## 4 Results and Discussion
### The Effect of H/C, O/C, ER, and T on Producer Gas Composition  
The results obtained from Equations (48)-(51) have determination coefficients (R\({}^{2}\)-adj) that are larger than 0.9354. Based on the sensitivity analysis, the results indicated that temperature has the biggest influence on the composition of producer gas. Figure 4 shows that, under constant O/C, H/C, and N/C, the highest CO that was simulated occurred at low ER and high T, whereas the highest CO\({}_{2}\), CH\({}_{4}\), and H\({}_{2}\) were predicted to occur at both low ER and T. The results could be attributed to the reaction equilibrium constants \(K_{i}^{*}\) during reactions within gasification, which has been displayed in Figure 3. Figure 3 shows that R3 has \(K_{3}*<1\) at T \(>\) 890 K. This indicates that the reaction would result in a higher proportion of H\({}_{2}\) than CH\({}_{4}\). In the case of R4 occurs at T \(>\) 970 K, \(K_{4}\) shifts into \(K_{4}*\) and \(K_{4}*<1\). As a result, R4 would result in more CO than CO\({}_{2}\) and H\({}_{2}\). The same holds for the shifting from \(K_{5}\) to \(K_{5}*\) at temperatures greater than 1110 K. \(K_{5}*>1\), which triggers R5 when to produce more CO and H\({}_{2}\) than CH\({}_{4}\). R6 would produce more C\({}_{6}\)H\({}_{6}\) than H\({}_{2}\) and CO because \(K_{6}*\) is always less than 1 when shifting from \(K_{6}\) to \(K_{6}*\) occurs. Low temperatures (900-1273 K) gasification [64; 65] would trigger R3 to produce more H\({}_{2}\), whereas R4 produces more CO, CO\({}_{2}\), and H\({}_{2}\). The reaction R5 and R6 would be responsible for producing CH\({}_{4}\) and C\({}_{6}\)H\({}_{6}\). High gasification temperatures (T \(>\) 1273 K) would lead to the production of H\({}_{2}\) by R3, CO by R4, CO, and H\({}_{2}\) by R5 and C\({}_{6}\)H\({}_{6}\) by R6. Other studies [10; 18; 19; 65; 66] show that the percentage of CO increases while the percentages of CO\({}_{2}\), CH\({}_{4}\), and H\({}_{2}\) decrease with increasing temperature. In contrast, some studies also show that the percentage of CO and H\({}_{2}\) decreases [42; 67; 68; 45] with increasing temperature. It seems that increasing gasification temperature may result in different compositions of producer gas. The composition of producer gas does not only depend on the temperature, but it also depends on the ER. Figure 4 shows that the compositions of CO, CO\({}_{2}\), CH\({}_{4}\), and H\({}_{2}\) decrease with increasing ER. The ER changes significantly affect the composition of CO and H\({}_{2}\), which may be explained by the oxidation zone. In the oxidation zone, series of isothermal processes (C + O\({}_{2}\) = CO\({}_{2}\)), (C + 12O\({}_{2}\) = CO), (H\({}_{2}\) + 12O\({}_{2}\) = H\({}_{2}\)O), and (CO + 12O\({}_{2}\) = CO\({}_{2}\)) produce heat [3]. As ER rises, the airflow in the reactor increases. Increasing air in the oxidation zone would affect the reactions of carbon, carbon dioxide, and hydrogen with oxygen. These reactions yield CO\({}_{2}\) and H\({}_{2}\)O [10; 65]. The reaction between CO\({}_{2}\) and H\({}_{2}\)O would subsequently be employed in the reduction zone. If the airflow in the reactor is too low, C will not be burned into CO, CO\({}_{2}\), and CH\({}_{4}\). Therefore, increasing ER leads to the reduction of CO, CO\({}_{2}\), H\({}_{2}\), and CH\({}_{4}\)[18; 65; 69; 70]. Equations (48)-(51) were further applied to simulate the effects of O/C and H/C on the composition of producer gas, under constant N/C, ER, and T. At N/C of 0.0198, ER of 0.332, and T of 1128 K, the lowest predicted composition of CO and CO\({}_{2}\) were 21.253% and 14.651% mol, respectively. These values were obtained at O/C of 0.71 and H/C of 1.792. The lowest predicted composition of CH\({}_{4}\) and H\({}_{2}\) were 1.531% and 13.584% mol, respectively, which occurred at O/C and H/C of 0.61 and 1.2, respectively. The highest predicted composition of CH\({}_{4}\) and H\({}_{2}\), i.e., 1.531% and 13.584% mol, respectively, were obtained with O/C and H/C of 0.831 and H/C of 1.792, respectively.