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jjuutinen · Joined: 13 Jul 2003 Posts: 180

Any data on lean/rich mixture rating of pure ethanol?

kmccutcheon · Posted: Thu Aug 16, 2007 13:41 Post subject:

For what it is worth, here is data on three alcohols. The person who sent this to me and did not cite the source.

Methanol
Percent Hydrogen: 12.6
Percent Carbon: 37.5
Boiling Point (° F): 148
Reid Vapor Pressure (psi): 4.5
Latent Heat of Evaporation (BTU/lb): 473
Freezing Point (° F): -144
Heating Value (BTU/lb): 8600
BTU per US Gal at 68° F: 57000
Specific Gravity at 68° F: 0.794
Weight per US Gal at 68° F: 6.62
PN, lean, no lead: 75
PN, lean, 4 ml lead/gal: <75

Ethanol
Percent Hydrogen: 13.1
Percent Carbon: 52.1
Boiling Point (° F): 173
Reid Vapor Pressure (psi): 2.3
Latent Heat of Evaporation (BTU/lb): 370
Freezing Point (° F): -174
Heating Value (BTU/lb): 11500
BTU per US Gal at 68° F: 76000
Specific Gravity at 68° F: 0.790
Weight per US Gal at 68° F: 6.58
PN, lean, no lead: 75
PN, lean, 4 ml lead/gal: <75

Isopropanol
Percent Hydrogen: 13.4
Percent Carbon: 60.0
Boiling Point (° F): 180
Reid Vapor Pressure (psi): 1.8
Latent Heat of Evaporation (BTU/lb): 290
Freezing Point (° F): -129
Heating Value (BTU/lb): 13100
BTU per US Gal at 68° F: 86000
Specific Gravity at 68° F: 0.786
Weight per US Gal at 68° F: 6.55
PN, lean, no lead: 75
PN, lean, 4 ml lead/gal: <75

This data seems to have come from the late-1940s or 1950s. The reference included the following Note:
Current rich mixture knock test methods do not assign Performance Numbers to alcohols due to their low heats of combustion. However, alcohols, if tested at very high specific fuel consumptions, have very high Performance Numbers. When blended with water the three alcohols listed all have very high Performance Numbers and very high resistance to preignition.
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Kimble D. McCutcheon

jjuutinen · Joined: 13 Jul 2003 Posts: 180

The PN data seems very odd. According to a recent Finnish article to achieve 1100 hp the Russian radial M-63 required 94/95 octane fuel (made from 74 octane straight gasoline blended with 4 cc on TEL/kg). Now, a fuel blend of 50% ethanol, 49.5% of 72 octane petrol plus 0.25% oil gave 1137 hp. The same Finnish article states that ethanol´s "octane rating" is 120. It also states that pure ethanol may pre-ignite in presence of high cylinder wall temperatures.

kmccutcheon · Posted: Fri Aug 17, 2007 08:00 Post subject:

The above data simply states that lean-limit PN of ethanol is 75, and that richer mixtures are "higher". Is that not in every way consistent with the findings of the Finnish article?
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Kimble D. McCutcheon

jjuutinen · Joined: 13 Jul 2003 Posts: 180

The lean PN seems too low for the Finnish article does not indicate any loss of economical cruising power and I believe the lean PN of the 95 octane petrol to be something more than 75 and the 50/50 ethanol blend gave more power than the 95 octane gas.

jrussell · Joined: 26 May 2004 Posts: 55 Location: Portland, Oregon

Well, here goes with more data points which do not agree. In the book " High performance automotive fuels and fluids" ( author is Jeff Hartman ) there is a table which gives a RON of 109 and a MON of 90. the table is attributed to the " Reston Publishing Co". Does anyone know the specific procedure which is used to develop a PN for aircraft fuels?
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It runs best just before it blows!

jjuutinen · Joined: 13 Jul 2003 Posts: 180

100 PN=100 octane
130 PN=allows 30% higher IMEP than 100 PN
150 PN=allows 50% higher IMEP than 100 PN

and so on.