Gasoline's Greater Range

Saturday, November 9, 2013

Some people have argued against flex fuel cars or the Open Fuel Standard because methanol and ethanol don't give cars enough range. In the same sized fuel tank, a full tank of gasoline would travel more miles than a full tank of methanol or ethanol.

There are two answers to this. One is that the range difference isn't as great as you'd think — especially if the car is optimized for alcohol fuels. Most of the comparison between gasoline and alcohol uses BTUs (British Thermal Units), which is a measure of heat. Gasoline produces more heat when it burns. But heat is not what creates forward motion. Gasoline produces more heat, but some of its energy is expended in producing heat, and that energy is wasted. More of alcohol's energy is used to power the car and less of it is wasted on creating heat.

Also, alcohol fuels become more efficient at higher compression. So the difference in miles per gallon between gasoline and alcohol will be smaller with a higher compression engine. Engineers are already in the process of perfecting a variable-compression engine.

The second answer is that if it is a flex fuel car, it doesn't matter that alcohol doesn't have as much range as gasoline because if you are going on a long trip or want more range, you can just buy gasoline. The car can burn gasoline too. That's the whole point. You will have a choice. If you want to burn nothing but gasoline, no matter how expensive it gets, you will be able to. Flex fuel technology doesn't reduce a car's ability to burn gasoline. That's why so many people own flex fuel vehicles now without even knowing it: Because they've been burning gasoline in their cars and it burns gasoline just as well as a gasoline-only car.


Adam Khan June 10, 2015 at 1:44 AM  

Someone emailed us asking for more clarification of the wasted energy of gasoline as heat. Here's what I said:

I have been "listening in" for about a year to a Yahoo group for people who make their own fuel (their conversations are emailed). It's very interesting. Some of these guys have been brewing their own fuel for a long time and know a lot about it, and one of them, who was an engineer, explained to me why there is a discrepency between the BTU measurement and the actual mileage you get from the car. In other words, why there's a large difference in the "energy density" of gasoline and ethanol, as measured in BTUs, but not such a big difference in mileage when you drive a car on the different fuels.

The engineer explained it to me better that anyone ever had. He just said heat is wasted energy. All the heat coming off the car is energy that COULD have been used to move the car forward but wasn't used. And the car further expends some percentage of its energy COOLING the car. Ethanol produces less waste heat and wastes less energy cooling the engine. So a higher percentage of its energy is used for propulsion.

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