The advantages of hydrogen fueled internal combustion engines are well known, certainly concerning the ultra low noxious emissions (only NOx is to be considered). Disadvantages are the backfire phenomenon and the gaseous state of hydrogen at atmospheric conditions. A complete control of the mixture formation is necessary and therefore a test engine with sequential port injection was chosen.
The tests are carried out on a single cylinder CFR engine with the intention to use the results to optimize a 6 and 8 cylinder engine with multipoint injection. Different positions of the injector against the intake air duct are examined (represented as different junctions).
A numerical simulation CFD code (FLUENT) is used under “stationary” conditions (continuous injection) for all geometries and under “real” conditions (sequential injection) for one situation.
For each of the geometries the influences of the start of injection, the air/fuel equivalence ratio, injection pressure and ignition timing on the power output and efficiency of the engine are analyzed. A comparison and discussion is given for all results.
It is clearly shown that the start of injection for a certain engine speed and inlet geometry influences the volumetric efficiency and thus the power output of the engine due to the interaction between the injected hydrogen and the inlet pressure waves. Furthermore, the small influence of the injection pressure and the contradictory benefits of the different junctions between power output and fuel efficiency are measured.
With retarded injection, so that cool air decreases the temperature of the “hot-spots” in the combustion chamber before the fuel is injected, backfire safe operation is possible.