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What in the World is Well-to-Wheels and Why Does It Matter?

By Norm Brinkman
GM R&D Technical Fellow

Since gasoline has been the predominant source of fuel for our cars and trucks for the last 80 years or so, you may not give a second thought to where it comes from and how it gets to the pump at your local station.

But if you care about the impact of transportation on energy and the environment, you might be like me and some of my colleagues at General Motors who ponder this as we plan the fuels and powertrain systems for future GM cars.

The energy conversion losses and greenhouse gas emissions (mainly carbon dioxide or CO2) that occur when fuels are produced and delivered to the service station is part of a science called fuel life cycle analysis, or LCA. When gasoline and diesel were alone in the market, we didn’t have to think much about LCA. But now with flexible-fuel vehicles running on E85 ethanol; people driving hydrogen-fueled Chevrolet Equinox fuel cell vehicles, and the Chevrolet Volt extended range electric vehicle coming late next year, we need to compare vehicles on more than just the miles per gallon sticker on the window. We also need to account for the energy and emissions that result from making the fuel also.

LCA is simply an accounting tool which measures all of the energy and raw materials used and all of the emissions (CO2) generated in the production of the fuel. In the case of petroleum-derived fuels, this means LCA includes everything from the time the oil is extracted from the ground, transported to the refinery, made into fuel and distributed to your local gas station. This is also known as a Well-to-Wheels Study because it starts at the oil well and ends at the wheels – or more specifically the tailpipe of your car or truck.

My colleagues and I at GM performed a study with Argonne National Laboratory that looked at these issues and found that E85 using ethanol made from corn reduced CO2 by about 20 percent compared with gasoline while ethanol made from cellulosic energy crops reduced CO2 by about 75 percent.

Let’s take the example of E85. To get ethanol, we grow corn that is used to make most of today’s ethanol in the U.S. Very soon, wood residues left over after logging will be used as the source, or feedstock, for ethanol conversion processes being developed by companies like our partners Coskata and Mascoma. Ethanol made from logging residues have near zero greenhouse gases on a lifecycle basis because the logging is going to happen whether or not the residue is used for fuel. We just need to account for transporting the materials and any fossil fuel emissions from the ethanol refinery. Depending how the plant is powered, those emissions can vary.

For a crop like corn ethanol, the LCA is much more complex. We keep track of the energy and emissions it takes to plant the corn, and make the fuels, fertilizers, and pesticides to grow the corn. We also estimate whether growing the corn increases or decreases carbon in the soil. Next we estimate how much fuel it takes to get the corn to the ethanol refinery and how much energy is consumed and the amount of emissions that are generated in the biorefinery. Corn ethanol refineries typically make a co-product called distillers grain, which is a high-protein feed for cattle. This production is counted as a credit in our accounting spreadsheet. We also include the impact of getting ethanol to the service station by rail and truck.

These are the conventional requirements for a fuel LCA. However, some influential scientists have written that more should be considered, speculating that planting more corn in Iowa sets off domino effects throughout the world, leading to rainforests being burned in Brazil. Most prominent fuel LCA scientists believe these indirect land use change (iLUC) effects should not be included in the lifecycle analysis. You can learn more about this from a recent blog by Bruce Dale of Michigan State University.

At GM, we care very much about the energy and environmental footprint not only of our vehicles (including their manufacture), but also of the fuels that go into them before they ever reach the vehicle. That’s why we contribute to developing a greater understanding of the full life-cycle issues surrounding personal transportation.

I hope this primer on Life Cycle Analysis was helpful. I’d be happy to read your comments and respond to any questions.

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