The present study was conducted to determine whether conjugate magnitude and temporal contingencies were effective in increasing the pre-ratio pause (PRP) duration and to determine the controlling variables that govern such contingencies. It has been reported in the literature that magnitude of reinforcement, if presented contingently, is effective in controlling performance and that inserting intervals of blackout (BO), during which responding does not lead to reinforcement, virtually always leads to control of responding, even though it has not been presented contingently. The conjugate schedules experimentally arranged reinforcement such that the longer the PRP, the longer was the duration of access to reinforcement and/or the shorter was the BO, located either after reinforcement or after the response. The results of this study demonstrated that the major independent variable which controlled mean PRP duration on the various conjugate reinforcement schedules studied was the delay between the response and reinforcement. The duration of the PRP was not reliably controlled by a contingency which equated PRP duration with reinforcement duration, nor by a contingency which, through imposition of a delay to trial onset, held the local delay to reinforcement constant. Additionally, cycle-to-cycle variation in reinforcement magnitude, whether presented contingently or noncontingently on PRP duration, had no reliable effect on PRP duration when compared to FR 1. The primary effect of variation in the duration of reinforcement was to reduce the variability, not the duration, of the PRP. The results of the study are briefly discussed in terms of a number of theories. These include: the maximization account (Logan, 1960); the matching law (Herrnstein, 1970); Harzem and Harzem's (1981) theory describing the unconditioned inhibitory stimulus function of reinforcement; behavioral contrast (Reynolds, 1961); and Dews' (1981) account of the importance of a response-reinforcer contiguity relation.

Variable Valve Timing (VVT) presents a powerful tool in the relentless pursuit of efficiency improvements in the internal combustion engine. As the valves have such ultimate control over the gas exchange processes, extensive research effort in this area has shown how valve event timing can be manipulated to reduce engine pumping losses, fuel consumption and engine out emissions. Pumping losses may be significantly reduced by use of throttleless strategies, making use of intake valve duration for load control, while alternative cycles such as the Miller cycle allow modification of the effective compression ratio. More recently, the value of single valve operation in part load conditions is exploited, bringing with it the concept of asymmetric valve lifts. Work in this area found the side effect of asymmetric valve operation is a significant change in the behaviour of the in-cylinder flow structures, velocities and turbulence intensity. Work presented in this thesis exploits asymmetric valve strategies to modify the in-cylinder flow conditions. The Proper Orthogonal Decomposition (POD) is a method employed in the fluids dynamics field to facilitate the separation of coherent motion structures from the turbulence. In the presented work, the application of POD to in-cylinder flow analysis is further developed by the introduction of a novel method for identifying the POD modes representative of coherent motion and those representative of the turbulence. A POD mode correlation based technique is introduced and developed, with the resulting fields showing evidence of coherence and turbulence respectively. Experimental tests are carried out using a full length optically accessible, single cylinder research engine equipped with a fully variable valve train (FVVT) to allow full control of both valve timing and lift. In-cylinder flow is measured through the use of Particle Image Velocimetry (PIV) at several crank angle timings during the intake stroke whilst the engine is operated under a range of asymmetric valve strategies. The exhaust valves and one intake valve have their respective schedules fixed, while the second intake valve schedule is adjusted to 80\%, 60\%, 40\%, 20\%, 0\% lift. The resulting PIV fields are separated into coherent motion and turbulence using the developed technique, allowing for analysis of each constituent independently. The coherent element gives insight to large scale flows, often of the order of magnitude of the cylinder. These structures not only give a clear indication of the overall motion and allow assessment of flow characteristics such as swirl and tumble ratio, but the variation in the spatial location of these structures provides additional insight to the cyclic to cycle variation (CCV) of the flow, which would not otherwise be possible due to the inclusion of the turbulent data. Similarly, with the cyclic variation removed from the turbulent velocity field, a true account of the fluctuating velocity, u' and derived values such as the Turbulent Kinetic Energy (TKE) may be gained. Results show how manipulation of a one intake valve timing can influence both the large scale motions and the turbulence intensity. By the reduction of lift, the swirl ratio is increased almost linearly as the typical counter-rotating vortex pair becomes asymmetric, before a single vortex structure is observed in the lowest lift cases. A switching mechanism between the two is identified and found to be responsible for increased levels of CCV. With the reduction in lift, TKE is observed not only to increase, but change the spatial distribution of turbulence. Of course, the reduction in valve lift comes with the penalty of a reduced valve curtain area. However, it was identified both in literature and throughout this study that the reduction in lift did not negatively influence the engine breathing as the same trapped mass was achieved under all cases with no adjustment of manifold pressure. While literature shows both bulk motion and turbulence are key in liquid fuel break-up during the intake stroke, the mixing effects under port-injected natural gas were investigated experimentally using Laser Induced Fluorescence (LIF). The valve strategy was found to have no significant effect on the mixture distribution at the time of spark.

[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 possibility of its implementation in future vehicles. / [ES] Los motores de combustión interna viven un momento en el que deben ser más limpios y eficientes de lo que han sido hasta la fecha. Este cambio viene dado por el endurecimiento global y continuado de las normativas anticontaminación vinculadas a su comercialización, que tratan de establecer el camino para proteger la salud de las personas que conviven con éstos, y avanzar hacia unos modelos más sostenibles de uso de las energías disponibles. Enmarcado en este contexto, el trabajo de investigación desarrollado en esta tesis se ha centrado en continuar avanzando en el camino para la mejora de los motores de encendido provocado. Para este fin se ha empleado un motor prototipo de dos tiempos con la idea de estudiar la combustión por encendido provocado en mezclas pobres 'lean SI') y la combustión mediante el autoencendido controlado de la mezcla ('CAI'). De esta forma la operación tradicional en condiciones estequiométricas de este tipo de motores es reemplazada, en busca de una mejora en la eficiencia energética, y una reducción, al mismo tiempo, de las emisiones contaminantes. Este trabajo se ha abordado desde un punto de vista principalmente experimental. En primer lugar se ha trabajado sobre el motor, operando los diferentes modos de combustión, fijando las estrategias de operación, y obteniendo gran cantidad de datos sobre el funcionamiento del motor en las diferentes regiones del mapa motor. Y, en segundo lugar, estos datos han sido analizados y estudiados en detalle para detectar los potenciales y las debilidades de cada modo de combustión aplicado a las diferentes condiciones de funcionamiento del motor. La combinación de estos dos trabajos ha servido para obtener gran cantidad de datos sobre las eficiencias alcanzables y los valores de emisiones obtenidos en cada modo de operación. Y, adicionalmente, se ha estudiado también la influencia de la recirculación de gases quemados en el motor ('EGR') sobre la combustión, como estrategia para reducir las emisiones y controlar la combustión a altas cargas en ambos modos de operación. En cuanto a la parte analítica del trabajo, se han detectado diversos problemas. En primer lugar, lidiar con la alta variabilidad de la combustión en este motor, y en segundo lugar, el acople de dos modos de combustión totalmente diferentes. Esto ha generado la necesidad de analizar los datos obtenidos de forma que nos den algo más de información sobre la forma en que se ha desarrollado la combustión. Para dar solución a estos dos aspectos, se ha planteado un punto de vista diferente a la hora de afrontar el diagnóstico de la combustión (análisis ciclo a ciclo) y se ha propuesto una metodología de análisis de la combustión que nos permita estudiar, desde un punto de vista más detallado, la forma en que se ha desarrollado la combustión, y tratar de diferenciar así los diferentes eventos de combustión que se desarrollan en el motor. Todo este trabajo ha dado sus frutos en forma de la definición de las estrategias para operar el motor en su totalidad mediante la combinación de los modos 'lean SI' y 'CAI'. Esta solución, en comparación con los motores actuales Euro VI, ha presentado unos valores de eficiencia superiores cumpliendo con los límites establecidos de emisiones, mostrando de esta forma un elevado potencial de estos modos de combustión aplicados a los motores de encendido provocado, así como una posibilidad real de implementación en los vehículos venideros. / [CA] Els motors de combustió interna alternatius es troben a un moment en el que deuen ser mes nets i eficients que mai. Aquest canvi ve motivat per l'augment de l'exigència de les normatives reguladores d'emissions contaminants vinculades a la seua comercialització, que tracten d'establir el camí per a protegir la salut de les persones que conviuen amb aquests, i avançar cap a uns models mes sostenibles d'aprofitament de les energies disponibles. Dins d'aquest context, el treball d'investigació realitzat en aquesta tesi, ha girat al voltant de la millora dels motors d'encesa provocada. Per a aquesta finalitat, s'ha emprat un prototip de motor de dos temps amb l'idea d'estudiar la combustió per encesa provocada amb dosatges pobres 'lean SI') i la combustió mitjançant una auto-encesa provocada per les condicions termodinàmiques de la cambra de combustió ('CAI'). D'aquesta manera l'operació tradicional en condicions estequiomètriques d'aquest tipus de motors és substituïda, buscant una millora en l'eficiència energètica i una reducció al mateix temps de les emissions contaminants. Aquest treball s'ha abordat des d'un punt de vista fonamentalment experimental. En primer lloc s'ha treballat sobre el motor, operant els diferents modes de combustió, fixant les estratègies d'operació, i obtenint gran quantitat de dades sobre el funcionament del motor en les diferents regions del seu mapa d'operació. I en segon lloc, aquestes dades han sigut analitzades i estudiades en detall per a detectar els potencials i les debilitats de cada mode de combustió aplicat a les diferents condicions de funcionament del motor. La combinació d'aquests dos treballs ha servit per a obtindre gran quantitat de dades sobre les eficiències assolibles i els valors d'emissions obtinguts en cada mode d'operació. I, a més, s'ha estudiat la influència de la recirculació de gasos d'escapament al motor ('EGR') sobre la combustió, com a estratègia per a reduir les emissions contaminants i controlar la combustió a altes càrregues en els dos modes de combustió. Quant a la part analítica del treball, s'han detectat diversos problemes. En primer lloc, tractar amb l'alta variabilitat de la combustió en aquest motor, i en segon lloc, l'acoblament de dos modes de combustió totalment diferents. Açò ha generat la necessitat d'analitzar les dades obtingudes de forma que ens donen més informació sobre la forma en que s'ha desenvolupat la combustió. Per a donar solució a aquests dos aspectes, s'ha plantejat un punt de vista diferent a l'hora de realitzar el diagnòstic de la combustió (un anàlisis cicle a cicle) i s'ha proposat una metodologia d'anàlisi de la combustió que permeta estudiar, des d'un punt de vista més detallat, la forma en que s'ha desenvolupat la combustió, i tractar de diferenciar així, les diferents combustions al motor. Tot aquest treball ha donat uns resultats en forma de la definició de les estratègies per a operar el motor en la seva totalitat mitjançant la combinació dels modes de combustió 'lean SI' i 'CAI'. Aquesta solució, en comparació amb els actuals motors Euro VI, ha ofert uns valors d'eficiència superiors, acomplint amb les limitacions establertes d'emissions, mostrant d'aquesta manera un elevat potencial d'aquests modes aplicats als motors d'encesa provocada, així com una possibilitat real d'implantació en els vehicles que estan per vindre. / Valero Marco, J. (2020). Analysis of the potential of SI lean combustion and CAI combustion in a two-stroke spark-assisted gasoline engine [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/138556