forced induction v.s. injection timing

[gtx1967jewison]

A Diesel guru question here:
With a N.A. diesel if forced induction is added, lets say 5-10a pounds of boost, either via turbo or supercharger, does this necessitate a change in injection timing? If so does it need to be later? Do diesels have rpm-related injection timing advance & is the curve readily adjustable?
Just curious thanks!
J

 

[buickanddeere]

Some diesels don't have advance. That's why they knock so loud when lugged to lower rpms.

 

[LJD]

A turbo IS a supercharger. Just one version that is exhaust driven instead of belt or gear driven.

Diesels tend to run more advanced at higher altitudes when there is less oxygen getting into the engine. So I assume that adding boost and more oxygen means perhaps a need for retarded timing? That being said -none of the diesels I know of auto-advance timing use advance curves any different between turbo an non-turbo.

Many if not most diesels have automatic timing advance. Usually 0 to 16 degrees - just like a gas engine. Stanadadyne/Roosamaster was one of the first to have it = and Bosch paid for permission to copy it the system. When used in tractors like Deere - the auto-advance is easily adjusted with the engine running. On other apps - like GM and Ford trucks - there is no direct adjustment on the outside of the pump. There is however - and outside adjustment screw on the fuel pressure regulator that runs the advance. Stanadyne, Bosch, and a few others use a low pressure rotary vane pump that increases flow and pressure with RPMs. The higher the pressure - the more advance. 0 PSI - no advance. 10 PSI - 2 degrees advance, etc. Goes up to 50-60 PSI. Often the first thing to wear out and stop working.

Raising injector nozzle opening pressure also advances timing. The higher the pressure, the lass injection "lag" and the sooner the fuel charge gets to the combustion chamber.

 

[F-I-T]

I was always told, especially by airplane guys, that a supercharger was like a belt driven Roots blower, while a turbosupecharger, shortened to turbocharger, was exhaust gas driven centrifugal impeller pair. I know one of our plants made different aluminum impellers for land engines, such as the blower on GE locomotives, belt driven, and their blueprint said "Supercharger" Impeller. But heck, it could have been for use in Europe. Curious to hear what others think.

You said "Raising injector nozzle opening pressure also advances timing. The higher the pressure, the lass injection "lag" and the sooner the fuel charge gets to the combustion chamber."

Could you explain this, because it seems exactly backwards in my mind. Like on my old 70 Diesel, the #1 inj is before TDC, and to make it squirt earlier, you have to decrease the cracking pressure. Sorry for being confused.

 

[LJD]

With a spark ignition engine - ignition inside the combustion chamber happens at virtually the same time as at the distributor or coil. That because spark travels at the speed of light. 186,262 MPH or something like that.

In a diesel - there is a pretty big time lag between the source (injection pump) and the combustion chamber. That because ignition time depends on the flow of liquid diesel fuel. The difference between the time the fuel is sent - and the time it arrives is called "diesel lag." The higher the pressure inside the injection lines - the faster the fuel gets to its destination. Thus more pressure = more advance. The shorter the injector lines - also the more advance. That is why attempts are made to keep line lengths equal.

Back to turbos. Anything the raises the air charge about what is drawn in naturally is called "super charging." The guy that invented McCulloch chainsaws invented one of the first practical exhaust driven superchargers (turbo). They were called "Paxtons" at the time . . or . . altitude compensators. "Paxton" was McCulloch's middle name.

 

[LJD]

One more set of comments . .

I have no idea how lowering injector opening pressure on what I assume is a Deere 70 diesel - is going to retard timing. Makes no sense to me. Speed of the diesel fuel increases with pressure. If it's timed with injectors set to open at 2400 PSI, lowering to 2200 PSI makes the fuel travel slower and get there later.

I can see where changing the fuel delivery rate MIGHT change timing - but can't say for sure one way or the other. A Deere 70 uses constant-stroke injector pumps unlike newer equipment that use variable stroke to vary fuel delivery. Fuel setting is changed by adjusting the pumps when fuel actually starts to get pumped within the fixed stroke (i.e. the "effective stroke").

 

[LarrySTN]

LJD.....What???? In one of your posts here, you state that increasing nozzle breaking pressure advances injection timing, in another you doubt that lower injection pressure in a 70 diesel would retard the timing. You sound like a politician. If increasing breaking pressure advances timing then lower pressure would retard timing, no? Truth is the injection pump controls injection timing not the injectors! In reality raising the breaking pressure would have no effect in timing if the pump delivery valve and injection nozzles are in excellent working order.

 

[LarrySTN]

And by the way, spark travels at the speed of light, aprox 186,000 miles per second.

 

[LJD]

Yeah . . . I made one mis-statement while typing in a hurry answering a guestion the guy asked me.
For that one mistake I am guilty.

He asked . . "on my old 70 Diesel, the #1 inj is before TDC, and to make it squirt earlier, you have to decrease the cracking pressure."

I responded . . "I have no idea how lowering injector opening pressure on what I assume is a Deere 70 diesel - is going to retard timing"

I should or, or meant to write "advance",not "retard." Seems it was in direct response to his question that would be obvious.

So, making one mistake in a post and not proof-reading makes me a politician?

Raising line pressure increases fuel charge speed. In fact I have a forumla here given by Isuzu and Standayne for calculating diesel lag (lateness) according to line length and pressure. The lower the pressure and/or the longer the line - the later the injection.

As to adjusting timing? Deere never gave recommendations about adjusting timing with injector nozzle opening pressure. It supposed to run within a 200 PSI range and stay there. If pressure drops below what it should be, timimg gets retarded a bit.

Seems you disagree with physics. I assume when you turn up the water pressure in your house and open a faucet - your water comes out slower??

In regard to your remark informing me of the speed of light??

I already had posted . . "spark travels at the speed of light. 186,262 MPH or something like that." Note I said "something like that."

To be technical - the speed of light in a vacuum is 186,282 MPH. So I was off by 20 MPH and you were off by a lot more. So what? What exactly is your point?

 

[LJD]

Yes, and I already posted it at approx 186,262 MPH. I was closer to the exact number then you. So what?

Did I not post it in the correct "tone" or something?

 

[skip33652]

depends how close to the ragged edge the said diesel is running or how many more hours it is expected to run. but yes generally they need the timing retarded as more an more power is made. look at engines like the older cummins 855 a 290 and a 400 were basically same engine but the 400 had lower compression retarded timing bigger injectors and bigger turbo .other engines were similar. as boost increases the peak pressures increase and the burn time decreases so pump must be retarded.

Generally they did not have advance mechanism but just set the static timing slower.Paul

 

[LarrySTN]

186,000 miles per SECOND

 

[LarrySTN]

The info you quote from stanadyne is concerning END injection as the timing specs are stated as END injection, Increasing nozzle pressure will shorten the during of injection because more pressure will flow more volume through a given orfice, BUT increasing nozzle pressure will NOT advance begin injection which starts the combustion of fuel. Also increasing nozzle pressure will minutely retard begin injection. I am NOT in dispute with pyhsics!