## 4 Conclusions  
The main findings that can be inferred from the results of this research work were as follows:  
In general, when power increased, combustion was more efficient, except with poplar pellets. When the pellet feed flow increased, combustion was more efficient, with a particularly positive effect with plum tree pellets. Carbon monoxide emissions were reduced, whereas inlet air and exhaust gas temperatures increased with power, except with poplar pellets.  
* Combustion was more complete when power and feed increased, decreasing energy loss except with poplar pellets. Regarding pine and plum tree pellets, thermal efficiency increased with a rise in pellet feed and power, as opposed to poplar pellets, for which this efficiency improved by modifying excess air.
* Some solutions to losses were proposed, such as sample homogenization to make the feeding rate more stable, a reduction in the excess air coefficient, and the implementation of an economizer (to reduce the exhaust gas temperature, which is a good step from both environmental and economic points of view).
* The optimum combustion conditions for pine pellets were obtained by selecting Position 5 and +25% biomass feed, with the highest yield, 92.34%, obtained with an excess air coefficient of 2.23, a burned gas ratio of 0.994, and flue gas and inlet air temperatures of 113.14 \({}^{\circ}\)C and 90.57 \({}^{\circ}\)C, respectively. Regarding plum tree pellets, Position 4 and +25% biomass feed were the optimum conditions, with the highest yield, 91.58%, obtained with an excess air coefficient of 2.91, a burned gas ratio of 0.993, and flue gas and inlet air temperatures of 91.71 \({}^{\circ}\)C and 49.14 \({}^{\circ}\)C, respectively. For poplar pellets, these conditions were P = 3 and +25% biomass supply, with the highest yield, 91.1%, obtained with an excess air coefficient of 3.18, and flue gas and inlet air temperatures of 87.66 \({}^{\circ}\)C and 84.66 \({}^{\circ}\)C, respectively.
* For this combustion chamber, it can be concluded that the three fuels studied are suitable for this facility in order to achieve optimum conditions, that is, an efficient combustion process, not showing considerable differences among the products to be selected as the ideal biomass for this experiment.  
Conceptualization, J.F.G. and A.A.M.; methodology, J.F.G. and A.A.M.; validation, J.F.G. and A.A.M.; formal analysis, A.A.M. and D.D.G.; investigation, A.A.M. and D.D.G.; resources, J.F.G.; data curation, A.A.M. and S.N.-D.; writing--original draft preparation, A.A.M., D.D.G. and S.N.-D.; writing--review and editing, J.F.G. and S.N.-D.; visualization, J.F.G., A.A.M. and S.N.-D.; supervision, J.F.G. and A.A.M.; project administration, J.F.G.; funding acquisition, J.F.G. and A.A.M. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
Data Availability Statement: Data is contained within the article.  
The authors would like to thank CICYTEX for providing the raw materials for this experiment.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.