## 4 Results and Discussion
### Effect of H/C, O/C, ER and T on Tar Content  
Tar produced by gasification is also affected by the biomass type, temperature, ER, and reactor [17]. The existence of tar in the producer gas is problematic when syngas is used for internal combustion engines [20]. The maximum tar concentration in producer gas that is allowed for internal combustion engines is 100 mg/Nm\({}^{3}\)[19]. The models M1A-M6D predicted the composition of tar in the form of C\({}_{6}\)H\({}_{6}\) in the range of 0. 885 and 2.835 mol\(\%\) (Table 11). If this percentage is converted to gr/Nm\({}^{3}\), Equation (45) yields 23,584-98,733 g/Nm\({}^{3}\) tar in the producer gas. The simulation shows that the producer gas satisfies the maximum tar requirement if it is applied as internal engine fuel. Equation (52)  
Figure 5: Simulation of the effects of H/C and O/C on gas composition at N/C = 0.0198, ER = 0.331: (a) CO at T = 1321 K; (b) CO\({}_{2}\), (c) CH\({}_{4}\), and (d) H\({}_{2}\) at T = 923 K.  
Figure 6: Plotting biomass properties on a [PERSON] scatter diagram. CRN—corn, SWD—sawdust, WCP—woodchips, WPT—wood pellets, MSW—municipal solid waste, PKO—palm kernel oil.  
describes that the tar concentration (g/Nm\({}^{3}\)) is sensitive to changes in temperature and O/C ratio. Figure 7 depicts the response of tar concentration to the changes of (a) ER and T, (b) H/C and O/C.  
Figure 7 shows that biomass with a high H/C and O/C ratio produces a high concentration of tar when T and ER are low. The tar concentration decreases with increasing T and ER. Tar content falls when H/C lowers and O/C increases. Figure 7a may be obtained if the ER is low and the temperature is high. Figure 7a can still be obtained at low a temperature, but the ER must be high. The results suggest that minimum tar production during biomass gasification could be obtained at T \(>\) 1073 K. The steam reforming process, as described in Equation (14), may reduce tar production at high-temperature ER. Conversely, the original models cannot predict tar content in the producer gas. The reaction constant in the original model \(K_{6}\) was more than 1. By modifying the models, \(K_{6}^{*}\) < 1, and the models accurately predicted the tar concentration.  
The results of the tar concentration simulated in this study are in line with the experimental findings of other studies. Gasification of corn straw with a downdraft reactor at an ER of 0.18 to 0.41 produced tar at concentrations of 7215 to 4617 mg/Nm\({}^{3}\)[73]. Gasification of the same biomass with a downdraft reactor at an ER of 0.2 to 0.28 produced tar with concentrations in the range of 369 and 67 g/Nm\({}^{3}\)[38]. Gasification of corn cob at ER of between 0.2 and 0.4 yielded tar with concentration from 1.7 to 2.4 mg/Nm\({}^{3}\); whereas the wood waste gasifier in the same setup resulted in 1.85 to 3.1 g/Nm\({}^{3}\) tar [74]. Gasification of MSW at an ER of 0.3 to 0.5 yielded a decreasing tar from 328.69 to 31.45 mg/Nm\({}^{3}\), respectively [40]. The tar concentration in the producer gas decreased from 418.95 to 78.57 /Nm\({}^{3}\) when the temperature of eucalyptus gasification was increased from 663.71 to 793.56 \({}^{\circ}\)C [56]. Another study also shows that tar concentration fell from 9.4 to 7.1 g/Nm\({}^{3}\) after the temperature was increased from 700 to 850 \({}^{\circ}\)C, respectively [75].