New Technology

[geoffreywh]

A friend asked me if I would weld a bung on his 1976 Bonneville exhaust to take a narrow range O2 probe. "Oh of course" I said and asked all about it. He has a data logger and wants to set up his Amal carbs using the 02 probe and a hand held readout. All the rage according to forums. I thought what a good idea for looking at Jabiru engines' carb issues. Also what a good thing to have in the cockpit with a lean mixture alarm? (or rich) Tuning my throttle body with the mixture control at altitude might be easier than "Lean it out until it misfires then richen up a bit" It looks like they cost around $200.... Any comments?.....BTW it seems that the probe should be about 18" from an exhaust valve...

 

 

[jetjr]

Generally wont work with leaded fuels

 

SDS uses one to setup injection on Jabirus, i think it lasted longer than anticipated

 

With he wide spread of mixtures in Jabiru engines you need towatch each cylinder separately to make sure theres not one way to lean or rich, the average wont cut it.

 

Hence why multi channel egt and cht are so common

 

 

[Downunder]

I sent an email to a company (can't remember which) about setting up one of their kits which had a dash mounted mixture ratio readout on my Rotax. They said it wouldn't work because of the varying altitude, oxygen level.

 

I couldn't get my head around technically why that was the case but left it there. Perhaps the oxygen levels moved beyong their calibrated levels.

 

Might have simply been the mention of the word "aircraft/aviation" which puts off some companies.

 

 

[pluessy]

A straight O2 sensor doesn't have the range to properly display the mixture from full rich to full lean. They have a "tipping point" at the stoichiometric ratio of 1 (=Lambda 1) where the signal changes significantly and that is used to maintain the mixture ratio at Lambda 1. To get the full mixture range displayed, you need a "Wideband" sensor. They are able to display a mixture from Lambda 0.7 to over 2.0 eg full rich to full lean. To just display the mixture ratio, the sensor doesn't have to be in the full exhaust stream, it can be mounted slightly out of the stream and exposed to a reduced gas flow, prolonging the life. At our flying altitudes (10,000'), any error from the sensor due to altitude would be negligible as cars are operating at altitudes of 8,000' without problems.

 

From the Bosch LSU4.2 sensor info:

 

Sensors Used with leaded fuel

 

Depending on the lead contents of the used fuel the expected service life

 

time is: (preliminary data)

 

- for 0.6 g Pb/l: 20 000 km

 

- for 0.4 g Pb/l: 30 000 km

 

- for 0.15 g Pb/l: 60 000 km

 

 

[Jaba-who]

As jetjr says not much use in a jabiru.

 

The major problem in Jabiru's ( and probably other engines too but we tend not to be monitoring all cylinders on a lot of certified engines) is that the individual cylinders can have quite a wide range of fuel mix but it's all mixed together on the output side in the exhaust.

 

So unless you had size or four of them each close to the cylinders all you get is averaged out data.

 

Which begs the question - in the auto field where this is apparently popular - how are they accounting for this phenomenon. Or are they not? Are they just kidding themselves?

 

If they have injectors I suppose you can hope the fuel mix will be the same in each cylinder but if it wasnt - say a (partially or fully) blocked jet to a cylinder you'd be back to guesswork and assuming lots.

 

 

[pluessy]

The idea of the Wideband sensor is to give you the mixture average. You will still need to measure each cylinder in the testing phase (re-jetted carb, throttle body injector etc) to work out the mixture distribution across all cylinders. Even in normal use, an engine that is very sensitive to excessive heat will need CHT and EGT on every cylinder to monitor the operating conditions of each cylinder. On certified engines, through lots of testing the critical cylinder(s) have been determined and they are the ones with the EGT/CHT probes fitted (pre-EMS).

 

The Wideband signal can be used to check the mixture distribution by putting it through an oscilloscope. The response time is fast enough to measure each cylinder if located in the exhaust stream. It won't tell you which cylinder is rich/lean but the variation between them. Pull a plug lead off and you can see which signal changes.

 

 

[Jaba-who]

The idea of the Wideband sensor is to give you the mixture average. You will still need to measure each cylinder in the testing phase (re-jetted carb, throttle body injector etc) to work out the mixture distribution across all cylinders. Even in normal use, an engine that is very sensitive to excessive heat will need CHT and EGT on every cylinder to monitor the operating conditions of each cylinder. On certified engines, through lots of testing the critical cylinder(s) have been determined and they are the ones with the EGT/CHT probes fitted (pre-EMS).The Wideband signal can be used to check the mixture distribution by putting it through an oscilloscope. The response time is fast enough to measure each cylinder if located in the exhaust stream. It won't tell you which cylinder is rich/lean but the variation between them. Pull a plug lead off and you can see which signal changes.

I wonder what help it would be in an air cooler aviation engine though. Particularly jab engines change dramatically in flight. What's happening in cruise changes in climb and at changes of airspeed and oat.

 

Needing an oscilloscope etcmakes me think it's a workshop only monitor so limits its use.

 

 

[Yenn]

Jaba. The EGT and CHT sensors do not average out for all cylinders. EGT sensors are usually about 50mm from the valve and that is in the outlet for only one cylinder.. CHts are mounted on each cylinder and if you only have one that may not be the hottest.

 

With a separate EGT and CHT for each cylinder you can lean accurately, so long as the fuel distribution is even. After take off, pull the mixture well back, even to the point of rough running, then keep steadily advancing it and watch the EGTs. You have to be lower than the max before you leaned it. Best bet is to read up on the theory. As others have said the Oxygen sensor doesn't like leaded fuel, but it should show fuel air ratio at any altitude I would think.

 

 

[Jaba-who]

Jaba. The EGT and CHT sensors do not average out for all cylinders. EGT sensors are usually about 50mm from the valve and that is in the outlet for only one cylinder.. CHts are mounted on each cylinder and if you only have one that may not be the hottest.With a separate EGT and CHT for each cylinder you can lean accurately, so long as the fuel distribution is even. After take off, pull the mixture well back, even to the point of rough running, then keep steadily advancing it and watch the EGTs. You have to be lower than the max before you leaned it. Best bet is to read up on the theory. As others have said the Oxygen sensor doesn't like leaded fuel, but it should show fuel air ratio at any altitude I would think.

We have been talking about O2/lambda sensors installed in the common exhaust pipe - a single one and further went on to mention attaching it to an oscilloscope to detect the pulses from individual cylinders (have been not talking at all about cht or egt).

 

 

[Nico13]

Automotive, an area I work in generally does not have the individual cylinder temp problems that aircraft engines do because of the inherent design and physical structure with their full water jackets and overall mass. Although most modern all alloy engines are a lot lighter they still maintain reasonably stable temps throughout.

 

A single O2 sensor is all that is required for primary engine control and is close coupled to the engine pre Catalytic converter and all its looking to do is control as mentioned previously is stoichiometric ratio of 1 (=Lambda 1).