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Old 12-03-2010, 01:26 PM   #71 (permalink)
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Well, the point of maximum pressure is usually reached when the mixture has been burning for some time, which does occur after TDC, but your point is well-taken.

The friction/oil pumping losses are, IMHO, not "closing the barn door after the horses escape". They are ways to very slightly reduce some of the losses in a system of (at best) modest efficiency. Not pointless, exactly, but likely of small enough benefit that you'd never recoup the costs of performing them.

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Old 12-03-2010, 03:26 PM   #72 (permalink)
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The Revetec design doubles the efficiency of a crankshaft design. If some of the other major losses could be addressed, then could the efficiency go above 50%? Is 60% possible?

The major problems with most current ICE designs:

Poor geometric / mechanical torque due to the inherent limitations of the sinusoidal motion of the piston and the connecting rod's angle relative to the crankshaft (vs a rotary design or an electric motor)

Long time periods between power strokes, requiring relatively large flywheels.

Large mechanical drag from the valvetrain having to work against the springs.

The acceleration and deceleration of the piston and connecting rods.

The brief / momentary pressure buildup of the fuel burn (vs the constant pressure reserve of a head of steam, for example)

The need to pump oil through tiny passageways, and to generate electricity.

The need to warm up to reach ideal operating temperature.

The amount of waste heat requires a lot of "stuff" and requires a lot more aerodynamic drag to be able to dump it out of the vehicle.

The relatively narrow torque band, requiring a multi-ratio transmission -- basically as many gears as possible. Seven or eight gears would be better than merely three to five.

The need to idle while not actually being used.
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Old 12-03-2010, 05:42 PM   #73 (permalink)
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Originally Posted by autoteach View Post
pretty sure that your wife is sitting on it. 4DSC.com : Articles
Ah, that is the VG30DE. It is very similar to the engine in my Villager, but it isn't the one in my 98 Max. Wonder if I could track down one of those intakes for the Villager. FWIW the intake runner, and I'm certain the distributorless ignition, boosted the power by 40 hp over the one in my Villager.

My Max has a VQ30DE, which had a variable intake available in the Middle Eastern Maxima, but not in the US.

That is a good pic of our car in the Wiki article!

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I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.
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Old 12-03-2010, 09:44 PM   #74 (permalink)
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Originally Posted by ShadeTreeMech View Post
Ah, that is the VG30DE. It is very similar to the engine in my Villager, but it isn't the one in my 98 Max. Wonder if I could track down one of those intakes for the Villager. FWIW the intake runner, and I'm certain the distributorless ignition, boosted the power by 40 hp over the one in my Villager.

My Max has a VQ30DE, which had a variable intake available in the Middle Eastern Maxima, but not in the US.

That is a good pic of our car in the Wiki article!

Well, about the variable length... Tuning is not that difficult. If you were going to invest the time, it would be a day on a dyno to program it. I just am not sure that it would be worth that much.

As for Blanchard's comment about narrow torque curve of gas engines, I would disagree. Can you show me a graph of a narrow torque curve.
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Old 12-03-2010, 11:27 PM   #75 (permalink)
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I guess I should clarify: a narrow efficiency band. Electric motors do not require transmissions, nor do steam engines.

Surely an ICE can be designed that beats the best we have now? Is an external combustion required? What would it take to get 50-60% efficiency?

'Cuz electrics are up close to 95%...
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Old 12-03-2010, 11:34 PM   #76 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
The Revetec design doubles the efficiency of a crankshaft design. If some of the other major losses could be addressed, then could the efficiency go above 50%? Is 60% possible?
It really depends on useful work obtained vs. thermodynamic heat input. Try modelling a Carnot cycle, using assumptions for Otto cycle, Miller cycle, and whatever other cycles you want. That'll answer your question in theory.

Quote:
Originally Posted by NeilBlanchard View Post
The major problems with most current ICE designs:

Poor geometric / mechanical torque due to the inherent limitations of the sinusoidal motion of the piston and the connecting rod's angle relative to the crankshaft (vs a rotary design or an electric motor)

Long time periods between power strokes, requiring relatively large flywheels.

Large mechanical drag from the valvetrain having to work against the springs.

The acceleration and deceleration of the piston and connecting rods.

The brief / momentary pressure buildup of the fuel burn (vs the constant pressure reserve of a head of steam, for example)

The need to pump oil through tiny passageways, and to generate electricity.

The need to warm up to reach ideal operating temperature.

The amount of waste heat requires a lot of "stuff" and requires a lot more aerodynamic drag to be able to dump it out of the vehicle.

The relatively narrow torque band, requiring a multi-ratio transmission -- basically as many gears as possible. Seven or eight gears would be better than merely three to five.

The need to idle while not actually being used.
If we're talking about the majority of cars on the road today, you forgot a couple of biggies.

The need to generate an intake manifold vacuum.

The need to suck air past a huge inefficient restriction (namely, the throttle plate).
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Old 12-03-2010, 11:57 PM   #77 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
The Revetec design doubles the efficiency of a crankshaft design. If some of the other major losses could be addressed, then could the efficiency go above 50%? Is 60% possible?

The major problems with most current ICE designs:

Poor geometric / mechanical torque due to the inherent limitations of the sinusoidal motion of the piston and the connecting rod's angle relative to the crankshaft (vs a rotary design or an electric motor)

Long time periods between power strokes, requiring relatively large flywheels.

Large mechanical drag from the valvetrain having to work against the springs.

The acceleration and deceleration of the piston and connecting rods.

The brief / momentary pressure buildup of the fuel burn (vs the constant pressure reserve of a head of steam, for example)

The need to pump oil through tiny passageways, and to generate electricity.

The need to warm up to reach ideal operating temperature.

The amount of waste heat requires a lot of "stuff" and requires a lot more aerodynamic drag to be able to dump it out of the vehicle.

The relatively narrow torque band, requiring a multi-ratio transmission -- basically as many gears as possible. Seven or eight gears would be better than merely three to five.

The need to idle while not actually being used.
I haven't really researched the Revetech, but I do know that cam replacements for con rods are nothing new. If they worked I'd think that after all these decades of development I'd at least be able to get one on a lawnmower or something.

All other points above are addressed to some degree... but not all on the same piece of equipment.

Con rod torque xfer> turbines
Power strokes> multi cylinders; 2 strokers
Valvtrain power requirements> 2 strokers; opposed pistons
Recip mass> short stroke geometry; small size (think Honda 50)
Intermittent combustion> turbines; is it necessarily a bad thing?
Oil pumping> 2 strokers, splash lube (think old Briggs and Stratton)
Electricity requirement> diesel; glow plug ignition; magneto (as a low drag source)
Need to warm up> heat storage ala Prius thermos bottle; preheat via various methods
Heat rejection> air cooling; water cooling (marine); thermosiphon
Narrow torque> dunno, 2 or 3 gears works for me
Need to idle> no they don't
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Old 12-04-2010, 12:10 AM   #78 (permalink)
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Thanks for the response, Frank. The trick seems to be combining as many of these features in one design, I guess?

This thread has flown along, and my design proposal has been buried:

http://ecomodder.com/forum/showthrea...tml#post206606

In a nutshell: a 2-stroke, rotary disk valve, opposed piston, with an offset that aligns the beginning of the power stroke with the crankpin at 45 degrees past top dead center -- oh, and only a turbo doing any compression; as there is no compression stroke...
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Old 12-04-2010, 12:15 AM   #79 (permalink)
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I've been looking at the animation on the Revetech site...

I see way more contact points + gears + sliding things + torsion loads per piston than a regular con rod set-up, so if in fact there are gains with this design they have to be from the mechanical advantage more than offsetting the increased internal friction. And then there is the expense and longevity of lobes + gearset vs rod and crank throw.
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Old 12-04-2010, 12:23 AM   #80 (permalink)
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Yeah, the torsion on the flat conrod must be a problem, for sure. But, in theory, there is very little piston slap (if that means the side to side force that the skirts resist), and the valve train is completely standard. They have more or less equaled the Atkinson efficiency of the Prius -- which is the best for any gasoline ICE, is it not?

I wonder what would happen with the Revetec as an Atkinson / Miller cycle? Or, if rotary ball valves could work?

Have you seen the Garric rotary design?

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