Porsche’s Hydrogen Engine, Prospects Proven On The Nordschleife

Resulting with an outcome of a high-performance powertrain with emissions equivalent to ambient air, Porsche Engineering’s study of hydrogen combustion engines.

The focus of the project was on examining the technical potential of the alternative drive technology and expanding the capabilities of existing engineering tools.

Porsche Engineering’s senior expert for engine simulation, Vincenzo Bevilacqua, remarked, “The study allowed us to gain valuable insights with regard to the development of high-performance hydrogen engines and add models and methods specifically for hydrogen to our virtual simulation methodology. With this know-how, we are ready to efficiently handle future customer projects.”

In a nutshell, hydrogen represents a potential alternative to conventional fuels or synthetic fuels (e-fuels) for use in combustion engines. 

Currently, work is proceeding on hydrogen engines worldwide, but this is mainly being done for commercial vehicles with a fairly low specific output of around 50-kW/l of displacement. 

“For the passenger car sector, this is insufficient. We have therefore developed a hydrogen combustion engine that aims to match the power and torque of current high-performance gasoline engines as a concept study. At the same time, we also had the objective of achieving low fuel consumption and keeping emissions at the same level as ambient air. The starting point for our study was an existing 4.4-litre eight-cylinder gasoline engine, or rather, its digital data set, since we conducted the entire study virtually using engine performance simulations,” explained Bevilacqua.

To begin with, modifications to the engine model included a higher compression ratio and combustion adapted to hydrogen, but most importantly, a new turbocharging system. 

Yet, conflicts were faced by using conventional turbochargers, thus four alternatives were examined, particularly powerful turbocharging concepts, some of which came from the world of motorsport. 

All systems consist of several electrically assisted turbochargers, some of them combined with additional control valves in the air system or electrically driven compressors. 

Bevilacqua added, “For clean combustion of hydrogen, the turbochargers have to, on the one hand, provide around twice as much air mass as they do in gasoline engines. On the other hand, however, the lower exhaust gas temperatures result in a lack of energy for their propulsion on the exhaust side. In the benchmark studies, each turbocharging system showed specific advantages and disadvantages. The choice of the right concept is therefore highly dependent on the requirements profile of the hydrogen engine in question.” 

In terms of the engine study, the development team has selected a turbocharging system that features back-to-back compressors. 

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. 

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

Notably, by producing an output of around 440-kW, the hydrogen engine is on par with the original gasoline unit.

For a better assessment of the powertrain’s performance, the team has tested it in a luxury-segment reference vehicle with a relatively high total weight of 2,650 kg on the Nürburgring Nordschleife.

Albeit entirely virtually, the drive was carried out using what is known as a digital twin, i.e., a computer-based representation of the real vehicle. 

With a lap time of eight minutes and 20 seconds, and a top speed of 261 km/h, the vehicle demonstrated high potential with regard to driving dynamics. 

Due to its chemical composition, no hydrocarbons, carbon monoxide and particulate matter were released during hydrogen combustion.

Furthermore, to optimize the hydrogen engine’s emissions, the experts at Porsche Engineering have opted for the usage of nitrogen oxides. 

Through extensive optimisation rounds, they adapted the engine’s operating strategy for the cleanest possible combustion. 

Their approach was to keep the level of raw emissions low by means of extremely lean and therefore colder combustion, making it possible to dispense with an exhaust aftertreatment system.

Porsche Engineering’s specialist engineer for engine simulation, Matthias Böger, expressed, “As it turned out, the nitrogen oxide emissions are well below the limits set by the Euro 7 standard currently under discussion and are close to zero over the entire engine map. Operating it therefore has no significant impact on the environment.”

Additionally, the hydrogen engine also offers high efficiency in the WLTP measurement cycle as well as in customer-relevant cycles thanks to its lean combustion. 

According to Porsche, the cost of a hydrogen powertrain in series production could be comparable to that of a gasoline engine. 

Although the turbocharger system and other mechanical parts are more complex and expensive, there is no need for the exhaust gas aftertreatment required for the gasoline engine under Euro 7.

Outstandingly, the team was able to carry out all tests virtually and efficiently. Porsche’s established simulation process, and experience in modelling and calculation provided the basis for this.

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

Overall, as aforementioned, the goal of the project was to study its potential usage, as the hydrogen engine is unlikely to enter production in its current form.