26 Chapter IV Modeling and Simulation IV.1 Workflow ANSYS Forte Programming The Rolls-Royce B35:40V20A2 engine was modeled and the combination combustion of natural gas and ammonia was simulated using ANSYS Forte 2022 R1 software. ANSYS Forte 2022 R1 is a CFD software developed by ANSYS, Inc., designed for 3-D multi-phase engine simulations with combustion (ANSYS Inc., 2018). This software is commonly used to simulate ICE to optimize engine design, improve fuel efficiency, reduce exhaust emissions, and enhance engine performance. The programming steps in ANSYS Forte 2022 R1 are presented in Figure IV.1 below. Figure IV.1 Workflow of ANSYS Forte programming. 27 IV.2 Assumption and Simulation Data Several assumptions were made in the modeling of the Rolls-Royce B35:40V20A2 at PLTMG Luwuk 40MW using ANSYS Forte 2022 R1. The assumptions used include the following: 1. The cylinder-piston system is modeled in a 45° sector angle. 2. The equation of state (EOS) used in the thermochemistry of gas flow is ideal gas, so the mole fraction can be considered as the volume fraction 3. The composition of air consists of 21% oxygen and 79% nitrogen expressed in mole fractions. The input data used to model the Rolls-Royce B35:40V20A2 at PLTMG Luwuk 40MW is presented in Table IV.1 and Table IV.2. In this study, spark ignition uses the number 25 0 Before Top Dead Center (BTDC) or -25 0 After Top Dead Center (ATDC) this value is in accordance with what Wei did in the natural gas-fueled gas engine experiment with the addition of ammonia (Wei et al., 2023). Table IV.1 Engine and air intake data specification (Bergen Engine AS, 2019). Data Specification Value Unit Connecting rod 780 mm Cylinder bore 350 mm Piston stroke 400 mm Rated speed 750 rpm Compression ratio 12.8 : 1 Crevice height 33 mm Squish 33.9 mm Spark ignition 25 0 BTDC Air pressure 3.05 bar Air temperature 50.5 0 C Engine output 100% load 9611 kW Table IV.2 Natural gas composition (Bergen Engine AS, 2019). Data Specification Value Unit Metane (CH4) 94.582 % mol Etan (C2H6) 3.866 % mol Propane (C3H8) 1.036 % mol Nitrogen (N2) 0.516 % mol 28 IV.3 Modeling The modeling step was conducted by referring to the programming workflow as shown in Figure IV.1. The following steps were taken in the process of modeling the Rolls-Royce B35:40V20A2 engine at PLTMG Luwuk 40M using ANSYS Forte 2022 R1. The geometry of the combustion chamber and piston, obtained from the service manual and direct measurements on the Rolls-Royce B35:40V20A2 engine, as shown in Figure IV.2 and IV.3, has been tabulated and presented in Table IV.1 above. Figure IV.2 Rolls-Royce B35:40V20A2 engine at PLTMG Luwuk 40MW. Figure IV.3 Piston of Rolls-Royce B35:40V20A2 engine.