Why does low-energy ethanol produce more power?This first requires an understanding of the air-fuel ratio characteristics of these two fuels. The ideal air-fuel ratio for pure motor oil is 147:1, while the air-to-fuel ratio of pure ethanol is only 9:1, which is obviously lower for ethanol. By mass, it provides 1221 kWh of energy, while each kilogram of ethanol can only provide 745 kWh of energy.
Imagine an engine that runs on both gasoline and ethanol. The ideal air-fuel ratio for gasoline is 147 kg of air plus 1 kg of petrol for a perfect fit of 14An air-fuel ratio of 7:1. However, in order to achieve the same air-fuel ratio, ethanol needs 147 kg of air with 163 kg of ethanol mix. If we multiply the energy density with the amount of fuel, the energy value of gasoline is 1221 kWh, while ethanol has an energy value of 1217 kWh, not much difference.
Although ethanol has less energy, due to its lower air-fuel ratio, more ethanol needs to be injected into the cylinder in order to produce the same power. In this respect, ethanol appears to be less economical. Based on the fact that a liter of pure gasoline can travel 30 kilometers, a liter of ethanol can only travel 20 kilometers, which means that gasoline is 50% more economical.
However, ethanol has a higher thermal efficiency and alkane number advantage. Its chemical properties and cooling effect are outstanding in two aspects: one is the characteristics of the fuel itself;The second is its enthalpy of gasification. In engines with variable compression ratios, when ethanol fuel is added and compressed to a certain amount, if there is no knocking, the compression ratio can be further increased until knocking eventually occurs. This method allows the study of the neoalkane number of the fuel. Assuming that premium gasoline has a neoalkane number of 97, then ethanol has a neoalkane number of 109, which is significantly higher. This means that higher compression ratios and more knock resistance can be used. This is also the reason why adding ethanol to gasoline can now increase knock resistance.
When gasoline starts to add ethanol, the neoalkane number of the fuel increases very significantly initially, but after it reaches about 30% or 40%, it does not increase further from a chemical point of view. Whether inlet injection or direct in-cylinder injection is used, this advantage is present. However, when using in-cylinder direct injection, the cooling effect will be more prominent. Theoretically, the maximum dropping temperature with No. 97 gasoline is 20 degrees, while ethanol drops by 80 degrees. This means that lower cylinder temperatures reduce the likelihood of knocking. As a result, for certain engines, higher ethanol content can result in higher compression ratios, greater thermal efficiency, and higher boost expectations, ultimately generating more power.