Break pressure to timing relationship - how many degrees per Bar?

[TylerDurden]

How many crank degrees difference in timing does a reduction/increase in break-pressure make? (i.e. 155bar sprays x-degrees later than 135bar)

Anybody got numbers?

(I expect it takes a line-sensor & timing light to determine.)


Thanks in advance,
TD

[bbob203]

watching

[libbydiesel]

I don't have numbers for you, but do have the equipment for testing.  How will knowing the degrees help you?

[TylerDurden]

Let's say, I know my break-pressures are 140bar...

If spec is 155bar and I know the shift of diminished or increased pressure; I could adjust the timing the shifted amount of crank degrees from spec timing, so start of injection is corrected to the off-spec pressure.

[Blownoiler]

It would be interesting if someone with some experience/knowledge  could comment on how the flame speed/pressure rise in the chamber would be affected by the different injection pressure as well as the timing issue! Anyone?.........

[libbydiesel]

Let's say, I know my break-pressures are 140bar...

If spec is 155bar and I know the shift of diminished or increased pressure; I could adjust the timing the shifted amount of crank degrees from spec timing, so start of injection is corrected to the off-spec pressure.

You can extrapolate fairly well between the 135 bar timing spec and the 155 bar timing spec and come up with the dial indicator reading for a pressure between them.  I will say that it is not linear as you raise the pressure above the 155 timing spec, tho.  I haven't tested below 135 bar.  As far as actual crank degrees, I have a pulse adapter and timing light with advance function, but you'd have to do a better convincing me of the usefulness of the measurement before I'll take the time to comparatively test injectors of differing break pressures. 

[TylerDurden]

Let's say, I know my break-pressures are 140bar...

If spec is 155bar and I know the shift of diminished or increased pressure; I could adjust the timing the shifted amount of crank degrees from spec timing, so start of injection is corrected to the off-spec pressure.

You can extrapolate fairly well between the 135 bar timing spec and the 155 bar timing spec and come up with the dial indicator reading for a pressure between them.  I will say that it is not linear as you raise the pressure above the 155 timing spec, tho.  I haven't tested below 135 bar.  As far as actual crank degrees, I have a pulse adapter and timing light with advance function, but you'd have to do a better convincing me of the usefulness of the measurement before I'll take the time to comparatively test injectors of differing break pressures. 

No worries... if you stumble over it, feel free to share.

Some folks like to set timing with the sensor and light, since it gives the true indication of start of injection, regardless of break-pressure... if injectors are spec, timing can be set to spec.  But if the break-pressure is known and the bar:degree ratio (within a reasonable range) is known, the timing can be set to start injection 12^o BTDC (or whatever preferred) easily without the variance of hilbilly technique, even if the break-pressures are off spec.

[TylerDurden]

It would be interesting if someone with some experience/knowledge  could comment on how the flame speed/pressure rise in the chamber would be affected by the different injection pressure as well as the timing issue! Anyone?.........

It's pretty well established that higher pressure injectors open later. We broached a bit of that recently... pressure, lift-off, soot and whatnot.

http://www.vwdiesel.net/forum/index.php?topic=32715.msg303232#msg303232 (The following post points out the docs linked are DI focused, but some info is relevant.)


There are some official Bosch docs online that also have a bit of that info.




The same question I asked, was asked back in 2004, but that might have been before a number of members had the fancy gear to determine the relationship of pressure:degree...
http://www.vwdiesel.net/forum/index.php?topic=56.0