Electric vehicles are big news at the moment with huge investment in research and development as well as firm plans for numerous gigafactories around the world for next-generation battery production. Listen to those developing batteries, motors and electrified powertains and it’s very easy to be convinced they are the way forward, but there are other options.
In the future, the internal combustion engine might not be petrol or diesel fed, but that isn’t to say it is the end for the component that has been a mainstay in the automotive industry for almost its entirety. One way of making the ICE a more sustainable proposition for the future is to look at different fuel options. A hydrogen economy has been talked about for generations and many people are firmly in favour of seeing it come to fruition. At the University of Bath, the chosen approach has been to use a fuel that will power the ICE, but remain independent of oil reserves and renewable energy by effectively harvesting solar power. There are a number of organisations using solar power or synthetic solar energy to generate liquid fuels. In some cases it even achieves higher levels of efficiency than biology manages in the real world. If it can be done economically – at a cost that is cheaper than extracting crude oil and refining it from the ground – or if crude oil and the refining process is taxed so heavily because of government legislation, the landscape to generate liquid renewable fuels will exist.
Experience from other transport industries.
If we want to maintain our way of life and meet the challenges facing us from climate change, we need high energy density fuel for both freight and aviation. For these industries, battery electric power just isn’t a viable solution because it will not be possible to generate the required energy density. So if we develop the renewable fuels independent of cost for those industries – because they WILL have to use them in place of hydrocarbons – the economies of scale might dictate that the technology trickles down into the automotive industry and becomes a viable alternative to what is already available.
So the real challenge is how can we convert renewable liquid fuels into mechanical work? They have to be housed in an affordable, efficient and recyclable device and made from cheap, readily available materials using simple and well understood manufacturing processes. Efficiency is key because the fuel will be expensive, even if it is carbon free. In reality, any new fuel is likely to be more expensive than a hydrocarbon-derived fuel because of the processes that they will have to go through to become useable. But that fact alone almost dictates why we have to use the fuels more efficiently.
If we want to maintain our way of life and meet the challenges facing us from climate change, we need high energy density fuel for both freight and aviation. For these industries, battery electric power just isn’t a viable solution because it will not be possible to generate the required energy density.
With the emergence of new fuels there are two options. There is the option of using them in the traditional, tried and tested internal combustion engine (which would be more efficient, but at a considerable investment cost). One alternative is to use solid oxide fuel cells. This system takes the fuel directly and uses fuel cell catalyst technology to regenerate electricity to power the vehicle. The difference between those two solutions is the product that is created. The ICE produces mechanical power (in the form of torque and speed) and the fuel cell approach generates electricity.
Hope for hybrids Whichever of those options we end up adopting in the future, the current state of legislation means that we are definitely going to see hybridisation of the vehicle, not least because it makes the powertrain more efficient. The use of hybrids is also being driven by the pollution concerns as well as the fuel economy legislation from the EU and other states around the world. Hybridisation of future powertrains is essential because it gives us a zero emissions drive phase, thanks to its ability to operate in pure electric mode. It also has the ability to recover energy from braking, which is an improvement over the efficiency of existing vehicles.
Hybrids also allow us access to better engine management. Hybridisation means that we are not restricted to fuel consumption being high and efficiency being poor. We can operate at higher pressures and engine speeds to boost performance. Using hybrid technology allows us to use the internal combustion engine or the fuel cell at high efficiency operating conditions – so it could be seen as a win-win technology.
Hybridisation of future powertrains is essential because it gives us a zero emissions drive phase, thanks to it’s ability to operate in pure electric mode. It also has the ability to recover energy from braking, which is an improvement over the efficiency of existing vehicles.
The big argument we have from the side of the internal combustion engine is that battery electric vehicles are ideal for inner city, short range journeys where the batteries don’t have to be too big. However, when you go down the route of building a car with a battery that offers a range that matches a normal combustion engine vehicle, you end up with 600kg of batteries in the vehicle. Until advancements in battery technologies bring smaller battery packs that can provide a larger range, the internal combustion-engine will remain the most efficient way to travel long distances.
The way forward
Depending on the politics involved, this ZEV (zero emission vehicles) requirement may drive the battery electric vehicle and eliminate the internal combustion engine. But that scenario would be driven purely by politics, because we will always be able to meet any practical air quality requirements with an internal combustion-engine, even if it comes at high cost. The process for what we are proposing is relatively straightforward. We take the energy from the sun – which isn’t likely to run out anytime soon – and then devise a method of converting that energy into a fuel. Hydrogen is a great option in many ways, but it is relatively difficult to store – it needs to be kept under pressure and in cold conditions, which adds a lot of weight to a vehicle. If you actually take carbon dioxide and combine it with thehydrogen you end up with a liquid fuel that is readily transportable – we have all the technology to do that now.
Based on some recent calculations, a 600kg battery pack in an electric vehicle can be equated to 35-40kg of fuel, so we’ve still got a massive energy density difference between storing it in batteries and in a chemical fuel.
Once you have the fuel, you then have the question of which route to go down – either a solid oxide fuel cell or a highly efficient internal combustion engine mated to a hybrid powertrain, which would allow some kind of onboard energy storage capability. The latter scenario would allow people to drive around in zero emission mode when they need to and incur no net CO2 increases, because all of the energy has come from renewables. It remains to be seen which path the industry will choose, but it is fair to say there will be a lot of discoveries on the way, which will hopefully help the manufacturers further improve efficiency, cleanliness and longevity of the internal combustion engine.