Winter Gas /Summer Gas

Talking heads on the news keep talking about gas prices and the soon schedualed switch over in the pipelines from winter gas to summer gas. Whats the difference between the two?

about 50 cents a gallon

yea,...50 cents a gallon mixed with a lot of BS mixed in

I think it has to do with the lighter compounds that have to be refined out for summer use but can be left in during the winter. Butanes, hexanes, ect... There is also talk of oxygenation but I have no idea of what that is.

Aaron

Yeah, I get about half po'd and half amused by the fact that they seem to feel that we have to be informed when gas prices rise. AAA, some watchdog organization, etc. all have to inform us every week. It's almost like they are advocates of high prices. Heck, if you drive you already know it, and if you don't, you're probably not that concerned.

Summer gas doesn't atomize properly in cold temperatures.
Certain compounds in winter gas evaporate away in hot weather.

It depends upon where you live.

Some areas use so-called designer blends to meet nonsensical EPA mandates. Such nonsense is not required in other areas.

In all areas winter formulation gasoline is more volatile than is summer formulation gasoline to aid cold weather starting.

Dean

In SE MN our gas has gone up $0.70 in the last month and we haven't made the switch to summer gas yet.

The price fluctuations are driven solely by commodities investors. Has nothing to do with summer/winter blends, or supply and demand. Get the stock market speculators out of it and the price would stabilize quickly, and probably somewhere around $1.25 to $1.50 per gallon.

What utter nonsense.

Dean

Agreed.

You can't devalue your currency as much as the US has without expecting a rise in commodity prices.

People are so amused by themselves,, some educated folks try to pull the wool over many folks. years ago Boron used to put in a bit of gas antifreeze to make folks think it was worth more , guaranteeing to never fail to start.

Now it has come to the point they try to tell us that there is a summer gas change over..

I have hauled all brands from the Pittsburgh area..

Thew difference between the brands was the length of the pipeline from the barge, to the terminals. the additives were determined by the punched card system we used to load with, and the numbers used to tell the terminal computers as to what we wanted. then additives were administered accordingly... so don't tell me refineries have to do the changeover.

While speculators can spike prices up or down In the short term. In the long term those speculators even out the long term price rises. They level off spikes in demand and supply.

We don't have a perfect system, but we are better off with the speculators than without them!

Paul

I can tell when we switch in New York State as my gas mileage goes down about 3 miles per gallon. They switch before it gets very cold here so its not the colder weather affecting mileage.

Yes, I live in a area where summer gas is required. Two things I know for sure it cost more and my mileage drops at least 2 miles per gallon. The idea of this super fuel is to reduce pollution. Also boosts bottom line of the major oil companies.

The difference is the RVP (Reed Vapor Pressure) or in layman"s terms, the evaporation point. It cost more to keep the evaporation point down for summer months. EPA has mandated this and RVP requirements are higher in the "HOT" south and change the further north you go.

The differance is the RVP (Reid Vapor Pressure) of the gas.
Fuels with higher RVP evaporate more easily than those with lower RVP.
Gasoline must have an RVP below 14.7 PSI which is normal atmospheric pressure And this is winter gas.
For summer months the EPA mandates an RVP below 9.0 psi or 7.8 psi depending where you live. Some local goverments have even lower standards.

The reason summer gas cost more than winter gas is they can use more butane in the winter gas. Butane is inexpensive and plentiful but has a RVP of 52 psi

Bingo.

Dean

Bingo.

Blame the EPA, not the speculators.

Dean

That may have been true at one time.

It no longer is.

Blame the EPA.

Dean

You ever notice that in the late summer, when the gas prices go up, they say it is because they have to switch from summer gas to winter gas, and winter gas is more expensive. Same thing now, except now summer gas is more expensive. It is a bunch of crap. Oil prices are not up much either. It is just plain speculation and profit taking.

(quoted from post at 17:34:04 02/19/13) The differance is the RVP (Reid Vapor Pressure) of the gas.
Fuels with higher RVP evaporate more easily than those with lower RVP.
Gasoline must have an RVP below 14.7 PSI which is normal atmospheric pressure And this is winter gas.
For summer months the EPA mandates an RVP below 9.0 psi or 7.8 psi depending where you live. Some local goverments have even lower standards.

The reason summer gas cost more than winter gas is they can use more butane in the winter gas. Butane is inexpensive and plentiful but has a RVP of 52 psi

Click to expand...

It is my understanding that RVP is measured at a gasoline temperature of 100 degrees F and is specified in units of PSI. The units of PSI are gauge pressure which is always pressure greater than atmospheric. The pressure gauge on my sealed chain saw fuel container always reads greater than atmospheric on a warm day.

Your post seems to say RVP is less than atmospheric. Am I confused or perhaps mis- reading your post?

Respectfully, Ken.

It's always refreshing to hear a response from someone who actually knows something about the topic.

Of course, there's always been a switch between winter and summer gas. Otherwise, in the days of carburetors and engine-driven fuel pumps, you would get vapor locking in the summer or your car wouldn't have started in the winter. It's just that now it's mandated primarily for emissions control purposes. A side benefit to low vapor pressure is longer shelf life; that's why avgas (7psia max RVP) is so much more stable than most automotive fuel.

And each time they switch the type of gas, they raise the price. People have short memories.

I'm no chemist, and I don't recall much about vapor pressure from high school chemistry, but I've always thought of RVP as the boiling point of gasoline. If atmospheric pressure is 15 psia, and the temperature of the gasoline reaches a temperature where the vapor pressure is 15 psi, then the gasoline will boil. Which is why vapor lock is a problem for fuel lines which are under vacuum and routed near an exhaust pipe. But evaporation will occur at much lower temperature than the boiling point, same as water evaporates at temperatures below 212F.

The thing you have to remember about your sealed fuel container is it is a system in equilibrium: The pressure has risen in the container to the point where no net evaporation can occur. If you raise the temperature, the pressure rises as fuel evaporates, until a new equilibrium is reached. Hence the best thing you can do to keep gasoline fresh is to keep in in a sealed container.

Let me try and explain it a different way and you tell me if you are confused or perhaps mis- reading.

RVP is the vapor pressure of the gasoline when the temperature is 100 degrees F.
If gasoline has a RVP of 14.7 The same as the air around us it would boil at 100 degrees in a open bucket.
If we change the RVP of the gas or increasing elevation and reduce atmospheric pressure we can change the boiling point of the gas.
The closer we get a liquid to its boiling point the better it vaporizes. Such as a dish of water. If we sit it on the counter at room temperature it will turn to a vapor and evaporate. But if we heat the water it will evaporate faster. The RVP of the water stayed the same we just messed with the temperture.

In the winter we want RVP high so the gas will vaporize in cooler temperatures because a engine will not run on liquid gas; it has to be vapors.
As the air temperature rises in the summer we lower the RVP to try and keep the gas in the tank long enough that we can use it but mostly to prevent pollution from evaporating gasoline. Yes some of it will evaporate but the lower we bring the RVP the less of it will.
The pressure in your gas tank is proof of this. Some of the gas is vaporizing in the tank from the heat (closer to the boiling point) and is building pressure in the tank. The same thing happens to a 5 gallon can set in the sun.

(quoted from post at 12:34:16 02/19/13) Talking heads on the news keep talking about gas prices and the soon schedualed switch over in the pipelines from winter gas to summer gas. Whats the difference between the two?

Click to expand...

Once again the old "wife tales" continue. The only thing that happens to gasoline with the summer to winter switch is that the RVP(Reid Vapor Pressure) changes. That means that the vapor pressure (volatility) is increased or decreased by adding more or less butane. I also agree that the market speculators screw up the pricing and that is why we get the price swings..

(quoted from post at 08:02:48 02/20/13)

(quoted from post at 12:34:16 02/19/13) Talking heads on the news keep talking about gas prices and the soon schedualed switch over in the pipelines from winter gas to summer gas. Whats the difference between the two?

Click to expand...

Once again the old "wife tales" continue. The only thing that happens to gasoline with the summer to winter switch is that the RVP(Reid Vapor Pressure) changes. That means that the vapor pressure (volatility) is increased or decreased by adding more or less butane. I also agree that the market speculators screw up the pricing and that is why we get the price swings..

Click to expand...

OK, explain this. How can you add butane to gasoline? After you explain that then tell me how the butane stays in the gasoline. You ever tried to put butane in a bucket? It won't stay there. Put some gasoline in a bucket then try to add some butane and it still won't stay there.

Yes, I understand what you are saying. My issue is how you compare atmospheric pressure to RVP. Perhaps I am nit picking however, allow me to explain.

RVP is a gauge pressure and has the units of PSI (pounds per square inch). Pressure gauges are calibrated at a reference pressure of 1 atmosphere (there are exceptions) and indicate the pressure above that reference point. That is to say the RVP gauge will read zero PSI when exposed to a pressure level of 1 atmosphere.

One atmosphere is 14.7 PSI however it is referenced to a pressure level of zero, that is the pressure, if the earth had no atmosphere. Since the presssures are referenced to difference values, to compare, the atmospheric pressure must always be added to the gauge pressure. This is the called the absolute pressure; one can think of it as the total pressure. Absolute pressure has the units of PSIA (pounds per square inch absolute), absolute, denoting the reference point is from zero pressure.

Therefore, a RVP of 14.7 PSI would be equal to 14.7 (atmospheric) + 14.7 (gauge) = 29.4 PSIA; 29.4 PSIA is not the "same" as one atmosphere of pressure (14.7 PSI). And, a RVP of 0 PSI would be equal to 14.7 (atmospheric) + 0 (gauge) = 14.7 PSIA which is the "same" and equal to one atmosphere of pressure.

That's it - that's my only issue.

Respectfully, Ken.

You're mistaken, Ken. RVP is an ABSOLUTE pressure. Remember back to your high school chemistry classes: When you have a mixture of gases (in this case air and gasoline vapors), the vapor pressure is the sum of the partial vapor pressures exerted by each of the constituent gases. That's why a closed container of gasoline becomes pressurized: the gasoline evaporates until an equilibrium is reached to where the pressure equals the sum of the partial pressures of all the gases in the container.
Wikipedia Reid vapor pressure

Just because you can't mix butane with other petroleum distillates in your garage doesn't mean they don't do it in a refinery. You'd also find it difficult to carbonate sugar water in your home, yet soft drink manufacturers do it every day. It is a fact that refineries use butane to raise the vapor pressure of fuel in the winter; google it.

Are you saying RVP is expressed in units other than PSI gauge?

Ken, did you check out the Wikipedia article in my previous post?

"It is defined as the [i:654c4848f0]absolute[/i:654c4848f0] vapor pressure exerted by a liquid at 100 °F (37.8 °C) as determined by the test method ASTM-D-323."

So vapor pressure is always absolute, NOT gauge. RVP is measured in psiA, not psiG.

(quoted from post at 19:15:31 02/21/13) Ken, did you check out the Wikipedia article in my previous post?

"It is defined as the [i:604b74db05]absolute[/i:604b74db05] vapor pressure exerted by a liquid at 100 °F (37.8 °C) as determined by the test method ASTM-D-323."

So vapor pressure is always absolute, NOT gauge. RVP is measured in psiA, not psiG.

Click to expand...

Yes, I read the Wikipedia article; I did not find a reference to the pressure units. However, the link to "Another RVP Definition" defines the pressure units as PSI. Also, in the link (bottom right of first paragraph) explaining the conversion between RVP and TVP, references the units of RVP as PSI.

The reason for my question was, did you see a definition for the pressure units or conclude the units were PSIA since RVP is defined as an absolute vapor pressure?

I also checked my copy of, Internal Combustion Engines by Edward Obert, third edition, 1968 to refresh my memory. He provides a summary of the RVP test in the Fuels chapter. In the summary he specifically states the units of pressure for RVP are in PSI (gauge). It is interesting that there is no reference to RVP as an absolute vapor pressure. Perhaps the absolute title was added later or maybe he felt it was confusing enough as is - I don't know.

My take is as follows:

RVP is measured using a bomb containing 4 parts air and 1 part chilled gasoline. The bomb is sealed and immersed in a 100 degree F water bath. Once the bomb and contents have stabilized at 100 degrees F the RVP is read on the attached pressure gauge. Therefore, the pressure gauge reads only the pressure increase from the initial condition to the final condition and is in units of PSIG.

Perhaps, since the pressure reading at the final condition of 100 degrees F includes the contribution of the 4 parts air and all components of the gasoline it is called an absolute vapor pressure. I am not a chemist and don't know. I did poke around the web however I did not find anything which actually explained why it is called absolute vapor pressure. Certainly this use of the word absolute is in a different context than for units of pressure.

Finally consider the following: Assuming a typical RVP of 7 PSI; using units of absolute pressure for RVP would mean, at 100 degrees F the pressure in a closed container of gasoline would be under a partial vacuum (14.7 PSIA - 7 PSIA = 8.7 PSIA. We know this is not the case.

Correction: The math in the last paragraph is in error and should be deleted. The paragraph should read as follows:

Finally consider the following: Assume a typical RVP of 7 PSI; using units of absloute pressure for RVP would mean , at 100 degrees F the pressure in a closed container of gasoline would be 7 PSIA which is a partial vacuum. We know this is not the case.

Sorrry for any confusion this error may have caused.

Ken