Mixture Formation and Corresponding Knock Limits in a Hydrogen Direct Injection Engine Using Different Jet Forming Caps

Abstract

<div class="section abstract"><div class="htmlview paragraph">The need for carbon-neutral transportation solutions has never been more pronounced. With the continually expanding volume of goods in transit, innovative and dependable powertrain concepts for freight transport are imperative. The green hydrogen-powered internal combustion engine presents an appealing option for integrating a reliable, non-fossil fuel powertrain into commercial vehicles. This study focuses on the adaptation of a single-cylinder diesel engine with a displacement of 2116 cm³ to facilitate hydrogen combustion. The engine, characterized by low levels of swirl and tumble, underwent modifications, including the integration of a conventional central spark plug, a custom-designed piston featuring a reduced compression ratio of 9.5, and a low-pressure hydrogen direct injection system. Operating the injection system at 25 bar hydrogen pressure, the resulting jet profiles were varied by employing jet forming caps affixed directly to the injector nozzle. Specifically, two cap geometries were used: a 1-hole cap, yielding a tightly concentrated jet with notable penetration, and a 4-hole cap, yielding a dispersed jet with a broader angle and reduced penetration. Manipulating the injection timing to achieve varying levels of mixture homogeneity within the cylinder, the minimum lambda values were examined before reaching the threshold of knocking for each timing configuration. All trials maintained a constant hydrogen mass flow, with an indicated mean effective pressure (IMEP) of approximately 11 bar and optimal phasing. To complement experimental insights, a comprehensive computational fluid dynamics (CFD) simulation was conducted, focusing on mixture formation intricacies. The results highlight a noteworthy reduction in knocking propensity for the 4-hole cap configuration at later injection timings. This observation demonstrates the intricate interplay between mixture formation and knocking tendencies. The study underscores the potential of jet forming geometries to optimize mixture formation while minimizing knocking effects in hydrogen direct injection engines.</div></div>