By capturing carbon dioxide, cars' emissions could be reduced

Producing carbon dioxide is an unavoidable part of burning fuel in cars.

The problem with this of course is that carbon dioxide is a greenhouse gas. And the more cars there are on the road, the more sources of this greenhouse gas there are.

The concept of carbon dioxide capturing has been theorized for a while now, but researchers at Saudi Aramco and ExxonMobil are starting to take it seriously.

Carbon capture would first be applied to large-scale applications, like power stations. Those burn carbon-based fossil fuels too.

But a smaller system could be applied to road vehicles, and in theory, fitted to almost anything.

As Wards Auto reports, automakers have worked to reduce carbon dioxide emissions for some time now, a strategy that goes hand-in-hand with improving fuel efficiency – since carbon dioxide emissions are directly proportional to the amount of fuel you burn.

The trouble with this method is expense: Designing ever-cleaner internal combustion engines leads to greater complication and greater costs – a penalty invariably passed down to the consumer.

It has produced some impressively economical vehicles, especially in Europe where small-capacity diesels in particular are desirable for their very low CO2 figures (even though burning diesel actually produces more CO2, per volume, than gasoline).

Carbon capture though could be used on any vehicle, regardless of fuel efficiency. It's a concept being studied by researchers at the University of Michigan Transportation Research Institute (UMTRI), who published a paper titled: 'An Overview of CAFE Credits and Incorporation of the Benefits of On-board Carbon Capture.'

The researchers suggest that even capturing a small amount of the CO2 produced by the average vehicle could have huge benefits on a larger scale.

Using 20 percent carbon dioxide capture on a 20 mpg vehicle could give it CO2 emissions equivalent to an existing 37 mpg vehicle – a massive improvement.

The upside to this is that the greenhouse gas emissions of every vehicle on the road could be reduced. The downside is that doing so is incredibly difficult and has a few rather large problems – literally.

The long chains of carbon in fossil fuels form a usefully compact structure, a clue to the incredibly high energy density of fuels like gasoline.

Combine them with oxygen though, during the combustion process, and the resulting carbon dioxide molecules are much larger. Wards illustrates this by showing just how much CO2 is produced by burning one gallon of gasoline--though we like to show our workings.

In a 30 mpg car, you produce about 292 grams per mile of CO2. In other words, over that gallon and those thirty miles, your car will have pumped about 8.8 kilograms of CO2 into the atmosphere, or 19.4 lbs.

The gallon of gasoline you burned weighs only 2.7 kilograms, or 6 lbs. And the average car dedicates quite a bit of space to storing gasoline, so you can see the scale of the problem here – where does all that captured carbon dioxide go?

Realistically, you can't capture all of it. UMTRI's researchers suggest about 20 percent would be captured, stored in a membrane within the gas tank.

When you fill up your car, the CO2 would be extracted as the fuel goes in. The trouble then is deciding how to manage such a system – and potentially, how much that might cut from the cost of the fill-up, since CO2 is a tradeable resource used in beverage processing and industry.

Carbon capture wouldn't solve other problems associated with burning fossil fuels in road transport – and indeed in power stations: dwindling fossil fuel reserves and pollutants from combustion.

But as a cost-effective way of reducing a significant vehicle emission, it could be well worth exploring.

You can read further details in previous UMTRI paper, 'Carbon Capture in Vehicles: A Review of General Support, Available Mechanisms, and Consumer-Acceptance Issues'(.pdf file).