Most of the power produced in the United States is via combined heat and power (CHP) systems, with most CHP installations using reciprocating internal combustion engines (RICE). RICE CHP systems offer several advantages, such as low installation and operational costs, high performance, load flexibility, and adaptability to various applications spanning from kilowatt to megawatt scales. Noble Thermodynamic Systems' (NTS) core technology, the Argon Power Cycle (APC), is a revolutionary, new power generation system that boosts the efficiency of RICE CHP generation systems while emitting zero greenhouse gasses or producing zero air pollutants, including nitrogen oxides (NOx). The APC uses the noble gas argon, a monatomic gas, which dramatically increases the specific heat ratio of the working fluid, resulting in a significantly higher ideal Otto cycle efficiency. The APC presents a promising solution to reach a carbon-neutral future for the energy needs of pivotal industries such as manufacturing plants. To optimize the efficiency of the APC-RICE, identifying the best engine design is crucial. Engines in CHP applications must operate efficiently across varying load conditions. For very lean operating conditions, using a pre-chamber (PC) can help accelerate the combustion rate and, thus, provide efficient and reliable combustion under diluted mixture conditions. With this motivation, in this work, the pre-chamber of a spark-ignited, natural-gas fueled APC-RICE will be optimized to extend high combustion efficiencies to lower load setpoints using lean and diluted mixtures. A level-set-based G-equation model is used to simulate the combustion process in the Reynolds Averaged Navier Stokes (RANS) framework. A validated 3D CFD model is utilized to investigate varying PC design parameters, viz., nozzle number, area, included angle, and PC size. Notable improvements are observed in modified designs when compared to the baseline geometry.