Engine Experimental Results with hydrogen Two-Step Direct Injection

In hydrogen-fuelled internal combustion engines, port fuel injection, compared to direct injection, allows higher range and is less expensive and more adaptable to existing engines, but leads to lower specific power and may cause backfire and pre-ignition. Conversely, direct injection is more complex and expensive, but provides even higher specific power than with gasoline, prevents backfire and makes pre-ignition less probable. The benefits of direct injection are added to those of port fuel injection in an innovative lowpressure (12 bar rail pressure) direct-injection system that is shown in this paper. The injection is accomplished in two steps: first an electroinjector meters hydrogen and feeds a small intermediate chamber, then the hydrogen stored in the intermediate chamber is timely injected into the cylinder by a mechanically actuated valve. The prototype was obtained modifying a production single-cylinder 650 cm3 engine for motorcycles. Experimental results show proper engine operation, without pre-ignition, knocking or roughness even with stoichiometric or slightly rich mixtures. Maximum power was higher than with gasoline.