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.

 

Ross at SDS is the authority on this...The heated exhaust gas oxygen sensor is great for helping get the base open loop calibration right. After that it depends on fuel being used. Two approaches are run.

If you are running unleaded fuel (auto pump gas) your HEGO may last a long time. At cruise and descent power settings, you can lean based on it, maybe go closed loop even. If it is protected from full exhaust gas temps, it could last a long time. Full power for take off and initial climb, you will run open loop run rich.

If you are running 100 LL, you can use the HEGO output to get your open loop programmed and tuned, but the lead will kill the HEGO eventually. Once you have it programmed, you will probably just remove the HEGO and plug the holes. No closed loop if the HEGO dies...

Billski

 

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?

 

Again, Ross is the authority here. As I understand it, the EGO/HEGO have two things killing them. Lead and heat.

On auto gas in cars, where they do not normally see extended periods of high temps, they can run the vehicle lifetime. In an airplane where they run all the time at high power and temps, these sensors might have shorter life unless they are kept a little cooler, which the extension might give them.

Run them with lead and they will have short lives. Good for calibrating. I suspect that finding structural ways to keep them cooler might cause them to be poisoned with lead even quicker...

Either way, they should probably only be considered a calibration aid in airplanes.

Billski

 

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.

 

Should not be...

Let's define terms. Open loop mode is where the ECU is calibrated to give your mixture based upon operating variables - sensor inputs for engine speed, air flow, etc. Open loop is not tuned as you operate.

Closed loop starts with and open loop mode programmed to be a safe for all engines, then it learns your engine and adjusts both the base programming and adjusts mixture in real time to keep the mixture right on the desired level, usually right at stoichometric.

Most of the EFI systems for airplanes are open loop - with them, the fuel dose based on operating variables is established and programmed using the EGO and EHT, but is not dependent upon the EGO in normal use.

Now if you run closed loop, the ECU is adjusting fuel dose to get a certain mixture during less than WOT with feedback from the EGO. These systems usually usually go open loop at WOT. They should have programming to identify EGO faults and revert to open loop mode, not a limp home mode. This is why carrying over the factory ECU can be a bad scheme.

Some ECU systems that are closed loop on EGO inputs were not programmed to identify EGO faults. What they should do is recognize the faults and revert to open loop programming. If they do not identify EGO faults, they chase the mixture to either dead rich or dead lean trying to bring the EGO back to neutral. Bad.... Most automotive systems now have EGO fault detection, but they may not immediately recognize the fault and get into open loop programming. I really do not like the idea of trusting the programming to recognize the fault or of it taking 500 engine turns before changing over, particularly if I am at 50 feet on takeoff or just pushed on the throttle for a downdraft on short final...

And the EGO in open loop mode is just a gage helping you know your mixture...

Billski