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Diesel? Gas? Hybrid?

11/17/2015 | Words: Yvonne Wirth | Pictures: Robert Hack

Maritime economy

The shipping industry with its heavy-oil and diesel propulsion systems is constantly wrestling with the issue of health-harming and environmentally damaging emissions. The main culprits are nitrogen oxides (NOx), sulphur oxides (SOx) and soot particulates. Demand for alternative fuels such as natural gas is growing. The combination of political pressure and the trend towards "green" shipping plays and increasingly important role, including for the shipbuilding and supplier industries themselves. Professor Friedrich Wirz chairs the working group on marine engineering at the Hamburg University of Technology. Together with his colleagues he is conducting research into increasing the efficiency of shipping as a means of transport. In this interview he talks about how alternative fuels are developing, what the future for shipping is and what he thinks future marine propulsion systems will look like.

You want to increase the overall efficiency of ships. What ideas do you have in that regard?
We are looking at the entire efficiency chain. Starting from the shape of the ship, through the type of fuel, the conversion into motive power and the drivetrain to the design of suitable propellers. We want to combine individual components into a system as effectively and usefully as possible so that the operators get ships that properly meet their requirements. In shipbuilding you simply have to remember that every ship is a one-off. And that is precisely what makes our work so exciting.

So, do operators come to you asking for the perfect ship?
Yes, we get that too. We are always looking for industrial partners with whom we can research solution concepts. But we also get shipbuilders and operators asking us for advice.

If you could choose the propulsion system of the future, what would it look like?
Good question. What the shipping business urgently needs are engines with wide performance maps. That means being able to call on high torque reserves across a wide range of engine speeds. That characteristic performance is needed in order to obtain significantly higher efficiency potential from the propeller. And to do so especially in operating ranges in which ships mostly work – the mid-power range. We are familiar with the same scenario in cars: however amazing the efficiency, it is only any good if you can call on it in the mid-power range. This is where high-speed diesel engines in particular have an advantage because they have a broader performance map than the medium-fast heavy-oil engines.

How important is the engine's role in the propulsion system?
The engine is a component of the overall system. If I improve the engine by one percent, that has precisely the same effect on the system as a whole as if I improve, say, the propeller by one percent. In a large container ship, one percent equates to about two tonnes less fuel consumed per day.

Natural gas or its liquefied form (LNG) could help the shipping industry clean up its imageDr. Friedrich Wirz

Natural gas as a fuel is particularly close to your heart. Why?
Mainly because of the environmental factor. Sometime or other there may even be a stable price advantage. If that were to happen, it would be used more widely. I keep the aspect of a CO2 benefit out of the equation because there may possibly be interactive effects with a loss of natural gas. If you compare a gas engine with a heavy-oil engine, there are clear advantages in terms of emission levels for sulphur oxides and soot particulates and, depending on the combustion process in the engine, nitrogen oxides as well. So natural gas or its liquefied form (LNG) could help the shipping industry clean up its image.

Why do ship operators actually choose gas engines?
In some cases, people use them because they really are concerned about the environment or are keen to do everything to make themselves look "green". Apart from that, there are legal requirements to be met, and natural gas offers an option in that respect.

So is gas the future?
I am of the opinion that ship operators who work at a global level will not restrict themselves solely to natural gas in the next ten to 15 years. They will maintain the dual-fuel capability as they must always expect to have to refuel at ports where there is no natural gas. Diesel, by contrast, is available virtually anywhere.

In the future, will it be slow-running, medium-fast or high-speed engines that are most needed?
Particularly when it is a case of natural gas as the fuel, we have seen in recent times that there has been a trend towards medium-speed four-stroke engines where in the past slow-running two stroke engines were used. But that is only because they came first. So not a major trend.

What will shipping look like in 2050?
Technically more complex because the good old diesel engine will no longer get by without denitrification, sulphur removal systems and particulate filters. In 2050 I think natural gas engines will make up about 15 percent and the rest will still be diesel. But that is just my gut feeling. It may be that we will have entirely different fuels by then. In addition, shipping will be very largely automated although I don't expect it will be entirely unmanned. I don't think that ships will one day sail the oceans without human crews – because who will repair an injection pump in an emergency? Sea travel will simply become more complex and more expensive.

In 2050 I think natural gas engines will make up about 15 percent and the rest will still be diesel.Dr. Friedrich Wirz

Will the emission restrictions one day be so strict that diesel will be entirely out of the question as a fuel?
Emissions legislation will undoubtedly become stricter in terms of nitrogen oxides, sulphur oxides and CO2 and there is almost no limit to that progression. But I do not believe that at some time the point will be reached when we will have to say that the diesel engine is no longer fit for purpose as the basic power unit. There will always be ways of controlling emissions or improving combustion processes so that those demands can be met. That applies both to diesel and gas engines.

What about hybrid systems?
What actually is a hybrid system? By some definitions, it has to involve an electrical energy store, i.e. a battery. But you could also say that you have a hybrid system as soon as you combine an combustion engine with an electric motor/alternator. Hybrids of that second type are already widespread and will make further inroads, especially since the cost of frequency regulators continues to fall, with the result that they are slowly becoming affordable. This technology has now even found its way into large container ships. For smaller ships there are already a few hybrid systems with batteries. If I look at this question from the viewpoint of the shipping industry as a whole, I don't think that this type of hybrid will become established soon because the energy storage capacities will remain much too small for the foreseeable future.

What is the most important issue for you in all of these imagined futures?
However shipping develops in the future, the most important thing for me is that the safety shipping remains a prime consideration. It is no use whatsoever having the most efficient propulsion system in the world if it suddenly packs up on you. Or you have a ship with too little motive power that becomes unmanoeuvrable in heavy seas. Despite the political pressure behind natural gas technology, gas propulsion systems should also be thoroughly planned, as natural gas is highly flammable. We shouldn't fall into the trap bandwagon-jumping just so as to satisfy all the environmental demands.

Are you a seaman yourself?
No, I am not a seafaring type at all; I've never travelled very far by sea either.

So how did you end up in this career then?
Marine technology is a very special subject in its own right. I also find it fascinating that every ship is a one-off. I grew up in Hamburg, right on the banks of the Elbe, so to speak, where ships pass right by you every single day. Then at university I specialised in marine engineering and so got to know and love this industry. And now I can't imagine doing anything else.

The content of the stories reflects the status as of the respective date of publication. They are not updated. Further developments are therefore not taken into account.

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