very high egt

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Originally Posted by Dougal

No the fuel isn't still burning in the manifold (unless you're retarded enough to think flames out the exhaust are cool), it's simply the hot gas has lost less heat to the cylinder, head and pistons. So when it passes your probe it's hotter..

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The same as what I was trying to explain, burning in the manifold would also show as a black cloud following you. ( which we don’t have in this case)

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Originally Posted by Dougal

This is completely counter-productive on a diesel. Dangerously high EGT's are the result of not enough air which requires more boost. To get more air in requires more boost and higher drive pressures.
The result of the higher boost and drive pressure is lower EGT's. It can take some getting your head around.
The other approach will lock you into a vicious circle which can only end with the turbo bypassed and extractors fitted. Needless to say, performance will suffer and you'll still need to greatly reduce fuel.

Turbos thrive on exhaust heat, the hotter they are they more efficiently they run and the less drive pressure they require.

A wastegate that opens based on drive pressure will kill your boost when accelerating with a cold manifold but do absolutely nothing to help high EGT's.
This is because drive pressure drops with temperature.

If you could guarantee your turbo won't overspeed and your head gasket will stay put then welding the wastegate shut will have the best positive effect on keeping EGT's down.

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Dougal i completely understand what you are saying and agree, but please think it though, what happens next. You keep on pushing more air in and as the hot gas will always be at a higher pressure than the cold gas coming in you will and Do come to the point where, after the outlet valve has opened not much of the hot gas been able to evacuate. Even to the point where it defeats the pressure of the inlet.
A simple argument
No cam overlap so rpm is not an issue
Inlet pressure of 20psi
compression ratio of 15:1

As soon as the hot gas pressure = 15 times the inlet pressure. it is safe to assume that the cylinder is already full and at an equal pressure to that of the inlet manifold when at BDC at TDC it will be equal to the hot manifold witch is 15 times the inlet temp. As the inlet valve opens before BDC the pressure in the cylinder will be greater than the gas trying to flow in, infact the hot gas will flow out the inlet until pressure equalises, etc you can think though the rest yourself.
In petrol the cosswerth is a well known example of this happening. In diesels the Cummings 908 is another when we were toping 1000 HP the result was a few Italian of shore power boats coming to a sudden stop in big black clouds.

The progressive waste gate, actuated on hot gas pressure against a spring ( known pressure) as opposed to a cold gas diaphragm actuated one is to keep the hot gas at a pressure below the 15:1 thus enabling the inlet cold gas flow in rather than being pushed out


as i siad before youir thinking is correct but you need to take it to the next stage. and to sort out what is realy going on you need at least 4 gages a very long hill and a speedo ( prefurably a few hours on a dino)

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Originally Posted by clean32

The same as what I was trying to explain, burning in the manifold would also show as a black cloud following you. ( which we don’t have in this case)

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Burning in the manifold doesn't necessarily create a black cloud. Remember your average diesel is still running 50% excess air so as long as there is heat there is plenty of oxygen remaining to burn the fuel.
Advanced timing results in black smoke because the fuel can get charred before it is cleanly burnt. It's a simple experiment to run, wind up your fuel pump, alter the timing and observe. Repeat until satisfied.

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Originally Posted by clean32

Dougal i completely understand what you are saying and agree, but please think it though, what happens next. You keep on pushing more air in and as the hot gas will always be at a higher pressure than the cold gas coming in you will and Do come to the point where, after the outlet valve has opened not much of the hot gas been able to evacuate. Even to the point where it defeats the pressure of the inlet.
A simple argument
No cam overlap so rpm is not an issue
Inlet pressure of 20psi
compression ratio of 15:1

As soon as the hot gas pressure = 15 times the inlet pressure. it is safe to assume that the cylinder is already full and at an equal pressure to that of the inlet manifold when at BDC at TDC it will be equal to the hot manifold witch is 15 times the inlet temp. As the inlet valve opens before BDC the pressure in the cylinder will be greater than the gas trying to flow in, infact the hot gas will flow out the inlet until pressure equalises, etc you can think though the rest yourself.
In petrol the cosswerth is a well known example of this happening. In diesels the Cummings 908 is another when we were toping 1000 HP the result was a few Italian of shore power boats coming to a sudden stop in big black clouds.

The progressive waste gate, actuated on hot gas pressure against a spring ( known pressure) as opposed to a cold gas diaphragm actuated one is to keep the hot gas at a pressure below the 15:1 thus enabling the inlet cold gas flow in rather than being pushed out


as i siad before youir thinking is correct but you need to take it to the next stage. and to sort out what is realy going on you need at least 4 gages a very long hill and a speedo ( prefurably a few hours on a dino)

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I have run pressure and temperature gauges throughout my inlet and exhaust manifolds, I've run three different turbos and measured the results on each. The results I acheived match exactly the explanations I have given (that's why I gave them).

In your above example, what is the drive pressure? My measurements put it at a mean (I had to heavily damp the line to stop needle flutter) of under 20psi with sufficiently high EGT (above 600C), this is less than the boost and nowhere near 15 times the inlet pressure.

The compression pressures of a healthy diesel are well over 400psi, the <20psi in the exhaust manifold is not enough to cause the problem you are describing. It's not applicable to this current high EGT problem.

[QUOTE=Dougal;916589]
In your above example, what is the drive pressure? My measurements put it at a mean (I had to heavily damp the line to stop needle flutter) of under 20psi with sufficiently high EGT (above 600C), this is less than the boost and nowhere near 15 times the inlet pressure.

QUOTE]

Are you saying you have 20psi hot and 20psi boost ( cold) ??

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Originally Posted by clean32

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Originally Posted by Dougal

In your above example, what is the drive pressure? My measurements put it at a mean (I had to heavily damp the line to stop needle flutter) of under 20psi with sufficiently high EGT (above 600C), this is less than the boost and nowhere near 15 times the inlet pressure.

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Are you saying you have 20psi hot and 20psi boost ( cold) ??

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For the fourth time in this thread.
Yes. (provided the EGT's are high enough).

The boost:drive pressure ratio constantly changes depending on exhaust backpressure and EGT, but yes there are regions where boost exceeds backprssure.
For my engine this is below 2000rpm (my 2.25" exhaust generates too much backpressure at higher) and with EGT's above 600C.

[QUOTE=Dougal;916603]For the fourth time in this thread.
Yes. (provided the EGT's are high enough).

[QUOTE]

Mate get in touch with green peace and take out a patient quick

Cold and hot being equal at 20 psi, but with cold temp at say 20 deg = 1.205KG m2 and hot at say even 400deg = 0.524 KG m2. that’s less than 50% of what you put in coming out LOL.

either that or you have 5 reverse gears and one forward :confused:

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Originally Posted by clean32

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Originally Posted by Dougal

For the fourth time in this thread.
Yes. (provided the EGT's are high enough).

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Mate get in touch with green peace and take out a patient quick

Cold and hot being equal at 20 psi, but with cold temp at say 20 deg = 1.205KG m2 and hot at say even 400deg = 0.524 KG m2. that’s less than 50% of what you put in coming out LOL.

either that or you have 5 reverse gears and one forward :confused:

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You need to learn some basic thermodynamics. The densities you have calculated above (using an incorrect EGT) are meaningless by themselves. Consider gas velocity or mass flow and it may become a little clearer.

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...and take out a patient quick

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:o
But if 'Dr Dougal' does this, he'll be de-registered by the Medical Standards Board!:p
Ian

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Originally Posted by Leo109

:o
But if 'Dr Dougal' does this, he'll be de-registered by the Medical Standards Board!:p
Ian

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Dr Dougal Houser please report to reception:wasntme:

cheers phil

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Originally Posted by Dougal

You need to learn some basic thermodynamics. .

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:D:D:D:D:D Guess what my last job was

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Originally Posted by Dougal

The densities you have calculated above (using an incorrect EGT) .

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not inccorect just an example, if i was to use your temp it would just look worce..[/QUOTE]

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Originally Posted by Dougal

are meaningless by themselves. Consider gas velocity or mass flow and it may become a little clearer.

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Clear as, if you have equal pressure hot side and cold side, logic would say that you have no resistance or in this case less resistance hot side.
no pressure build up no resistance no energy for the turbo simple.

you said you damped down your Gage, what did you use. ideally about 1.5 ltr canister concave on the inlet side and convex on the out side.

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Originally Posted by clean32

:D:D:D:D:D Guess what my last job was

not inccorect just an example, if i was to use your temp it would just look worce..

Clear as, if you have equal pressure hot side and cold side, logic would say that you have no resistance or in this case less resistance hot side.
no pressure build up no resistance no energy for the turbo simple.

you said you damped down your Gage, what did you use. ideally about 1.5 ltr canister concave on the inlet side and convex on the out side.

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So your last job was heavy on thermodynamics but you're struggling with turbocharger operation?
Brayton cycle will give you everything you need. Come back when you've run through that with the pressures and temps I've given.
Remember there's a piston engine in the middle, not just a heated combustion chamber.

I used a line restriction to damp out the pulses.

If you don't believe me and my results, take a look at the ramblings of someone who does it for a living. Like this guy:
TDIClub Forums

Or maybe Buchi's law of turbocharging:

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Originally Posted by buchi

choked flow excepted, the turbine pressure ratio in relation to the compressor pressure ratio is a function of the total turbocharger efficiency and the turbine inlet temperature.

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