Octane rating or ethanol. Which is more

Discussion in 'General Industry Discussions' started by Basilhayden, Sep 30, 2012.

  1. CL&T

    CL&T LawnSite Senior Member
    Messages: 493

    To answer the original question, all 2 stroke manufacturers tell you not to use lower than 89 octane. I don't know of any 4 stroke manufacturers that tell you that. So unfortunately if all you have in E0 (ethanol free) is 87 you are stuck with using E10 89 octane in your 2 strokes. I see no problems and only advantages to using the E0 87 octane in your 4 stroke stuff.
  2. CL&T

    CL&T LawnSite Senior Member
    Messages: 493

    Incidentally they are trying to push through the requirement for E15 (15% ethanol) even though any more that 10% is prohibited by all small engine manufacturers and will harm many other equipment and older cars. Both will likely be available from the same pump which will lead to huge misfueling problems from people not knowing what their car can run on. The government has even come up with the stupid idea that where both E10 and E15 are available from the same hose and pump that there be a 4 gal minimum purchase of E10 just to purge the pump and hose of E15 to make sure the ethanol content of the E10 is not greater than 10%.
  3. cgaengineer

    cgaengineer LawnSite Fanatic
    Messages: 15,778

    Alcohol dragsters go faster because the engines are built for alcohol, but once again...we are talking mower and trimmer engines, not supercharged high compression engines DESIGNED to run on ALL alcohol.

    Btus are still btus...in order to make more power out of less btus something has to change internally inside an engine...so they increase the compression ration and install superchargers that can utilize the higher octane ethanol, though lower btu and in turn they overcome the lower btu output of the fuel.
    Posted via Mobile Device
    Last edited: Oct 2, 2012
  4. GMLC

    GMLC LawnSite Platinum Member
    Messages: 4,345

    This has been talked about before. Yes ethanol has less BTU's than gas but has more energy density. Higher ethanol produces more HP. Below are the results from many studies done to prove this. Sorry its hard to read because the chart doesnt copy and paste just the text. Ethanol content is the second line down and HP is second from bottom. Results are listed in order from E10 up to E85.

    Table 4. Heavy-Load (4.7 L Engine)
    Fuel Ethanol Content 10% 20% 30% 85%
    BTU content (BTU/gal) 111,070 107,140 103,210 81,595
    % change in BTU’s per gallon 0% -3.5% -7.1% -26.5%
    65 mph
    Hp 50.8 52.1 52.0 54.4
    Gph 5.96 6.08 6.27 6.93
    Mpg 10.7 10.5 10.3 9.3
    BTU’s per mile 10,347 10,237 10,016 8,744
    Gallons per hp hr 0.117 0.117 0.120 0.127
    BTU per hp hr 13,035 12,514 12,431 10,393
    Fuel Trim % -2.6% -1.0% -1.4% -0.6%
    Injector Pulse Width (ms) 8.5 8.6 9.1 11.6
    % change in pulse width 0% 0% 7% 36%
    50 mph
    Hp 34.5 33.0 40.4 33.3
    Gph 3.81 3.91 4.01 4.51
    Mpg 13.1 12.8 13.1 11.1
    BTU’s per mile 8,459 8,348 7,908 7,338
    Gallons per hp hr 0.110 0.118 0.099 0.135
    BTU per hp hr 12,271 12,678 10,253 11,043
    Test Cycle
    Mpg 12.7 12.4 12.2 10.9
    % change in mpg 0% -2% -4% -14%
    BTU’s per mile 8,738 8,348 7,908 7,338
    % change in BTU’s per mile 0% -1% -3% -14%
    Cost per mile $0.193 $0.196 $0.198 $0.183
    % change in cost per mile 0% 1.6% 2.6% -5.2%
    Max hp (2nd gear) 195 197 198 202
    Max torque (2nd gear) 235 241 240 247
  5. cgaengineer

    cgaengineer LawnSite Fanatic
    Messages: 15,778

    This is an engine designed to run on either fuel and would naturally have ways to ret@ard timing when using straight gas to prevent preignition. Engine is tuned to generally run e85.
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  6. GMLC

    GMLC LawnSite Platinum Member
    Messages: 4,345

    These results are from a stock 2005 Dodge Ram with 4.7L Magnum. Test was also done on three other vehicles with similar results but I didnt want to copy and paste a bunch of the same stuff(I can if you want). Final conclusion was less BTU's per horsepower are needed with higher ethanol but more fuel was burned droping MPG. This was a HP and MPG study.
  7. Ridin' Green

    Ridin' Green LawnSite Fanatic
    Male, from Michigan
    Messages: 17,829

    Just for clarification- Stihl 4 mix engines may run on 2 stoke mix, but they are still 4 stroke. So are the Shindy C4 machines. They recommend 89 or higher octane as well for all their equipment to keep it from running too hot.:)
  8. Lean_Mean_Green_Machine

    Lean_Mean_Green_Machine LawnSite Member
    Messages: 18

    The reason why diesel is more expensive than gas in America, I believe, is because of the need for it to be ULSD. In alot of other countries, diesel is half the price of what their gas is, keeping in mind that it does not have the sulfur refined out of it..
  9. 32vld

    32vld LawnSite Gold Member
    Messages: 3,983

    Alcohol has been in gasoline since at least the early 1990's. It's there to reduce emissions the way diesel has limits on sulfur to reduce harmful emissions.

    To those that complain that alcohol is in gas, remember the days when dry gas (alcohol) was added in the winter?

    This means that small engine manufacturers have had 30 years to figure how to make their equipment run well on gas/alcohol mix.

    As to the price in diesel. I tried to google a chart on truck freight history that would point out what is common knowledge to know how diesel fuel demand has grown.

    The change over from rail to truck has steadily grown from the 1920's.

    Post WWII, the switch to diesel began. By the 1960's most 18 wheelers where diesel While many large straight trucks were still gas. In 1964 my local fire dept bought it's last gas powered fire trucks, two 1,000 gpm trucks.

    By 1970's Diesels were replacing gas engines in large straight trucks.
    I don't remember when school bus went diesel but their are no more diesel school buses whether full sized or mid sized.

    1980's small and mid size trucks started to switch over to diesel.

    Then since the 1990's the mall haulers, you know the 2,500 and 3,500 pickups whether SRW or DRW's, look like they are never used to carry anything but their wives shopping bags from the mall to their home have diesels in them.

    Supply vs demand controls price. Not only have the number of trucks on the road have increased the number of gas powered trucks has decreased the diesel powered trucks have increased.
  10. CL&T

    CL&T LawnSite Senior Member
    Messages: 493

    I think it's a stretch to say that ethanol has been in gasoline since the early 90's. I remember going from lead to MBTE. That disaster was banned starting in 2004 and replaced with ethanol, another disaster.

    You also can't compare the use of dry gas. A few ounces added to a tank of gas- the percentage would hardly approach the 10% and up we have to deal with today. Further, I doubt anybody used it for small engines.

    So your statement that small engine manufacturers have had 30 years to figure how to make their equipment run well on gas/alcohol mix is hardly inaccurate.

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