Hydrogen fuelled internal combustion engines pose severe challenges to the fuel admission system. To avoid back fire either ported fuel injection (PFI) or direct injection (DI) need to be applied. Both methods require precise timing of fuel injection and thus fast injection valves providing good repeatability, sufficient flow area and high durability. Moreover DI injectors have to withstand high temperatures and high pressure prevailing inside the cylinder. These challenges can be met by a basic design idea derived from compressor valves which have been around for more than 100 years: The basic design incorporates a multi ported plate and a matching ported seat. By lifting the ported plate only a small gap (e.g. 0.2 mm) is opened but a large flow area is achieved because of the large total length of the circumferential ports. The small lift design enables this type of valve to be switched within 300 - 1000 micro s. Injectors based on this design have been developed for ported fuel injection of medium sized gas engines and direct injection for large bore natural gas engines. These applications where used to develop the know how to guarantee trouble free non lubricated operation. Starting from 1999 derivatives of these injectors have been used for PFI in hydrogen fuelled internal combustion engines. Additional - hydrogen specific problems - such as cold welding and embrittlement had to be solved. The injectors have been selected and qualified by a German auto manufacturer to provide timed fuel injection for their first serial car powered by an H2 ICE. Ongoing research is dedicated to use derivatives of these injectors to be incorporated into the design of experimental DI engines. Fuel metering properties of said injectors can be used for setting up precise and extremely fast control of the anode pressure for fuel cell applications. Hydrogen flow has to meet the instantaneous power demand as close as possible. Deviations of demand to supply result in pressure fluctuations loading the membrane of the PEM fuel cell and thus causing fatigue problems. Analogue flow controllers are too slow to react to rapid changes of power demand whereas timed injection allows to react instantaneously to any variation in demand. Tests have demonstrated that injectors similar to the above mentioned PFI injectors meet the requirements for pulsed flow metering.
Timed injection of hydrogen for fuel cells and internal combustion engines
Zeitliche Abstimmung der Wasserstoffeinspritzung für Brennstoffzellen und Verbrennungsmotoren
2006
14 Seiten, 16 Bilder, 2 Tabellen, 1 Quelle
Conference paper
English
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