Fingers, say in a cruising situation where the injector open time is relatively short in relation to degrees of crankshaft rotation, is it better to have the injection timing a negative number so it can end at a certain number of degrees ATDC, or is it ok for all the fuel to be injected BTDC? Also, I think I remember reading where you posted that it is better to have your injection cycle end at 12° ATDC. Does that apply no matter what the injected fuel quantity or whatever? Even if that puts the start of the cycle at 6° ATDC?
Melting pistons.
- Thread starter McRat
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I'm not Fingers, we all know that :angel:, but I think peak cp is best around 12* atdc or even later for me.
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4 to 5 degrees advanced!!
I find that hard to believe, but I was CR schooled by Cummins Industrial, not bosch........ I'd believe 1-2 at the most. The velocity of the fuel from 26000 to 29000 psi isn't going to change much. If anything, you would likely just make for a better atomization of the fuel allowing it to ignite easier and it may advance a little as it ignites sooner but not because it got to the piston faster.
The fuel burn is not a simple on and off event. It ramps up exponentially, reaches a plateau and then fades off. Ideally, you look to get the leading edge of the burn's plateau just ATDC. All the usual factors will determine when that point is. Duration, Rail pressure, RPM, and Boost.
With the pressure monitor you will see a knee when the timing is too late. My goal is to increase timing from that point till the knee in the graph just goes away. This appears to be close to ideal in nearly all cases.
I wish it was that simple, and I might have generalized it that way at one time. But no, correct timing varies with changes in the primary four factors: Duration, Rail pressure, RPM, and Boost.
I probably said that too.
That would have been a generalization and is a reasonable starting point.
Winner Winner Chicken Dinner!:happydance:
Missed you a Stoneboro buddy!
Wanted to come but had other obligations.
I've been wanting to see the Big Stick up close and live.
Very Very true. Being the dubious owner of a low compression engine. I can vouch for that. Actually high enough temps to vaporize THEN flash the fuel.
Wanted to come but had other obligations.
I have missed getting to hang out with you and Tom. Good times.
So best we can do at the moment is calculate crudely from pressure, Temperatures. Still a huge guessing game.
If we can accurately measure cfm/lbs per minute air and we crudely calculate cylinder temps from pressure, we would have a starting point for mm3 injected?
We don't have a good handle on the ways the BTUs are flowing in the Chamber. Some are being absorbed into the piston, walls and head. Some get converted into mechanical power, and still more go out the exhaust pipe. We are not set up to account for them all. Cylinder pressures will only give us the instantaneous temperature at a given moment.
Timing VS Piston drawing
Please for give me. I have yet to figure where I stashed the Mastercam file so no screen shot in pretty colors.
Nor do I have a Scanner. So a picture of a print out is what you get.
What you see is the piston draw in postion to the Injection stream at 3 different timing location. TDC or 0*, 30*, and 40*. The left side of the piston is drawn to the same form as my delipped piston. The right side is drawn with the stock uncut form. You noticed two streams coming from the injector. The upper one is drawn at the stock 156* spary angle. The other at 145*. This drawing is done with the measurement off my race engine. accounting for actual piston protursion, "A" gasket, and actual injector protursion. I drew this back in 2007.
Please for give me. I have yet to figure where I stashed the Mastercam file so no screen shot in pretty colors.
Nor do I have a Scanner. So a picture of a print out is what you get.
What you see is the piston draw in postion to the Injection stream at 3 different timing location. TDC or 0*, 30*, and 40*. The left side of the piston is drawn to the same form as my delipped piston. The right side is drawn with the stock uncut form. You noticed two streams coming from the injector. The upper one is drawn at the stock 156* spary angle. The other at 145*. This drawing is done with the measurement off my race engine. accounting for actual piston protursion, "A" gasket, and actual injector protursion. I drew this back in 2007.
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There is a breakpoint and a downside. The additional O2 from more boost allows the fuel to burn faster, but we only inject fuel at a limited rate. So the instantaneous temperatures will get higher till we run into the available fuel limit. From there, we have a much larger air mass that we have to heat up with our limited BTUs. So the temperature rise starts to fall off.
The downside is as you raise boost, you also increase the chamber temps just from compression. I don't know if the above affect is more or less the increase from compression. It would have to be plotted out to see.
exactly what i was saying 10 pages ago...
i do think this is "a" primary cause of piston failure.
im going to equip my PS car with a data logger that will be able to log, timing duration, RP, Boost,NOS psi.oil temp,low side FP,RPM, clutch rpm, DS rpm, EGT and O2 sensors. i would like to get a CP sensor on there too! an over lay of these paramiters should allow for a very good discussion on how and why things work the way they do in a racing engine.
Any one have prior use of these O2 sensors on a diesel?
Any one have prior use of these O2 sensors on a diesel?
like i said, before the 03-04 has no post injection (after TDC) event. this i belive is the main reason the 03-04's are not melting pistons, but yet the 04.5 and up have multiple shots and post injection, and there melting pistons faster than you can blink.
lets look at the 12 valve, it has no pre, or post injection cycle right, yet it make the most HP right now, with(1) main shot and no melting pistons........
this goes back to what i said in the prior post's making most of your fueling advance BTDC would make more since, and if timed right would save pistons and would act close to the CR dodge 03-04's..........which we both know is making over 1200HP and no melted pistons... get my point of veiw john?
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You don't tune diesels much. Do you Wade.
Here is a plot of a LBZ running the popular 50/50 split on the main. Near perfect, IMO, for this pulse width with only the slightest hint of a knee in the pressure rise as it crosses TDC indicating it needs a little more timing.
The area between the lower blue line (adiabatic) and the black line represents, in rough terms, horsepower. Left of TDC is horsepower to compress the gas and right is the horsepower from the power stroke. Subtract the left from the right.
If/when you push the timing out even more, you will find that the area on the left grows much faster than the area on the right. You will also see CP spike to record heights. (4000 PSI or more)
Here is a plot of a LBZ running the popular 50/50 split on the main. Near perfect, IMO, for this pulse width with only the slightest hint of a knee in the pressure rise as it crosses TDC indicating it needs a little more timing.
The area between the lower blue line (adiabatic) and the black line represents, in rough terms, horsepower. Left of TDC is horsepower to compress the gas and right is the horsepower from the power stroke. Subtract the left from the right.
If/when you push the timing out even more, you will find that the area on the left grows much faster than the area on the right. You will also see CP spike to record heights. (4000 PSI or more)
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Yes, dodges every week.....
im sure your understanding and mine are close i just have a hard time typeing exactly what i think and all the contributing factors of my understanding....ADHD at it's best
Wow. We have a great bunch of members here.:hug:
Normally a tech thread like this blows up far before it gets 180 posts.
Thanks guys. :hello:
Normally a tech thread like this blows up far before it gets 180 posts.
Thanks guys. :hello: