Does Premium Gasoline Have More Energy Than Regular?

[RDY4WAR]

No, the BTU/lb of energy of 91-93 premium is the same as regular 87. (within MoE) The heavy aromatic content is slightly different (same concentration) to get the higher octane value. Distillation, flame speed, burn rate, vaporization, etc... all practically the same.

 

[RDY4WAR]

False on all of that. Again though it depends on how the octane rating is achieved. Once you are using an adjunct such as EtOH then you are also changing fundamental properties of the gasoline as expressed as a majority C-8 mixture.

The second part of your statement isn't true either. If the compression ratio stays the same as well as the ignition timing then a higher octane fuel will give the same power as a lower octane one. If the compression is increased or the timing advanced, then a higher octane fuel will be more efficient and yields more power per gram.

Don't confuse all of this with race fuels. I thought of that given your mention of 100 octane. Race fuels can be comprised of many compounds all of which do in fact change the combustion temperature, flame speed and other properties.

Yes. I was about to say that VP C25 is ~118 octane (R+M/2) and has a lower specific gravity and faster burn rate than regular 87 pump gas. Alcohols are weird and kinda do their own thing. Ethanol has a slower flame speed than gasoline but a faster burn rate. The high HoV also throws it off which is why getting an accurate octane value for ethanol or methanol in a CFR engine is practically impossible.

 

[RDY4WAR]

If you want to get the power potential of a given fuel, you can't look at the fuel's HoC alone. You have to factor in stoichiometry with a resulting value being in BTU per pound of air.

Say a fuel has 18,000 BTU/lb and stoich is 14.2:1. 18,000 / 14.2 = 1,267 BTU/lb of air
Say a fuel has 12,000 BTU/lb and stoich is 9.2:1. 12,000 / 9.2 = 1,304 BTU/lb of air

Which fuel do you think will make more power?

Let's look at nitromethane with ~5,000 BTU/lb and 1.7:1 stoich. 5,000 / 1.7 = 2,941 BTU/lb of air.

 

[fnbrowning]

No, the BTU/lb of energy of 91-93 premium is the same as regular 87. (within MoE) The heavy aromatic content is slightly different (same concentration) to get the higher octane value. Distillation, flame speed, burn rate, vaporization, etc... all practically the same.

@RDY4WAR
Thank you for posting the chart. My I cite the chart? May I have a link to more information if available?

 

[D1sc]

Just be careful that although the terms are often thrown around as the same, pre-ignition knock and detonation are not the same thing. In fact detonation (if it occurs) happens after ignition, and usually after spark plug initiation.

Thanks I need to study up. My builder is a big proponent of methanol systems and although I have two I don’t understand how they allow the timing to be advanced on a FI tune.

 

[D1sc]

Should be rocket fuel for the price.
[/QUOTE. That and the hassles of E85.Ill stick to meth injection as a back up on the tunes.

 

[RDY4WAR]

@RDY4WAR
Thank you for posting the chart. My I cite the chart? May I have a link to more information if available?

Go for it.

 

[tcp71]

No idea if the source is credible or if ethanol content in the regular fuel is different... or any other factors.

https://www.intelligenthq.com/under...s station may offer,it's around 142,700 kJ/l.

Never heard of energy expressed in BTU/lb. Joules, yes.

 

[kschachn]

Never heard of energy expressed in BTU/lb. Joules, yes.

That’s pretty typical here in the US. When I was in college and took automotive engineering and thermodynamics classes that’s how we still did it.

 

[fnbrowning]

No idea if the source is credible or if ethanol content in the regular fuel is different... or any other factors.

https://www.intelligenthq.com/under...s station may offer,it's around 142,700 kJ/l.

Never heard of energy expressed in BTU/lb. Joules, yes.

Thank you for posting. I cannot find the same energy output anywhere as written in the intelligenthq article. The best available information I can find on the stored energy in regular gasoline comes to about 32 -34.4 Mj/liter. I've written to intelligenthq asking where they got the numbers for their article. For now, without a reviewable cite, I'm going to have to say their numbers are incorrect.

 

[jeffy876]

Not relevant. How much energy can you extract from it is

 

[tcp71]

That’s pretty typical here in the US. When I was in college and took automotive engineering and thermodynamics classes that’s how we still did it.

cool. Metric system strikes again.

 

[SuperSalad]

So you originally asked about energy per volume, but the equivalence is in mass. If by volume, premium has more energy per unit volume because of the higher density. But @RDY4WAR 's chart shows premium as being lower density, so I guess that point isn't clear.

However, unless I'm mistaken, isn't the overwhelming majority of the energy in gasoline in the hydrogen bonds? @RDY4WAR 's chart also shows a higher ratio of H to C in premium, which would mean more energy per unit.

The other possibility is that I'm being stupid about all of this, so feel free to dismiss this post as a semi-technical half-thought.

 

[tcp71]

So you originally asked about energy per volume, but the equivalence is in mass. If by volume, premium has more energy per unit volume because of the higher density. But @RDY4WAR 's chart shows premium as being lower density, so I guess that point isn't clear.

However, unless I'm mistaken, isn't the overwhelming majority of the energy in gasoline in the hydrogen bonds? @RDY4WAR 's chart also shows a higher ratio of H to C in premium, which would mean more energy per unit.

The other possibility is that I'm being stupid about all of this, so feel free to dismiss this post as a semi-technical half-thought.

The old adage: Units are important.

 

[Rmay635703]

With premium being almost double the price of the cheap stuff it should double gas MPGs but sadly it’s usually only a few percent better due to better timing, oddly in hot weather the e15 fuel actually seems to deliver better knock numbers than 89.

 

[D1sc]

Small price compared to the cost of an engine that has its pistons sand blasted and rings hammered by pre detonation.Otherwise I would go for the bargain grade.

 

[Rmay635703]

Small price compared to the cost of an engine that has its pistons sand blasted and rings hammered by pre detonation.Otherwise I would go for the bargain grade.

Actually for most folks running rug on an engine requiring premium it takes many years until a rebuild would be required and in the case of one of my cars the engine is $99 at the wrecker.

Get yourself some inexpensive equipment and measure knock, on my Volt at 1500’ elevation 88e15 isn’t significantly more knock than premium.

Unless your running a turbo and a tune going to the track or towing up mountains in the desert it’s unlikely any of what you describe is going to happen.

Its rare an average vehicle on the road benefits from premium.

 

[Chris142]

No. More energy comes from higher cylinder pressures from things like higher compression or a turbo etc

 

[Warstud]

With premium being almost double the price of the cheap stuff it should double gas MPGs but sadly it’s usually only a few percent better due to better timing, oddly in hot weather the e15 fuel actually seems to deliver better knock numbers than 89.

View attachment 219951

You beat me to it. It looks like some gas stations have there own name for it

 

[D1sc]

Actually for most folks running rug on an engine requiring premium it takes many years until a rebuild would be required and in the case of one of my cars the engine is $99 at the wrecker.

Get yourself some inexpensive equipment and measure knock, on my Volt at 1500’ elevation 88e15 isn’t significantly more knock than premium.

Unless your running a turbo and a tune going to the track or towing up mountains in the desert it’s unlikely any of what you describe is going to happen.

Its rare an average vehicle on the road benefits from premium.

Exactly so many cars have turbos now and was watching a vid where the suburu mechanic was showing the damage to the pistons from knock. All my cars are turbo or supercharged and 91 is the bare minimum