The Argon Power Cycle (APC) is a novel zero-emission closed-loop argon recirculating engine cycle which has been developed by Noble Thermodynamics Systems, Inc. It provides a significant gain in indicated thermal efficiency of the reciprocating engine by breathing oxygen and argon rather than air. The use of argon, a monatomic gas, greatly increases the specific heat ratio of the working fluid, resulting in a significantly higher ideal Otto cycle efficiency. This technology delivers a substantial improvement in reciprocating engine performance, maximizing the energy conversion of fuel into useful work. Combined Heat and Power (CHP) operating under the APC represents a promising solution to realize a net-zero-carbon future, providing the thermal energy that hard-to-electrify manufacturing processes need while at the same time delivering clean, dispatchable, and efficient power.
Since the working fluid in an APC is synthetic, the concentration of argon, oxygen, fuel, and carbon dioxide (if combusting a carbon-based fuel) can be precisely adjusted for optimal performance across a wide range of loads. At low load, the in-cylinder mixture is highly diluted, which can present challenges in terms of achieving sufficient flame speed and therefore efficient and reliable combustion. Pre-chamber (PC) combustion has the potential to accelerate the combustion rate by creating multiple turbulent hot jets that provide spatially distributed ignition sources with enhanced turbulent mixing. PC combustion can also help reduce the tendency for knock because it promotes more uniform and timely combustion of the fuel-air mixture in the main-chamber. Computational fluid dynamics (CFD) simulations can assist in the optimization of PC design and operating strategy, but CFD models have not yet been validated against experimental data for the challenging conditions encountered in highly diluted APC engines. This study presents 3D CFD modeling for a natural gas, pre-chamber spark-ignition engine used in an APC. A skeletal mechanism for natural gas combustion in an oxygen-argon mixture is employed, and a level-set based G-equation model is used to simulate the combustion process. Simulations are performed under the Reynolds-Averaged Navier-Stokes framework, and the results are compared to experimental engine data in terms of cylinder pressure, apparent heat release, and mass fraction burned timing. The validated model is also used to investigate different oxidizer compositions and their impact on the indicated thermal efficiency.