## 1 Introduction
[25] developed a numerical study for a thermo-economic optimization of an ORC to recover heat from the exhaust gases of a marine diesel engine considering five working fluids, where the R1234 vf presented the best techno-economic performance, but the results only apply for this specific case engine and cannot be applied to the gas engine consider in this paper. Also, [PERSON] et al. [26] investigated different ORC configurations in a stationary gas engine of 34.4 kW for exhaust gas recovery using three working fluids from an exergo-economic perspective. The authors found that toluene was the working fluid with the best results for all the configurations in study, from an energy and economic focus; the last through the specific investment cost (SIC). In the study done by [PERSON] et al. [27], the specific investment cost (SIC) of the ORC system for waste heat recovery was conducted to seek the optimal working conditions for the economic optimization using R123, R134a, R1234 vf, R245 fa, R600, R601, SES36, and HFE7000; it was reported that R600 was the optimal working fluid with a specific cost (SIC) of 2136 \(\epsilon\)/kW and a net power of 4.2 kW. [PERSON] et al. [28] carried out a thermo-economic optimization of basic ORC and regenerative ORC for waste heat recovery using five different working fluids. Thermal efficiency and specific investment cost (SIC) were considered by using NSGA-II (nondominated sorting genetic algorithm-II). They found that R245 fa was the best working fluid under considered conditions with a SIC the 187 \(\$\)/kW. [PERSON] et al. [29] presented the parameter optimization of the subcritical and supercritical ORCs to minimize the levelized cost of energy (LCOE) and heat exchanger area per unit power output (APR). They found that R123 yielded maximal thermal efficiency and exergy efficiency in subcritical ORC. Also, the LCOE was studied by [PERSON] et al. [30] employing a multi-objective optimization by using a non-dominated sorting genetic algorithm (NSGA-II). They determined that the LCE of the ORC system was 21.1% higher than the BORC system under considered conditions. Thus, the authors found the function that minimized the transfer area and the LCOE but without considering an exergetic parameter, they do not present the decision variables of the NSGA-II method, which provide a detailed vision of the research contribution. Finally, [PERSON] at al. [31] carried out the thermodynamic and economic optimization of a subcritical ORC using a pure or zeotropic mixture working fluids. They found that the n-pentane was the best fluid with an LCOE of 0.08635 USD/kWh and a payback period (PBP) of 16.37 years. In this work, they found the optimal values of the thermoeconomic indicators, however there is no explanation about the high value of the PBP, which represents a very long period for economic retribution. From the literature reviews, and based on recent revisions [9], there is an evidence of the limited availability of exploratory studies concerning the recovery heat from exhaust gases using simple ORC cycles in stationary natural gas engines for power generation. In this sense, the main contribution of this research is to present a parametric analysis of the thermos-economic performance of an ORC integrated into a gas engine under real operation condition, taking four thermos-economic indicators. From the state of the art presented, it can be concluded that the use of ORC for the generation of energy from a source of residual heat at low gas temperatures (<300 \({}^{\circ}\)C) is technically and economically viable, which has allowed its presence in the market since the beginning of the 1980s; especially in applications of biomass, geothermal, and solar solutions in a wide range of power and temperature levels.