The injector breaks the fuel into a mist. Pre-ignition finishes the mixing.
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20 years ago
The injector breaks the fuel into a mist. Pre-ignition finishes the mixing.
I don't think that 50% efficiency is thermodynamically possible. The best designed fossil fuel powerplants barely make thirty percent. Carnot cycle limitation?
Wonder where Pete is when we need him.
Mike Eberlein
This is a turbocharged engine; that may be where the extra input VS output advantage comes from.
The supercharger(s) looked, um, wicked big.
I wonder how many cupolas you could blow with that ;)
Tim
-- In the immortal words of Ned Flanders: "No foot longs!" Website @
Actually the best fossil power plant, a combined cycle plant, currently holds the efficiency record at 52%. That's primary energy to electrical energy, so the prime mover efficiency has to be higher than that to account for generator losses. Large diesel electric plants typically run about 45%.
The Carnot cycle limit is
Ec = 100* (Th-Tc)/Th
where Th is the high temperature source and Tc is the low temperature sink, both expressed in degrees Kelvin, and Ec is Carnot efficiency. As you can see by inspection, you can only reach 100% efficiency if the sink temperature is absolute zero. But we don't have access to an absolute zero sink of sufficient capacity to be useful. 50% efficiency is possible if the difference between source and sink is half the high temperature. That's achievable in practical systems.
The Carnot limit actually permits any efficiency up to 99.999999......%. But to approach that, the Th has to be very high, and the Tc has to be very low. That's where practical limits come into play. Materials can't stand extremely high temperatures, and the atmosphere puts a practical limit on Tc. Gary
Pretty neat link.
Mike Eberle> read all links and learn
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ICs are now well over thirty. Yes, they are reaching 50% range.
Figures typically quoted for car engines (SI) are very old. Modern ones can get over 33-34% at full throttle (or at least near best specific fuel consumption settings). Increases in compression ratio and other factors account for this. 25% is very low for even an automotive or truck Diesel. This value must be for an old one.
For powerplants reach>
It looks like it exhausts at TDC but intakes at BDC. Is it sucking vacuum all the way down?
John
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"It looks like it exhausts at TDC but intakes at BDC. Is it sucking vacuum all the way down?"
The animation only has a few frames so timing is not precisely represented.
It is a two-sroke engine. The exhaust valve opens shortly before BDC and before the scavenging ports are uncovered.
Since it is a two-stroke engine there is no intake stroke as in a four-stroke engine.
"Intake" occurs when the piston uncovers scavenging ports around the cylinder wall shortly before BDC. Since at this point scavenging air pressure is greater than cylinder pressure the remaining exhaust gases are pushed out the open exhaust valve. The valve closes shortly after the piston begins moving upward and compression begins for another power stroke.
Rick
Same thing for an engine with fewer cylinders and same displacement.
The relativley long stroke (vs bore) also has no bearing on the compression ratio (and peak cylinder pressure) - that's determined by the ratio of cylinder volume at TDC vs BDC (which would be the same for any given bore size).
Laurie Forbes
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