# Promising Approaches for Heat Utilization in Agricultural Machinery Engines
## 2 Presentation of the Main Material
### Research Results
In Europe, 70% of companies are considering a payback period of up to five years or less [37]. The estimated lifetime of agricultural tractors is about 10,000 h [38], while that of combine harvesters it is approximately 3000 h [39]. In the European Union, the average annual use for a combine harvester is 188 h [40], and for agricultural tractors with a rated power of over 202 kW, it is around 306 h [12]. Outside the EU, the average annual use of tractors is higher. In India, for example, the average annual use of tractors is 856 h [13]. For combine harvesters, turbocompounding can be cost-effective if the rated power is above 300-320 kW and the simple payback period is less than five years. For agricultural tractors, the technology becomes appealing when the rated power of the diesel engine exceeds 275 kW (Figure 5). In addition, the higher the annual usage, the lower the required power threshold. If the machines are operated for more than 150-300 hours per year, this reduction occurs gradually (Figure 6). Figure 5: Maximum rated power (diesel fuel price—USD/L). Source: developed by authors. Figure 6: Maximum rated power vs. annual utilization (diesel fuel price—USD/L). Source: developed by authors. Work on the development of a Rankine cycle heat recovery system began back in the 1970s. It was funded by the U.S. Department of Energy and conducted by Mack Trucks and Thermo Electron Corporation [39]. BMW engineers tested a system using a recycled steam engine on a passenger car. This resulted in a 10% increase in torque and a 15% reduction in specific fuel consumption. The mass of the additional components exceeded 100 kg. This scheme was called Turbosteamer, and its first version was adapted for a BMW 3 series passenger car [40]. Research in this direction is being carried out by a number of companies, including AVL Power Train Engineering, Inc. (Plymouth, MI, USA); Cummins (Columbus, IN, USA); Navistar Advanced Technology (Lisle, IL, USA), etc. Simulations of recycling systems using the Rankine cycle show that the potential reduction in specific fuel consumption ranges from 6 to 11%, depending on the type of working fluid [41]. Organic Rankine Cycle systems are already in commercial use in marine and stationary power plants. However, their application in agricultural vehicles is still being researched and is expected to enter the market by 2020. Cooling by injecting water into the airflow at the compressor inlet is widely used in gas turbines [42]. The temperature drops to the dew point temperature and does not exceed 10 \({}^{\circ}\)C in most climates. Air cooling in recuperative heat exchangers provides greater temperature reduction. The cold needed to cool the outside air can be obtained in a heat-utilizing refrigerating machine (HRM) by using the heat of the exhaust gases. Studies show that the HRM ejector is the simplest and most reliable, with the working medium being a liquid with a low boiling point [43]. Modeling of the process shows that the decrease in air temperature for gas turbines (at an exhaust gas temperature of 450 \({}^{\circ}\)C) is 40...60 \({}^{\circ}\)C [44]. This technology can also be used for engines of agricultural machinery (Figure 7). Calculations based on standards [18] show that in summer, it is possible to increase the power of diesel engines by 10% and reduce the specific fuel consumption by up to 9% (Figure 8). This is because summer temperatures can help cool the air better, allowing the engine to operate more efficiently. In warm weather, the air is generally less dense, which can help the fuel burn better if the engine's injection and cooling systems are optimized. Summer temperatures can improve cooling systems, helping the engine run more consistently and efficiently. More consistent operating conditions can result in increased power and lower specific fuel consumption. When technologies such as water vapor injection or improved cooling systems are used, they can help ensure more complete and efficient combustion of the fuel.