Re: gas-flowed head on a diesel?

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A

Austin Shackles

Guest
On or around Sun, 14 Nov 2004 11:19:06 +0000, Mr.Nice.
<mr.nice@*nospam*clara.co.uk> enlightened us thusly:

>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?

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.

 
Austin Shackles wrote:

> On or around Sun, 14 Nov 2004 11:19:06 +0000, Mr.Nice.
> <mr.nice@*nospam*clara.co.uk> enlightened us thusly:
>
>>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?
>
> 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.

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
 
On or around Mon, 15 Nov 2004 06:45:08 +1100, JD <[email protected]>
enlightened us thusly:

>Austin Shackles wrote:
>
>> On or around Sun, 14 Nov 2004 11:19:06 +0000, Mr.Nice.
>> <mr.nice@*nospam*clara.co.uk> enlightened us thusly:
>>
>>>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?
>>
>> 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.
>
>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.

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.


 

"JD" <[email protected]> wrote in message
news:[email protected]...
> Austin Shackles wrote:
>
> > On or around Sun, 14 Nov 2004 11:19:06 +0000, Mr.Nice.
> > <mr.nice@*nospam*clara.co.uk> enlightened us thusly:
> >
> >>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?
> >
> > 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.
>
> 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


 

"Austin Shackles" <[email protected]> wrote in message
news:[email protected]...
> On or around Mon, 15 Nov 2004 06:45:08 +1100, JD <[email protected]>
> enlightened us thusly:
>
> >Austin Shackles wrote:
> >
> >> On or around Sun, 14 Nov 2004 11:19:06 +0000, Mr.Nice.
> >> <mr.nice@*nospam*clara.co.uk> enlightened us thusly:
> >>
> >>>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?
> >>
> >> 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.
> >
> >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.
>
> 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.
>
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.


 
On Sun, 14 Nov 2004 21:56:55 -0000, "Badger"
<[email protected]> wrote:

>> 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.
>>
>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.

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? :)

 

> 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.
>
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!


 
> 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.

Diesel does not rev as high as petrol engine so less is gained. Turbo engine
show little gain for lots of cash .....


 
> >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.

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.


 
On Sunday, in article
<[email protected]>
[email protected] "Austin Shackles" wrote:

> On or around Mon, 15 Nov 2004 06:45:08 +1100, JD <[email protected]>
> enlightened us thusly:
>
> >Austin Shackles wrote:
> >
> >> On or around Sun, 14 Nov 2004 11:19:06 +0000, Mr.Nice.
> >> <mr.nice@*nospam*clara.co.uk> enlightened us thusly:
> >>
> >>>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?
> >>
> >> 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.
> >
> >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.
>
> 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.

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.

--
David G. Bell -- SF Fan, Filker, and Punslinger.

"History shows that the Singularity started when Sir Tim Berners-Lee
was bitten by a radioactive spider."
 

"Aubrey" <[email protected]> wrote in message
news:[email protected]...
> > >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.
>
> 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.

Yep, very simple to do this, no really clever design of cooler required,
just as large a heat transfer area as possible.

>
> 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.
>

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.


 
On Mon, 15 Nov 2004 17:45:59 -0000, "Badger"
<[email protected]> wrote:

>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.

Do you want the full argument or just the half hour one?

AJH
 

<[email protected]> wrote in message
news:[email protected]...
> On Mon, 15 Nov 2004 17:45:59 -0000, "Badger"
> <[email protected]> wrote:
>
> >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.
>
> Do you want the full argument or just the half hour one?
>

No argument, elementary physics. Blame Mr. Bernoullis!
Badger.

Oh, go on then, send in the Spanish Inquisition! Hahaha.


 
On Mon, 15 Nov 2004 21:05:34 -0000, "Badger"
<[email protected]> wrote:

>
>No argument, elementary physics. Blame Mr. Bernoullis!
>Badger.

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 ****ing of gnats.
>
>Oh, go on then, send in the Spanish Inquisition! Hahaha.

I'll lay out the rack alongside the twin turbos when you visit ;-)

AJH
 

<[email protected]> wrote in message
news:[email protected]...
> On Mon, 15 Nov 2004 21:05:34 -0000, "Badger"
>
> His name is in the singular,

Ok, name spelling correction noted.

> 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 ****ing of gnats.

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.

> >Oh, go on then, send in the Spanish Inquisition! Hahaha.
>
> I'll lay out the rack alongside the twin turbos when you visit ;-)
>
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.


 
On Tue, 16 Nov 2004 18:38:57 -0000, "Badger"
<[email protected]> wrote:

>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.

I'd not thought about it that way but you are right, the vanes in the
compressor and the diffusers are aerofoils.

>The humble carburettor (as flow velocity increases,
>pressure and temp both drop, which is what causes the fuel to flow

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?
>
>> >Oh, go on then, send in the Spanish Inquisition! Hahaha.
>>
>> I'll lay out the rack alongside the twin turbos when you visit ;-)
>>
>Oooh! That smarts! I did have every intention to visit, but as I said, I was
>overtaken by locally dictated circumstances.

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
 

<[email protected]> wrote in message
news:[email protected]...
> On Tue, 16 Nov 2004 18:38:57 -0000, "Badger"
> <[email protected]> wrote:
>
>>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.
>
> I'd not thought about it that way but you are right, the vanes in the
> compressor and the diffusers are aerofoils.
>
>>The humble carburettor (as flow velocity increases,
>>pressure and temp both drop, which is what causes the fuel to flow
>
> 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?

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.

>>> I'll lay out the rack alongside the twin turbos when you visit ;-)
>>>
>>Oooh! That smarts! I did have every intention to visit, but as I said, I
>>was
>>overtaken by locally dictated circumstances.
>
> 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.
>

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.


 
Badger wrote:

>
> <[email protected]> wrote in message
> news:[email protected]...
>> On Tue, 16 Nov 2004 18:38:57 -0000, "Badger"
>> <[email protected]> wrote:
>>
>>>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.
>>
>> I'd not thought about it that way but you are right, the vanes in the
>> compressor and the diffusers are aerofoils.
>>
>>>The humble carburettor (as flow velocity increases,
>>>pressure and temp both drop, which is what causes the fuel to flow
>>
>> 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?
>
> 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.
>
>>>> I'll lay out the rack alongside the twin turbos when you visit ;-)
>>>>
>>>Oooh! That smarts! I did have every intention to visit, but as I said, I
>>>was
>>>overtaken by locally dictated circumstances.
>>
>> 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.
>>
>
> 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.
JD
 
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