Fuel talk - octane, ethanol, etc.

[JasonL]

There were a couple comments made during recent club meetings that I thought I might touch on, and thought that members might appreciate a spot to discuss things or ask questions.
I've worked for an oil & gas major for 25 years - most of it spent in the fuels business. While I wouldn't call myself a technical expert, I have, and continue to work very closely with many - who have been happy to respond to my various questions on fuel and lubrication over the years.

Two items off the top:
Ethanol in gasoline
-Concerns are largely overblown. Ethanol gas has a shorter shelf life than pure gasoline, but if it's getting used in a reasonable amount of time it's nothing to worry about. Don't leave it in seasonal equipment as it is prone to attracting water and separating. For the same reason, never use it for marine applications. Nothing to worry about for go-karts, though - unless you're somehow running a decades-old motor.
-Ethanol has about 2/3 of the energy content of gasoline. What we get from the pump is typically limited to 10% (though some jurisdictions are now moving to 15%), so the effective difference is 3%. A computer controlled engine will adjust flow rates to compensate, so in theory you'd see no change in power, but a 3% reduction in fuel economy. In a kart engine, theoretically, you might see a 3% reduction in power - if you could observe such a thing - but adjusting jetting, etc. accomplishes the same sort of thing - adding more fuel to reach the optimal mixture. In short, we'll never see a difference.
-No one is avoiding it. It's been in Regular gas for MANY years. Up until recently, if you REALLY tried, you could avoid it by buying premium gas at certain brands. That ended in late 2022. All fuel - regular or premium - that you'll find at any service station will have ethanol in it. All majors have ethanol in all their gasolines.

Power loss from using PUL in motors needing only RUL
-This caught my attention when mentioned during our meeting earlier this week - I believe coming out of the recent meetings with the Briggs tuners. I'd love more detail if anyone has some - particularly whether they said what caused this, if they had measured it on a dyno or whether it was purely theoretical, and what sort of fuel it was measured on.
-Octane is simply a measure of a fuels resistance to pre-detonation. This means that higher octane fuels can be exposed to higher temperature and compression than lower octane. If a motor doesn't take advantage of this, there won't be a benefit.
-I suspect that the claim that Briggs motors made less power on premium gas is based around the concept of "flame speed" - which is how quickly the flame caused during ignition moves from the spark plug through the fuel in the cylinder.
-There is generally an inverse relationship between flame speed and octane. So, the flame tends to move slower in higher octane gasoline than in lower octane fuel. As you can imagine, having everything go "boom" at one time will generally make more power than if it is spread over a longer period of time.
-I reached out to a couple of our PQ folks to get an idea of how significant an affect this would be. They couldn't give a specific affect as it will vary by fuel and engine. However:
-The difference in flame speed can often vary more between different gas suppliers than it does between regular and premium gasoline.
-We make a special blend of fuel for an F1 team, and specially optimize flame speed for that engine, as it becomes MUCH more important at high RPMs. Theoretically, engines have a maximum possible RPM, as at some point, the piston speed could exceed the flame speed.
-The impact on a Briggs motor is likely negligible. The motor only spins to ~6000 RPM. The displacement is ~200cc, with a ~9:1 compression ratio, which means that when compressed, the air/fuel mixture is occupying a space of ~24cc - so the flame doesn't have very far to travel during the combustion process. This would be about half what it is inside the cylinders of the 2L, 4 cylinder engines powering the vehicles I've got at home.
-In short, this will likely never be noticed in someone's track time or seat of pants. Furthermore, all CKRC members are required to use the same gasoline, so whatever minimal effect may exist, it will be experienced by all participants, equally. If you're racing somewhere else that allows it, go ahead and use RUL - you won't notice any power difference, but you might save a couple dollars for the day.

[Jackmazury]

Jason,

As always when you speak to fuels, thank you for the concise report.

While not an apples to apples comparison, I am curious on your thoughts regarding the slightly reduced efficiency with ethanol. In an ECU controlled vehicle you generally need more fuel to create the same output from say E85 compared to your standard pump fuels. Based on this theory, do you think there is a likelihood that a similar trend is observed in our application? My general train of thought is that a 125 jet in Rotax for example without ethanol would now equate to 125*1.03 = 128.75. This would seem to align with what I observed last season.

Thanks again for the write-up, always great to hear your thoughts on these things.

Jack

[JasonL]

Jack,
That is my understanding.

Hydrogen atoms in any fuel are what burns. A computer-controlled engine is going to adjust things to hit a certain air/fuel (hydrogen/oxygen) ratio. Ethanol and other alcohols contains oxygen atoms in their molecules, so the computer will automatically increase the amount of fuel it dumps into the cylinder to hit that ratio.
Our karts aren’t computer controlled, so we would need to manually adjust to accommodate. The three percent is likely a good estimate, however, since ethanol brings some additional oxygen to the party, the number may be a touch higher as you’d need even MORE ethanol to offset the extra oxygen that the ethanol brought into the cylinder (the air isn’t the only source of oxygen in this case). Since the next jet up would be a 130, a 128 would be the right choice in your example. If you were somehow running E85, you’d need a much larger jet - and possibly a special engine and fuel system.

There is some math that could be done to get a precise number - but I don’t have it in me at this time on a Friday night.

[Jackmazury]

Jason,

That all makes reasonable sense. That seems to somewhat confirm my suspicions on why the 118 jet seemed harder to make work last season.

It will be interesting this year if the ratio of ethanol fluctuates between 10% and 15% at different points as this difference is roughly a one jet variance as well based on my overly simple math. It could make tuning a touch more difficult.

Thanks again,

Jack

[JasonL]

Alberta’s not on the horizon for E15 right now. If/when it happens in any jurisdiction, it won’t go back again.

[Tjfast]

Jason, great post.

As someone who did alot of work this summer with E-85 research for racing, the info you have added for karting is awesome. Everything you have stated is inline with what I have researched, but I only considered it for fuel injection and computers. Like Jack was saying with jetting this year, I found that everything I was doing this year seemed 1 step too lean compared to 2022. I was using all the data from 2022 testing that I collected but found the jetting to be not working. This makes sense.

Maybe its time we all switch to running 100% race gas LOL .

Thanks for taking the time to layout this info so nicely.

[JasonL]

I hadn’t factored that the club moved to ethanol gasoline in 2023 into my jet choice ‘algorithm’. I’ll be sure to adjust this season.

Not that many of us follow the Rotax app recommendations, but I wonder what type of fuel they assume in their calculations.

[newson48]

Nice discussion.
I don't know if the fuel providers vary their supply batch by batch, but I did check the Co-op gas, sometime late (ish) in the season in 2023 and the fuel I tested did NOT contain Ethanol.
I just checked it on one occasion, out of curiosity more than anything.

Regarding the octane for any of the engines, remember that our altitude plays a role in how much octane we need. The conversation will differ when talking to the clubs in BC or PQ or ON.

Cheers
Blake

[Jackmazury]

I believe in Europe the fuel they use is 98 RON for Rotax generally. Fuel definitely plays a big role in throwing the app off, I wouldn’t suggest using it as the end all be all.

[JasonL]

Co-op was the last hold-out with non-ethanol gasoline and started converting their sites in late 2022. It's possible that where you sourced your sample from had not yet converted.
Sites won't go back and forth - aside from some disruption that forces them away from their typical supply point. With federal and province carbon & cap and trade regs, use of non-ethanol gasoline is much more expensive for suppliers.
Our higher altitude allows us to get away with lower octane fuel. As I said in my original post, octane simply allows a fuel to be compressed further. Given our altitude, our air is less dense, which means that less oxygen is taken into the cylinder with each stroke, which means that less fuel is added to maintain the target A:F ratio, so less stuff ends up in the cylinder to be compressed. This also means that our motors make less power up here than they would at lower altitudes. Use of forced air induction negates these effects.

There isn't a perfect relationship between the two, but 98 RON is generally the equivalent of our 91 octane. My wonder about the assumption within the Rotax app was more about what ethanol percentage it assumed when recommending jetting under certain atmospheric conditions. As you pointed out, a 10% ethanol blend would have us going one-up on jetting vs. pure gasoline.