Statistical Study of Combustion Characteristics and Optimal Operation Factor Determination in an Emulsion Burner Fueled with Vegetable Oils

This work experimentally investigates the combustion characteristics of refined soya, sunflower, and rapeseed vegetable oils and, by means of statistical techniques, determines the optimal operating factors of an emulsion burner to obtain the best combustion performance and low pollutant emissions. Given the high dimensionality of the study, principal component analysis provides a descriptive study of the variables involved in the combustion process and of the physicochemical properties of the vegetable oils so as to establish the correlations between them. ANOVA was then performed to identify which factors (type of vegetable oil, fuel flow, and airflow), as well as any possible interactions, have the greatest impact on the combustion results (performance as well as CO2, CO, NOx, CxHy, and SOx emissions). The ANOVA results showed that almost all of the factors and their interactions were significant, which makes it essential to analyze the interaction plots in order to see the optimal combinations of levels. This study showed that fuel flow rate was quite an important factor affecting combustion characteristics, that the type of vegetable oil influenced CxHy emissions, and that the airflow rate displayed no clear trend. Furthermore, the best combustion performance coupled with pollutant emissions below the lowest limits established by the current legislation were achieved for a combination of maximum fuel flow and minimum airflow rates, with soya exhibiting the best performance. In general, good combustion performances were obtained with extremely low NOx emissions. SOx emissions were not detected in any of the combustion experiments performed.