Engine Downsizing and Rightsizing Trends in Modern Agricultural Tractors and Their Impact on Power Demand, Efficiency and Emissions

The aim of this study was to analyse long-term changes in diesel engines used in agricultural tractors between 2015 and 2030, with particular attention to displacement, cylinder configuration, power output, power density, efficiency and emission compliance. Technical data from tractor catalogues published in 2015 and 2024 were examined for standard agricultural models representing 33 manufacturers and power ratings from 34 kW to 527 kW. Descriptive statistics, comparative analysis and linear trend modelling were used to identify design tendencies and to forecast changes up to 2030. The results showed a systematic increase in average power and torque, accompanied by a moderate reduction in average displacement and the almost complete standardisation of turbocharging. Downsizing, based on smaller displacement and higher specific output, was most evident up to approximately 2020. Later developments indicate a gradual shift towards rightsizing, in which engine size is better matched to sustained agricultural workloads, thermal robustness and durability requirements. This shift is linked to wider implements, higher working speeds, heavier tractors and the integration of emission-control systems required by Stage V regulations. The findings indicate that modern tractor engine development is moving from aggressive displacement reduction towards balanced optimisation of efficiency, torque stability, durability and emission performance.