## 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
Figure 4b further shows that both B5 and traditional diesel fuels indicated similar patterns of the in-cylinder pressure developed, though there were slight differences at various crank angle positions, under 6.5 bar IMEP. However, the figure depicted that use of B5 along with the premixed port-injected biogas, in reactivity, co-assisted in reducing the negative temperature coefficient causing smoother pressure development contrary to the outcome of the traditional diesel. To elaborate on the port injection at the valve, as a modified LRF delivery approach. Figure 4c depicted that, the combustion of the regular diesel and biogas, in a formally premixed RCCI mode, generates more in-cylinder pressure during compression, unlike the approach of port injection at the valve. The higher in-cylinder pressure could be due to the magnitude of the air-fuel mixing causing partial oxidation of the biogas during low-temperature heat release, in addition to the usual oxidation of the diesel. Besides, Figure 4c reaffirmed the benefit of premixing, though insignificant, in reducing  
pressure, for the regular diesel and biogas injected at the valve, were more significant at no-load to mid-load and decreased as the engine load approached 6.5 bar IMEP. As observed from Figure 6a, the maximum in-cylinder pressure, for the burning of B5 and premixed biogas, insignificantly increased as the engine load increases; thus, 5 bar IMEP indicated higher maximum in-cylinder pressure compared to mid 5.5 bar IMEP. Reaching balance in the energy provided by the reactivity fuels at a load of 5.5 bar IMEP resulting in various abnormalities might be the reason for the little rise in the pressure at this particular load. The combustion of B5 along with both premixed and biogas injected at the valve showed the same maximum strength developed at no-load condition, but injection at the valve comparatively developed higher maximum pressure as the engine load increased from 5 to 6.5 bar IMEP. The balance in the strength at no-load condition could be due to the effect of injection method on the maximum pressure was relatively independent of the engine load, hence could virtually rise or fall at any load setting. Besides, the margin in the maximum pressures also increased as the engine load increased. Above discussions showed that the rise in the engine load or reduced air to fuel mixing before entering the cylinder might be the cause for rising the cylinder pressure, as also evidenced in Figure 6b. Compared to the usual premixed approach, Figure 6b illustrates that the peak pressure developed was higher with the use of diesel and biogas in a premixed than port-injection at the valve for all the load conditions except 6.5 bar IMEP, which indicated relatively the same pressure. This pattern at 6.5 bar IMEP revealed that injection at the valve did not influence the attainment of the maximum pressure, as also shown in 4c above. It further implies that the variability of the maximum pressure could be dependent on the reactivity of the fuel at this particular load capacity. The figure also revealed that the variation in the maximum in-cylinder pressure was insignificantly influenced by the increase in the engine load though escalated at a maximum of 6.5 bar IMEP. According to Figure 5 above, the in-cylinder temperature traces for the combustion of B5 and biogas injected at the valve varies with the engine loads. The figure shows an increase in temperature with the increase in the engine capacity at certain stages of the combustion more, especially during expansion. As the injection of the B5 begins around 156-160\({}^{\circ}\) CA BTDC in the presence of biogas, the temperature builds up was steadily shown up to about 4 CA BTDC. At this stage, an apparent increase in the temperature as a consequence of the rise in the engine capacity can be seen mainly due to compression, B5 impingement and likely some ignited pockets. The temperature in the cylinder does not reach an autoignition temperature of the HRF until the piston gets very closed to the TDC.