## 3 Results and Discussion
### Throughput  
Throughput is an indicator of combine harvester efficiency, representing the amount of crop material processed over time.  
The feed rate (kg s\({}^{-1}\)) was assessed across six guide vane angle settings (10-35\({}^{\circ}\)) in both Combine A and Combine B. Engine load was maintained at approximately 90% for all trials, isolating guide vane angle as the primary variable influencing material flow.  
Feed flow rates increased consistently with guide vane angle in both machines. Combine A recorded an increase from 14.89 kg s\({}^{-1}\) at 10\({}^{\circ}\) to 23.78 kg s\({}^{-1}\) at 35\({}^{\circ}\), while Combine B increased from 11.42 kg s\({}^{-1}\) to 20.55 kg s\({}^{-1}\) over the same range. The Combine B throughput plateaued, rising only slightly from 19.89 kg s\({}^{-1}\) to 20.55 kg s\({}^{-1}\) from the 25-35\({}^{\circ}\) guide vane angle (Figure 14). This diminishing return suggests that Combine B's partially adjustable guide vane system had reached its functional limit in increasing throughput.  
As shown in Figure 14, Combine A exhibited a strong linear relationship between guide vane angle and feed rate (R\({}^{2}\) = 0.96), though the polynomial fit provided a better R\({}^{2}\) of 0.97. In contrast, Combine B showed better fit with a polynomial trend (R\({}^{2}\) = 0.84) compared to its linear counterpart (R\({}^{2}\) = 0.83), supporting the curvilinear behavior.  
Figure 13: Influence of guide vane inclination of broken grain (Engine Load \(\sim\)90%). Combine B.  
This confirms that larger vane angles accelerate material movement, enabling greater throughput even when engine power remains constant. The fully adjustable vane system in Combine A allowed for smoother and more uniform acceleration across the rotor length, resulting in a steeper and more efficient increase in feed rate compared to Combine B.  
The advantage of Combine A became especially evident at mid-to-high vane angles (25-35\({}^{\circ}\)), where its improved material guidance minimized internal flow restrictions and allowed higher feed volume without excessive grain losses.  
However, the increased throughput at higher vane inclinations came with trade-offs. As described in previous sections, separation and grain losses also increased beyond 30\({}^{\circ}\), particularly in Combine A. This highlights a performance threshold: while a greater feed rate improves productivity, it also risks exceeding the separation system's capacity, potentially leading to overloading, reduced cleaning efficiency, and increased losses.  
The guide vane inclination had a pronounced influence on feed flow rate. Combine A's full-length adjustable vane system enabled higher and more efficient throughput than Combine B, especially at 25-35\({}^{\circ}\), by maintaining consistent axial flow throughout the rotor. A paired \(t\)-test was conducted to compare the feed flow rate between Combine A and Combine B across the tested vane angles. The results showed a statistical difference (t = 4.80, \(p\) = 0.0049), confirming that Combine A's throughput advantage is not due to random variation. Nonetheless, the balance between throughput and grain retention must be carefully managed to avoid efficiency losses at higher flow rates.