## 3 Results
### Effects of Injection at the Valve and Reactivity Fuels on the Combustion Attributes
#### 3.1.1 Analysis of The In-Cylinder Pressure Traces  
The B5 fraction was maintained at 50% for the various load conditions, to study its effect as an oxygenated fuel on the RCCI engine using simulated biogas as LRF. According to Figure 4a, the pattern of the pressure traces, for B5 and port-injected biogas at the valve, varies as the engine load increases with the maximum pressure developed at the first peak for all the loads except 6.5 bar IMEP, which manifested at the second peak. As observed in Figure 4a, the broadness of the pressure curves increased as the load increased. The increase in the area under the pressure curve signified more work done during the combustion at higher IMEP. The work output increased by 1.79% as the load increased to 5 bar IMEP while an extension to 5.5, 6, and 6.5 bar IMEP, relative to no-load condition, increased the work done by 9.15%, 15.40%, and 26.56% respectively. The more work could attribute to the increase in the concentration of the methane, which was more combustible in the biogas, as the load increased. Although there might be an insignificant rapid explosion, the trend in Figure 4a indicated no rise in the pressure due to an explosion at the early stage of the combustion. This phenomenon could be due to the reduced amount of B5-diesel injected, for which the ignition could be initiated in some reactivity pockets causing a delay in the explosion due to its burning. Subsequently, the explosion of the small amount of B5 might not be significant to cause a sudden rise in the in-cylinder pressure and cause an explosion of the biogas for the primary combustion without delay. Another reason could be an insufficient temperature at the early stage of the combustion to cause the rapid explosion as shown in Figure 5 below. In addition to the delayed eruption of the biogas, the amount of low quality of the biogas injected also affected the sudden rise in the cylinder pressure developed, especially at lower engine loads. Figure 4a also portrays that the rise in the second peak increase with the increase in the engine load as a consequence of more heat generated due to the burning effect of the biogas injected at the valve. A relatively insignificant rise in the peak manifested at 4.5 and 5 bar IMEP capacity. This characteristic signifies that the quantity injected at 4.5 and 5 bar IMEP capacity might relatively be insufficient to cause a significant rise in the second peak of the cylinder pressure. However, extending the load further resulted in more substantial growth in the second peak due to increased quantity of biogas burned, though maintained relatively the same fraction. Figure 4a also showed that the second peak development occurred during expansion as the period in which most of the heat generated could be due to the burning of LRF in the RCCI combustion. The trends of the pressure development signify that the combustion of the B5 and biogas injected at the valve was affected by the poor quality of the biogas used. However, the in-cylinder mixing of the biogas, as a consequence of injection at the valve, has an insignificant effect on the variation of the pressure traces at 6.5 bar IMEP, as indicated in Figure 4b. Similar trends of the pressure traces were, also, observed at other load capacities. As seen in Figure 4b, the biogas injection at the valve resulted in higher in-cylinder pressure at the first peak compared to premixed mode. It is because the heterogeneity of the charge mixture facilitates more stratification of the methane compound causing early burning of the biogas. However, the combustion of B5 and biogas injected at the valve produces more negative temperature coefficient, which affects the progression of the pressure development before attaining peak stage contrary to that of the premixed port-injected biogas. Retarded combustion phase could be another factor that affects the cylinder pressure development [40].