The thermal energy supplied to agricultural tractors comes from a cyclical, thermodynamic process in which heat energy is transformed into mechanical energy. In this transformation and transfer of energy within the combustion chamber of an engine, certain factors (air + fuel) are taken into account so that the equation of consumption and performance equals low fuel costs, a result that is satisfactory from both an economic and environmental point of view. In order for this result to be realised in the producer's pocket and in the environment, the combustion process in diesel engines must be taken into account, especially the formation of the intake volume of oxidising air through the filtration system, and the conduction of air into the engine. This intake can be greatly influenced if there is an obstruction in the air filter element, for example, which will jeopardise the combustion process, plus, of course, the load conditions under which the tractor is operating. In view of the above, this study was carried out with the aim of evaluating energy performance and gas emissions at different drawbar loads and air intake flow rates in a diesel engine of an agricultural tractor.