Indiana University-Purdue University Indianapolis (IUPUI) / This study contributes to a better working knowledge of the equipment being used in a well-established combustion lab. In particular, several constant-volume combustion properties (e.g., time ignition delay, flame propagation, and more) are examined to deduce any buoyancy effects between fuel and air mixtures and to develop a method aimed at minimizing such effects. This study was conducted on an apparatus designed to model the phenomena occurring within a single channel of a wave rotor combustor, which consists of a rotating cylindrical pre-chamber and a fixed rectangular main combustion chamber. Pressure sensors monitor the internal pressures within the both chambers at all times, and two slow-motion videography techniques visually capture combustion phenomena occurring within the main chamber. A new recirculation pump system has been implemented to mitigate stratification within the chamber and produce more precise, reliable results. The apparatus was used in several types of experiments that involved the combustion of various hydrocarbon fuels in the main chamber, including methane, 50%-50% methane-hydrogen, hydrogen, propane, and 46.4%-56.3% methane-argon. Additionally, combustion products created in the pre-chamber from a 1.1 equivalence ratio reaction between 50%-50% methane-hydrogen and air were utilized in the issuing pre-chamber jet for all hot jet ignition tests. In the first set of experiments, a spark plug ignition source was used to study how combustion events travel through the main chamber after different mixing methods were utilized – specifically no mixing, diffusive mixing, and pump circulation mixing. The study reaffirmed that stratification between fuel-air mixtures occurs in the main chamber through the presence of asymmetrical flame front propagation. Allowing time for mixing, however, resulted in more symmetric flame fronts, broader pressure peaks, and reduced combustion time in the channel. While 30 seconds of diffusion helped, it was found that 30 seconds of pumping (at a rate of 30 pumps per 10 seconds) was the most effective method at reducing stratification effects in the system. Next, stationary hot jet ignition experiments were conducted to compare the time between jet injection and main chamber combustion and the speed of the resulting shockwaves between cases with no mixing and 30 seconds of pump mixing. Results continued to show an improvement with the pump cases; ignition delay times were typically shorter, and shock speeds stayed around the same, if not increased slightly. These properties are vital when studying and developing wave rotor combustors, and therefore, reducing stratification (specifically by means of a recirculation system) should be considered a crucial step in laboratory models such as this one. Lastly, experiments between a fueled main chamber and rotating pre-chamber helped evaluate the leakage rate of the traversing hot jet ignition experimental setup paired with the new pump system. In its current form, major leaks are inevitable when attempting traversing jet experiments, especially with the pump’s suction action drawing sudden large plumes of outside air into the main chamber. To minimize leaks, gaps between the pre-chamber and main chamber should be reduced, and the contact surface between the two chambers should be more evenly distributed. Also, the pump system should only be operated as long as needed to evenly distribute the fuel-air mixture, which approximately happens when the main chamber’s total volume has been circulated through the system one time. Therefore, a new pump system with half of the original system’s volume was developed in order to decrease the pumping time and lower the risk of leaks.

Indiana University-Purdue University Indianapolis (IUPUI) / Ignitability and the ignition delay time of a combustible mixture in a long combustion chamber, ignited by a hot combustion torch jet generated in a pre-chamber was investigated experimentally in relation to application as a viable igniter method for wave rotor combustors. Methane-air, ethylene-air, and propane-air in varying equivalence ratios were investigated as the combustible mixture in the combustion chamber. The effects of variation in the torch jet fuel, initial equivalence ratio in the pre-chamber, and nozzle geometry on the ignitability and the ignition delay time of combustible mixtures were observed and analyzed. The single-channel wave-rotor combustion rig at Combustion and Propulsion Research Laboratory at the Purdue School of Engineering and Technology at Indiana University-Purdue University, Indianapolis was used for this study. High-speed video imaging techniques to observe the ignition and flame propagation in the combustion chamber and fast-response pressure transducers to measure the dynamic pressure fluctuations in the combustion chambers were used in the current study. The present work explains how the experimental procedure and preliminary testing was carried out in order to conduct the necessary testing to find the ignitability and ignition delay time of a combustible mixture. Ignitability of methane, ethylene, and propane were much broader in range compared to conventional spark ignitable lean and rich limit equivalence ratios. The methane and propane ignition lean limits were similar to radical activated ignition lean limits found in previous studies of the same fuels. Ethylene exhibited the widest range in equivalence ratios from 0.4 to 2.4, while methane had the narrowest ranging from equivalence ratio 0.4 to 1.4. The ignition delay studies indicated both chemical kinetics and mixing between the combustion torch jet and the combustible mixture were critical. The mixing phenomena dominated chemical kinetics; unlike in ignition delay studies conducted using shock heated ignition techniques. Ethylene-air mixtures had the shortest ignition delay times ~1 ms for lean but near-stoichiometric mixtures. Methane and propane indicated similar ignition delay time characteristics with lean near-stoichiometric mixtures. The fuel-air equivalence ratio which was used to generate the combustion torch jet and the torch jet nozzle geometry had a direct influence over the ignition delay time in the main chamber combustible mixture. The slightly rich fuel-air ratios used to generate the combustion torch jet had the lowest delay times in igniting the main chamber fuel-air mixtures.

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Como consecuencia de las exigentes legislaciones medioambientales actualmente en vigor, como las Euro Emission Standards en Europa, los investigadores e ingenieros se ven forzados a "re-desarrollar" el proceso de combustión diésel para hacerlo menos contaminante. Uno de los principales contaminantes y más dañinos para la salud son los óxidos de nitrógeno (NOx) que están principalmente compuestos por: monóxido de nitrógeno (NO), dióxido de nitrógeno (NO2) y trióxido de dinitrógeno (N2O3). Centrándose en los NOx generados en una combustión diésel, una de las técnicas más populares para mitigar su formación es mediante la dilución de la corriente oxidante con productos de la combustión, previamente generados. De este modo, al reducir la reactividad de la corriente oxidante se consigue una disminución considerable de la temperatura de combustión y por extensión de los NOx. Sin embargo, dicha técnica causa nuevas interacciones físico-químicas entre los hidrocarburos y los NOx así como principalmente un notable cambio en la estructura del chorro diésel. Es por ello necesario considerar las diferentes vías de formación de éstos para poder predecir su generación. El hecho de considerar las diferentes vías de formación implica un incremento considerable de los recursos computacionales destinados a realizar las simulaciones, siendo en algunos casos inviable. Es por ello que el objetivo principal de esta tesis consiste en: desarrollar herramientas capaces de tener en consideración todas estas vías sin incrementar de manera considerable el coste computacional. Para ello inicialmente se realiza una exhaustiva revisión bibliográfica en donde se repasan las diferentes herramientas desarrolladas para la predicción de los NOx y se analizan sus puntos débiles. Éstos radican en simplificaciones de dudosa validez, que solamente tienen efectos positivos a altas y no a bajas temperaturas, o bien procesos demasiado tediosos y complejos para caracterizar los diferentes estados de una combustión. Posteriormente se diseña una metodología capaz de satisfacer el objetivo principal, basada en tres estudios. El primero permite profundizar en el proceso de formación de este contaminante a través de estudiar el incremento de la proporción de NO2 en los NOx debido a la recirculación masiva de estos productos. Por otro lado, los otros dos consisten en desarrollar diversas herramientas predictivas centradas exclusivamente en el NO, ya que como se dedujo del estudio anterior el NO2 se forma principalmente a partir del NO a través de un proceso de enfriamiento. La primera de estas herramientas está basada en una correlación empírica que a modo de ecuación correctiva mejora la capacidad predictiva, especialmente en condiciones de recirculación masiva, del mecanismo más implementado mundialmente, mientras que la segunda se sustenta en tabular únicamente la velocidad de formación del NO y el NO en equilibrio en función de la temperatura y de la cantidad de oxígeno disponible inicialmente para reaccionar. Finalmente para poder llevar a cabo estos estudios y cumplir con el objetivo principal se hace uso de un software comercial cinético-químico Chemkin, en su versión Professional, que sirve tanto de herramienta desarrolladora como de referencia. / Redón Lurbe, P. (2013). Modeling of the nitrogen oxides formation process applicable to several diesel combustion modes [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/33183

Call number: LD2668 .T4 1979 N44 / Master of Science

Call number: LD2668 .T4 1985 C47 / Master of Science

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Denna rapport baseras på experimentella försök där det undersökts hur pelletdensiteten påverkar utsläpp av kolmonoxid (CO) och stoft vid småskalig förbränning. I en testpanna med ansluten pelletsbrännare testades tre densiteter: låg, mellan och hög. Testerna uppdelades i tre faser i form av uppstart, kontinuerlig drift och släckning. Tre repetitioner gjordes på varje fas och för varje bränsle med undantag av släckning där endast en mätning per bränsle gjordes. Resultatet visade generellt en tydlig skillnad i CO-emission. Oberoende av densitet var CO-emissionerna mycket större vid uppstart och släckning än vid kontinuerlig drift. Avseende densitet gavs ett entydigt resultat där den lägsta pelletdensiteten gav högre stoftemissioner under alla driftsförhållanden. Skillnaden mellan de två pelletssorterna av högre densitet är däremot inte signifikant. För CO-emissioner sågs vid uppstartsfasen en tydlig trend mellan minskad pelletdensitet och ökade CO-emissioner. Vid kontinuerlig drift sågs emellertid det omvända: hög densitet gav högre CO-emissioner, varvid mellandensiteten gav något lägre CO-emissioner och låg densitet gav lägst CO-emissioner. Om skillnaden är uteslutande beroende på pelletdensiteten är svårt att säga. Ytterligare försök rekommenderas för att avgöra den exakta inverkan av pelletarnas densitet.