Diesel engine braking puzzle

[Christ]

You can buy exhaust cutouts and control them with variable resistors.

There are also decent exhaust brakes that can be found on eBay.

[Crazyrabbit]

So if the fuel cut-off connects the high side to the low side, fuel is recirculated within the pump from high to low which is too low to crack open the injectors and the engine cuts off, all components are still submerged in fuel as unlubricious as it is now due to the sulphur removal and all is well as it can be under the circumstances. Meanwhile, I have had a fill-up of in town driving since I put the cut-off switch in, switched to Pennzoil Synchromesh oil in the tranny, and removed two mudflaps. I have also been driving carefully to try to avoid the use of brakes, including using the enhanced engine brakeing when unexpected things happen in traffic, using the fuel cut-off to coast while still having brake and turn signals, and turning the engine off when expecting long delays. My city mileage went from 48 mpg to 55.2 mpg. I've quite stopping the engine at lights because the starter ground a couple of times. I plan on looking into a manual real time idle control next and perhaps the headers/low restriction exhaust/cold air inlet. Keep stretching.

[JasonG]

I can attest that exhaust compression brakes work very well.
They are basically a butterfly in the exhaust downstream of the turbo (yes I saw you are NA) connected to an actuator.
Really demonstrates the effect of exhaust restriction on a diesel.
Google "jake brake" for more info.
Oh, and they're fairly noisy too. Ever been next to a semi in traffic and heard that loud bbbwwaarrrrdrdrdrdrrr sound? Jake brake.
You probably won't find one sized for your car, but they are simple to make out of a biece of pipe, a rod, a 1/8" plate and an actuator such as an old popup headlight motor or an old cruise control actuator.

[Christ]

Originally Posted by JasonG

I can attest that exhaust compression brakes work very well.
They are basically a butterfly in the exhaust downstream of the turbo (yes I saw you are NA) connected to an actuator.
Really demonstrates the effect of exhaust restriction on a diesel.
Google "jake brake" for more info.
Oh, and they're fairly noisy too. Ever been next to a semi in traffic and heard that loud bbbwwaarrrrdrdrdrdrrr sound? Jake brake.
You probably won't find one sized for your car, but they are simple to make out of a biece of pipe, a rod, a 1/8" plate and an actuator such as an old popup headlight motor or an old cruise control actuator.

Check out how a pipe flue works for a wood stove. You can find those for 2" pipes, etc...

Put the rod through the pipe w/ the flue plate on it, tack weld it in place, put an arm on the rod w/ a cable attached to it, hook that to a lawnmower throttle control handle. When you need extra braking, that would be as simple as flipping the handle.

[comptiger5000]

Jason - You described 2 totally different things. An exhaust brake is an exhaust restrictor, and simply makes a mild hissing noise. A Jake brake (the loud type) provides more braking, but it does it by opening the exhaust valve to decompress the cylinders at the top of the compression stroke. Far more internally complex.

[Christ]

I thought the engine (jake) brake kept the exhaust valves closed longer so that the engine had to compress the air twice (bleeding off energy), but only partially the second time before it was let out of the engine in a high-pressure blast through the exhaust valve...

At least that's how I understood it... right or wrong?

EDIT: OK, I just ed-jama-cated muhself. Apparently, it opens the exhaust valve at the top of compression to keep the compressed air from acting like a spring and forcing the crankshaft back down, so the energy bleed happens just from the initial compression of the air intake in the first place.

Thanks for that!

[mechman600]

Originally Posted by Christ

OK, I just ed-jama-cated muhself. Apparently, it opens the exhaust valve at the top of compression to keep the compressed air from acting like a spring and forcing the crankshaft back down, so the energy bleed happens just from the initial compression of the air intake in the first place.

That's correct. A compression brake (Jake Brake being a manufacturer/brand name of compression brakes) is generally a device that sits on top of the valve train. On engines with EUI in injectors (electronic injectors that have their own dedicated camshaft lobe, push rod and/or rocker arm for injection), there is a master piston sitting on top of the injector rocker and a slave piston sitting on top of the exhaust valve of the same cylinder. Since you want the exhaust valve to open near the top of the compression stroke, you can use the injector can lobe to achieve this, as the injector plunger will be beginning movement for a possible injection event. On engines without EUI injectors (PLN, common rail, or HEUI systems), the master piston sits above an intake rocker of a different cylinder - a cylinder that will be beginning its intake stroke at around the same time the cylinder in question is nearing the top of compression.

When an engine braking event is requested by the ECM, a solenoid valve is energized, allowing engine oil pressure to fill the cavity between the slave and master pistons through a check valve, pushing the master piston down against its rocker arm. When the rocker arm is pushed by the camshaft, the oil in this cavity between the two pistons is locked in by the check valve, and a hydraulic link is created which pushes the slave piston and its exhaust valve(s) down. This pressure can reach up to 5000psi during high RPM/high boost pressure braking events. When the ECM wants to stop the braking event, it de-energizes the solenoid valve which blocks the flow of oil pressure to the cavity between the pistons, and vents this cavity to sump so the pistons can return to their normal positions.

The Cummins ISX engine actually has a dedicated camshaft lobe for the compression brake, consisting of two bumps: one that opens the exhaust valve near the top of the compression stroke, and another that opens the same valve at the bottom of the intake stroke. This allows the blast of released compression from one cylinder to scavenge to another cylinder through the exhaust manifold, thus charging the cylinder with 40% more air than normal, increasing braking and reducing noise levels substantially.

[Christ]

Originally Posted by mechman600

That's correct. A compression brake (Jake Brake being a manufacturer/brand name of compression brakes) is generally a device that sits on top of the valve train. On engines with EUI in injectors (electronic injectors that have their own dedicated camshaft lobe, push rod and/or rocker arm for injection), there is a master piston sitting on top of the injector rocker and a slave piston sitting on top of the exhaust valve of the same cylinder. Since you want the exhaust valve to open near the top of the compression stroke, you can use the injector can lobe to achieve this, as the injector plunger will be beginning movement for a possible injection event. On engines without EUI injectors (PLN, common rail, or HEUI systems), the master piston sits above an intake rocker of a different cylinder - a cylinder that will be beginning its intake stroke at around the same time the cylinder in question is nearing the top of compression.

When an engine braking event is requested by the ECM, a solenoid valve is energized, allowing engine oil pressure to fill the cavity between the slave and master pistons through a check valve, pushing the master piston down against its rocker arm. When the rocker arm is pushed by the camshaft, the oil in this cavity between the two pistons is locked in by the check valve, and a hydraulic link is created which pushes the slave piston and its exhaust valve(s) down. This pressure can reach up to 5000psi during high RPM/high boost pressure braking events. When the ECM wants to stop the braking event, it de-energizes the solenoid valve which blocks the flow of oil pressure to the cavity between the pistons, and vents this cavity to sump so the pistons can return to their normal positions.

The Cummins ISX engine actually has a dedicated camshaft lobe for the compression brake, consisting of two bumps: one that opens the exhaust valve near the top of the compression stroke, and another that opens the same valve at the bottom of the intake stroke. This allows the blast of released compression from one cylinder to scavenge to another cylinder through the exhaust manifold, thus charging the cylinder with 40% more air than normal, increasing braking and reducing noise levels substantially.

This is an interesting concept... do you have more information?

[mechman600]

Originally Posted by Christ

This is an interesting concept... do you have more information?

It's a concept that has been used for 50 years. I have tons of information, but most of it is in my head. I deal with this stuff at work; understanding this stuff is what gets me a paycheck.

I could dig up some diagrams or something.....

[Christ]

Originally Posted by mechman600

It's a concept that has been used for 50 years. I have tons of information, but most of it is in my head. I deal with this stuff at work; understanding this stuff is what gets me a paycheck.

I could dig up some diagrams or something.....

Sometimes the old stuff is more interesting and effective than anything invented lately, ya know?

I'm not all that great into diesel engines. I have more than a basic understanding of them, but auxiliary systems related to them are usually beyond me, so anything you could "dig up" would be appreciated.