# Pollutant Emissions and Combustion Efficiency Assessment of Engines Using Biodiesel
## 4 Conclusions  
Experimental tests in a single-cylinder engine show the following trend: NOx increases as the percentage of biodiesel increases, whereas CO decreases. It showed a positive behavior of the hydrocarbons present in the exhaust gases, with a decrease of the parts per million of 15.11% of the mixture B50 compared to B0, since the amount of these particles decreased, which could be indicative of better fuel combustion. A continuous decrease of carbon monoxide particles present in the exhaust gases was observed, which represents a decrease of 4.88% with the use of the B50 mixture compared to the B0 mixture.  
Figure 13: Maximum temperatures in the combustion chamber with the B10 mixture: (**a**) temperature in the chamber of 175.4 \({}^{\circ}\)C; (**b**) temperature in the chamber of 174.6 \({}^{\circ}\)C.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Blends**} & **Minimum Temperature in** & **Maximum Temperature in** \\  & **Combustion Chamber** & **Combustion Chamber** \\ \hline B5 & 174.12 \({}^{\circ}\)C & 174.37 \({}^{\circ}\)C \\ \hline B10 & 175.35 \({}^{\circ}\)C & 175.60 \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table}
Table 8: Result thermography tests.  
Considerable increases of 243.8% (NO), 219.32% (NO\({}_{2}\)), and 46.44% (NOx) in the exhaust gases were observed. In the literature, researchers have reported increases in NO and NO\({}_{2}\), related to the physical characteristics of the combustion chamber. A positive behavior of sulfur dioxide was obtained from the first use of biodiesel as fuel, decreasing 56.98% in the first test and maintaining between 4 and 5 parts per million during mixtures B20, B30, B40, and B50; this benefit could reduce the so-called \"acid rain\" in cities.  
In the case of the electric generator diesel engine, the B5 mix presented the highest trend for NOx and the lowest trend for CO. Combustion efficiency is severely affected by biodiesel blends from B5 to B20; this behavior has been reported by other studies, where it is mentioned that combustion efficiency is affected by fuel type, bed temperature, gas velocity, and excess air levels. Combustion efficiency increases with fuel volatile matter content and bed temperature. Combustion efficiency decreases with increasing superficial gas velocity [36].  
Biodiesel, as a fuel, may vary depending on proportion of mixture, combustion engine characteristics, and the operating conditions of the engine. The obtained results showed a constant decrease in most of the pollutant gases measured in each test, so it is a viable energy transition alternative for use in combustion engines. However, it is essential to mention that technical and operational problems arose when incorporating biodiesel blends into combustion engines; the main problems were ignition delay and low pressure in the fuel injection system.  
Formal analysis, J.C.P.R. and J.A.L.N.; investigation, J.C.P.R., R.V.M. and F.E.O.H.; methodology, C.R.T.S.M. and R.C.C. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Secretariat of Research and Postgraduate of the National Polytechnic Institute of Mexico with the following projects: 20200305, 20201433 and 20201964.  
The authors appreciate the financial support provided by the Secretariat of Research and Postgraduate (SIP) of the National Polytechnic Institute (IPN) Mexico through the SIP 20200305, SIP 20201433 and SIP 20201964 projects. We extend the same thanks to LaNDACBio--CMP+L- IPN for the facilities used in this research work.  
The authors [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] declare that there are no conflicts of interest regarding the publication of this paper.