O2 sensor/air fuel meter with 100LL?

I noticed in a video that FlyCorvair recently posted that WW advocates installing an air/fuel meter that runs off of an O2 sensor. Now, admittedly, the sensor is not mounted inside the main stream of exhaust, but rather is in an inch-long port welded up to the pipe. My question is, is that enough for the lead in the exhaust to not have a negative effect on the O2 sensor? OR... Is this just one of those things that will have to be replaced every 300 hours, sort of a sacrificial part in order to know what you want to know.

 

It will be a sacrificial part if used with 100LL. Life will vary tremendously, so you should probably avoid using it as an important part.

 

I think WW is still using carbs as he's always hated the idea of EFI on Corvairs, going as far as writing a ridiculous piece on the subject a few years back which I wrote a rebuttal to on my website.

Yes, lead lowers the lifespan of WB sensors substantially, Bosch publishes some guidance on this subject.

We've seen some go over 300 hours with proper care and some fail in 2 hours, though this may be due to thermal shock by lighting up the heater on startup which the auto OEMs don't do.

We've seen narrow band sensors last over 450 hours on 100LL. Narrow bands (0-1V, non linear output) are not very accurate compared to WBs (0-5V linear output) and are pretty well obsolete in the tuning world.

 

if the plan is to run 100ll, use the sensor to map the efi but don’t run closed loop. Not a lot of variety is needed once mapped out. If you were going to mix auto fuel in, you can have alternate maps for certain percentage mixtures. Just change maps.

 

I think you guys might have misunderstood my question. In the video, WW is showing an oxygen sensor mounted on the exhaust that is connected to a fuel meter that would be mounted in the panel. I am assuming it is some sort of fuel burn meter, as in gallons per hour but I could be wrong. The reason I am questioning this is I thought I had seen in the past where he advocates using leaded gas, yet he is installing a meter in the panel that runs off an O2 sensor.

 

The WBO2s can be used to run a meter to accurately indicate air to fuel ratio. With leaded fuel, the sensor will have a finite and somewhat unpredictable life. To run a meter that isn't flight critical, that is ok. I'd be inclined to use something like that to learn how EGT varies with AFR at various power settings. Your AFR meter goes down, switch to using EGT.

 

A stand alone meter would allow you to tweak the mixture if using auto gas. Maybe the engine builder chose to run pump gas. Or maybe its a temporary setup to dial it in. Link?

 

Sorry... Should have done that to start out with. Again, he doesn't say it in THIS video, but I have either read or heard him say something to the effect of "these engines were invented when cars ran on leaded fuel, so there's no problem running leaded fuel in them as flight engines."

 

He says its for his exhaust system and I know he prefers carbs and he refers to using the egt as well so I'm inclined to think he is using it to tune the mixture along with the egt. It pretty obvious on the test stand. But is it being used with 100ll permanently?

 

Affordable stand alone wideband O2 sensor kits have been around to tune engines for around 15 years now however I hardly see the point with a carb. The difference in power between 11.5 and 13 AFR is hard to measure. Anyway, it's well know that O2 sensors don't enjoy lead. This is not hooked up to anything other than the meter on his panel. It reads AFR directly.

I watched the video. WW is incorrect on several points about these sensors:

1. You don't need to ground these with a ground strap. They are electrically grounded internally using one of the 5 wires.
2. Not all O2 sensors are 18 X 1.5mm thread. Most are but some use a 2 hole flange mount- like millions of Toyotas.
3. The sensor is mounted into the exhaust stream on almost all OEM applications (tens of millions of them). A slower response time results in moving them out of the stream but when just using it to tune a carb, this isn't important. Moving the sensor out of the stream may extend life when using leaded fuels.
4. It looks like WW doesn't have 12 inches from atmosphere with his sensor installation. This is a no-no as flow reversion can contaminate the sensor and make it read leaner than true AFR.

There is nothing worse than believing in instrumentation which is not reading accurately when it comes to tuning engines.

 

Some engines need lead for decent exhaust valve and seat life. Other than that, they can run on either. Rebuild your engine with valves and seast that don't need lead, no need to to use it anymore. Modern engines can run leaded, though if they use an O2 sensor, those are adversely affected.
O2 sensors have a required temperature band to operate. They are located some distance from the engine to sit in that band. Too hot, move it away. Too cold, move it closer. With the long exhuast systems of cars, there is a spot that is Baby Bear's porridge.

 

100ll is ok for the engine. There is no issue there. The issue is O2 sensors are of a generation after leaded car gas. Catalytic converters can’t run on 100ll. There was no need to to develop an O2 sensor to use 100ll. Using an O2 sensor can be somewhat handy but it is only going to give an average of how many cylinders are tied to that pipe up wind of the sensor. Airplanes tend to run temp sensors. At work we run one in each exhaust, each cylinder head, and one on the turbo inlet. The mixture is extrapolated from that crossed with the fuel flow. If you want the efi to run on an o2 sensor like your car, you either have to run unleaded gas or be ready for the engine to run on a limp home mode when it gets fouled.

 

If we weren't such a niche market someone might have adapted optical O2 sensors for ICE on 100LL. It looks like the physics would work, but probably needs $^ to develop.

 

With everything, all it takes is $$$$$$.

 

Thank you all for your responses. I still contend he is advocating for running this in plane, and not just on his test stand. That is what I infer by this video. After all, he is talking about the proper weldment of it on your exhaust system. He may also be implying that it should be only used with Autogas, but he doesn't explicitly say that, which is what I was hoping to get all of y'all's opinions on. I just like it when people get very explicit so as not to publish (accidentally) contradictory information.

Anyway, good discussion.

 

If you have any doubt what he's saying or perhaps implying, why not ask him? Pretty sure his email (maybe even his phone number) is on his web site. William is also a member here; you could try sending him a PM.

 

Consider maybe what level the project you want and how it stacks up to what you are comparing it to. Most Corvair powered airplanes are hobbyists planes to the core. They are truly experiments. An O2 sensor in a carb engine is nice but unnecessary to be safe to fly. Engines have been tuned by ear since the first flight. A gauge just takes the skill and guess out some. If it is efi, it just became a primary requirement. Now you can’t have it fail to the detriment of safety. Now your life is in the hands of that sensor. No offense to the Corvair fliers out there, I love you and respect you, but y’all are cheap bastards. That is the whole point. An O2 sensor setup is $50-150; much cheaper than the $1200 one that I work with. One way is a cheap way to have nice to know information; the other is a required safety item. Same part. Different use and intent.