Two-Step Low-Pressure Direct Injection System for Hydrogen Fuelled Engines

2010-01-2156

10/25/2010

Event
SAE 2010 Powertrains Fuels & Lubricants Meeting
Authors Abstract
Content
The paper describes the CFD analysis, the arrangement and the first experimental results of a single-cylinder engine that employs an innovative low-pressure hydrogen direct-injection system, characterized by low fuel rail pressure (12 bar) and consequent low residual storage pressure. The injection is split in two steps: at first hydrogen is metered and admitted into a small intermediate chamber by an electroinjector (a conventional one usually employed for CNG), next a mechanically actuated poppet valve, that allows high volumetric flow rates, times hydrogen injection from the intermediate chamber to the cylinder within a short time, despite the high hydrogen volume due to the low injection pressure. Injection must be properly timed to maintain pressure below 6 bar (or little more) in the intermediate chamber and thus keep sonic flow through the electroinjector, to maximize volumetric efficiency and to avoid backfire in the intake pipe.
A preliminary CFD study based on code KIVA3v was carried out in order to compare the behavior of different injection valve and valve-seat geometries in controlling air-fuel mixing inside the cylinder and to address the choice towards the most suitable ones, i.e., those that allow adequate fuel distribution in the combustion chamber at ignition time for every operating condition.
As well, all the modifications necessary to obtain the prototype engine from a production one were based on KIVA3v predictions, especially as regards the volume of the intermediate chamber and diameter, maximum lift and opening duration of the injection valve.
The prototype derives from the single-cylinder Aprilia-Rotax 650 cm₃ with five valves (three intake and two exhaust). The cylinder head underwent deep changes to replace the central inlet valve and pipe with the ones for hydrogen injection. Special attention was paid to crankcase ventilation system to prevent the formation of hydrogen pockets.
Experimental results show the effectiveness of the solution. The engine proved to run correctly, without the typical drawbacks of hydrogen engines (preignition, knocking, backfire, roughness) even with stoichiometric or slightly rich mixture (for maximum power). Maximum power was higher than for the engine fed with gasoline.
A new CFD study based on AVL_Fire code recently started taking engine actual details into account with the aims to better predict engine behavior and to address the improvement of the whole system.
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DOI
https://doi.org/10.4271/2010-01-2156
Pages
14
Citation
Frigo, S., Zanforlin, S., Musu, E., Rossi, R. et al., "Two-Step Low-Pressure Direct Injection System for Hydrogen Fuelled Engines," SAE Technical Paper 2010-01-2156, 2010, https://doi.org/10.4271/2010-01-2156.
Additional Details
Publisher
Published
Oct 25, 2010
Product Code
2010-01-2156
Content Type
Technical Paper
Language
English