I like the idea that you could use an existing part of the car in a way that wasn't originally intended - I can not think of another automotive part that serves two different purposes like this might - so if it were possible to use a glow plug to measure temperature pulses I think that would be great. Though my gut feeling would be that a dedicated transducer that was designed to do the job would do it better.

Even though a glow plug is not intended to make measurements:- For it to do this the output from a glow plug need not have a correct magnitude (corresponding to a temperature) but it would have to be able to react quickly enough to a change in temperature. In electronics this is referred to as rise time. See:-

http://en.wikipedia.org/wiki/Rise_time

The rise time of a glow plug could be measured. As long as it is faster (and hopefully way faster) than the rate of ignition then it could be considered to be a transducer that is capable of measuring the pulses of heat caused at ignition.

To my mind that seems to be step one - ascertain whether a glow plug could in principle measure temperature changes at the rate of ignition.

Step two would be to ascertain when the point of ignition occurs in the cylinder and when the heat has propagated to the position of the thermocouple. So in effect a measurement of the "speed of heat" between the point (or points) of ignition in the cylinder and the glow plug that is positioned in the pre-chamber. I reckon this would be a complicated transfer function to measure.

I think step 2 is of vital importance as if you can not ascertain that the pulses that you can measure with your transducer occur at the time of ignition, then you are not going to be able to reliably use this information to estimate the timing.

In addition to these two problems there would undoubtedly be signal conditioning hurdles to overcome. But I like the idea - no matter how whacky it seems - mainly because it feels like you could almost get something for nothing!

If I can get hold of some decent instrumentation I'll start my own high school science experiment.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

That can be applied to anything, though that doesn't mean its always smart to do so.

Oh I completely agree - it could be a load of old hogwash - but if I can get my grubby paws on some instrumentation then I'm curious enough to see if I can make any sense out of it.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Army, before you spend too much time on that deal... have you visualized what you would actually be measuring and if that would be of any value ? Even if the rise time was very fast..
You do not have a static heat source which the glowplug is in contact with... out of the total 720 crank rotation only a split second is the hot air in contact with the end of the glowplug hot. The amount of heat it will be exposed to will thus be affected by the rpm in addition to all the other stuff....and I can not see how even if everything were in your favor with the physics of the ' thermocouple' your readings would be anything other than a ' dulled' average of what was happening... I think it is more likely you will be measuring convection derived head temperature more than combustion temperature.. or at the very least an unkown ratio of the two..... which itself will probably a ' moving target' as the engine heats up...

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

I agree that it is a complicated situation - I think the transfer function between ignition and the point of measurement inside the pre-chamber makes it particularly difficult. It would be easier if the transducer was positioned in the combustion chamber - but hey that's the way the car has been made. I'm going to see if I can borrow some equipment - I have a cunning plan!

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Army,
Just remember that the hottest combustion temp at idle has no relation to the correct injection timing above idle. kind of makes the whole process futile. Its a bit like adjusting the idle mixture on a gasser, it has little influence when the carby is opened up & on the main jet. If you advance the timing on a gasser it will idle faster, that doesnt show that it runs better at higher rpm.
Generally, higher combustion temps suggest too lean or too far advanced injection.

On my jeep there is a sensor on #1 injector that tells the brain box exactly when it starts to inject. They use this along with the crank position sensor to set the IP timing dynamically over the operating rev range.
The #1 injector looks just like the ones you have except it has a small elec loom coming out of it.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

As a theoretical exercise I will comment on the idea:

* The glow plug is a HIGH temperature heating element, NOT a thermocouple.
* Glow plug failure is common = false data.
* Minimum operating piston cylinder ignition temperature per MB is 850° F.
* Each cylinder is a totally separate environment.
* On an OM617 the math breaks down like this: 850 RPM ÷ 60 seconds = 212.5 power strokes ÷ 5 cylinders = 42.5 power strokes per cylinder = roughly 0.708 second of combustion data per cycle + immediately followed by exhaust (cooling), intake (cooling).

* Please review the reaction time of thermocouples in the following data, and note that it would be considered an insulated unit..


http://hypertextbook.com/facts/2005/EileenTang.shtml

Thanks for the added information - I'll let you all know how far I get. It is a bit like Mythbusters! Unfortunately unlike the Mythbusters I don't have the necessary equipment to hand - but I'm working on it. Don't hold your breaths it won't happen soon. I've got an engine rebuild to finish first.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Reaction time can be taken out of the equation by adjusting the timing slowly and waiting for the results.

That is what I have to do, it is not an instant response.

You guys have no idea what your talking about.
Any alloy of two or more dissimilar metals acts as a thermocouple, and as a resistor.

You guys do not have an ability to think outside of a very narrow view.

I will prove it to you !!

Answer this question,
how can you paint a perfect Mona Lisa with a 4 inch paint brush ?

__________________

When the power of love overcomes the love of power the world will know peace.
Jimi Hendrix

You havent considered the original false assumption that the idle or for that matter at any rpm hottest combustion temp is optimal or is what is best for the motor. It is not. In most cases it would cause the injection to be too early. That is what causes pinging in a gasser. A diesel will do the same thing.
The whole concept of using combustion temperature maximization to set injection timing has no merit, is based on totally false premises & could damage the motor long term. In some applications over fueling is used as a way to keep combustion temps down.
I would suggest that it is you who doesnt know what you are talking about! Your comment about painting highlights this.

Best you go and talk with a diesel design Engineer & stop believing the C##P you read on the internet.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Rich, if you want us to believe you know what you're talking about, it helps if you post some relevant data to support your position rather than attempting to insult anyone that doesn't completely believe you. layback40, leathermang, whunter and I have all provided actual scientific data that disprove your idea and prove you don't know what a thermocouple is or how it works. You claim you're a Kennedy, try to act professionally like one.

[QUOTE=layback40;2644227]You havent considered the original false assumption that the idle or for that matter at any rpm hottest combustion temp is optimal or is what is best for the motor. It is not.QUOTE]

The diesel engine operates on heat. It is heat that drives the piston downward. You are saying hotter combustion temp is not optimal?

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Incorrect, IC engines operate on pressure and leverage. Heat is a waste product.
Even those cute toy fans that spin when you put a candle under them aren't operating on heat, they move from the airflow of the hot air past the blades.


In other words; an engine burning cooler is burning more efficiently. A 100% efficient engine (impossible) would have zero heat coming from the exhaust.

Incorrect. Without pressure, there is no leverage. Without heat, there is no pressure. Atomized diesel is ignited by heat which generates pressure.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Correct; combustion = pressure.
Incorrect. Please explain why compressed air engines work without any heat.

Heat input is only needed for ignition, any further heat production after that point is wasted energy.