A highly optical, controlled trajectory rapid compression and expansion machine for gas phase chemical physics research.

Abstract

A highly optical Controlled Trajectory Rapid Compression and Expansion Machine (CT-RCEM) has been developed at the University of Minnesota (UMN) for fundamental research in gas phase chemical reaction kinetics, combustion, and high-temperature gas dynamics. Unlike traditional rapid compression machines, UMN CT-RCEM features precise piston motion control using an electrohydraulic actuation system and an active feedback motion controller, allowing digital adjustment of compression ratio, stroke, compression time, and piston trajectory. This innovation eliminates mechanical interventions, enables a higher number of experimental tests in a given time, and offers superior control over the thermodynamic states of the gas mixture under investigation. Equipped with multiple optical windows, including an end-wall, four side-walls, and their variants to accommodate various experimental scenarios, CT-RCEM provides exceptional optical accessibility, enabling fundamental studies utilizing advanced optical and laser diagnostics. Custom-designed UV-grade sapphire windows with specialized seals withstand high combustion temperatures and pressures of up to 250 bar. The optical windows are interchangeable with metal windows, allowing easy integration of equipment such as igniters, injectors, glow plugs, pre-chambers, and sensors. The versatility, functionality, and performance of the CT-RCEM were demonstrated through autoignition experiments with dimethyl ether/air, spark ignition, and optical pre-chamber visualization studies with methane/air. UMN's highly optical CT-RCEM provides a unique platform for gas phase chemical physics research and holds the potential to advance renewable fuels, plasma, and low-emission propulsion alternatives, promoting sustainable energy solutions.