Combustion Engines with CO2-Avoiding Fuel

Synthetic fuels from green electricity make gasoline and diesel engines almost climate-neutral

Studies on the entire life cycle of vehicles show that with today’s electricity mix and in view of the energy used to produce them, plug-in hybrids and all-electric cars still come very close to vehicles with a gasoline or diesel engine in terms of their CO2 emissions. Using synthetic fuels could even make conventional drive systems more climate-friendly than their electric counterparts. Gasoline and diesel from renewable power permit road traffic of a more sustainable type.

CO2 emissions from the mobility sector need to fall. All experts agree on that. But what are the best ways of reaching this goal? In the short term, electric mobility will not be able to make any noticeable contribution because there are still nowhere near enough e-cars on the roads – high costs, short traveling ranges and long charging times at stations are putting off many potential buyers. But there is a further aspect. On closer examination, battery electric vehicles hardly benefit the climate. Adding up all CO2 emissions over their life cycle produces levels that come very close to those of a vehicle with a combustion engine.

Allowing for all impacts on the environment

Life Cycle Assessments (LCA) take account of all environmental impacts that come with a product – from extracting the raw materials and manufacturing to the utilization phase and material recycling. In the case of vehicles with a combustion engine, the main contributor to global warming is the utilization phase. In an example comparison, it accounts for 144 grams of CO2 per kilometer for a gasoline engine, 109 grams for a diesel. In addition to consumption while driving, there is also the carbon-dioxide emission generated while producing the fuels. And the CO2 produced by manufacturing and recycling cars must also be included. For a mileage of 200,000 kilometers in the WLTC, this takes the gasoline engine to 167 grams of CO2 per kilometer, the diesel to 134 grams.

Based on the same calculation method, a plugin hybrid emits 145 grams of CO2 per kilometer – less than the gasoline engine but more than the diesel. “This is not only the result of the relatively high level of carbon dioxide emitted during production but also of the electricity generated with many fossil power stations”, explains Dr. Bernd Becker, head of the Vehicle Energy department at IAV. “This is because of the current power station mix. In Germany,
around 476 grams of carbon dioxide are produced for every kilowatt-hour of electricity generated.”

This explains why a plug-in hybrid emits 102 grams of CO2 per kilometer during its utilization phase, plus another 43 grams to produce and recycle it. A battery electric vehicle arrives at 65 grams of CO2 per kilometer for the utilization phase and a further 49 grams for production and recycling.

CO2 as a raw material for mobility

Particularly from the aspect of production, vehicles with a gasoline and diesel engine have clear CO2 benefits today. So, in combination with sustainable fuels, they could make a noticeable contribution to protecting the climate in the medium term. This is precisely the aim of running them on synthetic fuel which can be produced using renewable energies. In an initial step, hydrogen is produced from water by electrolysis with green electricity. Using CO2, this can first be converted into methanol, and from methanol it is then possible to make synthetic gasoline – turning climate-damaging CO2 into a raw material for mobility.

“Tests with modern gasoline engines reveal that in terms of ignition and power output, this climate-neutral fuel shows no appreciable differences to conventional fuel”, Becker reports. “It can be used to power millions of existing vehicles, making them carbon-neutral as a result.” Before carbon dioxide is emitted in the utilization phase, producing the fuel has already taken it out of the environment. With a gasoline engine and for a mileage of 200,000 kilometers in the WLTC, the above vehicle would arrive at no more than 35 grams of CO2 per kilometer.

The fact that this is not all a far-off vision is demonstrated by companies like Carbon Recycling International from Iceland. Every year, it makes around five million liters of methanol from CO2 and hydrogen that is produced using electricity from a geothermal power plant. A semi-industrial test facility in Freiberg has made synthetic gasoline from methanol. Although diesel can also be produced in a similar way, synthesis is somewhat more complex.

Stabilizing power grids

Besides the positive effects on climate, synthetic fuels made from renewable energies have a further benefit. They can be produced using surplus green electricity – and hence, by bringing together the mobility and energy production sectors, balance supply and demand in the power grid. “We have been working on the vision of carbon-neutral mobility for years, and are in general broadly positioned in matters of energy”, Becker says. “This is why IAV sees itself in a hub function. We want to liaise between the industries and work together with OEMs and research institutes on helping synthetic fuels to make a breakthrough.

Electric mobility doubtlessly plays a key part in providing sustainable mobility – but we should use synthetic fuels as a supplementary medium-term measure to help protect the climate through conventional vehicle fleets.”