Ethanol as Automotive Fuel

Remember in the last column we spoke about ethanol and how it is made. Today I would like to explore the role of ethanol in automotive fuel.

First, let’s take a quick look at gasoline. Gasoline, as with most fuels, is a hydrocarbon. That means that its molecules are made up of carbon atoms and hydrogen atoms, with the carbon atoms forming either a straight chain or a branched chain. Hydrocarbons make good fuels because they burn easily in the presence of air. You are already familiar with natural gas, a one-carbon hydrocarbon, with a simple formula of CH4, and called methane. Propane, the common barbecue fuel, is three carbons long, so its formula is C3H8. Methane is a gas at room temperature, and propane is a gas but becomes liquid when compressed. By the time we get to 6 carbons atoms, the hydrocarbons are liquids, and become solids above about 14 carbons… wax! So, gasoline is typically about 8 carbons. I say typically because gasoline is not a single compound, but a range of very similar chemical compounds that have a specific boiling point, or that boils over a narrow temperature range.

So, when gasoline and air are introduced into an internal combustion engine, compressed and ignited, the mixture burns very rapidly, and the resulting displacement of the piston in the cylinder turns the crankshaft and thus the wheels. However, we do not live in a perfect world. There is never quite enough air mixed with the fuel to burn everything, so as well as the carbon dioxide, we get carbon monoxide and some chemical fragments of the gasoline molecules that form soot and other compounds. If we add something to the gasoline that has oxygen in it, such as ethanol, (remember the formula for ethanol is C2H5OH) we can achieve a better and more complete combustion. Nevertheless we are still stuck with carbon monoxide and dioxide, serious greenhouse gases.

There is a downside, of course. The oxygen in the ethanol molecule means that weight for weight it doesn’t have the bang that gasoline has, so there is a fuel mileage penalty, estimated at up to 10%, but a cleaner exhaust. The trick is to add enough ethanol that the exhaust quality improves, but not too much to upset the fuel injectors and the internals of the engine management system. If you look at most pumps around Brockville, you will see a sticker saying “may contain up to 10% ethanol”. This level can be tolerated by most modern vehicles without modification. If we want to run higher levels of ethanol, we have to make sure our vehicle is equipped to handle the additional ethanol.

There is a current oxygen-containing additive called MTBE (we’ll skip the formula for now) which serves the purpose of providing extra oxygen, but there are issues around its safety and it is made from crude oil, whereas we know where we can get ethanol.

Some of you may be familiar with the situation in Brazil. There is little natural petroleum in Brazil, but a huge quantity of sugarcane and low cost labour. Therefore ethanol derived from sugarcane forms a large part of the Brazilian motor fuel supply, and all vehicles sold in Brazil are designed to use this fuel. As well, there would be operational problems using pure ethanol as a fuel in our winter conditions, something the Brazilians do not have to consider.

So, using ethanol as a fuel additive or substitute will have a beneficial effect upon emissions, and will reduce our reliance on crude oil, but it is not the magic cure that some have promised. The latest estimates, and they are only estimates, indicate that the substitution of a major portion of our gasoline with ethanol may result in a reduction of the transportation component of greenhouse gases of up to 25 – 40%. Another issue is that a major new market for ethanol will benefit farmers but may drive up the cost of chicken, beef, and other foods for which the corn from which ethanol is made is a food source or raw material.

There is also controversy around the overall energy balance of ethanol – that is, how much energy in diesel fuel, fertilisers, etc. does it take to make a kilogram of ethanol from corn, vs. how much energy it gives to the gasoline. I have seen estimates from 50% to 150%. It is easy to see how anyone with a vested interest can make the data look favourable for their cause.

The only fuel that can play a really significant role in reducing greenhouse gases is hydrogen, and we will look at that in a future column.