I don't know where you got your informations from MVD, but here is the Midwest, ethanol is not belended with the gas at the gas gas station, but is delivered already blended. What an invitation for explosion if it was.

 

You are confusing the cost of production with the price at the pump. Without government intervention through tax credits and other benefits, ethanol producers would not be able to sell their product because the cost of manufacture is too high. As for the price of 87 vs ethanol-enriched 89, there must be some supply - demand forces at work. Or more government intervention?

 

As I stated above, water is highly soluble in ethanol. Hence, if refiners were to add ethanol to gasoline at the refinery and then pipe it for distribution, it would accumulate water that would settle out in the tanks at the gaso station. This is an unacceptable risk as the end user (you) will ultimately get some in your car.

My statement that it's "blended at the pump" is industry jargon that means that ethanol is added at the last possible point. In reality, this is the pump rack where the trucks fill up, not literally at the station. For the consumer, this means added costs (because it can't be blended in the refinery like MTBE).

BTW, your comment that if ethanol were blended at the station, it would be an invitation for an explosion. I can't imagine why you would think handling ethanol is more dangerous than handling gasoline.

 

mvd, Thanks for the info and keeping us in line. We need a few more ChemE's on board! Too bad we can't readily get 93 in CA. I guess that may be a reason the new 987/997s require only 91 octane.

 

Where did you hear that? The 997 owner's manual still says the same as what all previous 911 manuals said:


.

 

(If you are interested, I'll be glad to explain how CA gaso differs from the rest of the US.)


mvd, I'd love to know the difference, this thread has been most educational, and it is nice to hear from someone with a fuller knowledge of the juice we run our toys on.

You say that putting 100 octane in our tanks is a waste, but I can feel a definate difference, especially at lower revs, which is where a car might 'pink'. Is this simply because I'm giving the octane sensor a 'green light' to run at it's 93 design maxium, while the CA 91 is telling it to back off a bit?

 

It may also be interesting to note that several states including CA asked for exemption to not include Ethanol in our gas. This was denied. Ethanol mixed with gasoline is actually worse for the environment than CA gasoline alone as
it significantly reduces gas mileage.

Ideally, we should standardize on a single blend of gasoline across the country with a winter and a summer variation and then we will finally get rid of
the pockets of high gasoline prices all the way across the country.

Unfortunately, the political process has failed the science and economics once again.

 

I'll admit this is all 2nd-hand info (not as authoritive as the manual), but I subscribe to all the major car mags, and they've all been consistently quoting Premium 91 octane as the requirement. I think I've even seen it in some Porsche literature. I did find some Porsche literature on the 2004 GT3, and it specs 91 octane (no method specified).

This perked my interest since the previous P-cars were 93 octane. This is (R+M)/2. My fuel filler door says 93 octane (R+M)/2. This is in California. I didn't check the manual, since the door reminds me every time I fill up. The requirements and measuring method are sure to vary outside of the US. Is your car US-spec?

 

Quote:

If you are interested, I'll be glad to explain how CA gaso differs from the rest of the US.

Comments:

As I'm sure most are aware, CA (and LA in particular) have suffered from high levels of air pollution. Back in the '80's, the refiners and the auto industry formed a committee to study ways to reduce auto emissions. It was agreed that the refiners would make cleaner burning gasoline and the auto industry would improve fuel injection and catalytic converter tech (among other improvements). As a side note, Unocal secretly patented the agreed upon gaso specs and demanded royalties from the other refiners. This legal battle continues to this day and it's also interesting to note that Unocal sold all their refining assets and they no longer refine gaso in any market!.

Gaso sold in CA is called CARB III (the third update to CA's clean gasoline specs) and is characterized by the following.

1. Lower average boiling point to reduce the amount of unburned hydrocarbons (ie, less CO and HC at the tail pipe) because the larger molecules are harder to vaporize and less likely to burn completely.

2. Lower sulfur as it's a contaminant that leads to SOx (and acid rain) and also causes higher NOx (the new diesel regs also called for significantly lower sulfur). This is a good rule for everyone.

3. Lower aromatics such as benzene as these as they suspected carcinogens (unfortunately, aromatics also have high octane numbers).

Taken alone, these changes in the gaso regs have no detrimental effect on our cars. However, the mandate to lower the ave boiling point effectively reduced the amount of gaso available on the market and also reduced the overall octane (because some higher octane components could no longer be blended into the gaso pool). This fact triggered the reduction in the octane rating of premium from 92 to 91. This hurts because, if our cars sense knock, the timing will be retarded and power will be lost.

What confuses me is Porsche's reference to a RON octane rating. In the US, we use the ave of the research octane number (RON) and the motor octane number (MON) as stated on every gaso pump. In a refinery, raw gaso from an FCC unit typically has a 93 RON and 83 MON. If this was sold at the pump, it would be an 88. So why the reference to 98 or 95 RON? Can we safely translate this to a 93 or 91 (R+M)/2? Don't know.

Quote:

Is this simply because I'm giving the octane sensor a 'green light' to run at it's 93 design maxium, while the CA 91 is telling it to back off a bit?

Comment:

It's certainly possible that your car is designed to take advantage of an octane as high as, say, 93 and our recently reduced premium at 91 just doesn't cut it. But I can't imagine that running anything higher than 93 will be beneficial (unless Porsche has a few tricks up their sleeve!).

 

You are correct that CA asked for an exemption from the oxygenate rule. After all, a common sense approach would be to mandate clean burning gaso (as measured at the tail pipe) and let the free market find the best way to achieve it. But no, the feds have mandated oxygenate. Since MTBE and TAME are nasty, we are stuck with ethanol (which is very expensive to produce).

You are not correct, however, the ethanol is worse for the environment or that it significantly reduces mileage. No such evidence exits (and it defies all logic).

Interestingly, the oxygenate rules were devised in the 80's and in fact improved tail pipe emissions in that era. But it's no longer true for modern cars and engine management technologies. The oxygen mandate is bad politics that contributes to higher prices at the pump without benefit .

 

Amen to that.

And for those wondering about winter vs summer gasoline, the winter version contains high amounts of lighter components such as butane to increase the vapor pressure. This improves vaporization in the combustion chamber to allow easier starting.

This chem eng grew up in MN and recalls squirting starter fluid into the carbuertor to start cars when the temp was 30F below. This was, of course, back in the 70's.

 

mvd,

thanks for all the time you put in the explanation. I was almost doing the same thing in the 997 forum. Luckily somebody linked us (997 drivers) to this thread. Saved me a lot of time!!

For the forum: I'm a chemical engineer too, and most of what mvd says is correct. The only worry I have is that we (chemical engineers, me included) have to be carefull by using too many abbreviations. Like FCC unit, also called the "cat cracker": that is the unit where most of the ingredients for your gasoline is produced.