## 4 Conclusions  
In the present study, the combustion characteristics and pollutant emissions associated with firing fast pyrolysis bio-oil/diesel blends in a 300-kW\({}_{\text{th}}\) furnace were investigated. The following conclusions are drawn:  
1. The air supply rates necessary to meet the minimum excess oxygen requirement were 246 and 256 Nm\({}^{3}\)/h, respectively, for pure diesel and the blend of 5% bio-oil + 95% diesel.
2. Combustion instability did not occur during the co-firing test without any modifications to the combustion system.
3. At a fixed fuel flow rate (20 L/h), burning the blend of 5% bio-oil + 95% diesel resulted in a slightly lower temperature in the combustion chamber than burning pure diesel, since the fast pyrolysis bio-oil has a lower calorific value and a high oxygen content of as much as 56.31 wt %. This indicates that similar furnace temperature distributions, and thus heating characteristics, were obtained during the co-firing test.
4. Compared with burning pure diesel, comparable NO emissions (smaller than 57 ppm) were obtained for burning the blend of 5% bio-oil + 95% diesel, and lower net CO\({}_{2}\) emissions were  
\begin{table}
\begin{tabular}{c c c} \hline
**Fuel** & **100\% Diesel** & **5\% FPBO + 95\% Diesel** \\ \hline \(T_{\text{w1}}\) (\({}^{\circ}\)C) & 985.6 & 925.1 \\ \(T_{\text{w2}}\) (\({}^{\circ}\)C) & 1279.2 & 1188.0 \\ \(T_{\text{w3}}\) (\({}^{\circ}\)C) & 1120.9 & 1076.5 \\ \(T_  
achieved because biomass is both carbon neutral and renewable. Moreover, the CO concentrations under these two burning conditions were very low (less than 35 ppm) because of the minimum excess oxygen operating conditions required to achieve complete combustion.
5. The SO2 emissions for burning the blend of 5% bio-oil + 95% diesel and diesel alone were nearly zero (smaller than 6 ppm) since both the bio-oil and diesel have a low sulfur content.  
This paper is the first report on the combustion characteristics and emitted pollutants of co-firing bio-oil produced from the fast pyrolysis process of coffee bean residue and diesel in a 300-kWth oil-fired furnace without any modifications to the system. It emphasizes the feasibility of using the blend as a substitute for diesel in industrial applications. Even though many interesting results are obtained, we realize that additional parametric studies are of significance and worth further study. For instance, the analysis of the effect of higher blend ratio, fuel pressure and atomizing-gas velocity on combustion characteristics and emissions is necessary. Furthermore, a study on reduction of PM (particulate matter) emissions is needed. These will be addressed in a separate study in the near future.  
This work was supported by the Ministry of Science and Technology, Taiwan, under contract of MOST 105-3113-E-006-004.  
[PERSON] performed the experiments and analyzed the results. [PERSON] generated ideas, designed experiments, analyzed the results, and wrote the manuscript. [PERSON] generated ideas, designed experiments, analyzed the results, and helped with editing the manuscript.  
The authors declare no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.