Air fuel ratio ...link from AOPA

[Jim Peace]

seems interesting. 

https://www.aopa.org/news-and-media/all-news/2018/february/pilot/pe-lean-on-me

[jaylw314]

7 minutes ago, Jim Peace said:

seems interesting. 

https://www.aopa.org/news-and-media/all-news/2018/february/pilot/pe-lean-on-me

I swear I read that very same article somewhere else last year, yet it says Feb 2018.

It's hard to imagine a lambda sensor being helpful for people already versed in LOP flying, and then it ends up being another thing that can break.  It's not really crucial to get the mixture EXACTLY right when LOP.

On the other hand, it would become VERY useful if the sensor could be used to control an auto-mixture device.  Of course, that is essentially the basis of closed-loop mixture control in most automobile engines today.

[jetdriven]

Thats interesting.

IDK if 100f LOP is a 16:1 AFR, that's very lean. I would rather guess a 16:1 is closer to 25-50 LOP.

I always assumed the lead in the fuel would ruin the sensor quickly. Now, im thinking again. I do have a spare tailpipe..

Edited February 21, 2018 by jetdriven

[N201MKTurbo]

Once you go LOP there is no harm going leaner until the cylinder misfires. The power just drops off. 

The claim that the guy in the article went from 11 GPH to 7.8 GPH only because of the oxygen sensor is ludicrous. If he used the leaning method mentioned in the beginning of the article, leaning till rough and enriching till it runs smooth will get you as lean as your engine will get without misfiring. No sensor will change that.

It would be great if we had electronic ignition with an oxygen sensor on each exhaust. We could have perfect mixtures in all the cylinders all the time. BUT, a current fuel injected aircraft engine with GAMIjectors, ran LOP by someone who knows what they are doing, can do just as good so there is no real advantage. 

With a higher power ignition system you could ignite a leaner mixture allowing the engine to run a little bit leaner than it will now. And if the ignition system could advance the spark while LOP it would increase the efficiency even more. The problem is a system that can control all those parameters can malfunction and destroy your engine almost instantly. It can do this by putting it in an overheating or detonation scenario. All that for less power and a little bit more range.

Well, advancing the spark would make a bit more power while LOP.

I've been designing and writing software for industrial control systems for almost 40 years. The more I work with automatic controls, the more I trust mechanical systems. Of course my software is perfect, its the other guy's that has the bugs. 

 

[Cruiser]

1 hour ago, N201MKTurbo said:

Once you go LOP there is no harm going leaner until the cylinder misfires. The power just drops off. 

The claim that the guy in the article went from 11 GPH to 7.8 GPH only because of the oxygen sensor is ludicrous. If he used the leaning method mentioned in the beginning of the article, leaning till rough and enriching till it runs smooth will get you as lean as your engine will get without misfiring. No sensor will change that.

It would be great if we had electronic ignition with an oxygen sensor on each exhaust. We could have perfect mixtures in all the cylinders all the time. BUT, a current fuel injected aircraft engine with GAMIjectors, ran LOP by someone who knows what they are doing, can do just as good so there is no real advantage. 

With a higher power ignition system you could ignite a leaner mixture allowing the engine to run a little bit leaner than it will now. And if the ignition system could advance the spark while LOP it would increase the efficiency even more. The problem is a system that can control all those parameters can malfunction and destroy your engine almost instantly. It can do this by putting it in an overheating or detonation scenario. All that for less power and a little bit more range.

Well, advancing the spark would make a bit more power while LOP.

I've been designing and writing software for industrial control systems for almost 40 years. The more I work with automatic controls, the more I trust mechanical systems. Of course my software is perfect, its the other guy's that has the bugs. 

 

the whole idea is efficiency.

BSFC minimum is around -40°F LOP this varies a little bit but if you are close to that you are getted the biggest bank for the buck from your engine.

Leaner than that just slows you down.

Richer than that just wastes gas.

[jaylw314]

16 minutes ago, Cruiser said:

the whole idea is efficiency.

BSFC minimum is around -40°F LOP this varies a little bit but if you are close to that you are getted the biggest bank for the buck from your engine.

Leaner than that just slows you down.

Richer than that just wastes gas.

I think @N201MKTurbo's point was that you can get to the point of maximum efficiency running LOP without a lambda sensor.  Realistically, the BSFC curve between peak and -100degF LOP is pretty flat, so there are only percentage points differences in efficiency in that range.

[N201MKTurbo]

30 minutes ago, Cruiser said:

the whole idea is efficiency.

BSFC minimum is around -40°F LOP this varies a little bit but if you are close to that you are getted the biggest bank for the buck from your engine.

Leaner than that just slows you down.

Richer than that just wastes gas.

There are a lot of charts out there. They show the BSFC peak at -40 to -65. I'm sure it depends on the individual engine. In all cases they show the peak BSFC very close to where the engine stops working. If you could control the timing you could probably straighten the line out some but we are still talking about a few percent at most.

[jetdriven]

13 minutes ago, jaylw314 said:

I think @N201MKTurbo's point was that you can get to the point of maximum efficiency running LOP without a lambda sensor.  Realistically, the BSFC curve between peak and -100degF LOP is pretty flat, so there are only percentage points differences in efficiency in that range.

I don’t think it’s that flat for all engines. In my personal plane, around 25f Lop is max efficiency. 100F Lop the NMPG is much worse than 25 LOP. I’ve heard pilots say you can set % power with FF only, and that is a lie. I can true 10 knots faster at 1500’ in the Same 10 GPH at 27” of MP than 29”. Same FF. Both LOP. Same RPM. But 27” is ~25 LOP and 29” is 100. 

[N201MKTurbo]

4 minutes ago, jetdriven said:

I don’t think it’s that flat for all engines. In my personal plane, around 25f Lop is max efficiency. 100F Lop the NMPG is much worse than 25 LOP. I’ve heard pilots say you can set % power with FF only, and that is a lie. I can true 10 knots faster at 1500’ in the Same 10 GPH at 27” of MP than 29”. Same FF. Both LOP. Same RPM. But 27” is ~25 LOP and 29” is 100. 

Yea, my sweet spot is 29" and 9.3 GPH. My TIT gets a bit high if I go any richer than that. I can get 185 KTS TAS at 16000 with that. Better mileage than my truck!

[jaylw314]

9 minutes ago, jetdriven said:

I don’t think it’s that flat for all engines. In my personal plane, around 25f Lop is max efficiency. 100F Lop the NMPG is much worse than 25 LOP. I’ve heard pilots say you can set % power with FF only, and that is a lie. I can true 10 knots faster at 1500’ in the Same 10 GPH at 27” of MP than 29”. Same FF. Both LOP. Same RPM. But 27” is ~25 LOP and 29” is 100. 

Yeah, that's a pretty big difference.  I suppose there could be some other factors, but it's more than you'd expect from the theoretical BSFC curve.

[1964-M20E]

he also had the P-mag electronic ignition which plays a role in the equation with variable timing and hotter spark than our ancient alien technology magnetos.

 

 

 

 

[N201MKTurbo]

2 hours ago, 1964-M20E said:

he also had the P-mag electronic ignition which plays a role in the equation with variable timing and hotter spark than our ancient alien technology magnetos.

 

 

 

 

Yes, our airplanes have the same ignition system as my lawnmower. My dirt bike (96 KX250) has a magneto with an inductive pickup that requires no external power. It seems that type of system could be incorporated into our mags without much trouble. It requires an external switch box. It would at least get rid of the points which have been the major failure point on my mag.