« Return to Thread: OT: Diesel compression, was: Range: 156Volts vs 312 volts
Re: OT: Diesel compression, was: Range: 156Volts vs 312 volts
by Son of Tesla
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Hello,
Sorry to continue this OT but I beg to differ here.
Diesels do NOT have as much compression braking as gasoline engines do.
That's why they ADD Jake brakes and "Retarders" in Allison and other automatic Transmissions.
Diesels are designed without an air "throttle" the intake air flow is unrestricted.
In a gas engine when the throttle is closed / idled, the restriction causes a compression and decompression imbalance within the cylinders in favor of a much quicker rpm reduction.
In a diesel, no throttle means the measure of intake air ingested is equal to the max flow for that particular rpm.
It would appear reasonable to assume that compressing all this air volume would take energy and that expended energy would decrease the RPM
BUT
while there is an increase in expended energy to compress the cold air charge it is offset by the now heated air which at full compression (piston @ TDC) produces slightly more energy
due to the thermal dynamics of "heat of compression" and the absorbed heat built up in the cylinder.
The only reasons a diesel slows down at all without additional assistance, is due to
1) The absorbed heat from the surrounding engine parts rapidly decreases due to the no fire condition that exists which tends to negate the "heat of compression" increase and
2) Mechanical friction.
Hence the need for the "Jake brake" and Allison's transmission feature the "Retarder"
I'd explain these further but
1) Enough OT and
2) Full explanations of their respective operational theory is available readily online and in print.
My.02 (OT as it is)
Cruiser
cowtown@... wrote:
>> Diesel powered cars have very little compression braking and seem to be
>> able to descend hills safely.
>
> Huh? What? Diseasel cars compression brake just fine! Hell you
> need a GP 27 battery to crank the damn things when it's cold! Of
> course they go down hills great in low gear, like throwing out the
> anchor!
Yeah - isn't that what a "Jake brake" on a big rig is used for? Noisy
as hell and not legal inside city limits, but they put that 15-25:1
compression to work as an air pump through the exhaust!
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For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev
_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev
Sorry to continue this OT but I beg to differ here.
Diesels do NOT have as much compression braking as gasoline engines do.
That's why they ADD Jake brakes and "Retarders" in Allison and other automatic Transmissions.
Diesels are designed without an air "throttle" the intake air flow is unrestricted.
In a gas engine when the throttle is closed / idled, the restriction causes a compression and decompression imbalance within the cylinders in favor of a much quicker rpm reduction.
In a diesel, no throttle means the measure of intake air ingested is equal to the max flow for that particular rpm.
It would appear reasonable to assume that compressing all this air volume would take energy and that expended energy would decrease the RPM
BUT
while there is an increase in expended energy to compress the cold air charge it is offset by the now heated air which at full compression (piston @ TDC) produces slightly more energy
due to the thermal dynamics of "heat of compression" and the absorbed heat built up in the cylinder.
The only reasons a diesel slows down at all without additional assistance, is due to
1) The absorbed heat from the surrounding engine parts rapidly decreases due to the no fire condition that exists which tends to negate the "heat of compression" increase and
2) Mechanical friction.
Hence the need for the "Jake brake" and Allison's transmission feature the "Retarder"
I'd explain these further but
1) Enough OT and
2) Full explanations of their respective operational theory is available readily online and in print.
My.02 (OT as it is)
Cruiser
cowtown@... wrote:
>> Diesel powered cars have very little compression braking and seem to be
>> able to descend hills safely.
>
> Huh? What? Diseasel cars compression brake just fine! Hell you
> need a GP 27 battery to crank the damn things when it's cold! Of
> course they go down hills great in low gear, like throwing out the
> anchor!
Yeah - isn't that what a "Jake brake" on a big rig is used for? Noisy
as hell and not legal inside city limits, but they put that 15-25:1
compression to work as an air pump through the exhaust!
_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev
_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev
« Return to Thread: OT: Diesel compression, was: Range: 156Volts vs 312 volts
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