[happytech]

OK - we know that the proper A/F ratio for a gasoline engine is 14.7 (or thereabouts) to 1. I'm curious how having to burn fuel with ethanol would affect that. The proper A/F ratio for ethanol is 9:1. Since our fuel typically has up to 10% ethanol, should the ideal A/F ratio be something more around 14.2:1? * In other words, if we're running our machines on a fuel that they weren't originally designed for (hence the 14.7:1 ratio), wouldn't it make sense that they should be run on a slightly richer mixture for best performance?

I know, my mind comes up with some strange questions but still, I find it interesting to think about such things.


* Pure gasoline - 14.7:1 and ethanol - 9:1

So, attempting to do the math, ((9 * 14.7) + 9)10 = 14.2 (or thereabouts).

 

[Bolzen]

But ethanol enriched fuel is not usually a constant blend but varies from station to station, season etc. somewhere between E60 and E90. You have to be sure that your using the same mixture to effectively reprogram ecu

 

[Elliott Larron]

I Accidentally put Premium gas in the tank, Once.

 

[ChipDoc]

I did the same a few weeks back; I didn't look up at the pump and was amazed that I'd put over $15 in the tank. But after kicking myself, I figured it'd be interesting to see how it affected mileage. It was terribly disappointing to see it affected it hardly at all and slightly for the worse if anything.

Not repeating that experiment, but I will eventually try non-ethanol.

 

[Elliott Larron]

I did the same a few weeks back; I didn't look up at the pump and was amazed that I'd put over $15 in the tank. But after kicking myself, I figured it'd be interesting to see how it affected mileage. It was terribly disappointing to see it affected it hardly at all and slightly for the worse if anything.

Not repeating that experiment, but I will eventually try non-ethanol.

Tried Super-Unleaded ,did not Notice any improvement Chip, But does Smell very bad.

Elliott,

 

[symtastic]

I have tried both 87 and 93 plain gas no ethanol ad can't tell any difference except in my wallet!! When I picked mine up in N.C. on the ride home I stopped for fuel and every station I went to (about 6 or 7) had ethanol, I ask someone about it and he told me I had to go about 20 miles down the road to find plain gas, so I went ahead and half a tank. didn't like it and neither did the 650, poor performance! Jay

 

[miken6mz]

In an engine equipped with an oxygen sensor, when the system's in closed-loop mode, it should automatically adjust the mixture ratio to compensate for that government-mandated s**t that's diluting the gasoline. I thought my K4 (no oxygen sensor) got better mileage burning pure gasoline, but when it got cold here the mileage went to h**l anyway, even on pure gasoline. Maybe I can do more measurements next summer, if we have one that is.

 

[happytech]

The reason for the question . . .

miken6mz, I forgot (another senior moment here) that the O2 sensor would help compensate. However, the sensor/ECM are programmed to run about 14.7+ regardless of how much corn whiskey is in the mixture. That being said, my curiosity was just a fanciful idea that if we have to use a diluted fuel (ethanol) and since ethanol has a lower optimal A/F ratio (9:1) if that wouldn't change the actual optional A/F ratio for a 90/10 gas/ethanol mixture?

If there was a lower A/F ratio for this mixture (giving 10% as a constant, for the sake of calculations), then having the ECM programmed at 14.7/14.77:1 would lean out an already lean mixture even more.

My last road trip, O2 sensor installed, gave me a spark plug that showed signs of too lean a mixture. Now, with the O2 out and the mixture set to around 13.8:1, I'm running a more normal plug.

Again, this is one of those questions that was put out there simply because I'm curious, I almost failed physics in high school and I've never had a chemistry or engineering course in my life. I'm just a curious type of fellow who likes to tinker.

BTW, the original question had nothing to do with the octane level of the fuel, just the mixture of it.

 

[Bolzen]

your right, tech -- the a/f ratio will be higher (more air) with ethanol blended fuel. if you meant if ecu changes it internally, i don't think it does. you need to reprogram it manually. However as i said, you don't know what composition exactly to reprogram it to, since fuel mixture is not constant

 

[happytech]

true, however . . .

True, bit if one is going to err, I would think it would be better to err on a touch rich than lean. That's why I would use a constant as 10% ethanol - the pump stickers say that it can be up to that. Just my thoughts.

 

[miken6mz]

Here's an anecdote on the rich/lean thing versus engine damage etc. Airliners such as the Super Constellation and DC-7 used a turbo-compounded piston engine with direct fuel injection via a mechanical system (quite amazing for late 1940s technology). When the aircraft reached its cruise altitude, the flight engineer would manually lean out each engine until he saw a 10% power drop. Actually it was a 10% brake mean effective pressure (BMEP) drop (they had torquemeters) but whatever. The result was better fuel economy and lower cylinder head temperatures, and longer engine life. Leaner mixtures run at lower combustion temps, and the highest combustion temps occur at the stoichiometric ratio which is about 14.7 as you say. From 14.7, either richer or leaner means lower combustion temp. The flight engineers avoided stoichiometric mixture at all costs -- that's where detonation was most likely to occur. The direct-injection engine was the only one that could be operated this way, because it was the only one that guaranteed precise/correct mixture ratio to all 18 cylinders. The original version of this engine (non-compounded, used on the B-29 and others) had such terrible variation in mixture ratios that some cylinders would be too rich, others too lean, and some detonating at stoichiometric. As my B-29 crewman dad used to say, the communist Migs didn't have to shoot at them over Korea, just wait for the engines to fail.

As fantastic as the turbo-compound engine technology was, the Super Constellation (4 engines) was sometimes called "the most beautiful tri-motor in the sky."

 

[Bolzen]

it would be better to err on a touch rich than lean. Just my thoughts.

"You are richer than you think"
Scotiabank (c)

Could be, the manufacturer always tune engines to better fuel economy anyways

 

[happytech]

Maybe so, but gee, how many complaints do you read about (may even had experienced) with bikes not running well due to mfgs leaning out the mixture so much to meet EPA standards.

Again, what can you say - it was a probing question.