Let’s talk gasoline -

Noobz347 · Apr 13, 2020

I would suggest a class/course in basic mechanical science.

MrPerfect2 said:
If compression stays same on boosted engines , why do they require higher octane fuel - Is it because the A/f ratio needs change when boost is added ?

MrPerfect2 said:
I read you have static compression and effective compression on a boosted engine - effective compression goes up when boost is applied - that why higher octane is needed if you want to run boost

Higher octane is needed because you increased the mass of the mixture prior to compression. Overall compression will be higher and exponential, not linear. Elevated octane has the property of causing the explosive mixture of gasoline to resist detonation through compression.

Let's also not forget that compressing air by any means also increases heat. There is a direct correlation between the flashpoint of the explosive mixture and the tendency to detonate from being compressed. That correlation would be indicated on a curve and would be different for every engine.

Octane ratings allow you to make an educated guess and cover a specific range of heat and compression. Those ranges were figured out ahead of time and just so happen to cover a good swath of the ranges that we operate combustion engines in. It's almost like they planned it that way

Ryuk · Apr 13, 2020

A few things I learned years ago when I was working for a fuel management software company.

Even branded stations can sell as much as 10% unbranded gas and still be considered branded.
Midgrade is a pump blend, you're paying more than if you mixed them yourself.
At that time, the FL terminals were Tampa, Orlando, and Port Everglades.
When you buy gas at a no name station, you can be getting gas from any manufacturer, it just depends on availability.

General karthief · Apr 13, 2020

JD08 said:
A few things I learned years ago when I was working for a fuel management software company.

Even branded stations can sell as much as 10% unbranded gas and still be considered branded.

Midgrade is a pump blend, you're paying more than if you mixed them yourself.

At that time, the FL terminals were Tampa, Orlando, and Port Everglades.

When you buy gas at a no name station, you can be getting gas from any manufacturer, it just depends on availability.

So what you are saying is the Mom and Pop Petrol Stop could be selling Shell gas that is nitrogen infused?
COOL!!

Olivethefet · Apr 13, 2020

I filled up yesterday for $1.34 a gallon. In Dothan it's as low as $1.24.

It my understanding that a lot of gasoline comes from fuel depots and depending on where it is going different additives are put into the tanker to make it brand specific. So you might be buying gas at a Chevron station that has a proprietary blend, but the base fuel came from the same supply that the fuel at Jonny's Super Gas an Go came from. Jonny just didnt pay extra for the additives.

WhiteCobra95 · Apr 13, 2020

General karthief said:
This could be an interesting discussion if we could get some boosted members in here to explain.
Who needs google when you got stangnet to answer your questions on this subject.
Maybe the short answer is detonation, I would explain more but I'm not qualified.

A static analysis can be done with an adiabatic compression calculation from thermodynamics. This will give you a simple estimate of the chamber pressure at TDC.

P1*V1 = P2*V2

V1 = displacement volume + chamber volume (piston at BDC)
V2 = chamber volume (piston at TDC)
P1 = chamber pressure at BDC
P2 = chamber pressure at TDC

You can approximate the chamber pressure at TDC by solving for P2. This can be calculated for each of the two engine cases mentioned above, boosted vs. N/A for comparison. Assume a REALLY good N/A moter reaches 90% of 1 ATM (1013 mBar) MAP at WOT when the intake valve closes - solve for P2. Now assume that the High boost engine reaches 2 ATM (2026 mBar) MAP at max boost when the intake valve closes - solve for P2. Use the same displacement and volume for each case to start. The effect of boost pressure is multiplicative. This can be managed a bit by lowering the static compression ratio (larger V2) on boosted engine to help shift the knock limit mechanically.

revhead347 · Apr 13, 2020

I like to fill up at the big gas stations, like the QT or the Racetrack; you know the ones with like 20 pumps. That's how you know the gas hasn't been sitting in their substandard underground tank for 3 weeks.

Kurt

General karthief · Apr 13, 2020

WhiteCobra95 said:
A static analysis can be done with an adiabatic compression calculation from thermodynamics. This will give you a simple estimate of the chamber pressure at TDC.

P1*V1 = P2*V2

V1 = displacement volume + chamber volume (piston at BDC)
V2 = chamber volume (piston at TDC)
P1 = chamber pressure at BDC
P2 = chamber pressure at TDC

You can approximate the chamber pressure at TDC by solving for P2. This can be calculated for each of the two engine cases mentioned above, boosted vs. N/A for comparison. Assume a REALLY good N/A moter reaches 90% of 1 ATM (1013 mBar) MAP at WOT when the intake valve closes - solve for P2. Now assume that the High boost engine reaches 2 ATM (2026 mBar) MAP at max boost when the intake valve closes - solve for P2. Use the same displacement and volume for each case to start. The effect of boost pressure is multiplicative. This can be managed a bit by lowering the static compression ratio (larger V2) on boosted engine to help shift the knock limit mechanically.

I knew I should have stayed awake in that class

Ryuk · Apr 14, 2020

General karthief said:
So what you are saying is the Mom and Pop Petrol Stop could be selling Shell gas that is nitrogen infused?
COOL!!

Or BP or Texaco or Mobil or anything else.

It's funny to hear the water in the gas stories. The company also had leak detection software that was made redundant by the double wall tanks.

MrPerfect2 · Apr 16, 2020

You guys know your stuff ! Thanks for the detailed info on compression , most went over my head , but if you know all this , you have a better understanding than me and trust your explanation .

General karthief · Apr 16, 2020

You have to remember that some members here have pretty fast turbo/blower cars and even some that race them or are involved in a race team. We have some very astute mechanics, engineers and even a few hackers, er, I mean computer techs. We even have an ex-genius!
Of course you also have me. I'm happy if I can put a whole sentence together with correct grammar and spelling.

DarthStang2003 · Apr 18, 2020

Potomus Pete said:
Gas in Fla. is @ $1.87. Im still driving around for work , and liking it.

I’m right here with ya, South a Florida and still driving to work! I run a 93 Octane tune so that’s what I use and I try my hardest to stick with one gas compass well!

1hot87gt · Apr 18, 2020

Same here. Always use Mobil. Think they are considered a Tier 1 brand, and I think they have a pretty good detergent package. I run straight 93 octane in my 500hp blown Fox street car with no additives. Never an issue. Only additive I do use is Stabil right before I lay her up for the winter as well as a good fuel system cleaner like Techron once a year. I run 89 octane in my Hemi Ram as well as my wife’s Wrangler. Again Mobil. Again no issues.

2Blue2 · Apr 18, 2020

Some stations here have ethanol in the gas,
My small engines (weedwacker, yamaha pw60, lawn mower, etc) run so much better I f i drive to the ethanol free stations for there gas.
I even have bought the fancy gas in home depot for the weed wacker. They is so much easier to start with ethanol free.
I do use Stabil for any gas not getting used soon.

7991LXnSHO · Apr 18, 2020

General, Sir!
My ex worked at an ethanol plant, and I can assure you ethanol it is denatured grain alcohol. One on the first steps is to ferment the grain with yeast into a 16% “beer”. This plant even had batches that were going to Russia that had a specifically low sulfur content and were not denatured. I cannot remember the cheap brand of Vodka it probably ended up as.
Maybe you are meaning something like it is not Methanol or isopropyl alcohol, or E85?

General karthief said:
It's ethanol not alcohol.

DarthStang2003 · Apr 18, 2020

1hot87gt said:
Same here. Always use Mobil. Think they are considered a Tier 1 brand, and I think they have a pretty good detergent package. I run straight 93 octane in my 500hp blown Fox street car with no additives. Never an issue. Only additive I do use is Stabil right before I lay her up for the winter as well as a good fuel system cleaner like Techron once a year. I run 89 octane in my Hemi Ram as well as my wife’s Wrangler. Again Mobil. Again no issues.

Yes Mobil is the brand I prefer!

General karthief · Apr 18, 2020

7991LXnSHO said:
General, Sir!
My ex worked at an ethanol plant, and I can assure you ethanol it is denatured grain alcohol. One on the first steps is to ferment the grain with yeast into a 16% “beer”. This plant even had batches that were going to Russia that had a specifically low sulfur content and were not denatured. I cannot remember the cheap brand of Vodka it probably ended up as.
Maybe you are meaning something like it is not Methanol or isopropyl alcohol, or E85?

I didn't go back and see what prompted that post.

Noobz347 · Apr 18, 2020

For our purposes, it's best to keep a broader perspective on how the pieces work together and not dwell on its atomic makeup

CarMichael Angelo · Apr 18, 2020

I can’t believe a thread about gasoline has lasted this long,..Goes to show what rung of the ladder most of the people are on that participate here.
Cant wait for the what oil filter; what spark plug; what hose clamp threads that will follow...

Noobz347 · Apr 18, 2020

CarMichael Angelo said:
I can’t believe a thread about gasoline has lasted this long,..Goes to show what rung of the ladder most of the people are on that participate here.
Cant wait for the what oil filter; what spark plug; what hose clamp threads that will follow...

This is at the very least the sixth one of these threads that I've seen over the years.

I use them as refreshers

General karthief · Apr 18, 2020

WhiteCobra95 said:
A static analysis can be done with an adiabatic compression calculation from thermodynamics. This will give you a simple estimate of the chamber pressure at TDC.

P1*V1 = P2*V2

V1 = displacement volume + chamber volume (piston at BDC)
V2 = chamber volume (piston at TDC)
P1 = chamber pressure at BDC
P2 = chamber pressure at TDC

You can approximate the chamber pressure at TDC by solving for P2. This can be calculated for each of the two engine cases mentioned above, boosted vs. N/A for comparison. Assume a REALLY good N/A moter reaches 90% of 1 ATM (1013 mBar) MAP at WOT when the intake valve closes - solve for P2. Now assume that the High boost engine reaches 2 ATM (2026 mBar) MAP at max boost when the intake valve closes - solve for P2. Use the same displacement and volume for each case to start. The effect of boost pressure is multiplicative. This can be managed a bit by lowering the static compression ratio (larger V2) on boosted engine to help shift the knock limit mechanically.

This sounds like it may be pretty high on that ladder.
Also keep in mind I have acrophobia

Let’s talk gasoline -

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

Ryuk

I love your drawers

General karthief

wonder how much it would cost to ship you a pair

Olivethefet

I will own your nuts! LOL

WhiteCobra95

revhead347

Apparently my ex-husband made that mistake.

General karthief

wonder how much it would cost to ship you a pair

Ryuk

I love your drawers

MrPerfect2

General karthief

wonder how much it would cost to ship you a pair

DarthStang2003

Member

1hot87gt

2Blue2

will be trying this sex one when I can find it

7991LXnSHO

wanna catch the space herp

DarthStang2003

Member

General karthief

wonder how much it would cost to ship you a pair

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

CarMichael Angelo

my rearend will smell so minty fresh,

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

General karthief

wonder how much it would cost to ship you a pair

Similar threads

Let’s talk gasoline -

Stangnet Facilities Maint Tech... Er... Janitor

I love your drawers

wonder how much it would cost to ship you a pair

I will own your nuts! LOL

Apparently my ex-husband made that mistake.

wonder how much it would cost to ship you a pair

I love your drawers

wonder how much it would cost to ship you a pair

Member

will be trying this sex one when I can find it

wanna catch the space herp

Member

wonder how much it would cost to ship you a pair

Stangnet Facilities Maint Tech... Er... Janitor

my rearend will smell so minty fresh,

Stangnet Facilities Maint Tech... Er... Janitor

wonder how much it would cost to ship you a pair

Similar threads

Privacy & Transparency

Privacy & Transparency