Study of hydrogen combustion characteristics and comparison between SI and CI combustion concepts for HD applications

The project "Hydrogen combustion and comparison PFI/DI concepts" deals with the potential analysis
of different mixture formation concepts for hydrogen combustion engines in the field of commercial ve-
hicle applications.
For this study, a single-cylinder commercial vehicle engine is equipped for hydrogen operation, both
with port fuel- and direct injection, and operated on an engine test bench. The basis for comparison is
the design with the port fuel injection, which is then compared with different concepts with direct injection
in terms of achievable power, efficiency and emission behaviour.
The test engine has a central spark plug, a displacement of 2116 cm³ and a compression ratio of 9.5.
Special focus is placed on the different combustion and emission behaviour of port fuel- and direct
injection due to different homogenisation in the combustion chamber.
With the help of suitable jet forming caps for the direct injection hydrogen low-pressure injector, the
mixture formation of the direct injection is to be improved. For this purpose, two different cap geometries
are designed. A cap with a central hole for a compact jet and a cap with four smaller individual holes for
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a more diffuse jet.
Accompanying the tests on the engine test bench, a 3D CFD model is being set up to simulate the
mixture formation processes, which should provide more detailed insights into the mixture formation and
homogenisation of the combustion chamber.
Compared to direct injection, port fuel injection shows significantly slower combustion, characterised by
higher combustion delay and duration as well as lower pressure gradients, with advantages in terms of
efficiency and nitrogen oxide emissions. The simulation proves better homogenisation compared to di-
rect injection. With a maximum available boost pressure of 3.4 bar absolute, the achievable indicated
mean effective pressure of the port fuel injection setup is limited to 18 bar due to pre-ignition. Direct
injection with a four-hole cap has the highest nitrogen oxide emissions and achieves an indicated mean
effective pressure of 19 bar before it is also limited by pre-ignition. The direct injection with single-hole
cap shows the highest load capacity with a maximum indicated mean effective pressure of 20 bar and
is only limited by the maximum peak cylinder pressure of 180 bar in the current configuration.