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Old 06-19-2009, 04:24 PM   #11 (permalink)
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...and then some (no internal engine friction for large chunks of your trip)

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Old 06-20-2009, 01:59 AM   #12 (permalink)
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Use this in conjunction with your pulse and glide and you've got something.
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Old 06-20-2009, 03:41 AM   #13 (permalink)
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Quote:
Originally Posted by dcb View Post
...and then some (no internal engine friction for large chunks of your trip)
The vacuum pump increases internal friction by forcing the rings to seat under non-combustion conditions... It reduces pumping losses by evacuating pressure from the crankcase, creating a positive pressure differential between the top of the piston and the bottom of the piston, which makes the power stroke "more effective", since the piston doesn't have to displace a mass of fluid (air) in order to reach BDC, nor does it have to fight against the same to reach TDC.

Also, increased ring seal prevents blow-by, so marginally better efficiency is produced due to less pressure loss into the crankcase.

The power loss due to the increase in friction is inevitably over-ruled by the decrease in crankcase pressure, which aides in more efficient production of power.
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Old 06-20-2009, 01:38 PM   #14 (permalink)
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pumping losses

The 2-stroke was the great hope of the auto industry,as with a power stroke for each rev,and same pressure above and below pistons,engineers hoped to exploit that tech.,and its high power/weight,and volumetric efficiency.They just couldn't lick emissions issues and everyone has pulled the plug.Honda has a "sparkless" gasoline engine with same BSFC as a diesel and is investigating computer controls to allow operation at low loads where an ignition system is required.------- I've been looking at the Navy's diesel-powered torpedo engine which has only half the "pumping",as a peroxide oxidizer is introduced to the combustion-chamber.There is no intake tract as we understand it in atmo engines.
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Old 06-20-2009, 08:11 PM   #15 (permalink)
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We have talked about pumping losses. Yer pretty much stuck with P&G, smaller engine swap, cylinder deactivation, and high re-gearing.
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Old 06-20-2009, 08:21 PM   #16 (permalink)
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Originally Posted by aerohead View Post
The 2-stroke was the great hope of the auto industry,as with a power stroke for each rev,and same pressure above and below pistons,engineers hoped to exploit that tech.,and its high power/weight,and volumetric efficiency.They just couldn't lick emissions issues and everyone has pulled the plug.Honda has a "sparkless" gasoline engine with same BSFC as a diesel and is investigating computer controls to allow operation at low loads where an ignition system is required.------- I've been looking at the Navy's diesel-powered torpedo engine which has only half the "pumping",as a peroxide oxidizer is introduced to the combustion-chamber.There is no intake tract as we understand it in atmo engines.
I kinda wondered about using a system kind of like that, where you spray the liquid oxidizer into the cylinder just before the fuel, so that the oxidizer heats up enough to create combustion diesel style. You could precisely meter the amount of fuel/oxidizer that goes into the engine, so you could control apparent "displacement" (even thought the physical displacement would be the same, you could control how much oxidizer is present, and how much fuel is used in turn.)
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Old 06-20-2009, 10:40 PM   #17 (permalink)
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We have talked about pumping losses. Yer pretty much stuck with P&G, smaller engine swap, cylinder deactivation, and high re-gearing.

Couldn't find anything, hate to cover old ground again for you guys. Any links off the top of your head? Either way around, I'll attempt it when this thing is in a testable state. Thanks
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Old 06-20-2009, 10:45 PM   #18 (permalink)
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It's OK to re-cover the same information, because there are always newbies and new information might come out. People who complain that "it's already been covered X-long ago" aren't usually interested in actually advancing technology so much as just talking about it, so don't worry if you bring up something that's already been covered awhile ago, especially if you don't understand. Better to explain something 20 times to people than have 20 people mis-explain it to someone else.
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Old 07-31-2009, 05:13 AM   #19 (permalink)
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Quote:
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They do this with vacuum pumps for race cars... yes, vacuum in the block is a good thing, and it actually provides more than "marginally greater" ring seals.

I'm not entirely sure how much vacuum they use, but you can get belt-driven vacuum pumps from Summit Racing and Jegs for the purpose.
Run 10"-12" Hg. At levels significantly higher than that you start getting into issues with seals and oil spray patterns, not to mention that you do need some atmosphere to allow your standard oil pump to work.

You can run lighter tension rings if you can consistently pull 5" or greater. Don't expect an exhaust extraction valve to accomplish this. Your engine may already have light tension rings. Best to check that out on an engine-specific forum with some very sharp techs. Fairly esoteric knowledge.

There are some common electric vacuum pumps that will draw down the engine like this. I think some of the large GMC SUVs used them for brake boosters; large BMW sedans as well. Be sure to use a well designed catch can inline to reduce the presence of oil vapors or neat oil in the pump -- internals probably not designed for that.

I have also been told that some Toyota diesel engines have an alternator with a vacuum pump built in. That would be trick to adapt over.

I would not expect something like this to survive, say, California EPA inspection -- it would fail the visual test immediately if the technician was familiar with the engine or your setup looked too "Home Depot Engineered." Note that the visual inspection does not "care" if the vehicle has the same or better emissions. There is a formal procedure for getting something like this approved.
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Old 07-31-2009, 05:40 AM   #20 (permalink)
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Quote:
Originally Posted by aerohead View Post
...I've been looking at the Navy's diesel-powered torpedo engine which has only half the "pumping",as a peroxide oxidizer is introduced to the combustion-chamber.There is no intake tract as we understand it in atmo engines.
Yes, they were pretty cool but it would be hard to think of a more dangerous propellant system in the hands of the general public. Maybe some types of rocket fuel. Might significantly help with any overpopulation problems, though. Much Darwin Awards fodder, for sure.

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