Machines with turbos- do you let them idle before shutting down

[JerryMT]

Jerry, I think what you've stated is absolutely true, theoretically I wholeheartedly agree that theoretically it is possible. However I think I've showed mathematically that there simply isn't enough pressure at the turbo to make it spin. Even if we ignore all of the real things that are going to cause pressure drop from the intake to the turbo.
So for the sake of discussion,

1. Do you agree with the calculation of intake pressure at 60mph? if not lets discuss.
2. For simplicity, I have assumed out all of the physics that lower intake track pressure and still cannot get to enough pressure to spin a turbo. If we account for all of those the pressure will be way less than .43psi at the turbo
3. Do you agree that the tangential force is measured in psi or some other force i.e. mmH2O, inHG or whatever unit you prefer and that if there is not enough tangential force, psi, to turn the turbo then it will not turn?

Here's what I got:

1. q= 0.0638 psi

2. I don't understand what you are trying to say in 2. above. It sounds as if you assumed that there is not enough pressure after the losses to turn the turbo, yet you have no way of calculating the losses

3. The tangential force is not cause by a pressure per se. It is the result of a change in momentum in the tangential direction cause by the blade turning the airflow with a component in the tangential direction. Static Pressure is a scalar and it acts in all direction at a point it doesn't know direction.

 

[BAP]

adventure bob, are you certain enough with your theory to back it up financially? You keep saying it is impossible to ruin a turbo by not covering the stack when hauling, yet many manufacturers tell you to cover them or risk damage. Unless you are absolutely certain or an engine engineer, you probably should not be telling everyone that the manufacturers are wrong unless you are willing to foot the bill. Some people read these forums and believe they are the final word because they feel if others are doing it it has to be true.

 

[JerryMT]

Man...my head is spinning like a turbo...

I'll just follow the directions and guidance that's printed in my owners manual thanks...


Transporting Machine on Trailer
c CAUTION: Avoid injury! Use extra care when loading or unloading the machine into a trailer or truck.

Close fuel shut-off valve, if your machine is equipped.

IMPORTANT: Avoid damage! Transporting a machine on a trailer or on a truck bed at high speeds can result in hood or engine cover raising and possibly coming off machine if not secured.

***8226; Position machine on trailer so hood or engine cover opens from rear of trailer to prevent wind from blowing hood or cover open.

***8226; Secure hood or engine cover with existing machine locks or latches.

***8226; Secure hood or engine cover with tie down straps if no locks or latches exist.


NOTE: Use a heavy-duty trailer to transport your machine.

1. Raise implements, if installed, before driving onto trailer.

2. Back machine onto heavy duty trailer. Position machine so hood will not raise in wind while being transported.

3. Lower any implements to trailer deck.

4. Lock the park brake.

5. Stop the engine.

6. Remove the key.

7. Close the fuel shut-off valve.

8. Fasten machine to trailer with heavy-duty straps, chains, or cables. Both front and rear straps must be directed down and outward from machine. Trailer must have signs and lights as required by law.

9. Plug exhaust pipe to avoid unintended turbo spinning and damage.

9. Plug exhaust pipe to avoid unintended turbo spinning and damage.[/QUOTE]

That's how this started. My NH TD95D owners manual has similar language and I related that. It makes perfect sense to me.

 

[adventure bob]

BAP, I'm not saying it cant happen and have even posted in concurrence with Jerry that it is theoretically possible. His statement of the phenomenon is accurate. I have not once said that the manufacturers suggestion not be heeded by anyone. However there's a lot of manufacturer suggestions that are legalese and not technical that folks on this forum public advise disregarding everyday.

One of the reasons that we went down this tangent is to discuss it with some realism. Its possible for your house to get hit by an airplane, but not real likely due to a host of reasons. Its possible for you to windmill your turbo when towing but not real likely, for a host of reasons. First and foremost is that towing a tractor on a trailer cannot generate enough force in the intake tract to make the turbo spin.

I agree with you on your statement about folks and the internet and I wholeheartedly agree with you that they should not, not, not, take anything anyone posts as gospel unless they can get behind, prove it their satisfaction or at least have a logical rationale as to why they've made the statement.

I am willing to bet you a beer that there you cannot get enough pressure at the turbo to make it spin if you tow the tractor at 60mph. If you'd like to get really geeky about it, Ill bet you the cost of the experiment to prove it. If I win, i.e. there's no pressure at the turbo when towing, you pay for the cost of the experiment. If you win Ill eat the cost and buy you a beer. All funds to be distributed by pay pal. Deal?

 

[adventure bob]

Jerry,
1. q= 0.0638 psi. Mine was a little more conservative and is possibly due to ref. So lets use your number: .0638psi. This has to be multiplied by the area of the intake duct. Remember I said lets use a 3inch (7.068sqin) duct. That gives us using your number .45 psi in the intake. Im good with that if you are.
2. I don't understand what you are trying to say in 2. above.
Do you agree that each thing that I have said is an assumption for simplicity sake imparts a drop in pressure? We can calculate all of those pressure drops, I showed for example what the measured pressure drop of a really good performing air filter is. We can calculate drop due to friction in a pipe, we can even calculate the drop over the valves with a general model, or if we know the valve area and lift at overlap we can calculate it exactly. My point is that at 60MPH you get about .45psi input to the system and we were really optimistic and ignore all the pressure drops, the most pressure we can have at the turbo is .45psi. I do not think .45 psi is enough to make it spin.
3. The tangential force is not cause by a pressure per se. This is where you loose me. Force has to be measured by something. In our case its the force, i.e. pressure of the air, moving through the intake, through the engine and onto the face of the turbine. If its tangential force, it is certainly a scalar value, direction and magnitude or it cannot be tangential.

 

[adventure bob]

Does anyone have a service manual for a turbo tractor that can tell us what the intake manifold pressure at idle is? We can use this to establish a comparison. If you post pls post model and intake pressure, should be in inHG or mmHG.

Thanks

 

[JerryMT]

Jerry,
1. q= 0.0638 psi. Mine was a little more conservative and is possibly due to ref. So lets use your number: .0638psi. This has to be multiplied by the area of the intake duct. Remember I said lets use a 3inch (7.068sqin) duct. That gives us using your number .45 psi in the intake. Im good with that if you are.
2. I don't understand what you are trying to say in 2. above.
Do you agree that each thing that I have said is an assumption for simplicity sake imparts a drop in pressure? We can calculate all of those pressure drops, I showed for example what the measured pressure drop of a really good performing air filter is. We can calculate drop due to friction in a pipe, we can even calculate the drop over the valves with a general model, or if we know the valve area and lift at overlap we can calculate it exactly. My point is that at 60MPH you get about .45psi input to the system and we were really optimistic and ignore all the pressure drops, the most pressure we can have at the turbo is .45psi. I do not think .45 psi is enough to make it spin.
3. The tangential force is not cause by a pressure per se. This is where you loose me. Force has to be measured by something. In our case its the force, i.e. pressure of the air, moving through the intake, through the engine and onto the face of the turbine. If its tangential force, it is certainly a scalar value, direction and magnitude or it cannot be tangential.

1. Your need to go back and look at the fundamentals, Bob. I don't know what you are doing to get a dynamic pressure of 0.064 to 0. 45 but it is wrong. This would violate thermodynamic principals.

2.With q= 0.064 psi psi for q, the stagnation pressure would be 14.7 + 0.064 = 14.764 psi. How could you possibly have a pressure higher than stagnation pressure in the supply duct without any work input. It simply cannot happen.

3. Certainly there are pressure forces along the surface of the compressor blade as a result of the flow over that surface. It like lift on a wing
But if you integrate those surface pressures, the resultant force will have a component in the tangential direction that will cause the blade to move in that direction IF the frictional forces are less than the tangential force.

Despite all the evidence to the contrary you want to assume your way to a conclusion that you want. You do not have the data to do a duct analysis and if you did have such data, I would advise you to look at a good text on internal fluid dynamics, because, respectfully, you analysis thus far is faulty.

if you want to continue this discussion, send me a PM.

 

[adventure bob]

PM'd you on the subject.

 

[BAP]

In the long run, you are better to do what your owners manual says to do. It has all the information that the manufacturer and designer of the tractors want you to know and recommend that you do. It will give you the best life out of your investment.

 

[adventure bob]

BAP, sage advice.
However please consider the very real condition that the owners manual is there to also protect them legally and may not be based on any reality other than a previous claim lost by them that resulted in a payout to a customer. Same reason your lawnmower says "do not stick hands or feet under the deck while the blades are spinning." That's not there to help you, its to protect them from a law suite.

 

[spacemanspiff]

i had a deere 310 turdo for 10+ years. Hauled it with out a cover over the exhaust for thousands of miles and never had a turbo or engine problem. I rebuild the part where the backhoe swings twice.

Have you ever spun a turbo with your finger? It don't freewheel very good The ones I have were on a ford truck and were either new or in bad shape.