Diesel instrumentation

[instarx]

Originally Posted by dcb

"The sensors measure vibration of the fuel line"
Nope, not according to Diesel_John. I found his original post and he says he saw the whole pulse on a scope:

I don't know what Diesel_John thinks, but the information posted on the manufacturer's own site says the meter measures vibration:

For easy engine revolution measurement on 4-cycle diesel engines by clamping the piezo-electric type vibration detector to the fuel injection pipe.

[dcb]

I read the English challenged site too, thanks. I trust Johns interpretation for now, or at least that the pulse width is somehow ascertainable.

[Gravedigger]

The 85 Mercedes was junk but I have purchased a 89 2.5l Auto. I wll be installing a egt gauge Thanks

[diesel_john]

Two different instruments. The piezo I was talking about was a timing light for diesels which I used to verify diesel timing before each sound test. Although the piezo lined steel ring was designed to trigger a timing light from an injector line, I looked at the raw signal on a scope and it clearly showed the entire injection pulse. True a piezo pulse does decay over time and true there is ringing on top of the signal caused by the needle bouncing on the seat in the injector among other system resonances, never the less the entire injection event can be discerned.

[dcb]

Cool, so if we know pulse width, and rpm, do we have enough info to figure out how much fuel was delivered with that pulse (at least relatively)?

I mean anyone can cut a strip out of a radioshack piezo and strap it to a pipe with a hose clamp (might need insulating in spots)

[diesel_john]

As i remember the steel pickup transducer was very stiff maybe 1/4" wide and thick. Found a photo. Looks like two semi circular chunks of piezo with a stiff collar backing it up. Loosening the thumb screw allows the piece to split. The contact area to the line needs to be paint, grease, dent, moisture etc. free. Available in most line sizes for about $60. or make your own. Charge voltages are high so a circuit to change to charge signal to a voltage signal would be good.

[consaka]

Originally Posted by instarx

Those steel-tubing fuel lines expand!? I suppose that's possible, but it sure wouldn't be by much.

Oh - I read the reference. The sensors measure vibration of the fuel line, not expansion. That seems more doable. You'd have a lot of work to do since it counts vibration events - not length of the events. Its response time appears to be 0.5 seconds, which is way slower than you would need. Still, you might be able to use some sort of piezo-electric sensor with different electronics. You could also use a microphone to detect the sound of the injector firing (which in its own way is detecting vibration). This is getting so complicated it might be easier to just buy a new car with OBDII.

Actually vibration is not a good way to describe it. The transducer really does pick up very small pulses of the steel line expanding when the injection even occurs. You are talking about alot of pressure here and it happens pretty fast. If it was vibration then what vibration? because the whole engine has tons of various harmonics and vibrations.
With these older engines the easiest way is to use two zemco like flow meteres and subtract the return line pulse from the supply pulses, take the leftover pulses and feed those into the mpguino. DCB could, I am sure modify the program to count pulses and associate fuel use to each pulse similar to the way we do now. Shoot with my peak and hold gasser injectors thats basically all the mpguino is doing anyway.

[consaka]

Originally Posted by instarx

I don't know what Diesel_John thinks, but the information posted on the manufacturer's own site says the meter measures vibration:

For easy engine revolution measurement on 4-cycle diesel engines by clamping the piezo-electric type vibration detector to the fuel injection pipe.

Ugh, its a case of manual being written by someone in another country. The manufactures site is WRONG. Tell them to re-evaluate that statement and run it by their engineers to get it fixed.
Maybe it got off in a translation or something but that is not the way these transducers work.
If the meter measured vibration it wouldn't work at all for the application because of the fact that there are tons of little vibrations from just about everything. Translation could easily render the pulse produced by the pump as a vibration. If the tiny bit of tube expansion that is picked up by the transducer could be considered a vibration it is still not a good word to use to describe the event. Hitting a gong causes vibrations. A tuning fork makes vibrations. The pulse event from an injector is just that. A pulse event. Not a vibration.
I went to school for this stuff and worked as a diesel mechanic some 15 20 years ago.
I have my doubts that you could pull off a signal good enough to calculate fuel usage from one of those pulse events.

[consaka]

Originally Posted by diesel_john

Two different instruments. The piezo I was talking about was a timing light for diesels which I used to verify diesel timing before each sound test. Although the piezo lined steel ring was designed to trigger a timing light from an injector line, I looked at the raw signal on a scope and it clearly showed the entire injection pulse. True a piezo pulse does decay over time and true there is ringing on top of the signal caused by the needle bouncing on the seat in the injector among other system resonances, never the less the entire injection event can be discerned.

Interesting.. And did that signal change based on load? Thats the test right there. Is it possible for you to capture a idle signal and post it along with a full load signal and post that image as well?

[dcb]

The premise is that the old timey diesel pumps are positive displacement. If the length of the injection event can be determined as well as the rpm (both from the same sensor) then it should be possible to get a relative consumption figure of the fuel that was just squirted into the cylinder. That would be the simplest in terms of installation anyway, but you might have to go through a few tanks to get it dialed in (business as usual for most fuel consumption gizmos)