## 3 Results
### Effects of Injection at the Valve and Reactivity Fuels on the Combustion Attributes
#### 3.1.2 Rate of the Combustion Heat Release  
Figure 7a above presented the heat generated when burning B5 along with the biogas injected at the valve. As observed from Figure 7a, the significant rise in the temperature began during expansion, as the period of which a considerable amount of the mixture gets burned. The rate of the heat development at various crank angles decreased as the engine load increased to mid-load, then rose as the load approached a maximum of 6.5 bar IMEP. This trend might be an attribute of short ignition delay exhibited at a load of 4.5 bar IMEP (refer to Section 3.1.4 for more explanation). The short ignition delay might increase the rate of burning of the mixture resulting in higher peak heat released though developed lower pressure at the second peak, as depicted in Figure 4a. According to Figure 7b, use of B5 and biogas in a conventional premixed mode resulted in higher maximum heat, at some crank angle position (210-240 CAD) during expansion, compared to that of the injection at the valve. The  
Figure 8: Variation of total heat release rate (HRR) for (**a**) B5/biogas RCCI in a premixed and injection at the valve and (**b**) diesel/biogas in a premixed and port injection at the valve.  
Figure 7: The heat release rate for the (**a**) combustion of B5/biogas injected at a valve for various load capacities, (**b**) B5/biogas RCCI in premixed and injection at a valve for 6.5 bar IMEP, and (**c**) diesel/biogas in a premixed and port injection at the valve for 6.5 bar IMEP.  
heat released pattern behaved otherwise at crank angles before and after such a range. The trend might be due to factors other than injection approach or in-cylinder temperature because Figures 6c and 8a, respectively, indicated that biogas injection at the valve yielded higher maximum in-cylinder temperature and total heat released at full load of 6.5 bar IMEP. Besides, Figure 7c justified that biogas injection at the valve contributed to raising the heat in the cylinder as a consequence of the higher temperature developed. Figure 8a presented some details on the total rate of heat generated for the combustion of these fuels at various load capacities. As observed from Figure 8a, the burning of B5 and biogas injected at the valve indicated a higher total rate of heat generated, compared to the conventional premixed approach, at all the load capacities, which could be a consequence of higher temperature generated as shown in Figure 6c under Section 3.1.1. Using diesel as test fuel along with the biogas injection at the valve indicated an escalated total heat at a load of 6.5 bar IMEP, which could be due to a higher engine efficiency compared to the use of B5 under both premixed and port injection at the valve. Although, Figure 8a further indicated that the total heat generated at the mid 5.5 bar IMEP was affected by the less in-cylinder temperature developed at this particular load capacity causing lower total heat compared to that of 5 bar IMEP. A balance in energy supplied by the reactivity fuels could be the reason for the lower cylinder temperature at 5.5 bar IMEP. Compared to the use of conventional diesel and biogas injected at the valve, the heat generated using B5 remained higher at all the engine load except full 6.5 bar IMEP. This higher heat generated could be attributed to the oxygenate property of B5 that led to high cylinder temperature. The benefits of the injection at the valve is, also, shown in 8b, though the figure indicated an abnormal behavior at a load of 6 bar IMEP likely because of the longer ignition delay that might affect the rate of the heat and temperature development (Figure 6d).