Atkinson motor and fuel octane

[dvibs07]

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?

Sponsored

 

[vap0rtranz]

+1. I'm all ears on this detail too.

I will say one thing: notice that Ford only listed the combined horsepower of the Hybird, and not the combined torque ...

 

[CASD57]

+1. I'm all ears on this detail too.

I will say one thing: notice that Ford only listed the combined horsepower of the Hybird, and not the combined torque ...

Good catch!
I read that you can use 87oct.....but to get the full horsepower you need to run Premium... but that could be for the Ecoboost...I don't remember I've read about both

 

[G Grampa Duey]

May I add a question to this thread? Does octane go down with aging, stored/unused fuel?

 

[r100gs91]

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?

Curious about that as well.

 

[Darnon]

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.

 

[eburatti]

I drove a 2010 Fusion hybrid (similar engine) for 140,000 miles and never once put premium in it and it was fine. Mileage was good as well - over 40 in city driving, 37 highway.

 

[vap0rtranz]

Ethanol, however, has less power density than gasoline

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

 

[dvibs07]

+1. I'm all ears on this detail too.

I will say one thing: notice that Ford only listed the combined horsepower of the Hybird, and not the combined torque ...

I just realized that too! That is crazy considering one of the best advantages of an electric motor is torque?

 

[fbov]

regular octane fuel without ethanol will produce the highest efficiency

This is what the ethanol difference looks like in a C-Max, about 5%. The third "suspect" data set is a reduction in tire pressure (long story).

 

[oljackfrost]

May I add a question to this thread? Does octane go down with aging, stored/unused fuel?

Gas does go bad, that’s why people storing their classic cars over the winter use Sta-Bil or Sea Foam stabilizers.

 

[oljackfrost]

Good catch!
I read that you can use 87oct.....but to get the full horsepower you need to run Premium... but that could be for the Ecoboost...I don't remember I've read about both

Only the EcoBoost

 

[dano0726]

Agreed^^^ with oljackfrost -- Wifey's 2.0 BS Badlands get max output with the Premium/PUG. But she only fills up with Regular/RUG

 

[Bikeric]

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.

Any idea if the Hybrid will be Flex Fuel compatible? I would consider the ability to run E85 a Bonus. My Flex Fuel Tundra feels like an extra 50hP on E85. The computer sees you're using E85 and adjusts the injectors accordingly. Mileage drops to 9 mpg, but DANG it's a fun tank of fuel. E85 also has a cleaning effect on the injectors and exhaust system. It takes any black soot in your tail pipe away. Downside to E85 is you have to get more frequent oil changes because it tends to let a bit go past the piston rings into your oil.

 

[cnp1234]

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.

Sponsored