Atkinson motor and fuel octane

[r100gs91]

That said it'd be super neat to make a dual mode atkinson cycle engine with turbo. Under full bypass it's an atkinson cycle engine, and under boost it's a miller cycle engine. Probably still needs some valve trickery though. If that could be done, you could drop the engine size down to 2.0, and have a super efficient cruising mode and a more powerful output than the 2.0 ecoboost. Maybe.

IIRC Ford doesn't do valve trickery right (5.4l VVT cam phasers), unless they farm out the job. (i.e. Yamaha)

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[Wire4money]

The compression ratio they list is the physical compression ratio of the cylinder. Due to the intake valves being held open well into the compression stroke, the effective compression ratio is much less. Sort of the opposite of how a turbo engine generally has a low physical cylinder compression ratio, but high effective ratio due to the turbo. I'd bet this engine actually does better with low octane in almost all conditions. In terms of getting more power, you probably can't. That said it'd be super neat to make a dual mode atkinson cycle engine with turbo. Under full bypass it's an atkinson cycle engine, and under boost it's a miller cycle engine. Probably still needs some valve trickery though. If that could be done, you could drop the engine size down to 2.0, and have a super efficient cruising mode and a more powerful output than the 2.0 ecoboost. Maybe.

My Tacoma had a “simulated Atkinson” which would use the variable valve timing system to leave valves open longer.

 

[Probity]

Since we don’t yet have a Maverick Owners Manual a good go-by is the 2021 Escape manual. Inside it says fuel specs for all offered engines (1.5l EB, 2.0l EB, 2.5l Atkinson cycle naturally aspirated) are minimum 87 octane.

Maybe you live in Denver where I’ve heard some stations might offer 85 and/or 87 and/or 91 and maybe even 93 octane (I don’t know, haven’t been in Denver since 1976), what to do? If you follow Ford’s advice and can’t find 87, don’t use 85 octane, use something at or higher than 87 octane.

At high altitude a lot of people use 85 octane (cheapest) and are fine, and my understanding is that it’s 100% gasoline (no ethanol). People can get by with 85 octane at high altitude because of thinner/less dense air which tends to prevent engine premature ignition of the fuel-air mixture (knock). Higher octane fuel reduces possibility of knocking.

Ford also says premium (91 octane) fuel is “recommended” for “best” performance (however you want to define that) and for towing, but for normal driving around 87 octane should be fine. When towing with my F150 2.7 EB I generally use something higher than 87 octane because you can notice a difference in performance under load between 87 and higher octane grades.

The 2.5l Atkinson is sequential multiport fuel injection (SMFI) where fuel is pumped under pressure through a small nozzle into various points in the engine's air intake section, and the atomized fuel then enters the engine cylinders past intake valves where it burns during the combustion cycle. “Top Tier” gasolines generally have more detergents/additives in them which can keep carbon deposits off the intake valves/valve stems and other fuel delivery system and combustion chamber components.

The 2.0l EB engine is a gasoline turbocharged direct injection (GTDI) where the atomized fuel is directly injected into the combustion chamber (doesn’t move past intake valves). Even though a Top Tier gas may keep other fuel delivery system/combustion chamber components clean, no matter how much of or how good the detergent is, it does nothing to keep carbon off the intake valves because the atomized gas never sees the backside of the intake valves.

 

[SgtLip]

I don't know anything about the science or any of that other stuff you smart people talk about. I have a 2021 Lexus ES300h Ultra Luxury auto with a little over 3,300 miles. The Dealer filled the tank with 87 Octane when I purchased the vehicle. I have ONLY put Pure's Ethanol Free fuel in the car since then. There Ethanol Free is 89 Octane and we won't discuss the price increase since January 20th 2021. Anyway, here is a screen shot of my Fuelly App. I'll let the numbers speak for themselves. I can only pray the Maverick can do the same.

 

[KimoCarew]

Don't tell that to just anyone. I'm suppose to be supporting corn farmers by buying gas w/ Ethanol

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

 

[oljackfrost]

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

Been doing it in Brazil for decades.

 

[dvibs07]

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

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

 

[dvibs07]

That doesn't mean it is a good idea.

I think he was making a joke about how Brazil is a third world country and they burn food or something

 

[CatsupGladiator]

The manual there is kinda funny, explicitly says not to use E85, but then identifies Flex Fuel vehicles having the yellow identification on the tank possibly labeled as E85. Some poor guy is probably in a conundrum with the conflicting information.

 

[Rivers90]

Regular for the hybrid, premium for the EcoBoost.
For max power and range.

But both can use regular.

 

[Rkbrumbelow]

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.

if you want to understand octane ratings better take a look at https://www.eia.gov/energyexplained/gasoline/octane-in-depth.php
modern engines have variable timing and knock detection, you can run 87 octane or AvGas (octane equivalent of 130, assuming you can find it unleaded) running a higher than needed octane gives you no benefit, running a lower rating will cause you to lose power as the engine changes timing to compensate.

you may find you do not need premium gas unless you are towing or under load, you may find the difference is not noticeable in your driving conditions. At 14.7:1 most 100 octane rated fuels will diesel around a compression ratio of 18:1, 13-14:1 is well below that. most vehicles develop the most power at around 12-13:1 air:fuel so even with 13:1 compression you will likely never have knocks.

https://x-engineer.org/automotive-e...nce/air-fuel-ratio-lambda-engine-performance/ if you really want to know how octane affects engine performance, but if you don't like maths, avoid it.

Or, do what my mom did in the 70's buy your gas, drive like you normally do and track your mpg. Buy the gas that gets you not the best mpg, but rather the best Mp$ and that varies on fuel cost.

Example: if you get 21mpg with 87 octane at $3, and 24mpg with 97 oct at 3.4$ which is better? 21 mpg/3$ = 7 mp$, 24mpg/3.4$ is 7.06mp$ so 97 is worth it, but only by 0.8% so its a wash really.

 

[fbov]

Regular for the hybrid, premium for the EcoBoost.
For max power and range. ...

Make that Regular E0 for the hybrid and we agree. Hybrids can benefit from the higher energy content. EcoBoost will never notice.

Buy the gas that gets you ... the best Mp$ ...

... and you'd never buy ethanol free. Put cheap gas in the EcoBoost and 90E0 in the hybrid for a meaningful cost comparison.

 

[Dbarr]

I’m looking for someone with intimate knowledge about engines to answer a couple questions for me. I’ve been researching Atkinson motors and learning about how they work. I’ve found that the Atkinson motor used has a compression ratio of 13:1 which is pretty high. So I would think premium fuel with a higher octane would work better. However, reading about the Atkinson motors I discovered that lower octane is recommended because the ignition rate works better with the natural cycle. So…

-Would running a low octane fuel with more ethanol produce a more efficient engine?
-Will premium work better or get more power or will it just knock?
-Any ideas to get more power out of the hybrid engine?

My son is still driving my 2007 Camry Hybrid… 370k and always used 87 octane

 

[CASD57]

I think he was making a joke about how Brazil is a third world country and they burn food or something

We know what your going to put in your bed cubby.......Hemp

 

[Ronaldo]

It’s not a true 13 to 1 because the compression stroke is bleed off in the first 20-30 percent back into the intake due to the valve being open. I would guess it’s true compression is more like 8.5-9.0. The negative to this setup is lack off low end power which made up for by the electric motors instant torque.

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