Intake Plenum flow - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 15 (permalink) Old 12-01-2013, 01:15 PM Thread Starter
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Intake Plenum flow

Found this little piece searching other things.

http://blogs.dieselpowermag.com/6769...num-flow-data/

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post #2 of 15 (permalink) Old 03-19-2014, 09:47 PM
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Intake flow

What a difference!, I'm presently making changes to the airflow system on my 3.1 litre IDI, in an effort to minimise pumping losses, starting at the air entry (the pipe feeding the air cleaner canister) right through to the tailpipe tip. There are a lot of small gains to be made which all add up to a much larger gain. Often overlooked on diesel engines is the Helmholtz effect, which is more relevant on a diesel as compared to a gasser, (as you know) the diesel is always operating at full throttle as far as the airflow is concerned. There is a strong pulse created at the air cleaner canister as it is a sudden large increase in volume, so experimenting with a different length induction pipe leading to the airbox allows one to tune the pulse to coincide with a particular engine speed. I found that a length of around 5 feet gave my previous diesel a free boost at cruise revs (3000 rpm), sometimes there is such a thing as a free lunch!
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post #3 of 15 (permalink) Old 03-19-2014, 10:42 PM Thread Starter
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I have been told differently, that Helmoltz tuning method is not as accurate with a boosted diesel situation CI.

Jim "Iron Giant" Fahlin ~ A high performance car is like a guitar, you have to tune it to achieve your best operation and pull ahead of the competition.

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post #4 of 15 (permalink) Old 03-19-2014, 10:43 PM Thread Starter
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The exact reason why I can not remember.

Jim "Iron Giant" Fahlin ~ A high performance car is like a guitar, you have to tune it to achieve your best operation and pull ahead of the competition.

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post #5 of 15 (permalink) Old 03-20-2014, 04:51 AM
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Originally Posted by Fahlin Racing View Post
I have been told differently, that Helmoltz tuning method is not as accurate with a boosted diesel situation CI.
I previously thought that the turbo would inhibit any wave transfer so didn't bother to investigate further at that point. One day I decided to add a cold air intake hose onto the air cleaners under bonnet inlet pipe, in order to get a cooler intake charge, and the result was a noticeable drop in performance, yet the engine had previously sucked in warm under bonnet air so I knew that the hose length was probably the reason for the drop (cooler air should have given more power). After trying a few different lengths it became obvious that the Helmholtz effect was indeed having an effect on the engine's breathing characteristics, so I tuned it to the most used revs (cruise). There may be a drop in airflow somewhere above and below the revs where the pulse is strongest, but I couldn't pick it on my vehicle.(generally speaking the wave effect can cover a range of about 1000 revs I'm led to believe....but don't know for sure, as obviously pipe diameter etc. will vary the effective range/strength). Flexible pipe is cheap. so experimenting with this mod won't break the bank.
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post #6 of 15 (permalink) Old 03-20-2014, 11:17 PM Thread Starter
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You bring up a good view, if the theory of the wheels is supposed to break up the wave, but, you say you still notice a level of resonant tuning even with a wheel. The thing that I haven't put much thought into is the wheel is not exactly closed like a valve on its seat however its not wide open like a hole either. In a sense the wheel hinders enough flow to create a reflection back to the air filter (the 'open' end) but how when the turbine wheel is driving the compressor which is creating the suction on the atmosphere.

Its obviously not entirely a pressure wave but strictly acoustic wave per say which still acts independently from a actual pressure wave produced by the closing valve or opening valve.

What's your view on what is going on here? I believe I need to get back to some more gas dynamics and see whats rock n rollin here from what you have said

Jim "Iron Giant" Fahlin ~ A high performance car is like a guitar, you have to tune it to achieve your best operation and pull ahead of the competition.

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post #7 of 15 (permalink) Old 03-21-2014, 04:44 AM
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Quote:
What's your view on what is going on here? I believe I need to get back to some more gas dynamics and see whats rock n rollin here from what you have said
My view is that a pulse will be created whenever the air flowing through a pipe encounters a sudden large increase in area. That means that the average diesel engine (depending upon intake design) can easily have 3 areas where the Helmholtz effect could be created, the intake manifold's plenum (assuming the intake manifold is of a tuned length/plenum design), the turbo's inlet.....(not sure on that one) and the aircleaner canister. I would also consider the entry and exit to an intercooler to be a large sudden change in area, so maybe there are waves created in the intercoolers end tanks too.
As you know,the problem with wave tuning on a diesel engine is that generally we need a reasonably linear flow of air from idle to redline in order to simplify the fuel delivery curve. It would be difficult to tune a mechanical injection system to an airflow curve that isn't reasonably linear, but we aren't talking about a major flow increase here, just a small boost of air at a particular point in the rev range. A tuneable computerised injection system would probably allow the fuel curve to be better matched to a surge in airflow, but I don't have any experience with computerised injection systems so am only making an assumption here.
The flow gain that I mentioned in my earlier post comes from the air cleaner canister's sudden increase in volume, so I'm thinking that the turbo isn't where the pulse activity is in this setup, and the turbo mustn't negate the positive increase in airflow....it's difficult to know exactly what waves are bouncing around in the inlet tract, maybe I killed a wave that was working against airflow at the particular revs by adding the pipe onto the filter canister, I can only theorise because I don't have an education in airflow dynamics, and (as you know) there isn't a lot of info available on the net when it comes to diesel engine mods. I should also mention that my test vehicle has only about 50-60 rear wheel horsepower, so any small gain (and loss) of power is easily felt with the butt dyno, yet a 6 litre v8 diesel engine might mask a few new found horses.

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post #8 of 15 (permalink) Old 03-23-2014, 01:31 PM Thread Starter
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You make some very good points within the 'delivery system' as I call it and the wave reflections. You may have caused a stronger pulse in one area too in addition to your elimination of the possible wave too. My education on flow is listening to the big boys in motorsports with some textbook reading to understand what they are saying with some fluids study. Asking them makes a difference when a question arises. In engine building, you chose a fuel to run and design around it in 'gas' engines. I believe the same can be used in diesel just not as critical due to compression ignition and a less volatile fuel.

Up to this point I have only believed that the delivery system is just that, routes the induction air to the plenum of the intake. How you have brought this Helmholtz discussion further and in particular places it seems the advancement of induction design does not stop with 'timing' within the tuned runner but continues prior to the plenum feeding the runners with adequate density.

Welcome to the forum too btw.

Jim "Iron Giant" Fahlin ~ A high performance car is like a guitar, you have to tune it to achieve your best operation and pull ahead of the competition.

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post #9 of 15 (permalink) Old 03-23-2014, 09:12 PM
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[QUOTE]=Fahlin Racing;1250209[QUOTE]

[QUOTE]Welcome to the forum too btw [QUOTE]

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Quote:
You make some very good points within the 'delivery system' as I call it and the wave reflections. You may have caused a stronger pulse in one area too in addition to your elimination of the possible wave too. My education on flow is listening to the big boys in motorsports with some textbook reading to understand what they are saying with some fluids study. Asking them makes a difference when a question arises. In engine building, you chose a fuel to run and design around it in 'gas' engines. I believe the same can be used in diesel just not as critical due to compression ignition and a less volatile fuel.

Up to this point I have only believed that the delivery system is just that, routes the induction air to the plenum of the intake. How you have brought this Helmholtz discussion further and in particular places it seems the advancement of induction design does not stop with 'timing' within the tuned runner but continues prior to the plenum feeding the runners with adequate density.
The Helmholtz theory came from David Vizards book titled "how to build horsepower". In the induction section he touches not only on plenum size, but on the tube (including a throttle body if a gasser) that is feeding the plenum on the intake manifold. If I am understanding him correctly then there are 2 pulses available to tune involving the inlet manifold (runner length and plenum feed pipe) before we even get to the air cleaner canister inlet pipe, so there are at least 3 potential waves to play with. I would assume that an intercooler end tank would also create a wave, which could probably be harnessed if the pipe lengths are optimized, but that may be difficult to do with limited space in the engine bay. It isn't hard to visualize the entry to the intercooler creating a pulse, but what exactly happens in relation to the exit side of the cooler is harder to understand..........maybe an intercooler of a certain length could be helpful, I really don't know, what do you think ?

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post #10 of 15 (permalink) Old 03-23-2014, 11:42 PM Thread Starter
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I have read a few of his books, I have a few because his pictures he publishes are great tools to help understand the port as well. Any book you see good port pictures in LOOK!!

On the exit side of the cooler I could see the same wave reflections we speak of prior. The flow in a cooler is not uniform so its more or less a reservoir IMO. Where the next wave would take place would be from the exit CSA and plenum entrance CSA which then dumps into another reservoir. However again, we still need the initiation phenomenon that is what I am trying to think of if its just flow demand changes or something else because we don't have a valve to open or close.

I am not sure how up on mathematics you are, I am still trying to teach myself calculus as I go here, but Potto.org has free fluid mechanics and gas dynamics books if you really want to get deep into flow. Look into Gordon P Blair and the book Scientific Design of Exhaust and Intake Systems from Smith & Morrison, that book goes through both systems and explains numerous things. Everything we are trying to find is easier to find once the basics of flow are known by any one person male or female.

The difference we have between our dry flow system is its above atmosphere and we dont have wet flow PERIOD, some have said that the angles the are at the valve change however others have disagreed and said flow is flow just a difference of density and temperature level. Remember whatever you hear or read THERE IS NO SECRET. I always check multiple sources to verify or mark as BS too.

With what we are speaking of here, the 'delivery' system I don't think we have as much complexity but to establish the origin of the wave and move further to tune the efficiency higher in quality.

Jim "Iron Giant" Fahlin ~ A high performance car is like a guitar, you have to tune it to achieve your best operation and pull ahead of the competition.

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