Atkinson motor and fuel octane

[Rkbrumbelow]

Not always, the maps are often quite complex now, and the engine really has no clue what octane fuel it is being fed, and the same octane at sea level on a dry day that's 120oF outside would have different knock resistance compared to high altitude icy humid air. Heck, even the same engine can benefit from higher octane just based on age, as carbon buildups can reduce knock resistance which higher octane fuel can compensate for.

So sometimes the maps can have a huge range of timing and a/f ratios and what not programmed in, and rely on the knock sensor that are extremely sensitive to "learn" what is appropriate for the particular conditions that day and the fuel. The only way to know for sure would be to throw in some 100 octane and run it on a dyno, but chances are its not worth the effort and just stick with whatever the user manual indicates is the "minimum recommended" fuel, which in the case of the 2.5H is 87. Higher octane can't hurt anything, but probably is a waste of money.

The ideal octane for your situation is the lowest one that doesn’t knock and your fuel system is not adjusting the trim to compensate.

for those of you who are interested in performance and how fuels affect it, grab a Bluetooth odb2 dongle that allows for real-time engine and fuel monitoring. As a scientist and vehicle enthusiast, I quickly became addicted.

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[Rkbrumbelow]

A page from the new manual made available today... there are reccomandation about high altitude/ towing and ethanol.. for everybody to look at. In my situation, I will be fine with 87 Octane.

I still say the way to do it is log everything. You drive how you normally do on a full tank of unmixed gas, see how far you get before the idiot light comes on. Figure out exactly how much fuel you used and determine dollars per mile. Then switch grades or even distributors, believe it or not those additives make a difference, and it is not necessarily a positive one. Once you have those numbers, go with the miles per dollar or least dollars per mile.

now in my case I can watch fuel and power real time so if the engine consistently is retarding timing or consistently altering the fuel trim, I need to go up a grade. If it is not, then I go down a grade till I see something start to happen.

I think I gave an example where premium might produce more output or evenbetter dollars per mile but the difference in pricing was negligible.

mitigate also depends on what tieof year it is etc because even gas gets reformulated 2 or more times a year

of course if you do not want to do all that, just go by the manual

 

[vap0rtranz]

grab a Bluetooth odb2 dongle that allows for real-time engine and fuel monitoring.

Got one of those! and getting excited to get into my Maverick.

Now that we're reading the owner's manual, I stumbled on a Q&A section when looking for something else. This blurb is a few pages before that octane screenshot:

Can I put E15 or E85 in my vehicle, and how will it affect my fuel economy?
Your hybrid vehicle can use E15 (15%ethanol, 85% gasoline) fuel, but you may notice slightly reduced fuel economy because ethanol contains less energy per gallon than gasoline. Your hybrid vehicle is not designed touse E85 (85% ethanol).

So that's ^ one reason for pumping whatever grade is 0% ethanol. In my State, it's usually 91/Premium.

I get that these efficiency / power differences are minimal, but running the #s doesn't necessarily make 91/93/premium a worthless moneypit. If you run the #s for premium being $1 more than low grade (it's usually less than $1 gap per the EIA's data), assume 25MPG EcoBoost vs 35MPG Hybrid driven 15,000/yr, well the Hybrid still saves money even if that Hybrid driver pays for premium. Run the #s yourself to see. So these arguments about premium being a moneypit get thrown out the window with these MPG gaps. The biggest savings is much better MPGs -- not low grade octane. If I get a slight efficiency boost in a Hybrid, good; but the big savings isn't from which fuel I pump but how much I pump.

 

[Rkbrumbelow]

I noticed on a pump today that the fuel is not temperature regulated in Georgia pumps so if the fuel is warmer then you get less actual fuel, as it is still sold volumetrically. Now underground storage temps are fairly stable but for every 1 degree temp increase of the fuel you receive 0.114 % less fuel

 

[mamboman777]

The problem with corn is that it requires crop rotation and a lot of resources like water and pesticides. The best way to make a natural based fuel would be with hemp. Grows like a weed (pun intended), grows in tons of biomes, no pesticides, no crop rotation, it cleans soil…and is extremely versatile. Ok end rant on future petroleum ideas

I heard something once about turning the unused parts of crops into ethanol (husk, cob, etc.)

I don't know how feasible today might be, but if possible, seems like a good plan.

 

[STARCOMMTREY1]

With an Atkinson engine the 13:1 compression is mostly theoretical. The intake valve is kept partially open at the beginning of compression so some of the A/F mix is pushed back out of the cylinder. Therefore the total compressed volume (and effective compression ratio) is lower allowing operation on regular octane. The advantage is this allows the post-combustion expansion to utilize the full stroke for maximum efficiency.

Octane rating, on its own, does not produce more power. It simply allows higher compression. So an engine that does not take advantage of this through high compression ratio or forced induction (turbo/supercharger) won't make more power. Ethanol, however, has less power density than gasoline. So regular octane fuel without ethanol will produce the highest efficiency. Availability of that will depend on where you are. Often only Premium fuel is available ethanol-free and if the cost difference is greater than the increase in efficiency it's not worth spending more.

I have never seen this. The only ethanol free I'm Alabama or Mississippi is ALWAYS 87. I would by 93 in a heartbeat if I could. My small engines get TruFuel for this reason.

 

[mamboman777]

I have never seen this. The only ethanol free I'm Alabama or Mississippi is ALWAYS 87. I would by 93 in a heartbeat if I could. My small engines get TruFuel for this reason.

Yeah...I seem to remember some places adding ethanol to make the higher octane rating, meaning that the 93 is likely closer to the %10 ethanol than the 87, but I'm no expert.

 

[STARCOMMTREY1]

I wonder if this truck will be like the 5.4. That truck could detect the octane rating of the fuel and would adjust the timing accordingly. It ran best on pure ethanol then on 93. But ethanol did give me worse fuel mileage. .

 

[mamboman777]

I wonder if this truck will be like the 5.4. That truck could detect the octane rating of the fuel and would adjust the timing accordingly. It ran best on pure ethanol then on 93. But ethanol did give me worse fuel mileage. .

This is how I understand it would work.

 

[Darnon]

I have never seen this. The only ethanol free I'm Alabama or Mississippi is ALWAYS 87. I would by 93 in a heartbeat if I could. My small engines get TruFuel for this reason.

Here in NY it's only certain gas stations that even offer it and it's always at least 90 or 91 with a few 93 Octane.

 

[Jezmund_Berserker]

Coincidentally, the kids and I watched this on Saturday. I don't know much about this stuff. I'm sure the video is over-simplified for the audience, but I wonder how much is still true?

 

[vap0rtranz]

I don't know much about this stuff. I'm sure the video is over-simplified for the audience, but I wonder how much is still true?

I'm not going to watch a video entitled "Premium gas is a waste of money".

What's really a waste of money? Low MPGs.

Boom! (mic drop)

 

[Sylvester]

This is right out of the owners manual, without specifying hybrid our ecoboost:

"Your vehicle operates on regular unleaded gasoline with a minimum pump (R+M)/2 octane rating of 87.

Some fuel stations, particularly those in high altitude areas, offer fuels posted as regular unleaded gasoline with an octane rating below 87. The use of these fuels could result in engine damage that will not be covered by the vehicle Warranty.

For best overall vehicle and engine performance, premium fuel with an octane rating of 91 or higher is recommended. The performance gained by using premium fuel is most noticeable in hot weather as well as other conditions, for example when towing a trailer."

 

[arkanos]

Ethanol is really stupid. Who on earth came up with the idea "hey, let's burn the food?"

Politicians pandering to corn farmers and corn states.

 

[ProDigit]

I was under the impression that Atkinson engines change the compression ratio, through some rocker joints underneath the piston, allowing the pistons to have a higher or lower top dead center.

This in turn, probably maximizes compression ratio for the lowest CC, and decreases compression at higher engine CCs, as the piston has a longer bore.
For instance, a 2.0 Atkinson engine like the FFH is 2.0 with top dead center being lower, causing a much lower compression ratio.
This in turn would allow the intake valves to be open longer, and allowing for more air/fuel in the cylinder. The engine will be operating more like a less efficient 2.0 NA engine.
Shifting the piston's TDC and BDC more upwards (towards the head gaskets), will increase compression to the rated 12:1 ratio (about the highest common compression ratio used in industry for 85 oct fuel); but at the same time will lower the cylinder CC content due to there being less space above TDC to the head gasket. In this setting, the engine will perform more like an 1.8l NA; basically having less power, but consuming less gas as well.

What I think this could mean, is that a turbo and an Atkinson engine need to be married together.
At operation below boost, the engine will act like a 1.8L, with the fuel efficiency of a 1.9L.
Paired with a CVT (eCVT) gearing ratio (normally assigned to larger engines when using an MT or AT), this means the car could get outstanding MPG numbers.

At operation under boost, it'll act like a less efficient 2.0T (more like a 1.9T).
Either high compression/low performance, or high performance/low compression will have drawbacks, and won't run as efficiently as a native smaller or larger engine.
But the higher dynamic range of power vs fuel efficiency would definitely make it the perfect marriage!

Now getting to E85 fuel,
Ford most of the time will label E15, or E20 fuel max.
These fuels can make much higher compression, like with forced induction, without heating the engine as much.
The drawback being a 30% or higher reduction in MPG, especially under boost.

For an Atkinson engine, the higher compression will allow it to run at the lower CC size (1.8L), without pinging. However, at those settings, the engine will have even less power.
This might be interesting on a Ford Fusion Hybrid or Energi, which has tires inflated to 40+ PSI (45 if possible), and fully charged battery.
It's a common issue with these vehicles that the engine has slightly too much power to maintain speed, without shifting to electric driving.
However, once you load the car, tires are inflated at 30PSI, or the battery is low on charge, the engine will have nearly zero acceleration, and trying to cruise at a fixed speed using the engine while charging the battery will result in a significantly lower MPG, as you'll have to press the throttle deeper, and make the engine rev higher.

In general terms, when an Atkinson engine is paired with a CVT like the fusion (eCVT), the optimal gear ratio, engine RPM, and fuel injection amount is automatically calculated by the ECU.
Using flex fuel or anything higher than E15, will only result in less power, and less MPG; with the exception under full load, where the engine can run at higher boost levels, or higher compression ratios without pinging or knocking as easily.

It would be my opinion that E15 or higher may work better in extreme high ambient temperatures (like 120 degrees and up deserts), or where an engine is ran at peak power constantly (as peak engine output power has a higher potential than on regular 85oct fuel).
That's usually not the case with Atkinson engines, as they're made for economy, not performance; and normally 95% of driving is done outside of peak performance.

Aside from Ethanol destroying aluminum engine parts, and rubber hoses; higher ethanol fuel would definitely work when upgrading your car with a turbo and bigger injectors; without having to modify too much else in the engine (perhaps fuel mapping). But you don't have to redesign a new head gasket, or grind down some metal out of the head gasket or cylinders to prevent pre-detonation.

I'd think that under normal operation, you're better off buying high octane gasoline, than flex fuel; and the only time you'll want to mix flex fuel with 85octane (or 91/93 high octane fuels), is when using forced induction.

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