At the Shootout on Sunday, I was talking to this guy who was looking at my car - wanted to know about the 36horser etc. Filled him in on the details, told him of the niggles a couple of weeks ago when we had that stinking hot day. He said straight of - oh that would've been vapour lock (which it was). I said to him how so? He then went on, that the density of the fuel is different in winter than it is in summer, and that went we had the hot days a few weeks ago, that the less dense winter fuel wouldn't have liked it. He also added that the more dense summer fuel is due out on the 15th November.
Has anyone else heard this about fuel densities and the seasons? Whilst it wasn't the main part of the problem, it was certainly bought on by some vapour lock issues.
VWCOOL ·
Yep. He's right... also have different brews for alpine regions, especially diesel so it doesn't go waxy at real low temps
squizy ·
Thanks Glenn. Your bro mentioned the same thing.
Baja Wes ·
He's partly right.
It's not the density that changes. If the density changed then you'd have to change jet sizes to compensate.
They have different fuels for different seasons. They change the volatility of the fuel.
High volatility fuel (winter) will get vapour lock easy in hot weather, but will start easier in the cold.
From the shell website; "Shell varies the volatility characteristics each month to ensure good cold weather starting in winter and prevent vapour lock in summer. Consequently, petrol should not be stored for long periods. "
bugboymatt ·
Fuel denisty does change.
Not a big difference but it is noticable if you measure it. It can be different morning to night, from storage tank to storage tank. And is different from month to month and season to season. Region to region.
Baja Wes ·
The petrol companies do not change the density between seasons.
Yes all liquids do change density with temperature a VERY small amount. Water is 0.6% denser at 5 degrees than it is at 35 degrees. But that is trivial.
Optimax is denser than regular unleaded, and because of that carburetted cars require rejetting to run the best on it.
Doug Sweetman ·
Be clear on this guys..... the measure of volatility in fuel is called RVP, or Reed Vapour Pressure. The federal and state governments created fuel specifications dependant upon boundaries (if you look hard enough on the web you can find the map which shows where the boundaries start and stop), and it is this RVP number (measured in kPa) that is changed and controlled to ensure good cold weather starting (fuel is harder to vapourise when its cold, hence winter RVP specs go up) and to stop vapour lock (which is where the fuel vapourises too early - in the fuel line, not the throat of the carby, so in summer the RVP number goes down).
Now, the density of the fuel will change..... but thats a side effect rather than a controlled parameter (although it too has to stay within stringent specifications), as the different feed stocks that we blend (yes, I work for BP) have slightly different densities.
Fuel blending is a very complex business - some of the mogas (ie petrol) specs that we sell can be blended from up to 6 or more feedstocks, and we have to manage to 6 or 7 different spec measurements..... and not everything blends in a linear fashion. I'm glad I'm not in control of the blending operations.....
U2U me if you ever have any fuels questions - I might not necessarily have the answer striaght up, but I do have the network to get it answered.
Cheers
Baja Wes ·
yeah, you can find the technical data sheets and msds's for most fuel companies fuels, and yes they have a limited range of fuel density that you must stay within (usually measured at standard temperature - 15degC or something).
The amount density changes with volatility is overshadowed by the variation between blends and batches anyway. It still has to fall within the same limits all year around.
:thumb
bugboymatt ·
Baja Wes wrote:The petrol companies do not change the density between seasons.
No but the density of the fuel changes. It has changed now from what i used this morning. And I'm sure it will be different again this evening. It isn't a constant when out in petrol holding tanks and such like.
bugboymatt ·
Doug Sweetman wrote:Be clear on this guys..... the measure of volatility in fuel is called RVP, or Reed Vapour Pressure. The federal and state governments created fuel specifications dependant upon boundaries (if you look hard enough on the web you can find the map which shows where the boundaries start and stop), and it is this RVP number (measured in kPa) that is changed and controlled to ensure good cold weather starting (fuel is harder to vapourise when its cold, hence winter RVP specs go up) and to stop vapour lock (which is where the fuel vapourises too early - in the fuel line, not the throat of the carby, so in summer the RVP number goes down).
Now, the density of the fuel will change..... but thats a side effect rather than a controlled parameter (although it too has to stay within stringent specifications), as the different feed stocks that we blend (yes, I work for BP) have slightly different densities.
Fuel blending is a very complex business - some of the mogas (ie petrol) specs that we sell can be blended from up to 6 or more feedstocks, and we have to manage to 6 or 7 different spec measurements..... and not everything blends in a linear fashion. I'm glad I'm not in control of the blending operations.....
U2U me if you ever have any fuels questions - I might not necessarily have the answer striaght up, but I do have the network to get it answered.
Cheers
Thanks for that Doug.
Baja Wes ·
bugboymatt wrote:No but the density of the fuel changes. It has changed now from what i used this morning. And I'm sure it will be different again this evening. It isn't a constant when out in petrol holding tanks and such like.
That's why I said "Yes all liquids do change density with temperature a VERY small amount. Water is 0.6% denser at 5 degrees than it is at 35 degrees. But that is trivial."
:thumb
[ Edited on 7-11-2006 by Baja Wes ]
bugboymatt ·
You'd be surprised a small amount can make a big difference.
VWCOOL ·
VWCOOL wrote:Yep. He's right... also have different brews for alpine regions, especially diesel so it doesn't go waxy at real low temps
lol... Maybe I shoulda said: 'Something like that, they have different brews...'