Experimental Study of Direct-Injection Compression-Ignition Hydrogen Combustion in an Opposed-Piston Two-Stroke (OP2S) Engine

<div class="section abstract"><div class="htmlview paragraph">The future heavy duty powertrain market is expected to be more diverse, with a gradual shift towards cleaner and more sustainable alternative fuels. Among various options, the hydrogen Internal Combustion Engine (ICE) holds the promise of significantly reducing carbon emissions while leveraging existing ICE technology. However, it also faces substantial challenges related to engine performance, fuel storage and delivery, infrastructure development, economic feasibility, safety and market acceptance.</div><div class="htmlview paragraph">This paper focuses on performance challenges of hydrogen engine, including knock and pre-ignition, as well as low thermal efficiencies, and introduces the Opposed-Piston Two-Stroke Hydrogen ICE (OP2S-H<sub>2</sub>ICE) as a potential solution. The study demonstrates that OP2S-H<sub>2</sub>ICE can operate using direct injection, compression-ignition (CI) combustion solely with hydrogen, under various low-load to partial load conditions. Specifically, as the load increases, the combustion transitions from partial-premixed controlled CI combustion towards mixing controlled CI combustion, resulting in thermal efficiency and power density comparable to those of diesel on the same OP engine platform. Compared with conventional four-stroke engine, the OP2S offers the flexible control of trapped temperature through scavenging by retaining more internal residual inside the cylinder. This feature enables the OP2S-H<sub>2</sub>ICE to overcome the high autoignition temperature, achieving CI combustion even at low load conditions. Initial tests demonstrated that ITE up to 47% can be achieved at these conditions with hydrogen CI combustion.</div></div>