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Old 12-01-2010, 11:12 PM   #61 (permalink)
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Quote:
Originally Posted by Old Mechanic View Post
I think there is a future in 2 cycle engines, but the stigma of the old designs is a hard prejudice to overcome. The cost of compression could be reduced by injecting the fuel and air into the engine in a homogenized state with no valves and exhaust ports at BDC to allow combustion by products to escape with a significant amount of residual byproducts for the purpose of EGR.
Is there any way that I could actually get you to elaborate on your two stroke theories? I asked a page or two ago, but now I need to do it again. As I read this, it doesnt make sense. I am not being argumentative, I just would like to understand (case in point, allowing combustion byproducts to escape with residual byproducts, which seems to be two of the same). Are you talking about a two stroke that uses neither poppet valves, reed valves, or cylinder porting? If so, how does this work? I think what is happening here is that you are thinking faster than you are typing and missing some content.

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Old 12-01-2010, 11:38 PM   #62 (permalink)
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Seems like I read somewhere about people "sharpening" their crankshafts, persumably so they would "slice" through the oil as it came down into it?

As much fun as it is to read all this theory and possibly engines in prototype, is there anything people are doing right now beyond the usual suspects, like careful airflow control? and diminishing electrical loads?
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Old 12-01-2010, 11:53 PM   #63 (permalink)
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I read about the german engineers testing thermoelectric generators to replace alternators completely, with a no move part replacement.

That reduces load on the engine.

Combined with electric water pump, fan, etc, thats a big deal. No assessory belt, what so ever.
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Old 12-02-2010, 12:15 AM   #64 (permalink)
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Quote:
Originally Posted by Old Mechanic View Post
Do a coast down test of a vehicle.

In high gear with standard engine. Highest loss
In neutral. No loss related to engine
Pull the plugs to eliminate the compression.
Pull the head to eliminate valve train losses.

You would have to push the car to speed in tha last two tests.
unfortunately that doesn't really answer the question... when the pistons (and some fraction of the connecting rods) are accelerated and decelerated energy is lost, question is how much. I did figure it out on the valves once and it was a trivial amount of power, assuming you aren't approaching redline.
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Old 12-02-2010, 12:58 AM   #65 (permalink)
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Lets say that you were to take a valve with a 9 mm stem and reduce that to 8mm, thereby being able to reduce the spring, the retainer, the strength (mass) of the camshaft, the camshaft supports, the drive chain, sprockets, and guides, how much would that constitute? Less than pistons, but significant nonetheless. If we want to talk about the parasitic drain of pistons on the cylinders, what would the gain be to reduce engine displacement and increase volumetric efficiency? smaller pistons, connecting rods, main bearings, crankcase, etc etc. I think that there is significant gains to be had with just sizing engines appropriately to vehicle size with increased volumetric efficiency and decreased engine size. This is not the end of the formula to more efficient vehicles, but its part of it.
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Old 12-02-2010, 06:51 AM   #66 (permalink)
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Of course smaller and lighter and streamlined vehicles help a lot too, especially with the right engine and technique. I assume everyone has seen the 470mpg deal, 1985 Matsu talks, http://www.craigvetter.com/pages/470...nomy-main.html . To the two wheeler crowd, the xprize figures are an efficiency joke Especially given the %25 occupancy rate of vehicles on the road.

also, lighter engine means less energy lost in rpm changes, as well as less reciprocating losses.
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Old 12-02-2010, 02:29 PM   #67 (permalink)
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autoteach;

Injecting both fuel and air into the combustion chambers, so no intake valves.

Ports at BDC to allow most of the exhaust gasses to escape.

Some residual byproducts (exhaust gasses) remain for the purpose of EGR.

Hope that helps.

You are correct about the thinking and typing situation. I once did that in an analytic geometry class and left out a step in the calculation. It was a 4 problem test and everything I wrote was perfect. Because I left out the one line in a half page calculation the teacher took off 10 points. I told her that if I had left the whole thing blank, at that rate of deduction the test score (which supposedly can never be below 0) would have been -300.

My grade for that grading period was 98.7 and the only mistake made in 6 weeks was the omission of the one step that was calculated but not written down on the paper.

42 years ago. Your remark made me think of that long ago time when my brain was ahead of my hands LOL.

regards
Mech
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Old 12-02-2010, 08:53 PM   #68 (permalink)
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So, you are thinking of a Aprilia Ditech design, but with more air injection capacity, if I am understanding you properly. Even systems like this have some issues, and I am not sure if the tech exists yet to overcome it. There is mixture issues that cause starting and running problems. I also have questions on the ability to overcome the speed of the motor with air injection as well as eliminating the compression losses but then injecting air at the top of the stroke, as this is the attempt in cutting down the parasitic losses, right?
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Old 12-02-2010, 08:56 PM   #69 (permalink)
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Quote:
Originally Posted by todayican View Post
Seems like I read somewhere about people "sharpening" their crankshafts, persumably so they would "slice" through the oil as it came down into it?
"Knife-edged crank". Helps cut friction losses from oil (usually a mist, not a slug of liquid) that the swinging crankshaft hits. Also, to some extent, air. "Boat-tailed mains" also are for helping air flow inside the engine.

Some gains can be had from pulling a vacuum on the crankcase, because there is less air for the moving parts to push around. It allows more power to be made in large engines; my guess is that it would cost more power to drive the vacuum pump than could be saved in small-displacement low-RPM engines.

There are small gains (reduction in friction and other parasitic losses) to be had from paying lots of attention to everything that flows in the engine, from air that moves in the crankcase, to oil flowing through the oil passages, to coolant being pushed through the coolant passages. I have heard of noticeable gains in power (again, high-RPM moderate- to large-displacement engines) being made from careful match-porting of the oil pump inlet and outlets and the oil passages to and from the pump in the crankcase. And friction and other parasitic losses tend to be less in "worn-in" engines than in fresh "tight" ones.

Some gains may also be made with specialized coatings on some parts; I have heard that even something like coating the inside of the sump with Teflon (obviously not just dumped in there with the oil, but professionally coated/baked on) can produce more power by getting the oil out of the way of everything faster.

Pretty much all of the above is taken from the context of improving power in high-powered engines that are of large or at least moderate displacement, and run at high RPMs. That said, reductions in friction (and other losses) are still reductions. They may be too small to notice at the sorts of RPMs that economy-minded folks run at, but they would still probably be there.

I would think the break-even period for money saved on fuel versus money spent on the coatings and machine work and such would be longer than the engine would last, but that is a total guess.

-soD
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Old 12-03-2010, 09:37 AM   #70 (permalink)
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What about the terrible leverage that the connecting rod has on the crankshaft at top dead center? The timing of maximum pressure from combustion happens at the worst possible time in the crankshaft position. The typical piston engine losses MOST of the energy before doing any mechanical work, at all.

Oil friction is closing the barn door after the horses have left...

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