[EN] Internal combustion engines are in a situation in which they must be cleaner and more efficient than they have ever been. This change is motivated by the global and continuous evolution of the emissions regulations linked to their commercialization, which try to establish the path to protect the human health, and move towards more sustainable energetic models. Framed in this context, the research work developed in this PhD thesis has focused on the way to continue improving the spark ignition engines. To this end, a prototype two-stroke engine has been used, with the idea of studying the Spark Ignited combustion in lean conditions ('lean SI') and the Controlled Auto-Ignition combustion 'CAI'). In this way, the traditional 'SI' operation in stoichiometric conditions of this type of engines is replaced, looking for an improvement in fuel efficiency, and a reduction, at the same time, of the pollutant emissions. This work has been approached mainly from an experimental point of view. Firstly, different works have been performed on the engine: operation of the different combustion modes, definition of the operating strategies, and compilation of experimental data coming from the engine operation in the different regions of the engine map. And, secondly, all this data has been analyzed and studied in detail to define the strengths and weaknesses of each combustion mode applied to the different engine operating conditions. The combination of these two works has led to obtain a large amount of data about the achievable efficiencies and the emissions values obtained in each combustion mode. And, in addition, the influence on the combustion of the burned gases recirculation in the engine ('EGR'), has also been studied as a strategy to reduce emissions, and control the combustion at high loads in both combustion modes. Regarding the analytical part of the work, several problems have been detected. Firstly, the high combustion variability in this engine, and secondly, the coupling of two completely different combustion modes. These issues have generated the need to analyze the data obtained in a more detailed way, in order to get more information about the combustion process. To solve these two aspects, first, a different point of view has been raised when dealing with the combustion diagnosis, the cycle to cycle analysis, and secondly, a combustion analysis methodology has been proposed in order to allow the combustion analysis from a more detailed point of view. In this way the combustion development is studied, and thus, the differentiation between the different combustion events that take place in the engine can be studied. All this work has been useful to define the strategies to operate the whole engine map by combining the 'lean SI' and 'CAI' combustion modes. This solution, compared to the current Euro VI engines, has presented higher efficiency values complying with the established emissions limits, showing in this way, the high potential of these combustion modes applied to 'SI' engines, as well as a real… Advisors/Committee Members: López Sánchez, José Javier (advisor).

Compression-ignition (CI) engines, also known as “diesel” engines, can produce higher thermal efficiency (TE) than spark-ignition (SI) engines, which allows them to emit less carbon dioxide (CO2) per unit of energy generated. Unfortunately, in practice the TE of CI engines is limited by the need to maintain sufficiently low emissions of nitrogen oxides (NOx) and soot. This problem can be mitigated by operating CI engines in dual-fuel modes with port fuel injection (PFI) of gasoline supplementing the direct injection (DI) of diesel fuel. Several strategies for doing this have been introduced in recent years, but these operating modes are usually studied individually at discrete conditions. This thesis introduces a classification system for dual-fuel CI modes that links together several previously studied modes across a continuous two-dimensional diagram. The combustion modes covered by this system include the standard modes of conventional diesel combustion (CDC) and conventional dual-fuel (CDF); the well-explored advanced combustion modes of HCCI, RCCI, PCCI, and PPCI; and a relatively unexplored combustion mode that is herein titled “Piston-split Dual-Fuel Combustion” or PDFC. The results show that dual-fuel CI engines can simultaneously increase TE and lower NOx and/or soot emissions at high loads through the use of Partial HCCI (PHCCI), despite an increase in emissions of carbon monoxide (CO) and unburnt hydrocarbons (UHC). At low loads, PHCCI is not possible, but either PDFC or RCCI can be used to further improve NOx and/or soot emissions, albeit at slightly lower TE and still higher emissions of CO and UHC. This multi-mode strategy of PHCCI at high loads and PDFC or RCCI at low loads is particularly useful when low engine-out NOx emissions are required. Advisors/Committee Members: Boehman, Andre L (committee member), Lastoskie, Christian M (committee member), Lavoie, George A (committee member), Middleton, Robert John (committee member), Wooldridge, Margaret S (committee member).