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  #31  
Old 02-10-2004, 01:03 PM
SaabTuner SaabTuner is offline
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"The alcohol plot is quite mis-leaning if it was described in text only. The engione virtually runs on alcohol rather than gasoline. The experiment is probably done on 2-valve per cylinder, long stroke enigne - octane demand/performace is that much greater is BMEP is "detonation threshold limited". However, it give a good indication of fuel quality against power. "

I don't believe that is entirely true. Remember that the alcohol/water is injected at a fixed percentage relative to the fuel. If the fuel is leaned, so too is the alcohol. At a 22:1 A/F ratio, which is at the far left of the alcohol plot, the alcohol included A/F ratio is still only 16.5, and if you take into account the fact that alcohol is stoichiometric at less than half the A/F ratio gasoline is, it's realistically going to act like a 19:1 A/F ratio.

The engine in this experiment was running on AN-F-28 aviation fuel. The relative octane enhancement of the Methanol would depend on the octane of that fuel.

But whatever "octane enhancement" the Methanol provides should be constant across the air-fuel ratios. It would not enhance disproportionately more in the lean regions.

Adrian~
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  #32  
Old 02-10-2004, 01:36 PM
Forum Admin Forum Admin is offline
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It is difficult to arise at a stoichmetric ratio betwen fuel and gasoline when the alcohol is at a fix ratio to fuel (it can be calculated).

At rich air fuel ratio, all liquid acted as a coolant when oxygen is fully consummed. But at lean air/fuel ratio, alcohol becomes a high octane fuel rather a coolant.

We need to define what portion of fuel is used for combustion across the plot, with the exception of water, air/fuel/methanol is still any unknown variable.

I suppose the details doesn't really matter as long as it produced a repeatable result.
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  #33  
Old 02-10-2004, 02:15 PM
SaabTuner SaabTuner is offline
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Quote:
Originally Posted by Forum Admin
It is difficult to arise at a stoichmetric ratio betwen fuel and gasoline when the alcohol is at a fix ratio to fuel (it can be calculated).

At rich air fuel ratio, all liquid acted as a coolant when oxygen is fully consummed. But at lean air/fuel ratio, alcohol becomes a high octane fuel rather a coolant.

We need to define what portion of fuel is used for combustion across the plot, with the exception of water, air/fuel/methanol is still any unknown variable.

I suppose the details doesn't really matter as long as it produced a repeatable result.
Since this methanol was injected at essentially the same location as the fuel, and by the same method, it may as well have been mixed with the fuel.

Therefore I think it would be reasonable to use the "blending octane" listed for Methanol:

(Different from the straight octane. These are used when Methanol is blended with other fuels, which is essentially what is happening in this case.)

RON: 133
MON: 105

The blending octane for methanol should very accurately describe the effects of the methanol on octane given the method for injection.

The only variable now is the octane of the AN-F-28 Aviation fuel used in the study.

Also it should be noted that the consumption of methanol relative to fuel does not increase in the lean region, therefore if you have sufficient air you might find that running lean with a high meth/water injection level could allow for serious amounts of power without running a huge fuel tank for the methanol.

Adrian~
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  #34  
Old 02-10-2004, 02:31 PM
Richard L Richard L is offline
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We are now getting into the realms of comparing power and octane valve, as stated on the (just about possible to read) - the chart is plotted against the resistance to knock. so if race gas is added to the chart, we will be able to another interesting curve. Keen to know the octane value of the fuel used on the test.

Most californian fuel is oxygenated, it doesn't seem to prodcue the same effect as the chart I wonder what happen to the knock resistance properties?
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  #35  
Old 02-10-2004, 02:50 PM
SaabTuner SaabTuner is offline
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"Most californian fuel is oxygenated, it doesn't seem to prodcue the same effect as the chart I wonder what happen to the knock resistance properties?" -- Richard L

MTBE, which is what is used primarily in other states, is also an Oxygenate. California just has much lower octane in most places because the cost to refine 93 octane fuel at the VERY low Sulfur requirements of California would raise the price of fuel to beyond what most gas stations think the average consumer will buy.

So they makeup for the added cost of refining low sulfur by selling ultra low octane cheaper gasoline. Though you can buy 100 octane fuel at some pumps in CA, it just costs more than it does anywhere else in the US. (Except maybe Alaska or Hawaii.)

According to most tuners CA gas behaves like 89 octane everywhere else in the country. :roll: Sucks to live here.

Adrian~
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  #36  
Old 02-10-2004, 07:55 PM
hotrod hotrod is offline
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Default AN-F-28 fuel

The Fuel: Spec AN- F- 28, is Graded as 100/130 using the aircraft PN system. The 130 corresponds to the rich power condition, and the 110 is the lean mixture max power rating.

For those who have never heard of the Aircraft PN system, it is an attempt to rank fuels that exceed the maximum octane of 120 that can be determined using the automotive octane tests. They extrapolate the "effective octane" of the fuels based on how much TEL would be needed to get a conventional gasoline to reach the same performance levels.

The Rich max power setting is the typical condition you would use for max take off power, using a rich mixture to prevent detonation under heavy load .

The lean max power setting would be the condition an aircraft would use for high altitude cruise, with lean fuel mixture to get maximum range.


Quote:
"Most californian fuel is oxygenated, it doesn't seem to prodcue the same effect as the chart I wonder what happen to the knock resistance properties?" -- Richard L
I suspect if you looked at the specs for the California RFG gasolines you would find they are a "high sensitivity" blend. Sensitivity is the difference between the RON and the MON. RON has the most effect on engine run on at shutoff and low rpm knock, MON has most effect on high power high rpm condtion knock ( ie. exactly what most performance situations demand)

The R+M/2 AKI system used in the U.S. is simply the average between those two numbers but there (to my knowledge) is no requirement on how large a spread is allowable between the two. Most gasolines are blended with a sensitivity of 6 -10.

If your target is 91 octane you can get it with many different blends that average to that R+M/2 number. YOu could have a fuel of Ron 95, MON 87 and you would have an AKI of 91, and you could also get the same AKI with a blend that rated as RON 93, MON 89. Obviously the former would not be as suitable to use in a high performance car as the latter.

If your comparing fuels for high performance applications, pay attention to the MON numbers they are the most important.

Larry
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  #37  
Old 02-10-2004, 08:55 PM
Richard L Richard L is offline
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Thanks, Larry.
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  #38  
Old 02-10-2004, 08:58 PM
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Quote:
Originally Posted by SaabTuner
"Most californian fuel is oxygenated, it doesn't seem to prodcue the same effect as the chart I wonder what happen to the knock resistance properties?" -- Richard L

MTBE, which is what is used primarily in other states, is also an Oxygenate. California just has much lower octane in most places because the cost to refine 93 octane fuel at the VERY low Sulfur requirements of California would raise the price of fuel to beyond what most gas stations think the average consumer will buy.

So they makeup for the added cost of refining low sulfur by selling ultra low octane cheaper gasoline. Though you can buy 100 octane fuel at some pumps in CA, it just costs more than it does anywhere else in the US. (Except maybe Alaska or Hawaii.)

Thanks for the information.

I am still puzzled why don't they add more alcohol to their fuel to boost the octane number to some where near the chart?


According to most tuners CA gas behaves like 89 octane everywhere else in the country. :roll: Sucks to live here.

Adrian~
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  #39  
Old 02-10-2004, 08:59 PM
Richard L Richard L is offline
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Quote:
Originally Posted by SaabTuner
"Most californian fuel is oxygenated, it doesn't seem to prodcue the same effect as the chart I wonder what happen to the knock resistance properties?" -- Richard L

MTBE, which is what is used primarily in other states, is also an Oxygenate. California just has much lower octane in most places because the cost to refine 93 octane fuel at the VERY low Sulfur requirements of California would raise the price of fuel to beyond what most gas stations think the average consumer will buy.

So they makeup for the added cost of refining low sulfur by selling ultra low octane cheaper gasoline. Though you can buy 100 octane fuel at some pumps in CA, it just costs more than it does anywhere else in the US. (Except maybe Alaska or Hawaii.)

According to most tuners CA gas behaves like 89 octane everywhere else in the country. :roll: Sucks to live here.

Adrian~
Thanks for the information.

I am still puzzled why don't they add more alcohol to their fuel to boost the octane number to some where near the chart?
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  #40  
Old 03-10-2004, 04:37 AM
SaabTuner SaabTuner is offline
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Quote:
Originally Posted by Richard L
Thanks for the information.

I am still puzzled why don't they add more alcohol to their fuel to boost the octane number to some where near the chart?
Too much alcohol and the Stoichiometric A/F ratio changes a great deal. Most cars are designed to be able to run on up to 20% Ethanol/Methanol blends ... but they have to make sure that the cars which are not designed for that can still buy gas.

Adrian~
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