36 Chapter V Results and Analysis V.1 Results and Analysis of Combustion Characteristics This chapter presents the results and analysis of combustion characteristics based on a model and simulation of a Rolls Royce B35:40V20A2 engine conducted using Ansys Forte 2022 R1 software. Results and analysts include combustion characteristics: ignition delay, HRR, combustion duration, cylinder pressure, and cylinder temperature. V.1.1 Ignition Delay Ignition delay is observed in the phenomenon from ignition until a heat release rate of 10% (CA10) is achieved. The ignition delay of the combined combustion simulation of natural gas and ammonia in the variation of ammonia mole fractions is shown in Table V.1 and Figure V.1. Table V.1 Results simulation of Ignition Delay. NH3 Mole Fraction CA10 Delta Ignition Delay (%) 0 CA (%) 0 CA 0 -23.51 Datum 1.49 10 -23.95 1.87% 1.05 20 -23.82 1.31% 1.18 30 -23.79 1.17% 1.21 40 -23.45 0.25% 1.55 50 -23.81 1.26% 1.19 60 -23.47 0.20% 1.53 70 -23.79 1.19% 1.21 80 -22.82 2.94% 2.18 90 -23.50 0.03% 1.50 100 -23.13 1.61% 1.87 37 Figure V.1 10% Heat release at various ammonia mole fraction. Based on Figure V.1 above, the ignition timing occurs at an angle of 25 0 BTDC and ignition is observed at a heat release rate of 10% (CA10). The results showed that the ignition delay increased slightly as the molar fraction of ammonia increased. Ignition delay tends to be stable between 1.18 0 – 1.55 0 from 0% to 80% of the molar fraction of ammonia. A significant increase in ignition delay occurred at 80% ammonia mole fraction that CA10 occur at -22.82 0 BTDC with an ignition delay 2.18 0 CA. At 100% of the molar fraction of ammonia ignition delay drops to 1.87 0 CA. Xiao et al explained in their research that ammonia has a higher flash point and a lower combustion rate compared to methane (the dominant composition in natural gas) (Xiao et al., 2020a). Lhuillier in his research started of ignition at 40 0 BTDC to compensate for slow NH3 flame propagation (Lhuillier, Brequigny, Contino, et al., 2020). Chiong et al said that the autoignition temperature for ammonia 651 0 C is higher than CH4 which is 630 0 C, further also ammonia requires a higher activation energy compared to natural gas, causing a longer ignition delay at a higher mole fraction (Chiong et al., 2021). According to Valera-Medina, methane in an ammonia mixture accelerates the initiation of combustion because methane has a faster reaction rate (Valera-Medina et al., 2024). This explains why at the 10% ammonia fraction, the ignition delay is the shortest, because the role of methane is -27 -26 -25 -24 -23 -22 -21 0 10 20 30 40 50 60 70 80 90 100 10% Heat Release / CA10 (degCA) Ammonia Mole Fraction (%) CA10 Ignition 38 still dominant in the mixture. This study shows that the mole ammonia fraction between 10%-70% provides a relatively stable and shorter ignition delay and is considered optimal for the operational condition of the Rolls Royce B35:40V20A2 engine at PLTMG Luwuk. V.1.2 Heat Release Rate Heat release rate analysis is used to determine the heat released by combustion against changes in time or crank angle. HRR provides insight into the characteristics and effectiveness of combustion that affect power output, thermal efficiency, and emissions from engines. The effect of the addition of the molar fraction of ammonia on the heat release rate profile is shown in Figure V.2.