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

The future heavy duty powertrain market is expected to be more diverse, with shifts gradually towards cleaner and more sustainable alternatives. Among various options, the hydrogen ICE holds the promise of significantly reducing 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. This paper focuses on performance challenges of hydrogen engine, including knock and pre-ignition, as well as low thermal efficiencies by introducing the opposed-piston two-stroke hydrogen ICE (OP2S H2ICE) as a potential solution. The study demonstrates that OP2S H2ICE can operate using direct injection, compression-ignition (CI) combustion solely with hydrogen, under various low-load conditions. Specifically, as the load increases, the combustion transitions from partial-premixed controlled CI combustion towards mixing controlled CI combustion, resulting in thermal efficiencies comparable to those of diesel on the same OP 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 as the uniflow passes through. This feature enables the OP2S H2ICE to overcome the high autoignition temperature, achieving CI combustion even at low load conditions.