I've heard of machineing being done to the cylinder head of a petrol engine which improves performance and/or economy. Is there a similar thing can be done with a diesel engine with the head?
Regards. Mark.(AKA, Mr.Nice.)
On or around Sun, 14 Nov 2004 11:19:06 +0000, Mr.Nice. enlightened us thusly:
In principle, the same rules apply - gas-flowing is all about getting the engine to "breathe" better, by reducing any obstructions to air-flow. Same should apply to diesels - might improve the high-rev performance.
Whether anyone does it, I don't know.
On or around Mon, 15 Nov 2004 06:45:08 +1100, JD enlightened us thusly:
yeah, but the accountants want the cylinder head and manifolds to be a simple casting with the minimum of machining, so the chances are that the tracts are rough inside all 32 and moreover don't line up correctly.
Never heard of it being done, but it should be even more use on a diesel as they effectively operate at full throttle all the time as far as air flow is concerned, and there is no venturi to restrict flow, so any flow restriction in the manifold/head would represent a larger percentage restriction. Because of this performance should improve in the lower speed ranges as well, assuming the pump is adjusted to increase fuelling to use the extra air. On the other hand, the designers know all this, and there may be little improvement available. JD
Years ago I had a Series 111 Safari 2.25 diesel that I had a turbo fitted by Allards in Ross on Wye. It gave me at least 30% extra power and negligible increased fuel consumption. Several years later I had a piston break up, and Turner Engineering near Gatwick did the rebuild for me. They reckoned then that they could have flowed the head and given me the same or more power without the turbo. Incidentally I was very impressed with their set up - they were just applying for BS5750 / IS9001 approval and everything was lickaty spick.
AWEM
Fitting a good extractor exhaust system and manifolds can help the scavenge side of n/a diesels greatly, as can free-flow systems on a turbodiesel. Fuelling has to be altered to get the benefit from any increased oxygen availability, obviously. BTW, you can even fit a charge cooler to a n/a diesel and get more available oxygen in that way, by making the air more dense by cooling it. Badger.
What is a charge cooler? Like an intercooler but it just goes before the inlet manifold? What can i pull one off in the scrapyard? :)
How exactly would you do that then?
You couldn't use a air to air chargecooler, as the air inside the cooler would be at the same temp as the air outside, and would not get any cooler.
You couldn't use a air to water chargecooler as the water would be hotter than the air, and would heat it, not cool it.
The only way to cool the air would be to refrigerate it somehow, which would probably use more energy than it creates!
Diesel does not rev as high as petrol engine so less is gained. Turbo engine show little gain for lots of cash .....
The intercooler works best in a turbo as the pressurized air is heated in this action and the intercooler reduces this temp way above ambient. The intercooler reduces the charge temp and result s in a more dense charge (more oxygen) into the engine.
Adding an intercooler to a NA diesel will have very little to no effect unless you can reduce intake temp below ambient. A snorkel picking up outside cooler air may in fact work better on a NA diesel.
I did a bit of googling on this a couple of years ago.
Roughness of the surface may not be a bad thing.
Misalignment at the head/manifold joint is.
Airflow around the valve is also important. Effectively, if the curves are wrong a part of the valve opening can be in a sort of shadow. Think of the airflow around the back end of a van as an example.
Yep, very simple to do this, no really clever design of cooler required, just as large a heat transfer area as possible.
Hmmmm. Not strictly true. if you consider that the frontal area of a cooler is "x" and the actual area taken up by the core is "y", then the available area for air to flow through the cooler matrix is then "x"-"y", let's for the sake of argument call it "z". Now, to pass the same mass of air approaching the front of the cooler through the lesser area ("z") the airflow must, by the laws of physics, accelerate as it passes through the reduced area to maintain the same mass airflow. If you increase the velocity of airflow, it's temperature drops. See high school physics, Bernoulli's theorem. The really clever bit is in the design of the cooler matrix - to present as aerodynamic a gas flow as possible combined with the greatest possible surface area for heat exchanging. As a simple experiment, try blowing on your hand through a straw and compare the temp of the air with simply breathing on your hand. Same mass of air (a lungfull), higher velocity of air through straw causes a considerable temp drop.
Badger.
Do you want the full argument or just the half hour one?
AJH
No argument, elementary physics. Blame Mr. Bernoullis! Badger.
Oh, go on then, send in the Spanish Inquisition! Hahaha.
His name is in the singular, his principle is known as Bernoulli's, it's actually a conservation of energy principle but in the context of cooling one airflow below ambient by increasing the velocity of another ambient flow through a restriction to increase charge density its with the pissing of gnats.
I'll lay out the rack alongside the twin turbos when you visit ;-)
AJH
Ok, name spelling correction noted.
But it does work. Airflow through a convergent/divergent nozzle. It's the same basic theory behind the operation of the compressor, combustion, guide vane and turbine sections of a gas turbine engine, which works very well indeed, thankyou. The humble carburettor (as flow velocity increases, pressure and temp both drop, which is what causes the fuel to flow and be added into the airflow via various jets etc and by the way is also why some carbs ice up at ambient air temps of greater than zero centigrade), and there are no doubt countless other marvels of "modern" engineering that prove Bernoulli's theorem.
Oooh! That smarts! I did have every intention to visit, but as I said, I was overtaken by locally dictated circumstances. All the best, Badger.
I'd not thought about it that way but you are right, the vanes in the compressor and the diffusers are aerofoils.
Again you're not wrong, all gases will abide by the gas laws until high pressures and here we have venturi making used of the effect. You used the term "considerable" for the temperature drop. I guessed at it being minute. The reason I thought this is that there are limits with what energy changes you can make on an unducted airflow (Betz I think) any more than about 60% power extraction and the flow just goes elsewhere, this is a fundamental limit on wind turbines.
Now if we can use the effect in causing a depression in a carburetor as an example, what sort of depression do you think it needs to suck petrol from a chamber 10mm below the jet? In the order of 50Pa I would guess. So IIRC the expression for adiabatic expansion is PV^gamma/T(absolute)=constant. We know that energy is conserved pressure has changed by about 50 in 100,000 volume through the nozzle is constant so temperature does change but by how much?
I know, it was in jest and I would be interested to see I am mistaken if you have results that show my wrong thinking.
AJH
Ooh, me head hurts! To try and disprove any of the above, I'd need to go and dig out many old course notes dating back 20 or so years as I've forgotten most of it! I'll take your word for it. My day job involves the performance testing and setting of RB199 gas turbine engines, but nowadays we never resort to such theory type stuff, the engine test-bed has no less than 3 computers doing it all for us, we are nowadays merely operaters with a working knowledge of the mechanicals.
As I said, I don't have that ammount of knowledge available to me to try, but I suspect you are right in what you say, especially the comments re. ducting. My use of the word considerable was intended to mean a drop over ambient of around 10degrees c, I dont think that would be unreasonable given a well designed intercooler (and duct!) and I'd imagine it would make a measurable albeit relatively small difference to engine output. Unsure what the percentage change of available oxygen mass would be, but I know that a change of just 20mbars ambient pressure makes a noticeable change in thrust on a jet engine, assuming it isn't running on it's max temp limit and is able to make use of the extra oxygen.
Badger.
A drop of 10degrees C will give an increase in available oxygen mass of
10/300 (assuming an ambient of 27C, which is fairly typical here) assuming everything else stays the same. With appropriate fuelling adjustment this would mean the power would increase by about 3%. But I think your figure of 10 degrees is probably a bit optimistic, and I would guess that in practice 2 or 3 is more likely. JDMotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.