Re: How to Blend Your Own Fuel, and Why You Should
 

Sometimes it doesn't. My testing in Huntsville indicates three brands, Shell, Exxon, and Chevron, appear to have about 11% more energy in their 87 octane gas than the other brands, Conoco, BP, Texaco, and Citgo. The lower energy brands have the same energy content as the better brand, 93 octane, Shell and Texaco.

I was able to see this in my gasoline testing at the higher power levels.

Bob Wilson

Re: How to Blend Your Own Fuel, and Why You Should
 

Higher octane fuel allows for higher compression engines. Higher compression engines are capable of getting more energy out of gasoline than are lower compression engines. At least at their thermodynamic limits. This is the ONLY reason that diesels get better mileage than gas cars.

So while there might not be any more energy in the fuel, you can access more of it.

Also, low octane fuel in a high compression engine can self ignite due to the compression. This is the cause of engine knocking. Adjusting the spark timing won't do jack for it. But, fuel mixtures can be adjusted to prevent it.

You can not get the full engine power off of low octane fuel.

In my experience premium fuel has more detergents than regular. Now, does it matter? I don't know. I'm betting not, but still I think it's important to be accurate.

BTW, I'm looking forward to the results of the E30 testing. I had read the articles mentioning it as the sweet spot, and have been really curious about the results.

Re: How to Blend Your Own Fuel, and Why You Should
 

Maybe I should have stated my sources - the American Petroleum Institute themselves. Here are direct quotes from their website:

http://www.api.org/aboutoilgas/gasol...ine-octane.cfm

"Octane number is a measurement of fuel’s resistance to engine knock. Engine knock is an abnormal combustion associated with using gasoline with too low of an octane number. Ordinarily, your vehicle will not benefit from using a higher octane than is recommended in the owner’s manual."

"Knock Sensors
Many modern vehicles are equipped with an electronic device that detects and eliminates light knocking before you can hear it. The devices suppress knock by retarding the spark."

"Gasoline with a higher heating value (energy content) provides better fuel economy. Traditionally, premium gasoline has had a slightly higher heating value than regular, and, thus, provides slightly better fuel economy, but it is difficult to detect in normal driving. There can be even larger differences in heating value between batches of gasoline from the same refinery, between summer and winter volatility classes, or between brands of gasoline from different refineries because of compositional differences. The differences are small and there is no practical way for the consumer to identify gasoline with a higher-than-average heating value."

But this is from the API, so they do have to claim that there is some value in that premium gasoline you are buying. They do represent the petroleum industry, you know.

And higher compression engines don't actually gain any power using higher octane gasoline, they just don't lose that portion of power that sometimes happens during acceleration from pre-ignition (knocking) that they would with lower octane. The power in the gasoline is the same, it's just the point in the compression cycle when the ignition happens that determines how much power the engine gets out of the gasoline. Knocking happens when the fuel starts to ignite before the piston reaches the top of its stroke. If that happens you lose horsepower because then some of the energy from fuel combustion is working against the power stroke of the engine. That's being a bit simplistic because the ignition phase of the stroke actually does start just before the absolute top of the stroke (Top Dead Center), usually about 10-25 degrees before TDC, but the maximum power of the combustion cycle doesn't happen until just after TDC. Knocking happens when the fuel burns too fast and the maximum power of the combustion happens before TDC instead of after. Modern engines will detect that this is happening and retard the spark so that maximum power happens after TDC.

Re: How to Blend Your Own Fuel, and Why You Should
 

i use 110 octane in my track car... then again it is 10.2:1 compression, 12psi and turns at 8000rpm :shade:

Re: How to Blend Your Own Fuel, and Why You Should
 

I was just reading up some more on E85. I don't think I saw it mentioned here, but they have a winter/summer mix of E85 too! in the winter E85 is really E70. can someone else please confirm this as it would put our table all off.

Also, even in the summer E85 is the rating of the gas before it's denatured. So it's really about E81 given the standard 4% denatured rate of normal. Flex fuel vehicles don't have a problem with the variation in percentages since they have a fuel sensor. but since we're trying to work off of a fixed value we need the proper values to start with.

Re: How to Blend Your Own Fuel, and Why You Should
 

Ethanol is manufactured as 200 proof, or E100 at the distillery.

This is, for all practical purposes, whisky, and could be digested by humans.

In order to comply with ATF rules, the pure "whisky" must be poisioned, or "denatured" on the premises... no 100% ethanol is allowed to leave the property, or else it would be taxed as a beverage, and cost the same as liquer. ( What does Vodka cost per gallon anyways? $40 a gallon? More? )

So to comply with ATF rules, all ethanol leaves the plant with 2.5% to 5% gasoline in it from the get go. All rail tankers, and all truck tankers are denatured with on average, 4% gasoline.

The gas station then adds 10% of whatever gasoline they have on hand ( probably in most cases the lower Octane ).

The E85 pumps in Minnesota say "contains at least 85% ethanol".

If the ethanol they got this week had 4% denaturant, they would be selling E86 this week. Next week they could get ethanol with the minimum amount of denaturant ( as gas prices rise, this is more likely ) and they could be selling E87.5

I have never ever heard of "winter E70".

-John

P.S. Cars would run fine in warm weather on pure alcohol. Indy cars run on E98, only because they too must have denaturant to comply with ATF. The 15% gasoline is added, mostly, to make it burn easier in cold weather.

Re: How to Blend Your Own Fuel, and Why You Should
 

http://genomicsgtl.energy.gov/biofue...ortation.shtml

Re: How to Blend Your Own Fuel, and Why You Should
 

Fadi, thanks for the insight into this matter.
I did additional research and here is what I found.

The American Society for Testing and Materials (ASTM) and the Alliance of Automobile Manufacturers have

Re: How to Blend Your Own Fuel, and Why You Should
 

sure, and thanks for your additional legwork.

I actually came about that info as I was researching what it would take to convert my track car to run on E85.

Re: How to Blend Your Own Fuel, and Why You Should
 

This morning I was getting irritated getting 'only' 32 MPG.

It was 15'F outside, but I did use the block heater this A.M.
What gives?! I was thinking to myself.

Oh ya.... I forgot I was using ( appox. ) 35% ethanol this week.
Until I get my graduated cylinders and pipets, I can't be sure on the %.

I did notice on "Long term fuel trim" with a ScanGauge, I was running with fuel trim at +8.5. Normally with plain gas, this number hovers about zero.

I'm not sure if that number really equals 8.5% more fuel, or if it is just some number. Ideas?

With gas, the number will be negative a few (%?) when coasting, and positive a few (%?) when accelerating, with the median about zero. With 30% ethanol and greater, this number hovers about 8.5, and goes to 12.x when accelerating, and down to 3.x when coasting.

-John

P.S. The mechanics handbook says -20 to +20 are normal values with regular gas. I wonder if that is some limit, or if +25 is possible?
The lowest I've ever noticed was -10 and greatest was +15.