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Old 09-07-2012, 09:45 PM   #1 (permalink)
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Super V.E. for diesels

Super Volumemetric Efficiency
I studied this years ago, around 2004. Reason back then was to make gas powered cars go faster. I hadn't thought about it in a long time.
Something reminded me of it and I realized it could be used for fuel economy too, mainly on diesels.
Basicly you get inside your intake runners harmonic range (depending on how long they are) and you stuff up to 10% more air into your cylinders, with no additional parts or moving parts.

With a turbodiesel you have boost. Increased pressure does effect harmonics.
10psi of boost and the heat you would expect from it (after being intercooled) has the effect of making the runners seem like they are about 10% longer. The added heat and pressure slows down the speed at which the intake pulses move.

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Old 09-08-2012, 12:28 AM   #2 (permalink)
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how would one go about getting inside the intake runners harmonic range on a 1.9 tdi ?
I actually have never heard of this before but i am thinking it has to do with shaping the intakes intake ?
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Old 09-08-2012, 01:41 AM   #3 (permalink)
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Since we have diesels and dont have throttle bodies to worry about you can almost design the intake any way you want.
Makes intakes a lot easier to design.
Basicly you are measuring the distance from the intake valve area to any surface that opposes it. So the distance from the intake valve to the back wall of the plenum in side the intake manifold, an example of this would be a tunnel ram, these typically have shorter runners.
Or you are measuring from intake valve to intake valve on duel plane manifolds found on V8 engines, these always have longer runners.
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Old 09-08-2012, 02:32 AM   #4 (permalink)
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yay for helmholtz resonance; if you have a newer gas car like the 2000 chrysler 3.5l v6(depending on car) it has two runner lengths, ones for high rpm(shorter) and ones for low rpm(longer) the computer switches between the two. it can also be used to tune exhaust. but you also have to match the camshaft to make it easier if it's a single length intake runner.
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Old 09-08-2012, 08:48 AM   #5 (permalink)
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Could you explain how stuffing the engine with more air is going to help increase fuel economy?
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Old 09-08-2012, 09:39 AM   #6 (permalink)
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Quote:
Originally Posted by Daox View Post
Could you explain how stuffing the engine with more air is going to help increase fuel economy?
It's more a matter of not having an intake that is fighting with the incoming air, I think Honda is doing something like this on their engines in the last few years where the intake varies to match the needs at a given RPM.
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Old 09-08-2012, 09:54 AM   #7 (permalink)
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Quote:
Originally Posted by Daox View Post
Could you explain how stuffing the engine with more air is going to help increase fuel economy?
Because its a diesel.
Diesel and brayton cycle engines make both more power and are more efficient when they are fed as much air as you can get them. You never want to restrict the air flow into one of these engines. It just doesn't do anything beside burn more fuel and make less power.
The isentropic process starts the cycle, this means the more energy you start with in the cycle the more energy you will have through out the entire cycle and less energy will have to come from fuel.
Its not the air its self but the heat and pressure you get from compressing it is part of your energy for driving the engine.
The cool thing about diesels is their power stroke is an isentropic process also, that is where your compression energy is returned along with whats added by your fuel burn.
So there is no reason to start this process off with any less than the maximum amount of air you can get throught the air filter and down intake manifold.
This is well proven by N/A diesels running at high elevation, if you want the same level of power from them with say 10% or 20% less air you have to burn a lot of fuel to make up for it.
Brayton cycle engines at high altuide use ram air to make up for lack of air density. They depend even more on their air supply as they need it for cooling.

You can not get more fuel economy on a gas engine by trying to stuff more air into it because of isobaric expansion (throtteling losses) at the start of the cycle. Many have tried, all have failed. Simple thermodynamics forbids it the way we run our gas engines at 10% to 15% load nearly all of the time.
You can make them more efficient for the 5% of the time you really do need power when going up a hill, passing or getting up to speed on an on ramp.

So if you have a gas engine, this isn't going to do anything for you unless you are looking to "go fast" and generally get a lot less fuel milage.
For diesel owners its a ticket to more power and more fuel efficiency.
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Last edited by oil pan 4; 09-08-2012 at 10:20 AM..
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Old 09-08-2012, 11:52 AM   #8 (permalink)
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This idea has been in my mind for some time for something like a genset that runs at a constant RPM so the ram tuning can have some value, then use trubo compounting (maybe two stages) on the exhaust side. Would make for a really efficient engine.
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Old 09-08-2012, 12:12 PM   #9 (permalink)
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I know it can be done, although I wish I understood more about it. I've heard that they've done this type of things on F1 car engines, achieving over 110% volumetric efficiency on a naturally aspirated engine.

Unfortunately, vol eff has been a reletively low priority for diesels because they're typically turbo'd and aren't contrained to a fixed AFR. Therefore, you can compensate somewhat (in terms of power output) either by running slightly lower AFR or by running a little higher boost. I think there is definitely a lot of room for vol eff improvement in diesels. After all, increasing vol eff is just like boosting turbo efficiencies. Why it's not done more still puzzles me.

Unfortunately, it's typically pretty hard to do both the design and fabrication DIY.
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Old 09-08-2012, 12:19 PM   #10 (permalink)
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Quote:
Originally Posted by Daox View Post
Could you explain how stuffing the engine with more air is going to help increase fuel economy?
The benefit is coming from two places.

First, increased vol eff decreases the pumping work. This is because as the piston moves down during the intake stroke it's being pushed down by the incoming air. The higher the air pressure during the intake stroke, the lower the pumping losses. Higher vol eff means higher in-cylinfer pressure during the intake stoke--even though the pressure in the intake manifold may be the same. The second source of the benefit is from the increased combustion efficiencies due to the higher AFR.

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