## 1 Introduction  
Energy efficiency is seen as a promising technology for reducing energy-generation costs and has become the best hope for controlling climate change [1, 2]. Therefore, it is necessary to propose methodologies for the rational use of energy in waste-heat recovery systems (WHRS) in stationary generation engines, which are widely used in the industrial sector [3, 4]. The thermal efficiency enhancement of industrial engine requires a cost-effective thermal design of WHRS configurations. Thus, it is necessary to evaluate project costs looking forward to achieving a proper cost-efficiency ratio [5]. The total investment costs have been evaluated for the suggested ORC systems, allowing the development of a thermal-economic analysis [6], but the natural gas engine has not been considered. Total investment capital (TCI) has been studied in some research results, involving the operation and maintenance (O&M) costs, but the heat source is a thermal oil without taking into account the thermal conditions of the engine exhaust gases [7]. The tendency in research related to exergoeconomic analysis increased exponentially from 2015 to 2017, based on thermodynamic models such as that proposed by [PERSON] and [PERSON] [8] using biomass fuel and solar power as a heat source, where an economic analysis of a micro-scale triggering system was conducted to produce combined heat, electricity, and refrigeration, operating combined with an organic Rankine cycle (ORC) and a vapor compression cycle. The three systems were connected to the same shaft, obtaining, as a result, electricity production of 1.42 kWe, heat power of 53.5 kWh, the net electrical efficiency of 2.38%, and a net electrical efficiency of 2.38%, while the energy efficiency of the ORC was estimated at around 7%. In addition, the development of multi-generation energy systems based on geothermal energy has achieved optimizations of the system by coupling heat recovery cycles, as proposed by [PERSON] et al. [9], including an ORC for electricity generation and heating, performing an energetic, exergetic and exergoeconomic analysis of the system to achieve an energy and exergetic efficiency of 34.98% and 49.17%, respectively. However, the study is limited to a simple ORC configuration in a geothermal application, so the results cannot be expandable for waste-heat recovery (WHR) in the natural gas engine. Therefore, because of the moderate studies carried out on natural gas engine modeling to characterize the exhaust gas flow and temperature, few studies are available in the literature considering the WHR based on the ORC from these types of stationary engine [10]. On the other hand, WHR with on-board ORC systems from vehicle engines, has also been developed, where through simulations of the performance of a high-resistance truck, truck/engine and ORC/cooling system models were conducted and experimentally validated. The results presented reveal the effects of the truck engine speed on its performance with the ORC system, and the truck engine has a power gain of 3.07 kW at the speed of 95 km/h under full load conditions [11]. The most recent applications of ORC for WHR have focused on determining the technical feasibility of the integration of an ORC to diesel engines, not gas engines, without evaluating the effect of engine operating parameters on the economic viability of the integrated generation system, but they lack a detailed exergoeconomic analysis [12; 13; 14]. However, it is necessary to highlight the research carried out with the diesel engine WP12 336E40, which produced 247 kW at 1400 rpm. The study evaluated different working fluids such as R600, R600a, R601a, R245 fa, R1234 yf, and R1234 ze in a simple configuration, where the evaporation pressure, condenser temperature, exhaust temperature at the outlet of the evaporator and degree of overheating were studied and optimized by means of a thermoeconomic analysis, in which a recovered power was ranging from 5.2 kW to 13.2 kW for the working fluids [15].