Exhaust Brake on an M35A2

[DieselInfantry711]

Try this. http://pacbrake.com/exhaust-brakes-how-do-they-work-and-what-benefits-do-they-bring/


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[plym49]

Super, thanks for that.

When the engine is Jaking or Pacbraking, isn't fuel still being injected into the cylinders? Potential washdown or wet fuel in the exhaust that can ignite when you get back on the throttle? How is that handled, especially like in a retrofit as OP is building?

 

[74M35A2]

Only an idle amount because you are not on the throttle.

An exhaust brake valve does not have to mount directly to the turbo. There are factory applications where it is further downstream.

Here is a good single page brochure of it from a Cummins perspective, as it is an option with them, includes braking hp effectiveness. https://quickserve.cummins.com/info/qsol/products/newparts/jacobs_md_nondodge.html

 

[rustystud]

I realize that I can probably Google it, but would someone please explain how this type of engine brake and a Jake Brake works?

Jake brakes open the exhaust valves just before top dead center allowing all that compressed air to exit out the exhaust. It also stops the fuel. So each time the piston is coming up to top dead center the engine is compressing all that air which requires HP and then just letting it go. It can really bring a heavy loaded trucks speed down fast but it is "loud" !!!
An Exhaust brake is just a flap that partially or almost totally closes off the exhaust from the turbo which causes the engine to slow down. In the newer trucks it also shuts-off the fuel with a signal to the ECM.

 

[rustystud]

Super, thanks for that.

When the engine is Jaking or Pacbraking, isn't fuel still being injected into the cylinders? Potential washdown or wet fuel in the exhaust that can ignite when you get back on the throttle? How is that handled, especially like in a retrofit as OP is building?

Like I posted earlier in most modern engines with ECM's there is a signal that is sent telling the ECM to shut-off the fuel.

 

[plym49]

Jake brakes open the exhaust valves just before top dead center allowing all that compressed air to exit out the exhaust. It also stops the fuel. So each time the piston is coming up to top dead center the engine is compressing all that air which requires HP and then just letting it go. It can really bring a heavy loaded trucks speed down fast but it is "loud" !!!
An Exhaust brake is just a flap that partially or almost totally closes off the exhaust from the turbo which causes the engine to slow down. In the newer trucks it also shuts-off the fuel with a signal to the ECM.

Like I posted earlier in most modern engines with ECM's there is a signal that is sent telling the ECM to shut-off the fuel.

That makes sense that a factory setup would have provisions for shutting off the fuel. I am not sure how OP will accomplish that or if it is not considered necessary, in which case I still wonder if even idle fuel accumulating in the exhaust could not pose a problem.

 

[rustystud]

That makes sense that a factory setup would have provisions for shutting off the fuel. I am not sure how OP will accomplish that or if it is not considered necessary, in which case I still wonder if even idle fuel accumulating in the exhaust could not pose a problem.

It's a "yes and no" kind of question. Yes there is excessive fuel going out the exhaust. No I don't think it will be hurt much except for exhaust emissions. Since we don't have to test for emissions that is not a problem. You can have a little problem if your exhaust is extremely hot and you unload a bunch of unburnt fuel into it. You can cause a stack fire which I've seen happen. It was on an extremely hot day and the truck had been used hard for most of that day. It just blew flames for a few minutes until all the fuel was burnt out. Didn't hurt the engine or even the exhaust.

 

[Another Ahab]

IYou can have a little problem if your exhaust is extremely hot and you unload a bunch of unburnt fuel into it. You can cause a stack fire which I've seen happen. It was on an extremely hot day and the truck had been used hard for most of that day. It just blew flames for a few minutes until all the fuel was burnt out. Didn't hurt the engine or even the exhaust.

Too bad there wasn't any time to sell tickets!

I'd have bought one in the front row.

 

[WillWagner]

Only an idle amount because you are not on the throttle.

^^THIS is correct. There is a fueling mode called throttle leakage on the mechanical pumps and "motoring fuel" on electronic engines, Cummins anyway, other manufacturers have different terminology, but it is same same. It is there for a few reasons, one, if there is no fuel circulating, internals will be damaged. The moving parts in the injector are referred to as class fit, they are manufactured together as a unit so the contacting surfaces are uniform, clearances are in the .00001 range. If there is no, zero, fuel delivery, the parts will adhere to each other and you will have a failed injector(s). Think about how many times a single injector is fired at say 2000 RPM, no lube would kill it. Heat, one of the other reasons there is not zero delivery in an off throttle mode. The tip of the nozzle protrudes into the cylinder in a direct injected engine, compressing air to the point of ignition makes alot of heat, the leakage or motoring mode makes the cooling happen.

Don't spread FUD

OP will be fine, no fire out the tailpipe, with a flap style brake installed.

 

[rustystud]

^^THIS is correct. There is a fueling mode called throttle leakage on the mechanical pumps and "motoring fuel" on electronic engines, Cummins anyway, other manufacturers have different terminology, but it is same same. It is there for a few reasons, one, if there is no fuel circulating, internals will be damaged. The moving parts in the injector are referred to as class fit, they are manufactured together as a unit so the contacting surfaces are uniform, clearances are in the .00001 range. If there is no, zero, fuel delivery, the parts will adhere to each other and you will have a failed injector(s). Think about how many times a single injector is fired at say 2000 RPM, no lube would kill it. Heat, one of the other reasons there is not zero delivery in an off throttle mode. The tip of the nozzle protrudes into the cylinder in a direct injected engine, compressing air to the point of ignition makes alot of heat, the leakage or motoring mode makes the cooling happen.

Don't spread FUD

OP will be fine, no fire out the tailpipe, with a flap style brake installed.

Are you saying I'm spreading FUD ? Really ?!?!
Take a good look at the electrical diagram from "Jacobs" . I circled the important part.
View attachment Scan0202.pdf
Your statement that injection pumps circulate fuel is correct, but the part about the injectors is totally wrong. As far as heat on the injector tips in braking mode there is not enough heat generated due to the fact the compressed air is released before ignition could occur or put another way, the air is not hot enough to enable ignition. Second you totally ignore the whole emissions aspect of it. "NO" unburned fuel is ever allowed to leave any engine today. Can you imagine the havoc that would wreak on a catalytic converter !!!! And yes modern diesels have them. Check it out. Really talk about spreading FUD !!!!!

 

[rustystud]

View attachment Scan0203.pdfView attachment Scan0204.pdf

OK, time for a little tech lesson. The average combustion chamber reaches the temperature of 2732 degrees Fahrenheit. That is of course using fuel. Now if we take away the fuel the temperature is only several hundreds degrees of Fahrenheit.
So for those who think the injector cannot handle that kind of temperature and needs some kind of cooling I say take a look at the first chart. That injector is under constant pressure and extreme temperature.
Another thing to consider. The high temperature is "after" the injector fires. It is not before or during but after. That means there is "NO" fuel coming out when it experiences that extreme temperature. So where is the supposed cooling from the fuel coming from ? Yes it helps cool down the injector a bit but that is later.
Now take away the fuel (like say in the operation of a Jacobs brake) and you no longer have the "extreme" temperatures of combustion to deal with, hence no need for any kind of cooling for the injector.
You know, after 4 decades of working on diesel engines I have picked-up a few tid-bits of knowledge. I know there are a ton of "arm chair" mechanics who want to let everyone know how much they know (or think they know) and will go on web sites that supposedly have all the answers and spew forth what they have heard. But actually working on these machines and having to make them work you find out much more then the average web site will ever tell you. Like that stupid wire that came loose and now the Jake brakes no longer work correctly. You know, that wire that "shuts off" the fuel pump for one. Now I'm not saying that I'm "all knowing" . I'm not GOD, and as the years have passed I have forgotten a few things, but I have learned and have been taught a few more things then the average shade tree mechanic knows. You will never find me giving any kind of medical advice, or law, or business management or anything else that I was not trained for. I also will never knowingly give "FUD" advice.

 

[Floridianson]

Both you Rusty and Will are well respected members here on SS so for the sake of our love of the hobby we should play nice. Share learn and have fun.

 

[WillWagner]

This is the switch you circled...

 

[WillWagner]

Modern diesel engine DO put unburnt fuel directly into the exhaust, be it into the pipe just past the outlet of the turbo via separate injector or via 5th injection (dosing) cycle when the exhaust valve is open and evacuating the cylinder of the burnt gasses, That is how the catalyst starts the reaction needed to get the DPF inlet to the required temp to turn the soot to ash, don't care if it is Cat, Cummins, Navistar, Volvo, Mack, Isusu, Deere, Ford, VW, they ALL hydrocarbon dose the aftertreatment to start the process.

The above switch completes a circuit when the throttle is released (at idle position) that allows DC voltage to energize the EB solenoids, it doesn't shut fuel off, drive by wire engines use the TPS to send that signal.

 

[Floridianson]

I would not make a good teacher. The way information is shared should be free to all without attitude or taking it personal. I much rather be a dumb azz about somethings and have the respect of all men then be a no it all and no respect.
Rustystud aka Greg Will has gained a lot of respect here by sharing info without attitude or taking it personal and you have shared a lot too but I think sometimes you take it to personal. Keep the respect and just share the facts.

 

[WillWagner]

Sorry, i'll play nice. Done.

 

[plym49]

What's FUD?

 

[Floridianson]

Farting Under Darkness ?

 

[Another Ahab]

What's FUD?

Farting Under Darkness ?

Floridanson might be right, but I was figuring that the "D" was for data.

And the "FU" part meant that maybe it wasn't the very best of data, and kind of low on the totem pole of quality.

 

[rustystud]

I would not make a good teacher. The way information is shared should be free to all without attitude or taking it personal. I much rather be a dumb azz about somethings and have the respect of all men then be a no it all and no respect.
Rustystud aka Greg Will has gained a lot of respect here by sharing info without attitude or taking it personal and you have shared a lot too but I think sometimes you take it to personal. Keep the respect and just share the facts.

Well when someone says I'm giving "FUD" advice that is not a very nice thing to say. The advice I give is from my decades of actually doing mechanical work. Not something I learned from reading a web site's tech column. If you disagree with something I have written that's fine. I will explain my reasons and usually back it up with actual technical reports. Not just my opinion. Mr. Wagner still has not presented any Technical documentation for his "opinion" will I have. At my age all I have left is my good name and when someone attacks that it does make me extremely angry. So I will leave this now. I will be contacting some friends at Cummins technical to see if they can send me some information on this whole thing.