## 3 Results
### Effects of Injection at the Valve and Reactivity Fuels on Performance Attributes  
The efficiency of the engine for B5 and biogas injected at the valve, as the reactivity fuels, increases with the increase in the engine load from 4.5 to 5.5 bar IMEP then steadily decreased as the load increase, which is depicted in Figure 12a. According to Figure 13a, the highest indicted thermal efficiency achieved was 36.33% at a mid 5.5 bar IMEP during the combustion of B5 and biogas injected at the valve, as a consequence of fewer heat losses through the cylinder wall at this particular load. This trend also deviates from the expected gradual decrease in the indicated thermal efficiency with the increase in the engine load, showing the highest ability at mid 5.5 bar IMEP. As earlier stated, 5.5 bar IMEP could likely remain an equilibrium capacity for the change in reactivity status that is the energy supplied by the reactivity fuels could be balanced, hence causing some abnormal behaviors. A similar trend manifested for the combustion of B5 and premixed biogas, though more efficient at 4.5 bar IMEP compared to that of B5 and biogas injected at the valve likely due to reduced heat loss under no-load condition. The trends also looked closely similar to that of the conventional diesel at all the load conditions, but the traditional diesel demonstrated a little bit higher efficiency at high IMEP while less at low IMEP in comparison with the B5 and biogas injected at the valve. The indicated efficiency was found higher for all the engine loads compared to that of B5 and premixed biogas combustion. Figure 13b also shows that the burning of the conventional diesel and biogas injected at the valve, demonstrated high indicated thermal efficiency, at all the load conditions though insignificant at certain levels, compared to the usual premixed injection. The difference could be a result of more heat generated and relatively less heat loss through the cylinder wall with the in-cylinder mixing of biogas [44], though contrary to the fact that retarded combustion phase resulted in lower indicated thermal efficiency as reported by [PERSON] et al. [44].  
The specific amount of fuel consumed decreased drastically as the engine load increase for all the pilot fuels used, under both premixed and in-cylinder mixed methods, as shown in Figure 14a. As observed from Figure 14a, the burning of B5 and premixed biogas indicated the highest brake specific fuel consumed for all the load capacities compared to the approach of injecting the biogas at the valve. More of the specific fuel consumption could be due to the poor quality of the biogas used and its mixing rate. Considering the economy of the pilot fuels used under port injection at the valve, Figure 14a displayed that B5 and regular diesel competing at various engine capacities. At no-load condition, B5 shows higher brake specific fuel consumed likely due to some power loses leading to more fuel consumed besides Figure 13a shows that the B5 was less efficient at no-load condition, hence could also lead to fuel consumption. As the competition progresses at the various engine capacities, a wide margin was exhibited at 6 bar IMEP showing that regular diesel has high BSFC. As the low-quality biogas get premixed, more of the biogas get trapped in the cylinder due to extended ignition delay.  
However, Figure 14b shows that the injection of biogas at the valve has little influence on the rise in fuel consumed; hence, the attribute is mostly because of the poor quality of the biogas.