## 3 Results and Discussion
### Fuel Consumption and Engine Load  
Fuel consumption is a performance and economic metric in combine harvester operation. It reflects not only engine efficiency, but also how effectively the machine converts power into material throughput. The fuel consumption was evaluated both in absolute terms (L h\({}^{-1}\)) and relative to output (L t\({}^{-1}\)), across guide vane angles from 10-35\({}^{\circ}\), with engine load maintained at approximately 90% for both Combine A and Combine B. At low vane angles (10-15\({}^{\circ}\)), Combine A consumed 69.7-71.11 L h\({}^{-1}\), while Combine B showed slightly higher consumption at 74.89-78.9 L h\({}^{-1}\). This difference narrowed at mid-range settings (20-25\({}^{\circ}\)), where both machines began to operate more efficiently due to increased feed flow. The minimum absolute fuel consumption for Combine A was observed at 25\({}^{\circ}\), at just 63.63 L h\({}^{-1}\), which coincided with a throughput of 20.6 kg s  
Figure 14: Influence of guide vane inclination on the feed rate of both combines. (Figures 15 and 16). Combine B reached its lowest absolute fuel rate at 35\({}^{\circ}\) (73.6 L h\({}^{-1}\)), but its output increase during this stage was limited. When fuel efficiency is analyzed in terms of fuel consumed per ton of harvested grain (L t\({}^{-1}\)), the differences between the two combines becomes more pronounced, as illustrated in Figure 13. Combine A demonstrated better fuel-use efficiency across the entire guide vane range. At 25\({}^{\circ}\), its specific consumption was just 0.86 L t\({}^{-1}\), while Combine B required 1.06 L t\({}^{-1}\) at the same setting. At 10\({}^{\circ}\), Combine A used 1.30 L t\({}^{-1}\) versus 1.82 L t\({}^{-1}\) for Combine B, underscoring the higher energy cost of low-throughput operation. For Combine A, polynomial regression provided a near-perfect fit for specific fuel consumption (R\({}^{2}\) = 0.98), slightly outperforming the linear fit (R\({}^{2}\) = 0.97). However, nei  
Figure 16: Influence of Guide Vane Inclination on Fuel Consumption (Engine Load \(\sim\)90%). Combine B.  
Figure 15: Influence of Guide Vane Inclination on Fuel Consumption (Engine Load \(\sim\)90%). Combine A.  
ther model fit the hourly fuel consumption data well, with R\({}^{2}\) values of 0.58 and 0.23, respectively. This suggests that while guide vane angle has a measurable influence on fuel efficiency per ton, its effect on total hourly fuel use is limited. For Combine B, polynomial regression produced stronger fits for both specific fuel consumption (R\({}^{2}\) = 0.89) and hourly fuel use (R\({}^{2}\) = 0.94), outperforming their respective linear fits (R\({}^{2}\) = 0.81 and 0.71). These results indicate that fuel consumption behavior in Combine B is better represented by a curvilinear trend, reflecting nonlinear efficiency gains as guide vane angle increases. The fuel efficiency in Combine A is attributed to its ability to maintain higher feed flow rates and smoother crop acceleration through the rotor. The full-length adjustable vanes optimize material progression, reducing torque fluctuations and internal resistance, which translates into lower fuel demand per unit of output. In contrast, Combine B's segmented vane configuration likely created local flow inefficiencies, especially at high biomass intake levels, leading to more erratic engine load responses and higher relative fuel use. While absolute fuel use in both machines increased again at higher vane angles (30-35\({}^{\circ}\)) due to elevated throughput and engine response demands, Combine A maintained more stable and efficient operation. At 35\({}^{\circ}\), it delivered the highest throughput (23.78 kg s\({}^{-1}\)) at a low specific fuel rate of 0.84 L t\({}^{-1}\) compared to Combine B, despite similar fuel consumption (1.08 L t\({}^{-1}\)) and achieved throughput (20.55 kg s\({}^{-1}\)).