type temp sg BTU/gal Alcohol, methyl 25 C 786.51 80.000 Gasoline, Vehicle 60 F 737.22 120,000 Virtually all newer vehicles use three-way catalyst exhaust after-treatment systems. For maximum catalyst efficiency the A/F target average is stoichiometric (or the chemically correct mixture ratio). For 100% gasoline this is nominally 14.6:1. Most engine control systems purposefully dither on either side of stoich to maximize catalyst efficiency. As alcohol(ethanol)is added, the feedback ECU controls will adjust the fuel system to keep the mixture at the mixture's stoichiometric value. Here's a simple table to illustrate how stoich varies with %EtOH %EtOH Stoich A/F 0 14.6 5 14.16 10 13.74 15 13.35 20 12.98 85 9.55 100 9.00 ****** MBTE ****** %MBTE Stoich A/F 0 14.6 5 14.42 10 14.25 15 14.07 20 13.91 100 11.69 ****** Methanol ****** %MeOH Stoich A/F 0 14.6 5 13.73 10 12.96 15 12.27 20 11.65 55 8.61 (most energy per unit mass of air) 100 6.45 "Lean", to me, indicates a mixture which does not have an excess of fuel, or may even have an excess of the oxidant. It requires more oxygen to burn a unit amount of MTBE than it does to burn the same unit amount of ethanol, and the energy released is consequently greater. Most of the energy is derived from the oxidation of the hydrogen atoms in a hydrocarbon to form water. Less energy is derived from oxidation of the carbon to give CO2. The oxygen (in oxygenates such as alcohol and MTBE) just occupies space and doesnt contribute to the energy derived from combustion. So, since the ethanol has a higher percentage of oxygen in the molecule, it has a lower amount of energy that it can contribute upon combustion. The "octane rating" takes into account different properties of the fuel, not directly related to the stoichiometry. \================ You probably meant the amount of energy "liberated" when burning; it's an exothermic reaction after all. LHV - Gasoline: 42 MJ/Kg LHV - Ethanol: 26.68 MJ/Kg LHV - Methanol: 19.95 MJ/Kg LHV - MBTE: 35.12 MJ/Kg For 1 kg of air here are some interesting data. Terms: LHV - lower heating value (liquid fuel into reaction, uncondensed water vapor in exhaust). The blend energy@stoic is the theoretical yield from a reaction using one kg of air and stoichiometric amount of fuel. Blend Blend Blend EtOH % Stoic LHV energy@stoich A/F MJ/Kg MJ/kg-air 0% 14.60 42.0 2.88 2% 14.42 41.7 2.89 5% 14.16 41.2 2.91 10% 13.74 40.5 2.94 15% 13.35 39.7 2.97 20% 12.98 38.9 3.00 40% 11.69 35.9 3.07 45% 11.41 35.1 3.08 50% 11.14 34.3 3.08 55% 10.88 33.6 3.09 60% 10.63 32.8 3.09 65% 10.40 32.0 3.08 85% 9.55 29.0 3.03 90% 9.36 28.2 3.01 95% 9.18 27.4 2.99 100% 9.00 26.7 2.96 Blend Blend Blend MeOH % Stoic LHV energy@stoich A/F MJ/Kg MJ/kg-air 0% 14.60 42.00 2.88 2% 14.24 41.56 2.92 5% 13.73 40.90 2.98 10% 12.96 39.80 3.07 15% 12.27 38.69 3.15 20% 11.65 37.59 3.23 40% 9.70 33.18 3.42 45% 9.31 32.08 3.45 50% 8.95 30.98 3.46 55% 8.61 29.87 3.47 60% 8.30 28.77 3.46 65% 8.02 27.67 3.45 85% 7.04 23.26 3.30 90% 6.83 22.16 3.24 95% 6.64 21.05 3.17 100% 6.45 19.95 3.09 Blend Blend Blend %MBTE Stoic LHV energy@stoich A/F MJ/Kg MJ/kg-air 0% 14.60 42.00 2.88 2% 14.53 41.86 2.88 5% 14.42 41.66 2.89 10% 14.25 41.31 2.90 15% 14.07 40.97 2.91 20% 13.91 40.62 2.92 40% 13.28 39.25 2.96 45% 13.13 38.91 2.96 50% 12.98 38.56 2.97 55% 12.84 38.22 2.98 60% 12.70 37.87 2.98 65% 12.57 37.53 2.99 85% 12.05 36.15 3.00 90% 11.93 35.81 3.00 95% 11.81 35.47 3.00 100% 11.69 35.12 3.00 While not shown above, in all cases if the amount of air is reduced to maintain constant energy@stoich, more fuel is still needed for all three oxygenates as the percentage increases. ============