve" wrote As already stated, 2-stroke diesels really don't have a power-to-weight advantage over 4-strokes. They still have to have a camshaft and exhaust valves (they aren't like weed whacker engines, you know), so they don't save that weight. Plus they have to have a blower for scavenge air. The only area where they save weight is in that the connecting rod and crank can be lighter, and that only helps offset the added weight of the blower. How about the fact that they have power pulses in each revolution? They could possibly have half the displacement, and still get the same power, (or close to it) with less weight than the double displacement 4 cycle. Yes, the blower weight is added, but it is nice to make good power, way up there. -- Jim in NC |
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