## 3 Results and Discussion
### Emission Characteristics
#### 3.5.5 Fuel Energy Distribution  
This section concludes by examining the fuel energy distribution within the engine for the tested fuels. Accordingly, Figure 11 summarizes the fuel energy allocation based on the power output and exhaust gases directly measured on the experimental assessment. Notice that the energy loss comprises lubrication oil, refrigerant, among other energy losses such as blow-by gas that limit energy conversion [34].  
Figure 10: Smoke emission for fuels tested.  
Figure 11: Energy distribution in the SI engine, (**a**) load 50%, (**b**) load 75% and (**c**) load 100%.  
According to the results, increasing the engine load intensifies the energy contribution of both the power output and exhaust gases. This result is consistent with WHR applications where higher loads facilitate the fuel utilization ratio. The exhaust streams feature higher temperatures which corroborate the imminent escalation of NOx emission as depicted in Figure 9[3,5]. However, the negative pattern of increasing the engine load is the significant rise in fuel consumption, as ratified in Figure 6. The results demonstrated that almost half of the fuel energy results in energy losses and other sources. Partial fuel substitution with ABE reduces the heat recovery potential from exhaust gases compared to conventional gasoline, which can be associated with the lower calorific value of this fuel blend.  
Overall, ABE 10 + HHO features the best performance on the power output distribution from the tested fuels ranges in all the engine load conditions. An average increment of nearly 2.4% can be achieved compared to the baseline fuel. Contrarily, the maximum heat potential in the exhaust gases is higher in the gasoline fuel, with an improvement between 0.6-0.9% compared to the rest tested fuels. Subsequently, Figure 12 describes the behavior of thermal efficiency for the different fuel blends.  
According to the results, the thermodynamic efficiency directly relates to the engine load while representing a sensitivity between 4-6%. The latter can be attributed to non-optimized combustion derived from lower \(H_{RR}\) and pressure ranges. This pattern is consistent with similar applications in diesel engines operating in dual-fuel mode [15,16]. Moreover, the comparative assessment between fuel blends demonstrates that the addition of ABE in gasoline endorses engine efficiency, while hydroxy doping favors efficiency escalation. For the tested conditions, the maximum thermal efficiency of 31.81%, 32.49%, 32.52%, 32.63%, and 33.01% was obtained when operating with gasoline, ABE5, ABE5 + HHO, ABE10, and ABE10 + HHO, respectively. The above behavior is mainly attributed to a complete combustion process due to the presence of ABE and hydroxy, which is reflected in the reduction of CO emissions (see Figure 7).  
Figure 13 shows the exergy distribution of the engine for the different operating conditions and fuel blends.  
Figure 12: Thermal efficiency for different types of fuels.  
Figure 13: Exergy distribution in the SI engine, (**a**) load 50%, (**b**) load 75% and (**c**) load 100%.  
Results show that exergy destruction represents the greatest share from the sources analyzed. The latter can be attributed to several factors such as residual fuel mixing, turbulence flow instabilities during combustion, among other irreversibilities that limit the chemical energy conversion [47]. Besides, as the engine load increases, both the useful exergy (mechanical power) and exhaust gas exergy rise, which implies improved combustion efficiency as both internal and external irreversibilities decrease [47; 48]. The engine reaches a maximum of 29.9%, 30.6%, 30.9%, 31.0%, and 31.4% for the useful exergy when implementing gasoline fuels ABE5, ABE5 + HHO, ABE10, and ABE10 + HHO, respectively.