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.

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 ?

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.

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.

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.

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.

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.

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.

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.

The biggest problem with using super V.E. on diesels is the intake runners will need to be really long to keep the motor a harmonic range at cruise speed.

If you have 24 inch runners and start going up a hill and start pushing 20psi of boost the runners are going to effectivly become 28 inches long. Thats more useful.
If you could stretch them out to 32 inches, with a little boost they could become quite useful for towing/crusing. Use the 4th (+4%) harmonic range for cruise, put your foot down and bring it out of over drive and add more boost to get into the 3rd harmonic range (+7%), and when you drop it into 2nd or 3rd gear going over a mountian pass RPMs and PSI go up and bring you into the 2st harmonic range (+10%).

I am pretty much stuck with my OEM 24 inch runner intake. I dont think I could beat them for towing and power. I dont think I have enough room for the 32'' long runners needed to take advantage of harmonics at cruise RPM.
Maybe some of the 4cylinder guys do.

I like flow harmonics. I'm putting an expansion chamber exhaust on my chainsaw too.
Its kind of hobby.

Also water injection will slow down the pluses, but to what degree I do not know.

was diesel in the title the whole time? d'oh

pulled this from allpar

I changed the title.

I did some investigation into intake runners this morning,for my TDI they would need to be 3 feet long to have effect at the lowest rpm possible, around 4100 rpm.
The max rpm i drive is 2150, at my hwy speed & shift at 1500 to 1700 rpm.
Now i know why some hot rods have huge piped intake runners, I assume the headers/ exhausts work in conjunction.

when i hear this type of talk, encloding pipes needing to be certain lengths. First thing that comes to mind is a Transmission Line speaker project. for compactness and efficiency

[IMG]http://image.moparmusclemagazine.com...-intake-us.jpg[/IMG]

1960 Chrysler 300F (and a few other models through 1961 or so)

Helmholtz resonator affect. Specific tuning. Mid-range passing times bested maybe by a Maybach or other ultra luxury gasser today.

Is there really measurable gain there? Deisel engines optimize both of those thing better than most other engines already.

Would we measure from the intake valve to the turbo?

Also is there any way to calculate the change in the harmonics in respect to length of the runner with an increase to boost?

No, you would measure from the intake valve around most bends all the way back to the first and pronounced surface that the wave can bounce off from.
Some vehicles its the inside of the plenum, others like mine its another valve on a different cylinder.
I have a feeling a plenum would give the best wave return.

It would be easy to figure out, but the temperature is always changing under boost even if the pressure is not changing. Intercoolers start off working real well then get heat soaked and as you get up to speed they loose heat so its a cluster. One intercooled engine does not run the same temperature and boost as another.
Roughly every 10psi or at least for the first 10psi you add will cause the air pulses to slow down to the point where the air in the runners will behave as if the runners are about 10% longer.
I only worked this through 10-15psi because this was originialy for a gas application and I could only find post intercooler IAT numbers for the 10 to 15 psi range.

Yes, the gain is measureable (from both sources). I don't know as I've ever done it myself in a vehicle, but I've seen in many times on engines on dyno test stands.

Diesels typically aren't as optimized for reduced pumping losses (high VE) as you might think. In typical spark-ignited naturally aspirated gassers, high VE is pretty much the only way to get more torque at any given speed. So if you want to get more torque you pretty much have to increase the VE. On a diesel however, you can just add a little more fuel and/or a little more boost and you'll get the torque. Sure the FE will be sub-optimal, but it's just so much easier than redesigning heads and intakes.

It just goes to show you how well the efficiency concept of a combined cycle intercooled turbodiesel engine works.
They started off real efficient and cranked out amazing power levels with out much added complexity or engineering.
Fuel economy didn't matter much as diesels could beat their gas fuelled counterparts with ease in head to head tests and on top of that diesel fuel was quite a bit cheaper than gas until about 10 years ago.
But times are changing and with diesel fuel prices projected to soon rocket past $4/gal in the U.S., adaptations need to be made.

I have read some large diesel engine papers that show loss of efficiency when intake air temperatures start to drop below 30'F to 40'F.

Diesel pr0n

tuned intake, exhaust header, turbo, monster intercooler, and a blower.

I have read some that they are good down to -5F

That's a whole lotta hardware just for a clanky old 617.952. I wonder if they got more than 200hp or 200 hours of life out of it....

They got a tad over 400 HP.

200 hours of life might be right. They made a couple of videos one of a drag race and one of it doing doughnuts. After which it disappeared only to reappear with a om603 engine.

I was reading my cummins manual today and apperantly cummins recomends that when operating at +20'F or less to locate your intake inside the engine enclosure.
Also to use grill shutters below 32'F and a winter front below 0'F.

Doesn't this kind of go against the theory of super VE? Cold air is more dense so you get more air in the engine which is what super VE is about, right?

Diesels require heat for efficient combustion, and they already run with an excess amount of air. So colder air will not improve performance in the way it will for a gasser.

The concern is that for super cold air you can start to extend to combustion delay and start getting bad combustion (white smoke, etc.). It's not as much of an issue on the newer common rail engines as it used to be on the older diesel with mechanical fuel injection and low fuel pressures.

It would appear the MAN diesel and Cummins are saying close to the same thing.
Man diesel was claiming air temps lower than 30'F to 40'F hurt fuel milage and cummins recomends staying above 20'F.
I knew cool air was good to a point, but never new what those numbers could be till now.

Cool air above 40'F and intake harmonics are the way to go.
Cold air intakes are good more often than not, just have to keep the air going into the enigne after the intercooler above 40'F.

I have a -40'C to +40'C temperature probe on order to put down in the intake manifold to get some real numbers.
I have the problem of 0'F temperatures in winter here.

What factors effect benefit from cold air and what factors penalize for it?

My fuel economy on my diesel goes to crap in the cold, but I have no edea how much of it is idle time & warmup and hom much is the lower energy content of diesel and how much is intake temperature. I do have some -30C highway runs recorded but wind direction is a vairable as well. I do know that it is significant for me though.

Our Macks at work say under hood air at -12C and winterfronts at -18C I believe.

Winter fuel is playing less and less of a role in reduced mileage in cold weather. The ULSD energy content is much closer to that of kerosene, the winter mixer.

The cooler air benefits in 2 ways:

First cooler air means more dense air and therefore, you'll run a higher AFR (at least on most diesels--some more modern ones have some sophistcaed electronic controls). The higher AFR increases the combustion efficiency. Fundamentally, the thermodynamic benefit comes from the fact that mixtures with higher AFR have a higher specific heat ratio (gamma). Secondly, the lower air temperature itself increases the specific heat ratio and thus the combustion efficiency. You can see the dependence of specific heat ratio on temperature and AFR here (pg. 2392):
http://muhserv.atauni.edu.tr/makine/..._files/A/c.pdf
and the also the dependence of theoretical diesel efficiency on the specific heat ratio here:
The Diesel Engine


Now, for the downside:

In a diesel the ignition takes place due to compression, not due to spark as it does in a gasser. Therefore the ignition doesn't take place until the pressures and temperatures reach the point where the fuel evaporates and the mixture self-ignites. The time between when the fuel in injected and when ignites is the "ignition delay". Cooler air temps can prolong the ignition delay to the point where the ignition doesn't take place until very late in the cycle or, in extreme case, the ignition never happens and you get a misfire. Later combustion typically means lower efficiency because the heat release happens in a larger volume. Now, how much the ignition delay is affected depends on how cold it is as well as the type of fuel system. Newer common rail systems have extremely high injection pressures (30,000 psi+) so the ignition delays are very short and less affected by temperature. Also, many of the new systems will electronically advance the injection timing for cold air temps to compensate. The older mechanical fuel injection systems were more affected because the injection pressures were relatively low and the ignition delays were quite long.

I think dave nailed it.
Just ran adiabatic compression for a 22:1 diesel like mine and with 0'F air the temperature in cylinder at TDC is only going to be like 860'F.
A more normal 18:1 compression diesel will only hit about 800'F.
40'F air in a 22:1 engine gives me 930'F and a 18:1 engine will hit 860'F.

The hotter the air the better, to a point.
800'F does not seem hot enough.

Ok so we have Mack, cummins, Man and adaibatic calculations all saying air below 30'F isn't good and air in the >20'F range is bad.

Thats good enough for me.

Seems like we should try to shoot for <40'F IAT and keep it as cool as possible when the out side temperature is well above 40'F.

Diesels already use tuned length manifolds.

They aren't tuned for what we want.

I've never seen one myself. Do you have any examples?

FYI, here's what the intake looks like on my Cummins:
http://image.off-roadweb.com/f/91340...inder_head.jpg
The style is sometimes referred to as a "flower box"--similar to a flower box hanging off a window. The style has been known to be sub-optimal (performance wise), but the style has remained unchanged for decades because it's rugged, simple, and easy to manufacture.