The objective of this study is to evaluate the energetic, exergetic, sustainability, economic and environmental performances of a 4-cylinder turbodiesel aviation engine (TdAE) used on unmanned aerial vehicles for the take-off operation mode to assess the system with large aspects. Energy efficiency of the system is found as 43.158%, while exergy efficiency 40.655%. Thermoeconomic analysis gives information about the costs of the inlet and outlet energy and exergy flows of the engine. Hourly levelized total cost flow of the TdAE is found as 21.036 $/h, when the hourly fuel cost flow of the engine is found as 30.328 $/h. The waste exergy cost parameter is determined as 0.0144 MJ/h/$ from exergy cost-energy-mass (EXCEM) analysis, while it is estimated as 14.043 MJ/$ from modified-EXCEM analysis. Environmental damage cost analysis evaluates the cost formation of the exhaust emissions. The total environmental damage cost of the TdAE is computed as 12.895 $/h whilst specific environmental damage cost is determined as 0.054 $/MJ for 494.145 MJ/h TdAE power production. It is assessed that the main contributors to the environmental impact rate of the TdAE are the fuel consumption and the formation pollutants of combustion reaction.
The carbon footprint for the downstream dairy value chain, milk collection and dairy processing plants was estimated through the contribution of emissions per unit of collected and processed milk, whereas that for the upstream dairy value chain, input supply and production was not considered. A survey was conducted among 28 milk collectors and four employees of processing plants. Two clusters were established: small- and large-scale milk collectors. The means of carbon dioxide equivalent per kilogramme (CO2-eq/kg) milk were compared between clusters by using independent sample t-test. The average utilisation efficiency of milk cooling refrigerators for small- and large-scale collectors was 48.5 and 9.3%, respectively. Milk collectors released carbon footprint from their collection, cooling and distribution practices. The mean kg CO2-eq/kg milk was 0.023 for large-scale collectors and 0.106 for small-scale collectors (p < 0.05). Milk processors contributed on average 0.37 kg CO2-eq/kg milk from fuel (diesel and petrol) and 0.055 from electricity. Almi fresh milk and milk products processing centre emitted the highest carbon footprint (0.212 kg CO2-eq/kg milk), mainly because of fuel use. Generally, in Ziway-Hawassa milk shed small-scale collectors released higher CO2-eq/kg milk than large-scale collectors.
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