| soletek |
05-14-2008 06:29 PM |
Ethanol hmmmmm . . .
Maybe I can shed some light on this subject. Iso-octane, the standard that all fuels are measured against, is a 100 octane gasoline. Octane is a measurement system not unlike an inch, or an hour. It is a fuel's ability to resist the combustion process. The resistance allows an engine to be built specifically for best efficiency to complete the one task the internal combustion engine has: The conversion of chemical energy into mechanical force. Iso-octane has a stoich. air/fuel ratio of 15.1:1 and a heating value 19,100 btu/lb. The specific energy at stoich. air/fuel ratio is 2.9 and the heat of vapor is .027. The formula is C8H18 and the molecular weight is 114. The oxygen content is 0 which makes a very energy rich fuel. As you all know, gasoline at the pump depending on grade has a 87 to 93 octane, on average. The increased dilution lowers the heating value and therefore the specific energy in each gallon of gas that your engine consumes. This is dually beneficial for fuel manufacturers. The shorter distance you get per gallon of gas forces you to return back to the pump earlier at higher prices. This is why it is beneficial for them to put greater quantities of ethanol into their mix. Ethanol (C2H5OH) has a molecular weight of 46, and next is one of the big ones: Oxygen content is 34.8 with a horrible stoich. air/fuel ratio of 9.0:1, a heating value of only 11,500 btu/lb, a specific energy of 3.0, and a desirable heat of vapor of .93. Boiling point is 78 degrees. That can be a plus or minus. Depending on whether your fuel tank vents to the atmosphere, (The next time you go to start your car it may not have the same amount of gas as when you shut it off.); as well as, an octane number varying between a RON of 109 and and MON of 90. To put this in layman's terms: a gallon of gas from 1969 compared to a gallon of gas today would yield much greater mileage due to the specific energy that the '69 gasoline had (usually around 100-108 octane). Oil companies discovered a long time ago that diluting the fuel couched under the guise of cleaner, therefore better, allowed them to increase their profit margin while providing a much poorer product to the public. This is why vehicles from the '60s and '70s were built with very high static compression ratios. They were built for the fuel that was being sold at that time. Inversely, the late '70s to '90s vehicles had low compression ratios because they were built to burn the fuel sold at that time. Today's pump gasoline in California is not required to have a posted ethanol content if it is lower than 15 percent. That might answer some people's questions about why they consistently get worse mileage at one station and better mileage at another. Today's vehicles use very elaborate fuel management systems to optimize the engine's performance with today's overly diluted fuels. Many of today's newly manufactured vehicles are starting to be built with higher static compression ratios due to better combustion chamber and cylinderhead designs. Now the next whammie: Flex-fuel vehicles have noticed an understandable 26 percent decrease in mileage when using E85. One would wonder whether the use of smaller quantities of the higher specific energy original gasoline would produce higher emissions compared to much larger quantities of the highly diluted fuel of today. Especially using today's much more design efficient cars. It has been a question in my mind for a long time.
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