The main objective of this research has been to identify and analyze the potential of Atkinson and Miller cycles to reduce the level of pollutant emissions and fuel consumption in a diesel engine heavy transport equipped with a flexible distribution system under both low and high load. This strategy has been evaluated in combination with more conventional ones such as the late start of injection and decreased oxygen concentration through the exhaust gas recirculation.

This thesis was developed under an approach to understand as much as possible the basic phenomena involved in the various processes under study, and thereby generalize results at best. This analysis has arisen from a combination of different theoretical and experimental tools in order to maximize information. 

To obtain this objective a sequential structure has been followed, where it was first developed a specific methodology, adequately designed under the operating conditions of this study. Subsequently, we have characterized the changes in the thermodynamics of the gas trapped inside the cylinder, which develops during the combustion process, to implement both an Atkinson cycle and subsequently Miller.

In the next stage, research has been performed to obtain a comprehensive analysis of the diesel combustion process, including the formation of the mixture, the characteristics of the combustion process, the formation of emissions and, finally, the thermal efficiency to identify the influence of previous changes introduced in these processes.

Finally, as the final stage, the different strategies under consideration have been compared and the advantages and disadvantages obtained by implementing an Atkinson or Miller cycle have been discussed in detail.