Hydrogen engine with waste heat recovery for stationary applications

Hydrogen engine with waste heat recovery for stationary applications

In the course of the traffic turnaround, the discussion about the hydrogen engine also comes up again. Its efficiency could be increased by waste heat utilization. But that makes the units heavy.

Hydrogen engines have so far been built almost exclusively as four-stroke engines. Operation as a two-stroke engine is also possible.


The replacement of fossil fuels is not imaginable without green hydrogen. For a long time, fuel cells (FCE) were considered the only strategic solution to generate electricity and mechanical work from hydrogen. But BSZ are still heavy, expensive and inflexible.

Combustion engines have advantages and disadvantages compared to the BSZ, whereby operation with hydrogen would eliminate most of the disadvantages. "The carbon-free nature of hydrogen makes it the only fuel that, at least in theory, allows engine combustion without emitting carbon dioxide, carbon monoxide, or hydrocarbons", describes this a Springer-Vieweg author collective around Helmut Eichlseder in his book chapter Direct injection of gaseous fuels on page 521.

2017 | OriginalPaper | Book Chapter

Direct injection of gaseous fuels

Already during the historical beginning of engine development, which was well before the development of N. A. Otto and was often based on atmospheric gas engines, internal mixture formation was investigated. Thus, after initial ..

The hydrogen engine not only plays a role in the current discussion about a decarbonized transportation transition. It was already the subject of research and development 40 years ago. The Daimler-Benz car company was a leader in this technology at the time. Several patents have been filed for this, including one for a regenerative combustion engine.

Low efficiency a disadvantage

The most significant remaining disadvantage of the internal combustion engine compared to the BSZ is its comparatively modest efficiency, and this is a key cost factor when running on green hydrogen.

The best way out of the dilemma could be a corresponding increase in the efficiency of internal combustion engines. At that time (and again today), it was possible to reach into the mothballs of old inventions to find a solution. The core of the patents at that time was the regeneration of the waste heat of the combustion process within the regular working process. Regeneration of waste heat in the process must be clearly distinguished from waste heat utilization, which is quite widespread today and is downstream of the actual combustion process and largely independent of it.

Regeneration in the process directly and seriously increases the efficiency of the engine and leads to significantly less waste heat, which can then still be used for waste heat recovery if necessary. Of course, this additional technology also incurs costs and additional weight. But it also takes away some of the performance dynamics of the internal combustion engine.

This engine process also has several other disadvantages compared to conventional internal combustion engines. In order to achieve good regeneration of the waste heat, power densities must be dispensed with. The engine becomes relatively large and heavy in relation to the power output. Because of regeneration, it also needs non-sooty fuels, i.E. Methanol, natural gas or hydrogen (gasoline is borderline). The modulation (approximately between 25 and 100 percent) goes over wide ranges with good efficiency, but takes minutes to react. For these reasons, the engine is not suitable as a conventional motor vehicle engine, but it could perform well as a range extender in e-cars or for combined heat and power plants with high efficiency.

Too early for the time

At that time, the time was not ripe for such inventions, because on the one hand, the engines could not meet the demands of motor vehicles at that time, and on the other hand, cheap nuclear power was the measure of all things in the 1970s. So this knowledge from back then has simply become dusty and forgotten. The advantages, however, are considerable. Combustion is exceptionally clean, complete and proceeds with virtually no formation of nitrogen oxides. If hydrogen is used, the combustion process is also completely free of carbon oxides.

The engine can achieve efficiencies above 50 percent even at fairly low power levels (about 0.5 kW). This was shown by practical tests combined with computer simulations. For larger motors, 60 percent or more should be achievable. An initial small prototype as a proof of concept with 250 to 500 W and 40 to 45 percent efficiency was still being designed at the time, but no longer executed.

Today, however, with the political vision of hydrogen, the project could be resurrected. However, whether it has the potential to be put into practice is a completely open question. For here, too, are resource efficiencies. Rationality a must. Springer author collective led by Dimitri Seboldt in his journal article Hydrogen Engines for Future Passenger Cars. Light-duty vehicles on page 47 one of these necessities.

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