Implementation of a novel hydrogen direct-injection concept in single and multi-cylinder engines: CFD, experimental and engine powertrain design studies

A novel low-pressure hydrogen direct-injection system, characterised by low storage residual pressure and simple mechanical solutions, has been implemented in single and multi-cylinder engines. Based on two-step operation, this system keeps hydrogen metering apart from injection. The first step relates to the system with constant H2 flow rate and variable opening duration. The second step is characterised by variable H2 flow rate and constant angular duration. A prototype has been realised modifying a single-cylinder production engine, following the results of a wide CFD activity during which in-cylinder hydrogen injection and mixing phases have been simulated to investigate how valve and seat-valve geometries affect mixing characteristics. The prototype engine ran properly at full load, without pre-ignition, knocking or roughness even with stoichiometric or slightly rich mixtures, providing higher maximum power than with gasoline. At part load the engine worked correctly even with very lean mixtures. Current research is directed to explore the feasibility of applying the two-step injection concept in a multi-cylinder engine. The CFD analysis together with the design study aimed to integrate the injection system in the engine powertrain are shown and discussed.