## 4 Conclusions  
This study uses thermogravimetric experiment and differential thermal analysis to investigate the effects of different wood pellet species and mixing ratios on the combustion performance of blended fuels. The synergistic effect of bituminous coal (SC), biomass (HTB, KOL and BA) and oil sludge (OS) is evaluated. The kinetic analysis is conducted utilizing both the FWO and Dolyc techniques. The main conclusions are as follows:  
1. The weight loss rate curve of bituminous coal exhibits a distinct peak value. The combustion of wood pellets could be divided into two processes, including the combustion of compound carbon (236.0-382.0 \({}^{\circ}\)C) and fixed carbon (383.0-610.0 \({}^{\circ}\)C). The combined combustion index (\(C_{\rm i}\)) of BA wood pellets is as high as 1.88 \(\times\) 10\({}^{-7}\). The combustion properties of oil sludge are poor with a large amount of ash.
2. The effective blending of wood pellets enhances the combustion capacity of the tri-fuel and raises the Ci. The largest weight loss peak is correlated with a lower temperature and a more intense combustion. The KOL wood pellets exhibited the most pronounced effect in reducing the ignition temperature (Ti) to 265.0 \({}^{\circ}\)C among the three different wood pellets. The mixing ratio has the most significant influence on the combustion performance of tri-fuel with HTB.
3. The blending combustion of SC, HTB and OS has a significant synergistic effect. The char combustion of SC and HTB promote each other. When there is a high SC mixing ratio, an excess of OS inhibits the tri-fuel's combustion. As the OS ratio increases from 10% to 20% with 45% HTB, \(T_{\rm i}\) decreases from 354.9 to 269.8 \({}^{\circ}\)C, while \(T_{\rm h}\) drops by 12%. The impact of OS on the ignition performance is greater than that on the burnout performance.
4. The most probable function \(f(\alpha)\) of tri-fuel is obtained by the master plot method. The \(f(\alpha)\) is \([-\ln(1-\alpha)]^{2}\) for tri-fuel of most mixing ratios when the conversion rate \(\alpha<0.5\), while \(f(\alpha)\) becomes \([-\ln(1-\alpha)]^{3}\) at \(\alpha>0.5\). At the high HTB level, an increase in OS content causes the activation energy to decrease to 35.87 and 49.04 kJ mol\({}^{-1}\) and the pre-exponential factor increases significantly at \(0.5<\alpha<0.8\). OS particles provide numerous relatively small units for combustion, so that HTB and SC with the dense particle arrangement can be exposed to more oxygen. The moderate blending of oil sludge improves the pre-finger factor and the combustion performance.  
Conceptualization, L.D. ([PERSON]), X.H., J.R., L.D. ([PERSON]) and Y.D.; data curation, L.D. ([PERSON]), X.H., L.D. ([PERSON]) and Y.D.; investigation, L.D. ([PERSON]), J.R. and L.D. ([PERSON]); resources, L.D. ([PERSON]); supervision, L.D. ([PERSON]); writing--original draft, L.D. ([PERSON]) and L.D. ([PERSON]); writing--review and editing, Y.D. and X.H. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China, grant number [51406147].  
Not applicable.  
The data that support the findings of this study are available from the corresponding author.  
The authors also thank the staff at the Instrument Analysis Center of Xi'an Jiaotong University for their assistance with sample analysis.  
The authors declare no conflict of interest.