## 4 Conclusions
The results showed that the best configuration is that of RORC with toluene as the working fluid, because it improves operational performance by achieving an overall conversion efficiency of 11.58%, a net power of 146.25 kW, a reduction in fuel consumption of 7.67% and an ORC thermal efficiency of 28.4% at an engine speed of 1482 rpm, 1.78 lambda, a natural gas flow of 120.2 L/min, and 1758.77 kW of mechanical engine power. However, to contribute in the industrial adoption of this technology, it is necessary to conduct energy, exergy, and thermoeconomic optimization to obtain performance indicators of the waste heat recovery system, and viable thermal solutions to increase the thermal efficiency of this type of natural gas engine. The exergetic analysis showed that the condenser had the highest percentage of exergy destroyed with 40.99%, while the lowest was obtained in Pump 1 with a value of 0.19%. The components with greater irreversibilities such as the evaporator, regenerator, and condenser were the devices that allow, according to the proposed analysis methodology, for the improvement of the system under consideration, since they concentrated 85% of the destroyed exergy and had greater opportunities for improvement. Due to this, the conditions were analyzed where the endogenous destroyed exergy was greater than zero and less than the \(E_{d,k}\) for each device. The advantages of performing an advanced exergetic analysis for each component was that we established that the most significant opportunities for improvement occurred in the turbine with 63.8% of exogenous character and in the evaporator with 38.88% of endogenous character and 17.35% of exogenous character. For future study, it is recommended to apply an optimization of the heat transfer mechanisms on the components to minimize the exergy destroyed, since this could represent a limitation if a more realistic model was desired, which could be complemented with a computational fluid dynamic (CFD) analysis of some components such as the turbines. Conceptualization, J.C.G. ; Methodology, J.C.G., G.V.O., and J.D.-F.; Software, J.C.G., J.D.-F., and G.V.O. ; Validation, J.C.G., J.D.-F., and G.V.O. ; Formal analysis, J.C.G., J.D.-F., and G.V.O. ; Investigation, J.C.G., J.D.-F., and G.V.O. ; Resources, J.C.G. ; Writing--Original Draft Preparation, G.V.O. ; Writing--Review & Editing, J.C.G. and J.D.-F.; Funding acquisition, J.C.G. and G.V.O. All authors have read and agreed to the published version of the manuscript. This research was supported by the Universidad Francisco de Paula Santander and the Universidad del Atlantico, located in Bucaramanga and Barranquilla, Colombia, respectively. This research was supported by the Mechanical Engineering Program of Universidad del Atlantico and the Universidad Francisco de Paula Santander. The authors consider there is no conflict of interest. The following abbreviations are used in this manuscript: \begin{tabular}{l l} CRF & Return on capital factor \\ FCI & Investment of fixed assets \\ ICE & Internal combustion engine \\ ITC 1 & Heat exchanger 1 \\ ITC 2 & Evaporator \\ ITC 3 & Condenser \\ ORC & Organic Rankine cycle \\ RC & Heat recovery \\ TCI & Total capital to be invested \\ TOC & Thermal oil circuit \\ TPC & Total production cost \\ \end{tabular}   
**Nomenclature**