machine work
05-02-2006, 10:01 PM
#22
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Join Date: Aug 2005
Posts: 1,654
Re: machine work
Originally Posted by Joseph Davis
Det is most prevalent at tq peak, not high rpm. Now google turbine pressure curves and watch your blood pressure rise.
05-04-2006, 12:04 AM
#25
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Join Date: Feb 2003
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Re: machine work
Originally Posted by baldur
There's the most heat buildup at high rpm though
You're going to have to explain that one to me.
05-04-2006, 08:31 AM
#27
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Join Date: Feb 2003
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Re: machine work
Originally Posted by baldur
There's less heat produced per cycles but there are a lot more cycles.
Originally Posted by Joseph Davis
The cylinders fill less, so there is less heat produced per cycle, but the piston skirts are seeing just as much contact area to transfer heat out of the chamber.
Vizard did a big fat lot of work on detonation in the 70's, really extended on Ricardo's ---- and published it both for engineers as well as diseminated it to the laymen as best as possible. Long story short, there are three factors that directly relate to detonation: heat, time, and density. In high rpm Honduh operation, density is lacking - check Random Asshat's thread about his dad's car @ 17 psi - 465 whp, 279 tq, perfect example. In high rpm operation time required to both transfer heat (as well as detonate) is lacking.
The heat generation itself isn't as great as at naturally occurring aka not boosted peak torque, where detonation is most prevalent due to greatest cylinder filling at the lowest possible rpm aka highest dwell time. Since combustion speed of isooctane based fuels stays more or less proportional to piston speed, there isn't a higher "duty cycle" of heat generation vs heat dissipation in high rpm operation vs lower rpm, for a given tq.
It's a shame I took down Ricardo's High Speed Internal Combustion Engine, you need to leech + read it. Ask SiShane on HT if he still has a copy, leed here might, otherwise I will get it to you.
05-04-2006, 04:04 PM
#29
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Join Date: Feb 2003
Posts: 0
Re: machine work
Burn takes less time, so there is less time for it to transfer to the engine before going out the exhaust. Thermodynamic transfers are functions of time. Also, as exhaust density goes up combustion chamber surface area remains unchanged... 95 percent of those hot exhaust molecules never come in contact with chamber surface to transfer that "more heat from more fuel" which is incorrect anyway as fuel follows tq not hp and rpm. Go ask for the 75 year old basic engineering text already, spoonfeeding basicknowledge into the Grand Canyon is getting tedious.
