Oxygen/Lambda sensors

[RFguy]

Has anyone got any direct experience with Lambda sensors  in this rather sooty , poorly mixture controlled service ?

[Geoff_H]

Yes.  I have used them extensively for oxygen trimming controls in exhaust gas systems.  They need constant recalibration, so nitrogen and part oxygen gases to frequently calibrate.  The best systems automatically calibrate.  I am not sure that they would be suited to aircraft, but I think that many vehicles use them.

[RFguy]

Hi Geoff. Thanks for the message .

All EFI vehicles use them of course... yeah I know from my fuel injection experimental days in the 1980s  that they can get contaminated  if something runs amok . That happened in the course of programming up my fuel injection computer (own design) .  Looking at the exhaust pipes of rotax and jabs makes me thing suitability is low for this soot problem. The control loop on them performs a small amount of drift compensation, but there are limits.

 

In something like jabs or rotax where there is considerable variation between the cylinders, one would need sensors in the manifold for all cylinders separately.  (otherwise the average is not all that much use) . Am thinking EGT is easiest telltale here, or short term use of the Oxygen sensor in order to put some numbers against EGT numbers. 

NIR+VIS spectroscopy  would be another option.

 

-glen

 

 

[Geoff_H]

The ones that I used required heaters to keep the element at a constant temperature, around 1600deg if my memory serves me right. I agree that one for each combustion chamber would be needed to get an accurate engine situation.  I don't know what the IC injection systems use.

The early ones were not nearly as reliable as the later ones.

[onetrack]

RFguy, have you thought of a colour sensor? Flame colour is one of the best indicators of correct fuel burn. I can recall owning a small device called the Gunson Colortune Plug, in the late 1970's.

This device contained a spark plug with a glass window, that you screwed into the spark plug hole. You viewed the combustion flame through the window and adjusted the mixture to get the best flame colour.

I see it's still for sale, and still an effective tool - although ECU-controlled EFI has obviously altered the automotive-engine landscape since the 1970's.

I don't know what happened to my Gunson tool, it got lost in one of my numerous location moves (probably stolen) and I went over to mostly diesels, anyway, thus the Gunson device gathered dust.

 

https://www.howacarworks.com/engine/tuning-the-engine-with-a-colortune-plug

[RFguy]

HI OneTrack. I've only read about their existence yonks back.  Thanks for the link. 

 

I would love for the Jab head to have a third "diagnostic" screw port..... Was thinking about how to measure compression before engine start.  If doing hand method- a very small orifice would do the job, because rate of change is small. 

Seems like the easiest way is to measure starter current (once starter  rpm established) , the different compression is very easy to see on starter current.    You can measure pressure by relating the firing voltage of the plug (just to spark- no mixture present) but the plug needs to be squeaky clean to get reliable numbers. Higher pressure = higher firing voltage. 

[facthunter]

Having the throttle closed will lower starter current  needed.  If you have good sealing the compressed gas acts like a spring and you recover most of what you put in. Nev

[RFguy]

yeah good point !

I have done this on a single cylinder motor only before. 

Getting relative numbers it wouldnt matter too much the gulps.  The starter current WILL be seen to spike pushing that piston over TDC on the compression stroke.

 

But. hmm other cylinders will be assisting, aiding and otherwise . IE one on #1 compression stroke , #3 on ....

But there should be useful information.

Remember, I'm talking about high resolution current sensing- a resolution of perhaps 1 degree of crankshaft revolution. 

Might also see it in the torsional vibration measurement ( re purposing of the tacho sensor off the ring gear) .

That can be combined with the hi res current measurement to yield something useful. IE can provide instantaneous tangential   velocity of the crank.

 

 

 

 

 

 

 

 

 

 

 

 

Edited October 6, 2020 by RFguy

[Cooko]

Oxygen sensors will fail after a short time of being exposed to lead. You will therefore be limiting yourself to Mogas.

[RFguy]

yes, MOGAS it will be. Last time I mucked around with O2 sensors, I used "super" .. 1987 ish