## 2 Methodology
### System Description  
For this study, a natural gas ICE with the reference 2 MW Jenbacher JMS 612 GS-N (see Figure 2) was used, in which the intake air and fuel were initially mixed at an atmospheric pressure of about 1.007 bar (7a) at a temperature between 30 and 40 \({}^{\circ}\)C and a relative humidity of approximately 80%. Then, the mixture was compressed as it passed through the turbo-compressors (3b), increasing its pressure and temperature. The mixes were later joined at the outlet of the turbo compressors to enter the intake of the combustion chamber where the mixture was first cooled (4a), and then passed through the throttle valve (4b) which took a percentage opening of 80% for island mode and 98% in synchronism, as shown in Table 1. The turbo bypass valve took opening values between 15% to 50% (6a), recirculating the mixture, and regulating the flow supplied to the equipment. After combustion (1b) in a prechamber, exhaust gases were generated (2a) and (2b) at temperatures between 580 and 650 \({}^{\circ}\)C. Both exhaust gas flows were mixed (10). It should be noted that the physical parameters of the engine when operating an off-grid mode such as gas temperature and pressure, and likewise, showed the performance indicators in Table 1.  
Figure 1: Flowchart of research methodology.  
Figure 2: Physical structure of the waste heat recovery configuration based on recuperative organic Rankine cycle (RORC).  
In the same way, through line (10) (see Figure 2) where the exhaust gases circulate towards the WHR system which the heat exchanger (ITC 1) takes advantage of the waste heat, by which, the heat transferred to the secondary circuit (TOC) which consists of a pump (B1) through which it conducts thermal oil from the line (3 AT) to the line (1 AT) to achieve thermal stability of the organic working fluid and ensures that the RORC working fluid does not exceed its maximum temperature. The heat transfer process between the working fluid and the pentane was performed in the evaporator (ITC 2) which was optimized to minimize both the investment costs of the equipment for the system and the irreversibilities of the heat transfer [48]. This equipment was divided into three zones called preheating (ITC 2c), evaporation (ITC 2b), and overheating (ITC 2a) which serves as a thermal source for the ORC with regenerator where the organic fluid described above as the pentane which when driven by (1 ORC) expands in the turbine (T1) before entering a preheating in the recuperator (RC) where the pressure decreases to enter the condenser which consists of two stages, condensation (ITC 3b) and cooling (ITC 3a). Then, at the pump (B2), the fluid is returned to this recovery unit (RC) at the exchanger evaporation pressures (ITC 2), thus completing the RORC cycle. In Figure 3, a T-s diagram of the RORC system is presented.  
\begin{table}
\begin{tabular}{l l c c} \hline \hline  & & **Value** & **Units** \\ \hline \multirow{8}{*}{Parameter} & Gas flow & 120 & L/min \\  & \(\lambda\) & 1.784 & – \\ \cline{1-1}  & Engine revolution & 1482 & rpm \\ \cline{1-1}  & Gas pressure & 1163.6 & mbar \\ \cline{1-1}  & Throttle valve & 80.0 & \% \\ \cline{1-1}  & Turbo bypass valve & 9.1 & \% \\ \cline{1-1}  & Gas temperature & 389 & \({}^{\circ}\)C \\ \cline{1-1}  & Engine coolant temperature & 63.9 & \({}^{\circ}\)C \\ \cline{1-1}  & Mechanical engine power & 1758.77 & kW \\ \cline{1-1}  & Effective engine efficiency & 38.59 & \% \\ \cline{1-1}  & Heat recovery efficiency & 40.78 & \% \\ \cline{1-1}  & Heat removed from exhaust gases & 514.85 & kW \\ \cline{1-1}  & Specific engine fuel consumption & 177.65 & g/kWh \\ \hline \hline \end{tabular}
\end{table}
Table 1: Physical engine parameters and internal combustion engine (ICE) performance indicators.  
Figure 3: T-s diagram of the process.