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Fuel article

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Posted by: SUnruh

since we are always talking about fuel, i though i might mention this.

in the March 2001 issue of Hot Rod magazine, there is an article on fuel. it describes distillation curves, vapor reed pressure, T10, T50, T90, boiling points and octane. it also shows the math formulas for some of the equations as well as a specific gravity conversion table. the talk about the cracking process and lots of other info.

it might be worth looking at if you are interested in this info.

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Steve Unruh - Texas Championship Hare Scramble Series - T14
'01YZ250F (un-crowned '01 Bike of the Year)
98yz250 (put to pasture)
81yz125 (for friends to ride),'00ttr125l (wifes)


Posted by: 48

While I was at the gas station today mixing up MX fuel I was curious about the freshness of premium gas at the pump. I think most of us mix a blend of 50/50 with race fuel and premium gas. With all of the new cars today only requiring regular gas and the high price of premium gas, how fresh do you think the premium gas is these days? Regular gas has such a higher turnover rate would we be better off mixing the race fuel with regular?


Posted by: Vic

48- You might be surprised how many people put "Super" in their cars. Many people assume that the higher octane number and price mean higher quality.


Posted by: spanky250

Vic is right. I have argued with friends about this before. If your car says to run regular, you are wasting money putting higher octane in, and in fact this can hurt te performance of some newer cars that use engine sensors to advance the timing just to the point of detonation. Too much octane in these engines results in too much advance. Higher octane gas also doesn't evaporate quite as easy as a lower octane, which is the reason it is more resistant to detonation. But try to convince someone of this after the years of being deluged with ads trying to convince people that premium gas will somehow magically make their car run better or have better performance. Look around you at the gas pumps at a busy station sometime. You will see lots of people put premium in cars that do not need it. I asked a friend about this that works at a gas station once, he said probably 40% of their gas sales were premium.

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1992 KDX 250-FMF porting,two-stage power reeds, Fatty pipe, Power Core silencer,titanium rod,Wiseco Ultra-lite, Pro-Action suspension...Why didn't I take the blue pill???


Posted by: Rich Rohrich

Quote:
Originally posted by spanky250:
Higher octane gas also doesn't evaporate quite as easy as a lower octane, which is the reason it is more resistant to detonation.


Octane has no specific influence on the vaporization curve, endpoints, or the latent heat of a hydrocarbon based fuel. The vaporization curve has no specific influence on the fuels resisitance to autoignition (octane rating) either.




Posted by: spanky250

Rich, I am not a chemist, so pardon my ignorance, but this sort of thing does interest me, so I will ask what may be a stupid question. For a fuel to be more resistant to pre-ignition, doesn't it have to be less volatile? And doesn't lower volatility mean it takes more heat energy to evaporate it? Just trying to learn something here...


Posted by: Rich Rohrich

Quote:
Originally posted by spanky250:
For a fuel to be more resistant to pre-ignition, doesn't it have to be less volatile? And doesn't lower volatility mean it takes more heat energy to evaporate it?



You could write a book answering the fuel volatility question. http://dirtrider.net/ubb2/smile.gif Volatility is the tendency of a fuel to evaporate {to change from a liquid to a gas state}. Volatility has a major influence on the vapor-air ratio in the cylinders at the time of ignition. The greater (higher) the volatility of a fuel the greater the tendency to evaporate. In a normal engine nearly all the fuel needs to be evaporated before ignition. So for any Engine/Air Temperature combination there is a minimum volatility that is required for proper running. Fuel is made up of a variety of hydrocarbons with different boiling points. By combining the various hydrocarbons the blender will design a "Volatility Curve" or "Distillation Curve" for the fuel. The ASTM Distillation test provides a measure, in terms of volatility, of the relative proportions of all the hydrocarbon components of a gasoline. The ASTM distillation curve designates the maximum temperatures at which 10%, 50%, and 90% of the fuel will be evaporated as well as the maximum end point temperature. These distillation characteristics, define and control, starting, warm-up, acceleration, vapor lock, and crankcase dilution. The significance of any point on the ASTM volatility curve depends on the temperature range in question. Under low temperature conditions as in cold weather starting, when only a small portion of the fuel is evaporated, the low temperature end of the curve is the most. While for higher temp ranges like those in the intake of a hot engine the shape of the low temp end of the curve is much less important since all of this part of the fuel is evaporated anyway. Oil companies vary the 10% distillation point seasonally to correspond to the weather. Different parts of the country will have their fuels blended to compensate for regional elevations as well. Most Racing fuels have Distillation curves that fall into a much more narrow temperature range that is held consistent year-round.

I have some basic guidelines I use that have proven to be fairly effective.

- The 10% temp has a big effect on throttle response. Short intake tracts, and big throttle transitions with big rpm swings usually require lower temps (below about 150F). The shorter the intake distance and the lower the intake temps the lower you need to go to get good response. With more heat in the intake tract you can go higher.

- As rpm rises above about 7000 the 90% temp needs to get lower. Once the rpm is in the 7000+ range I like to have the 90% point below ~240F

It gets tricky. You need the fuel to stay liquid until it gets to the intake tract where you want it to vaporize. If it vaporizes too early you risk vapor lock. If it doesn't vaporize, it will tend to leech heat from the combustion chamber, and get blown out the exhaust. Can you say SPOOGE? It can be a delicate balance.

None of this has any influence on the octane rating of a fuel. The octane rating, or the fuels resistance to auto-ignition (detonation) is influenced by the hydrogen/carbon bonds and basic chemistry.

If this isn't clear there is more info @ http://www.ericgorr.com/tech/Fuel_Basics.htm




Posted by: wayneo426

Whoa, thats heavy.

Thanks, I needed that as well.


Posted by: WFO

This may be a little off subject, but what the heck. I always enjoy reading Rich's responses because I like to know how things work. From a practical standpoint (for me at least) I will continue to get gas at one of the local Shells, Exxons, etc. 'cause that's what I have access to.
From that viewpoint, I was wondering. As stated, octane has nothing to do with the inherent energy of the fuel. I assume this content is expressed in btu . In any event, has anyone ever done an analysis of the major brands to see which ones have a higher energy content, or are they all about the same?

[This message has been edited by WFO (edited 02-16-2001).]


Posted by: Rich Rohrich

This is about as close to what you're looking as I've seen.

SAE paper # 1999-01-3584

Title: An analysis of 1996-98 gasoline quality in the United States

Abstract:
The importance of the fuel in providing improved vehicle performance and reduced emissions has become widely recognized, especially in the past ten years. In 1998 an SAE paper was presented providing a systematic analyses of 1996 United States gasoline quality. This paper extends the methodology of that paper to include the impact of fuel composition on evaporative emissions, and it provides analyses of gasoline quality for the years of 1996, 1997 and 1998.

The vehicle performance and emissions characteristics of gasolines were determined using data from surveys of United States'' service station gasoline samples. Results are presented for: gasoline type (California RFG - reformulated gasoline, Federal RFG, low RVP - Reid Vapor Pressure, and conventional); gasoline grade (regular, intermediate and premium); individual cities; individual brands (coded); and for sulfur content. It is concluded that: differences exist among commercial gasolines for all of the items evaluated; the differences are narrowing; and overall gasoline quality is improving.

Author(s):

Name Affiliation
Joseph M. Colucci Automotive Fuels Consulting, Inc.
Thomas L. Darlington Air Improvement Resource, Inc
Dennis F. Kahlbaum Air Improvement Resource, Inc.

Other Info:
Publisher: Society of Automotive Engineers, Inc., Warrendale, Pennsylvania, USA
Publishers Segment: SAE
Country of Publication: United States
Meeting Name: 1999 SAE International Fall Fuels and Lubricants Meeting and Exposition
Meeting Location: Toronto, Ontario, Canada
Meeting Start Date: 10-25-1999
Meeting End Date: 10-28-1999
Larger Publication: SP-1479


Posted by: WFO

[QUOTE]Originally posted by Rich Rohrich:

Title: An analysis of 1996-98 gasoline quality in the United States

"It is concluded that: differences exist among commercial gasolines for all of the items evaluated; the differences are narrowing; and overall gasoline quality is improving."

Guess I should interpret this as, "..if you find one you like, stick with it"!



[This message has been edited by WFO (edited 02-17-2001).]


Posted by: spanky250

Rich, you constantly amaze me. Where do you find some of these things that you post? I think that Einstein Avatar is definately accurate. http://dirtrider.net/ubb2/smile.gif



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