Working fluid replacement in gaseous direct-injection internal combustion engines: A fundamental and applied experimental investigation

Replacing air with argon theoretically allows for large thermal efficiency increases in internal combustion engines. Before such cycles can be realized, fundamental research on fuel injection into argon and laboratory-scale engine tests are needed. We investigated non-reacting methane jets into argon and nitrogen atmospheres in a constant volume chamber using high-speed schlieren imaging. We subsequently assessed the feasibility of methane direct-injection in a modified single cylinder research engine with an argon-oxygen mixture as the working fluid. We compared engine performance by measuring fuel flow, in-cylinder pressure, torque, and emissions. Results show that the penetration depth and spread angles of methane jets are notably different but not significantly reduced in argon compared to nitrogen. Additionally, running the modified engine with an argon-oxygen mixture in compression ignition operation leads to improvements in efficiency up to 50 percent relative to spark-ignited air cycles, and NOX emissions are nearly eliminated. The results encourage more studies in which the exhausted argon is recycled into the intake.