## 3 Results and Discussion
### MCDM Principles and Selected Criteria  
Multiple Criteria Decision Making principles employ standard criteria and parameters for a comparative evaluation of the potential of using slurry technologies. MCDM provides an optimal solution when there is a great number of random arguments; it uses a single approach for a consistent and repeatable decision-making.  
To estimate the resulting efficiency of fuels, all the calculated and measured values were divided into groups (Table 4): energy performance, environmental, and economic. Energy performance indicators allow us to evaluate the ignition and combustion characteristics of fuels of different component compositions. This group includes ignition delay times, maximum combustion temperature, minimum ignition temperature, heat of combustion, and ash content. Environmental indicators incorporate the concentrations of sulfur and nitrogen oxides, measured as different fuels are burnt. Economic indicators consider the cost and capital costs. The cost (C) characterizes the total price of the fuel mixture and how cost-efficient it is for power generation plants. The capital costs are expenses incurred on the purchase of fuel system equipment at plants, as well as its refitting [17].  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Group** & **Criteria** \\ \hline \multirow{4}{*}{Energy performance} & Ignition delay times, \(\tau_{\text{d}}\) (s) \\  & Maximum combustion temperature, \(T_{\text{b}}^{\text{max}}\) (\({}^{\circ}\)C) \\  & Minimum ignition temperature, \(T_{\text{g}}^{\text{min}}\) (\({}^{\circ}\)C) \\  & Heat of combustion, \(Q^{\text{s}}\) (MJ/kg) \\  & Ash content, \(A^{\text{d}}\) (\%) \\ \hline \multirow{2}{*}{Environmental} & Nitrogen oxide emissions, NOx (ppm) \\  & Sulfur oxide emissions, SO\({}_{\text{x}}\) (ppm) \\ \hline \multirow{2}{*}{Economic} & Fuel cost, \(C\) (USD/kg) \\  & Capital costs, \(N\) (USD) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Criteria of fuel efficiency evaluation using the Weighted Sum Method (WSM).  
Based on the criteria presented in Table 4, it was calculated the resulting efficiency indicator of slurries, using the Weighted Sum Method. This method, being universal for different applications, is one of the most common MCDM techniques used in the energy industry [21].  
The WSM combines all the multi-objective functions into one scalar, composite objective function using the weighted sum by the formula:  
\[A_{\mathrm{n}}=\sum\gamma_{\mathrm{j}}X_{\mathrm{ij}} \tag{1}\]  
where \(\gamma_{\mathrm{j}}\) is weight coefficient for each criterion; \(X_{\mathrm{ij}}\) is normalized value of criterion.  
The normalized value was determined by comparing each criterion with one optimal value within each criterion. The normalized criteria values corresponded to the interval 0-1. There are frequently objective difficulties in the tradeoff of weight coefficients, since the subsequent decision depends greatly on this step. It is critical to take into account the priorities in each particular region of the world. It is reasonable to use non-equal weight coefficients, when priorities are ranged to solve certain applied problems for a particular world's region, country, or enterprise. In this case, realistic weight coefficients are introduced based on particular legal regulations (laws, taxes, duties) and large volumes of statistical data (geographic aspects, current economic situation, state of environment, level of technological facilities, and availability of energy resources). It is possible to introduce non-equal weight coefficients for some world's regions. However, obtained results will be too specific to hold interest on the international level. The main purpose of this work was to study the potential advantages of fuel compositions with biomass. Therefore, the calculation results for equal weight coefficients are presented. The best fuel in terms of the criteria under consideration will be the one with the highest weighted sum (\(A_{\mathrm{n}}\)).