# Promising Approaches for Heat Utilization in Agricultural Machinery Engines
## 2 Presentation of the Main Material
### Research Results
In the range of engine power from idle to 45%, it is advisable to use an auxiliary electric fan drive (with a power of about 0.8 kW) with a periodic mode of operation [32]. Consider a possible application of diesel engines with a power turbine in agricultural machinery. It is obvious that the turbocompound system is inefficient when using engines with rated power not exceeding 100 kW (Figure 2). The maximum rated power of diesel tractors of the CIS countries is, in kW, as follows: KhTA-300--183.8; Belarus-3022 DV--222; K-710S--236; K-704-4R--294. Thus, at the present stage of technical development, it is advisable to use turbocompound engines on general-purpose wheeled tractors with a traction class of at least 5. With regard to combine harvesters, the following should be noted. Combines with a harvesting capacity of up to 10...11 kg/s have a rated diesel power of up to 200 kW. For example, the power of the engines of combine harvesters with the indicated harvesting capacity is, in kW, as follows: \"Skif-230\"--169; \"Skif-250\"--184; Vector-410--154; DON-680--213; GS-812-16--176. More productive machines are also equipped with more powerful engines, as follows, in kW: ACROS-580--221; TORUM-740--294; GS-12--243, etc. It is recommended to use turbocompound engines [33; 34; 35; 36; 37]. The Caterpillar company has developed the concept of an electric turbocompound system (Figure 3). Its implementation is expected to reduce specific fuel consumption by 5...10% [38]. Let us evaluate the effectiveness of waste heat recovery systems. The simple payback period (SPP) is influenced by both investment cost and revenue and is calculated as follows:  
\[SPP=\frac{I_{\mathrm{R}}}{R-OE},\ \mathrm{h}, \tag{6}\]  
where \(R\) is the return in USD per year, \(\mathrm{I_{R}}\) is the investment cost in USD, and \(OE\) refers to the annual operating cost in USD. Figure 2: Relative power of the power turbine as a function of the rated power of the diesel engine. For turbocompound diesel engines, the investment costs range from USD 2000 to 3400 [22], while for the organic Rankine cycle systems, the costs range from EUR 2000 to 3000 [31], with annual operating costs of EUR 100 for the latter. The return (\(R\)) is calculated using the following formula:  
\[R=\frac{\Delta b_{e}\times P_{e}\times P_{vdf}\times Lf}{\rho},\;\text{USD/h}, \tag{7}\]  
where \(\Delta b_{e}\) is the reduction in specific fuel consumption, kg/kWh, \(P_{e}\) is the rated engine power, kW, \(Lf\) is the engine load factor, \(P_{vdf}\) is the price of diesel fuel (USD/L), and \(\rho\) is the density of diesel fuel, kg/L. Currently, the rated power of truck engines with turbocompounding ranges from 265 to 460 kW [32; 33; 34; 35]. The simple payback period was calculated based on diesel fuel for the U.S., Germany, and Ukraine, which were USD 0.84, 1.51, and 1.04 per liter, respectively [36]. The calculations show that for engines with a rated power above 370 kW, the payback period remains relatively stable and is less than 750 h. Within this power range, fuel prices have a minimal impact on the payback period. However, for engines with a power rating below 300 kW, fuel prices play a more significant role (Figure 4). Figure 4: Simple payback period (PBP) for turbocompound system. Source: developed by authors. Figure 3: Electric turbocompound system: 1—electrical load; 2—storage battery; 3—electric motor/generator; 4—compressor; 5—electric generator/engine; 6—turbine; 7—piston engine. If the relative power output of turbocompound systems varies between 4% and 11.5% (Figure 5), and the diesel engine efficiency is 0.4, the total waste heat utilization factor ranges from 0.0267 to 0.0767, while the exhaust gas energy utilization factor is 0.171 (at \(T_{g}\) = 873 K, \(T_{a}\) = 288 K, and \(T_{b}\) = 773 K). Companies are increasingly adopting energy-saving technologies, and a longer payback period is becoming more acceptable. In the USA, 56% of respondents reported a maximum payback period of three years or less.