correct

With higher pop pressure there is not a certain value of timing retard. It depends on the engine and its overall condition.

If you set your engine to 15°ATDC that might be a real timing of 18°ATDC because of engine wear. I had that situation more than once, so Tomniks way makes the most sense.

My guess would be you´ll end up at 11-13°ATDC

Gruß
Volker

Happy that you are back.
What exactly do you mean with 'nailing' in this context? Is there a point when there is no doubt that the sound is different at idle? (I mean it all sounds like nailing to me!..well I love the sound of a V8 gas engine...much better)

Or do you mean nailing during driving?
I have advanced now from 14 deg ATDC by 2 deg to 12 deg ATDC with the indicator at the IP port. Engine noise sounds 'normal' to me. This means I am not at the point of 'nailing' yet.

This MB locking tool is really kind of accurate. I was scptical and tested it at my spare IP. It locks the IP at a precision of 0.17 deg! relative to the IP shaft and 0.33 deg at the crank.

I am not sure what Volker says that the cam position of the IP would be off with engine wear... Yes if the chain is stretched an the IP was timed ages ago when the chain was good I understand... but my timing chain is relatively new and the sprockets were not too badly worn when I chanced the chain and adjusted timing last. Without offset keys i could 'almost' align the cams. But in theory the offset keys would only align the head cams to the crank.... wouldn't affect the cam of the IP if the IP is aligned according the service port method or the strobe light....correct?

So... measured in degrees (start of injection) would you guess the 'nailing' is happening? Would this be beyond 26/27 degrees BTDC?

Martin

Hi Volker, very good
I don't quite understand what you are saying.
I was thinking that increased pressure must retard the injection and Tom was confirming this matter.
The logic is that building up a higher pressure takes a tick more time and this tick is retarding the injection. In order to compensate I'd need to advance the injection in order to be at the same timing as compared to the lower pop pressure.
I believe this should not have something to do with engine wear but is a linear relationship between crank (piston position) and IP cam (injection).
Maybe if the IP is really worn out the pump would possibly have a hard time to even produce the higher pressure. Maybe this is what you mean and that might be right.
But I have no experience what these pumps might be able to produce? can the pump make 200bar? Or is there a test in order to know about the condition of the IP? How do I know about the condition of my pump?
Maybe I am asking for too much (producing 150bar) with an 350K engine and most possibly the first IP?
Question: If you say engine wear ...do you mean IP wear?

If I set my crank at 15 deg ATDC it really means piston position at 15 deg...not 18deg. If the timing chain is worn.....say 3 deg...then the cams are retarded by 3 deg (crank) or 1.5 deg (cam).
But if I put crank at 15 deg and lock the tang at the IP port... then the IP is aliged with the crank, no retard here... I think.

Martin

I have one question and this has nothing to do with higher pop pressures.
Lets say we are having a stock engine in good condition. injection timing-start of injection at stock 24 deg BTDC..... What is happening if I advance timing to 27 degrees? Is this the point when the engine will start 'nailing'...? So no good.....I understand.
What would be the reason why people try to get a tick more advanced timing...say 26 or 25 degrees... and engine is not nailing any more (whatever this nailing is). Is the engine performing better?
More low rev torque?
Less fuel ..or higher efficient engine?
What are we talking here 3 % or 5% improvement?

Hi,

let me try to summarise:

stock engine, injectors, good overall condition:

Timing is a compromise: low emission, low noise level. Therefore the combustion pressure peak is somewhere well after TDC.
Regardless emission (this is not necessarily smoke but rather some components) and noise (typical diesel noise, not hard knocking) this combustion pressure peak is preferably just a bit after TDC.

Imagine the cylinder pressure curve over crankshaft angle.
What pushes the piston downwards is the area below the cylinder pressure curve but only the part that is after TDC. Part of this area before TDC means that combustion pressure pushes against the upward moving piston - no good.
On the other hand: Too late combustion pressure peak in relation to crankshaft angle will cause smoke and higher temperatures due to incomplete
burning because of decreasing pressure and temperature in the cylinder and not enough time until BTDC.

Now back to injectors:

No matter when you start injection the essential question is when or where is your combustion pressure peak.
Basically this depends on the ignition delay.
Ignition delay depends on the following:

- temperature in the combustion chamber (higher temps - less delay)
- droplet size or atomisation of the fuel (smaller droplets - less delay but against this: smaller droplets - kind of cooling effect of cylinder temperature)
and maybe some other things...

Temperature in the combustion chamber itself depends on engine condition (compression), rpm as the temperature drop is less at higher rpm (less time for cooling down).

Droplet size depends on:
- nozzles
- elements (actually fuel flow through the nozzles)
- fuel viscosity

In your case the higher pop pressure first delays start of injection and (assuming that the nozzles then atomise better) cool down the temperature (also delays start of ignition) but better atomised fuel burns faster.
All this combined with your engine condition it is impossible to tell you the best timing.


Combustion peak pressure before TDC will knock heavily, so again:
Advance until you reach this and go back 1-2 deg on a warm engine and test drive though all rpm range. The most obvious rpm range for knocking is idle and 1500-2500/min.


The accuracy of your locking tool is only as good as the guy who fixed the fly weights on your IP cam shaft!

Tom

Wow, this is A good summary, well explained. Thanks.
There are obviously many loose ends or 'unknown', even changing parameters
a) condition of injectors/atomization/ droplet size
b) accuracy of IP cam/flywheel adjustment (what is the tolerance of this adjustment?)
c) Temperatures in burning chamber (depending on speed, fuel, compression rate) mostly defining the time delay between injection and combustion..

I think I understand what you are saying.... and I will proceed with 'experimenting' meaning I'll do what you are saying...advancing timing to a point when it starts knocking at lower revs. then back off 2 degrees

What it tells is also: Even with the strobe light you'll face the same diffculties...
you might just eliminate some of the IP flywheel misalignment of the tang..

Now I understand when you talked earlier about a method to measure the combustion peak rather than the start of injection.

thanks again , Martin

the tolerance of the fly weight to cam position? No idea, but even if this is correct it does not tell you anything...
Use all outside measuring methods to verify how much you moved timing on your engine and to make sure that you are within a reasonable range (assuming all parameters are not too far off).

Tom

Tom,

don't you think if this flywheel adjustment was accurate at least it would tell you the IP cam position relative to the crankshaft position.
This would then make you doing the basic adjustment ...what I did. More is not possible without knowing the other parameters.


But indeed this (the IP cam position) is a very limited assumption as you well pointed out. We are missing a few parameters and not sure how many of them are measurable (like combustion). From here (with limited access to sensors etc) only trying out helps....advance and when it starts hard knocking (meaning combustion too early..before piston reaches TDC) then retard 1 or 2 deg. The knocking seems to be the only hard fact indicator of where combustion is... or do you have a more scientific one now?

Thanks... Martin

the issue here is that you just don't know if the position of the fly weights were fixed correctly by the bench man.

the more scientific way is to indicate the combustion pressure peak in relation to TDC. At least for me this is mandatory to design (or later to prove) my element geometry working together in the entire engine set-up.
Together with Volker we did i.e. the measurements attached.
You can see the blue TDC signal and yellow the pressure in the combustion chamber.

Tom

Attached Thumbnails

 

Very cool, so now it is really getting interesting.
In the diagram I see that combustion pressure is 'almost' at its peak before the piston is reaching TDC...peak pressure slightly after TDC.
Would you say this is an optimal diagram for an efficient combustion?
Is this how it should be and if yes what range or 'tolerance' would you find acceptable retarding or advancing injection...
It would be interesting to see diagrams of the same engine with e.g. 5deg advance and retard.

Great... How do you measure combustion pressure in real time..what is the lab setup?

the physical work of the combustion is roughly the area below the pressure curve. You can imagine on the diagram that the vertical TDC line divides this area in a part before TDC and another part after TDC.
The part before TDC retards the piston- so no good. Only the part of the area after TDC can push the piston downwards.
It is clear that the pressure rises instead of just jumping to max.
Pushing all the area after TDC seems to be good at first thought as max physical work is now pushing the piston but only near TDC the internal conditions like pressure and temperature will burn the fuel properly not later on when pressure and temperature decrease. (a good example is a maxed out pump where injection is still going on although pressure and temperature decrease and the fuel ends up in smoke and heat instead of physical work on the piston).

Back to your question if this is optimum: retard: gradually gets less efficient.
Advanced: risk of knocking when even the peak is before TDC or the part of the negative physical work (before TDC) get bigger and bigger. Trail and error or testing will give you the sweet spot.
The diagram is not for adjusting but verifying where we are.


Tolerance of timing? wrong question. You learned that there are no fixed values and it depends on what you want and many open parameters. For top speed priority or super smooth engine run you rather retard, for low end and efficiency you advance...

If you want to see the diagram with +- 5 deg variation, just move the peak by 5 deg. TDC mark to TDC mark is 360 deg.

For the lab setup Volker can inform you. Engine wise I made a fake glow plug with a piece of tube ending in a pressure sensor that Volker brought.
TDC signal comes from an inductive sensor.

Tom

Lab setup is at the moment a 100MHz oscilloscope UTD2102CEL, a few sensors (industrial grade) and a bunch of cables + about 15-20 hours of calculations and labor to make all that stuff work together in a car.
Needless to say it´s not cheap.

Gruß
Volker

While this is normally true, I was seeing high EGT from advanced timing. I adjusted it this weekend and retarded it and saw 200* drop!

Fwiw I saw 1650 on more than one occasion.

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tell us more about the complete setup.
Nozzles?
pop pressure?
IP max. delivery, elements?
Turbo?

Did you hear hard knocking?
was the performance better after retarding?
If yes, the explanation could be: Too far advanced in combination with much fuel. EGT limit is 680 - 700°C on the 603a.

Tom

Whatever injectors are in there. Been meaning to pull them but have lacked motivation. It could easily be that several have low pop pressure. Diesel mekkens 7.5mm second gen I believe. Hx30w. No knocking. No performance seems slihtely decreased. I adjusted about 3/4 a degree.

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

Not so sure about the performance, only have the butt o meter. This morning she was pretty damn peppy. There is a boost or fuel issue of some sort, I had a blip of power loss at WOT.

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42