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28.04.2023 from 
Research + Transfer
The end for combustion engines - now what?

On March 28, 2023, the EU finally decided that after 2035, no new cars may be registered in EU states that run on diesel or gasoline. One exception is e-fuels, synthetically produced fuels that can power an internal combustion engine. In theory, this sounds like a good alternative to fossil fuels. In practical terms, the production of e-fuels requires a lot of renewable electrical energy, which is why they are very expensive. In the mobility debate, the use of synthetic fuels is viewed critically, as there is still a lot of need for optimization of the framework conditions. Can designer fuels then really make a contribution to green mobility? What are their limits? What alternatives are there to the internal combustion engine and will mobility be a luxury good in the future? Hermann Rottengruber from the Institute for Mobile Systems at the University of Magdeburg talks about this in an interview.

Portrait Prof. Rottengruber (c) Jana Dünnhaupt Uni Magdeburg

First of all, let's clarify the terminology. What exactly are e-fuels?

E-fuels are synthetically produced liquid fuels derived from electrical energy. So simply put, they are derivatives of regeneratively produced hydrogen that are then converted via chemical processes into a fuel similar to diesel or gasoline.

Of course, many drivers are now asking themselves the question: What will happen to their diesel or gasoline engine? Is it possible to operate the combustion engine with e-fuels?

E-fuels are artificially adapted fuels whose quality is designed in such a way that they can also be used for existing vehicles. When these fuels will be available in adequate or sufficient quantities is precisely the point of contention and the major criticism of this type of fuel.

Can you expand a little bit on the criticism on those fuels?

Yes, as already mentioned, the basis for these e-fuels is electric power, which is currently still largely generated from fossil or non-renewable sources. And in order to be able to produce e-fuels that are really green, you need large amounts of renewable electrical energy. And as we know from the public debate, there is a lack of this. There are expansion targets, but it is questionable whether we in Germany will be able to meet the demand we need in the transport sector or in other sectors at all with green electrical energy. That's where the criticism of e-fuels comes in, that people say there won't be enough electricity available to produce hydrogen and then to drive the energy expenditure further, so that liquid fuels comparable to diesel or gasoline can be produced from this hydrogen.

Up to now, a lot of renewable energy has been needed to produce e-fuels in the first place. Do they really represent a good alternative?

I would say that they are an indispensable alternative, because at the moment there are very many mobility applications that cannot be replaced by the battery-electric system, which will certainly become more widespread in passenger cars. If we now take heavy-duty, international transport, shipping or air traffic, e-fuels play an indispensable role there in the future in a CO2-neutral future, so there will definitely be e-fuels in some form. The big point of contention at the moment is what role or contribution can these e-fuels make in private car transport? There's a big discussion and a big argument going on there right now.

Will the market have improved the energy balance of e-fuels in a few years?

So scaling up, further expanding production and power generation capacities, will certainly also be accompanied by an efficiency advantage or a gain in efficiency. But the processes that are needed to generate hydrogen from renewable electricity and then to process the whole thing are subject to natural laws or the conditions that the individual molecules have. There will be no chemistry reform and no physics reform in the next few years. We won't be able to do that, so the basic expenditures that you need in terms of activation energy to run these processes are all known and you won't be able to change them. You can increase efficiency through the processes there. But it won't be in such a way that it shrinks by half, but rather incrementally. My vague estimate would be 10-20 percent.

But the primary energy demand, that will first increase massively through the use of e-fuels or through the use of e-fuels. However, these fuels have the significant advantage that once they are available, this energy can be stored almost indefinitely, just as in hydrogen, for example. And that is the big advantage. It is relatively easy to transport regeneratively generated electricity that cannot be used locally, such as the much-cited example of wind power harvested by Porsche in Chile, from the other end of the world to us and then store this regenerative solar or wind power for an unlimited period of time. This is not possible with the electrical power that we generate regeneratively somewhere in the world and which is then to be "refueled" in battery-electric vehicles here in Germany. That's why, in my opinion, e-fuels will play a very important role. Possibly also as so-called drop-in fuel, which you can continue to use in your vehicle after 2035 if you still want to drive your current gasoline vehicle.

The change of course toward e-mobility is already in full swing. Will we have reached the point where e-mobility can completely replace the combustion engine by around 2035?

No, definitely not. We in Europe always make the mistake of extrapolating our boundary conditions, our view, to the whole world. In Germany and especially in Europe, we are currently having a much more heated discussion about whether our power grids, in terms of their load-bearing capacity and performance, can withstand an increase in electromobility, electric heating and everything else that is to become electric. And we have also been having a very tense discussion about charging points for quite some time in Germany and in Central Europe. In other parts of the world, this issue is still completely different. In Europe, in the European and Asian economic areas, and in the USA, there will be a very strong increase in battery electric vehicles in the fleet. But even there, the battery-electric drive will not completely replace the combustion engine, be it in the form of a plug-in hybrid drive. In the areas that still have to develop, such as India, South America, emerging and developing countries, which undoubtedly also have a need for mobility, the internal combustion engine will still be needed for a long time due to the infrastructural conditions there.

In addition, there are also internal combustion engine applications here in Germany in the area of transportation, commercial vehicles, for example, railroad applications on non-electrified routes or ship applications. There will be combustion engines there for the foreseeable future, and the combustion engine will remain the dominant drive variant for a very long time to come. Quite simply because the battery-electric systems are not able to serve these applications economically.

Due to high demand?

Simply because the storage density is not sufficient to achieve great transport performance or work output. In agriculture, for example, it is undisputed today that it is impossible to make a combine harvester battery electric. This would be absolute nonsense from the operating times that such a machine has and the mass that this vehicle then has, since an excessively high axle load must not be applied in a field. With a battery system that has to be powerful to do this amount of work of a combine, it wouldn't work because the vehicle would be so heavy that the field would break. You would ruin the field from soil compaction so that nothing would grow next year. And it doesn't make economic sense to change the battery system of a combine harvester every few hours, and you need highly potent energy storage systems, such as e-fuels or hydrogen, to keep such applications running at all. At the moment, there is no solution in sight at all. The situation is similar for heavy-duty transport, which today is the backbone of our transportation system, our economy and our supply. Here, too, there is still no feasible solution that offers an alternative in the form of battery-electric drives. Comes up very short in the public discussion, in my opinion. But it really is, as they say, critical infrastructure. If the supermarket stays empty because the food can't be distributed by truck or because it's uneconomical, then we all suffer. But people are being led to believe that everything can be done battery-electrically and therefore climate-neutrally, which is yet another lie, because if you look at the electricity mix in Germany today, it is more CO2-heavy than it has been for years. That's where the solution is missing at the moment, and that's where the internal combustion engine still has a very, very broad application. This is often swept under the table in the discussion.

Since you just mentioned range, let's go back to private passenger transport. Car manufacturers are constantly bringing e-cars onto the market that enable an ever greater range. Until now, however, users of e-cars have had to accept longer breaks for charging when traveling long distances. Would there be a good alternative to e-mobility that offers more range?

The question is whether private users who go on a long-distance trip every holy time I call it a long-distance trip even need additional development, that you then really need a greater range. There will be applications that require constant availability, such as emergency services or emergency vehicles. It will certainly be very difficult to provide these on a battery-electric basis, simply because they must always be available. I'm thinking of firefighters, police or other vehicles. But for normal private individuals or people who have to commute to work and always have a fixed route, I think the current state of the art and the foreseeable state of the art in terms of range is quite sufficient. The vehicle industry is already well on the way to achieving this. For the few people who really need long distances or constant availability, the hydrogen fuel cell, which is also an electrically powered vehicle, is of course a combustion-engine-free solution that enables longer or much greater ranges without constant recharging.

In addition to the alternatives already mentioned, there is also hydrogen, as you have just mentioned. So far, only a few hydrogen cars are on the market. Why is that? And why do we hear comparatively little about this alternative in the mobility debate?

At the moment, two vehicles are available for sale in Germany. One from the Hyundai company and one from the Toyota company, i.e. from two manufacturers from the Asian region. In Korea and Japan, in particular, the path of hydrogen mobility has been massively advanced in recent years, whereas in Europe, on the other hand, there has been a very strong focus on the battery-electric system. It has to be said that the process technology involved in these fuel cell vehicles is relatively complex. You need a lot of components. The drive system is much more complex than a battery-electric system. I would even say significantly more complex than an internal combustion engine drive. As a result, the vehicles are relatively expensive to buy and are set in a somewhat upscale segment. Since the middle of the last decade, the so-called noughties, there has been a clear commitment in Europe to focus more on the battery-electric system. And the Asians are somewhat ahead of us in terms of openness to technology, which of course partly explains why we are lagging behind them in development to a certain extent. And the hydrogen infrastructure in Germany is still much less developed than in Asia. In addition, to be fair, there is also another energy conversion step. As mentioned earlier, e-fuels are produced from electrical energy, which is converted into hydrogen via electrolysis. And it makes no sense at all to convert CO2-heavy generated electric power into CO2-heavy hydrogen and then convert it CO2-neutral in the vehicle. Then you are lying to yourself. It is the same lie that is spread when people say that a battery electric vehicle is already CO2-neutral today. If you look at the electricity mix in Germany, it's anything but CO2-neutral. The CO2 emissions are currently on a par with those of a diesel engine. The game is not being played honestly. But I'm sure there will be vehicles in the future that rely on this form of mobility. We are back to vehicles that have a long range and have to cope with large transport volumes. The fuel cell vehicle will certainly find its place there.

The mobility revolution involves a great deal of investment and expense. Will mobility be a luxury good in the future?

What is luxury? In the past, mobility was extremely inexpensive for broad sections of the population, especially in Central Europe. If you look at developments on the energy market, it will be difficult for us to return to this favorable price structure. It should also be noted that in the public debate it is always argued that it does not make sense to replace all internal combustion engine vehicles with battery electric vehicles. In the climate debate, climate activists argue that they are not doing the planet any great favors. That is also correct, because there will be restrictions and bans on certain technologies that you can steer development in one direction there. And the future will then probably no longer be as inexpensive as we were used to. We will see whether it then becomes a luxury good. But you also have to see, in order to save the planet, we can't continue as we have been. So getting from A to B will become much more unpleasant.

What do you think the mobility of the future will look like?

In the mobility of the future, we will see a stronger trend toward shared transport when it comes to personal mobility. At least for the European Economic Area, i.e. Germany and the EU countries, I see that the per capita number of private motor vehicles will certainly not continue to rise. There will be fewer vehicles, but they will be used more collectively and will look very different from what we know today. As far as the drive system shift is concerned, I already see a very strong trend in Europe toward electrification, i.e., battery-electric drive systems. All the talk about this legal regulation preventing vehicle manufacturers from questioning or discontinuing the path to electrification - the time has long passed. If you look at the vehicle manufacturers in Germany, some of them no longer have the capacity or know-how to produce new generations of internal combustion engines. At least the car manufacturers where I have some insight. The people who could do that are either retired or have left, or they are working on battery-electric concepts. But there will still be combustion engines in individual cases or in niche applications. And public transport will be significantly strengthened. In my opinion, rail-based mobility for long-distance travel will increase very strongly and we will probably fly much less for short distances. I personally have my problems with bicycle mobility, because I'm not a cyclist at all and because I don't think it's feasible all year round in our latitudes. And cycling in Magdeburg also brings with it some special problems. There is a very high bicycle loss, I have suffered from that several times. But I don't see the bicycle as the solution that will bring us much further.

Personally, I think there will be fewer vehicles, most of which will be electrified - either battery-electric or plug-in hybrid vehicles. Hydrogen will play more of a role in the larger vehicles, in the form of the fuel cell and possibly also in the form of the hydrogen combustion engine. And everyday mobility will and must be developed very strongly in the direction of shared public transport.

Now we've already arrived at the last question. You were a guest on our science podcast last year. There you were asked whether you would choose a car with an internal combustion engine, an electric car or a hydrogen car. You said that with your driving style, a lot of long-distance driving, you would opt for a diesel with an internal combustion engine. What does that look like as things stand today? Is your answer still the same?

Yes, definitely. Since last weekend, even more so. The discontinuation of nuclear power in Germany means that more coal-fired power is being fed into the grid. And if you look at the CO2 impact of an electric vehicle compared to a diesel vehicle with the same driving style, the CO2 emissions are very similar. This is based not least on CO2 emissions of over 400 grams per kilowatt hour in the current German power grid. That's why I'm similarly climate-friendly with my diesel vehicle as I am with an electric vehicle of comparable size - in terms of availability and costs, I'm also in a better position. I assume that this will not change in the next few years to the extent that I will have to change my thinking there.


Thank you very much for the interview.