Porsche Engineering examined the potential of hydrogen combustion engines

In a study, Porsche Engineering examined the potential of hydrogen combustion engines. The result is a high-performance powertrain with emissions on par with ambient air.

Different powertrain solutions, including hybrid systems, electric drives and efficient combustion engines, are currently all being developed in parallel for use in future vehicles. Hydrogen represents a potential alternative to conventional fuels or synthetic fuels (e-fuels) for use in combustion engines. This was investigated as part of a study on the subject by Porsche Engineering.

High performance hydrogen engine for passenger cars

Work is currently underway on hydrogen engines worldwide, but these are mainly intended for commercial vehicles with a relatively low specific power of around 50 kW per liter of displacement.

Vincenzo BevilacquaSenior Expert Engine Simulation at Porsche Engineering, said:

For the passenger car sector, this is insufficient.

“So we developed a hydrogen combustion engine that aims to match the power and torque of today’s high-performance gasoline engines as part of a concept study. At the same time, we also aimed to reduce fuel consumption and keep emissions at the same level as the surrounding air.

“The starting point for our study was an existing 4.4-liter eight-cylinder gasoline engine – or rather, its digital dataset, since we conducted the entire study virtually using simulations of engine performance.”

Changes to the engine model included a higher compression ratio and hydrogen-friendly combustion, but most importantly, a new supercharging system.

“For the clean combustion of hydrogen, turbochargers must, on the one hand, supply approximately twice as much air mass as in gasoline engines. On the other hand, however, the lower exhaust gas temperatures lead to a lack of energy for their exhaust-side propulsion,” says Bevilacqua.

This discrepancy cannot be resolved with conventional turbochargers. Porsche Engineering has therefore studied four particularly powerful alternative supercharging concepts, some of which come from the world of motorsport.

All systems consist of several electrically assisted turbochargers, some of which are combined with additional control valves in the air system or electrically driven compressors. “In benchmark studies, each supercharging system showed specific advantages and disadvantages. Choosing the right concept is therefore highly dependent on the requirements profile of the hydrogen engine in question,” says Bevilacqua.

For the engine study in question, the development team chose a back-to-back compressor supercharging system. The special feature of this design is the coaxial arrangement of two compressor stages, which are driven by the turbine or the supporting electric motor using a common shaft.

Process air flows through the first compressor, is cooled in the intercooler and then recompressed in the second stage.

With an output of around 440 kW, the hydrogen engine is on par with the original gasoline unit. In order to better assess the performance of the powertrain, Porsche Engineering tested it in a luxury segment benchmark vehicle with a relatively high total weight of 2,650 kg on the Nordschleife at the Nürburgring – albeit entirely virtually: the driving was carried out using what is known as a digital twin, i.e. a computer representation of the real vehicle.

With a lap time of eight minutes and 20 seconds, the vehicle demonstrated high potential in terms of driving dynamics. Due to its chemical composition, neither hydrocarbons nor carbon monoxide are released when hydrogen is burned, nor do particles play a role.

In terms of optimizing emissions from the hydrogen engine, the experts at Porsche Engineering have therefore focused on nitrogen oxides. During extensive optimization cycles, they adapted the engine’s operating strategy for the cleanest possible combustion.

Their approach was to keep the level of gross emissions low thanks to an extremely lean and therefore cooler combustion, making it possible to dispense with an exhaust gas after-treatment system.

Matthias Bogerengine simulation engineer at Porsche Engineering, said:

It turned out that the nitrogen oxide emissions are well below the limits set by the Euro 7 standard currently under discussion and are close to zero on the whole engine map.

In order to better contextualize the results of the emissions tests, it draws a comparison with the air quality index. It is used by government authorities and other institutions as a reference to assess the level of air pollution. In general, a concentration of up to about 40 micrograms of nitrogen oxide per cubic meter is synonymous with good air quality.

“Emissions from the hydrogen engine are below this limit. Its operation therefore has no significant impact on the environment,” says Böger.

Emissions at the same level as ambient air

In addition to its barely measurable emissions, the hydrogen engine offers high efficiency in the WLTP measurement cycle as well as in customer-relevant cycles thanks to its lean combustion. “We have thus achieved the objective we had set ourselves: the development of a clean, economical and sporty hydrogen engine, at all levels”, concludes Bevilacqua.

The cost of a series hydrogen powertrain could be comparable to that of a gasoline engine. Although the turbocharger system and a number of mechanical components of the hydrogen engine are more complex and therefore more expensive, the exhaust gas aftertreatment required for the gasoline engine under Euro 7 is not necessary.

The Porsche Engineering team was able to carry out all the tests virtually and therefore very efficiently. The established simulation process provided the basis for this, as well as the company’s extensive experience in modeling and calculation.

“It only took us six months from the initial idea to the completion of the study,” says Bevilacqua. “This included fundamental work such as creating new simulation models that take into account the different chemical and physical properties of hydrogen compared to gasoline.”

Consumption benefits of up to five percent

The hydrogen engine is unlikely to enter production in its current form, but that was not the goal of the project anyway. Instead, the focus has been on examining the technical potential of alternative drive technology and expanding the capabilities of existing engineering tools.

“The study allowed us to gain valuable insights into the development of high-performance hydrogen engines and to add hydrogen-specific models and methods to our virtual simulation methodology,” says Bevilacqua. “With this know-how, we are ready to effectively manage future customer projects.”

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