Porsche Engineering is investigating the potential of hydrogen as an alternative to conventional fuels and e-fuels in combustion engines. And tested the engine on the Nordschleife.
The current development of hydrogen engines is mostly aimed at use in commercial vehicles and does not exceed an output of 50 kW per liter displacement. This is not enough for Porsche for use in cars. "That's why we developed a hydrogen combustion engine as a study, which should offer power and torque at the level of current high-performance gasoline engines. At the same time, our goal was to achieve low consumption and keep emissions at the ambient air level," says Vincenzo Bevilacqua, technical officer Engine simulation at Porsche Engineering.
Modified 4.4-litre eight-cylinder
That's why Porsche used the 4.4-litre eight-cylinder petrol engine as the basis for its investigation. To be more precise: the digital data set, since the entire study was tested in the simulator – a common procedure in the development of aggregates and other technical elements for years.
The power of the virtual engine is 440 kW and is therefore at the level of the basic petrol engine. In order to check the performance of the drive, the engineers installed it in a "luxury-class reference vehicle with a total weight of 2,650 kilos" and let the model loose on the Nürburgring-Nordschleife. The lap time: 8:20 minutes. Despite this remarkable time, the focus was on emissions – especially nitrogen oxides, since the combustion of hydrogen does not release any hydrocarbons, carbon monoxide or particles. Accordingly, the aim was to keep raw emissions low with lean and colder combustion in order to dispense with exhaust aftertreatment.
Emissions well below the Euro 7 limit
"As has been shown, the nitrogen oxide emissions are well below the currently discussed limit values of the Euro 7 standard and are almost zero over the entire speed range," reports Matthias Böger, Development Engineer Engine Simulation at Porsche Engineering.
Another result was low consumption in the WLTP cycle thanks to lean combustion. This puts the costs for series production at the level of a conventional combustion engine. On the other hand, the high costs for the new charging system and the mechanical components are saved in the exhaust aftertreatment for Euro 7.
New turbocharger technology
The core of the modifications to the virtual hydrogen engine are the higher compression, the adapted combustion and a new turbo system. Because, as Porsche explains, the turbochargers require around twice as much air mass as a petrol engine for clean combustion. On the other hand, the energy for the turbo drive is missing due to the low exhaust gas temperature.Conventional turbos cannot handle this technical dilemma; Therefore, Porsche has examined four alternative charging concepts, some of them from motorsport.
All these systems consist of several electrically assisted turbochargers, which are combined in parts with additional control flaps within the air system or mechanical compressors. "In the benchmark investigations, each charging system showed specific advantages and disadvantages. Choosing the right concept therefore depends very much on the requirement profile of the respective hydrogen engine," says Bevilacqua. "For the present engine study, the development team chose a turbo system with so-called back-to-back compressors. Their special design feature is the coaxial arrangement of two compressor stages, which are driven by the turbine or the supporting electric motor via a common shaft. The process air flows through the first compressor, is intercooled in the intercooler and then post-compressed in the second stage."
Porsche is testing - purely virtually - based on data from an existing engine how a hydrogen unit could perform in a car. To do this, the engineers had to adapt the supercharging in particular. The result: Clean combustion, hardly any emissions, low consumption and a lap time on the Ring that is impressive.