**1. Introduction**

When harvesting, the feed rate of WCHs constantly changes due to factors including header height, harvesting speed, crop moisture content, and density [1–4]. Farmers have recently used plant growth regulators in the wheat plantation process to improve wheat yield, which leads to the high moisture content of wheat stalks during harvest. Compared with the low moisture content of wheat stalks, the feed rate of the WCHs will increase at the same harvest speed, which further increases the workload imposed on the operating parts of the WCHs and even causes blockages. Methods such as elevating the header or reducing the cutting width and operating speed of WCHs are usually adopted to adjust the feed rate to avoid blockages. However, elevating the header will increase the stubble height, which affects the operation quality and is not conducive to subsequent crop planting [5]. At the same time, reducing the cutting width and operating speed will reduce the operational efficiency and increase the harvest loss [6].

As an essential part of the WCH, the header significantly impacts the harvest quality [7]. Most WCHs in China use rigid screw conveyor headers and a mechanical transmission system. Large-scale WCHs in other countries mostly use flexible transmission belt headers with high intelligence. Many scholars have also researched the automatic control of header operation parameters in recent years. Through automatic adjustment of header height [8–14], reel height and rotation speed [15–17], and screw conveyor clearance [18], problems such as combined harvester congestion and increased harvest loss caused by

**Citation:** Yuan, L.; Lan, M.; He, X.; Wei, W.; Wang, W.; Qu, Z. Design and Experiments of a Double-Cutterbar Combine Header Used in Wheat Combine Harvesters. *Agriculture* **2023**, *13*, 817. https://doi.org/ 10.3390/agriculture13040817

Academic Editors: Vadim Bolshev, Vladimir Panchenko and Alexey Sibirev

Received: 8 March 2023 Revised: 30 March 2023 Accepted: 30 March 2023 Published: 31 March 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

changes in feed rate can be mitigated. Still, it is only partially suitable for China's wheat harvest operation. In their research on the structure of the combine header, Li et al. [19] optimized the structure parameters of the header frame. Xie et al. [20] designed a belt conveyor header for the soybean combine harvester to solve the problems of uneven feeding and congestion. Zhang et al. [21] designed a double crank plane five-bar reel mechanism to solve issues such as easy winding and hanging straws of the reel. Qing et al. [7] designed a reel with improved tine trajectory for harvesting oilseed rape to reduce harvest loss. Van et al. [22] designed a screw conveyor based on a cam mechanism for retracting the fingers to solve the problem of a dead zone between the screw conveyor and inclined conveyor and to improve conveying performance.

The factor limiting the performance of the combine harvester is its ability to handle a large amount of stalk and separate the grain from it. To reduce the number of stalks entering the combine harvester, Shelbourne Company designed the stripper header, which only combs the grains off the stalks and feeds them into the combine harvester, which can effectively reduce the feed rate but results in a high harvest loss [23,24]. Wang [25] once proposed to feed only the head of grain into the combine harvester and designed a secondary cutting and directional conveying device. The test results show that reducing the feed length can effectively reduce power consumption and improve operation efficiency, but its adaptability could be better. Dai et al. [26] designed a plot wheat seed harvester, which realized the harvest of wheat spike and effectively reduced the load of the threshing and cleaning system. The above research shows that harvesting only the upper part of the wheat plant is feasible. This paper proposes a method to reduce the feed rate by reducing the feed length of the wheat stalk and determines the optimal feed length of the wheat stalk through bench tests. The DCH of the WCH is designed to solve the problems of congestion and increased power consumption.
