There is a growing interest in alternative transport fuels. There are two underlying reasons for this interest; the desire to decrease the environmental impact of transports and the need to compensate for the declining availability of petroleum. In the light of both these factors the Diesel Dual Fuel, DDF, engine is an attractive concept. The primary fuel of the DDF engine is methane, which can be derived both from renewables and from fossil sources. Methane from organic waste; commonly referred to as biomethane, can provide a reduction in greenhouse gases unmatched by any other fuel. The DDF engine is from a combustion point of view a hybrid between the diesel and the otto engine and it shares characteristics with both. This work identifies the main challenges of DDF operation and suggests methods to overcome them. Injector tip temperature and pre-ignitions have been found to limit performance in addition to the restrictions known from literature such as knock and emissions of NOx and HC. HC emissions are especially challenging at light load where throttling is required to promote flame propagation. For this reason it is desired to increase the lean limit in the light load range in order to reduce pumping losses and increase efficiency. It is shown that the best results in this area are achieved by using early diesel injection to achieve HCCI/RCCI combustion where combustion phasing is controlled by the ratio between diesel and methane. However, even without committing to HCCI/RCCI combustion and the difficult control issues associated with it, substantial gains are accomplished by splitting the diesel injection into two and allocating most of the diesel fuel to the early injection. HCCI/RCCI and PPCI combustion can be used with great effect to reduce the emissions of unburned hydrocarbons at light load. At high load, the challenges that need to be overcome are mostly related to heat. Injector tip temperatures need to be observed since the cooling effect of diesel flow through the nozzle is largely removed. Through investigation and modeling it is shown that the cooling effect of the diesel fuel occurs as the fuel resides injector between injections and not during the actual injection event. For this reason; fuel residing close to the tip absorbs more heat and as a result the dependence of tip temperature on diesel substitution rate is highly non-linear. The problem can be reduced greatly by improved cooling around the diesel injector. Knock and preignitions are limiting the performance of the engine and the behavior of each and how they are affected by gas quality needs to be determined. Based on experiences from this project where pure methane has been used as fuel; preignitions impose a stricter limit on engine operation than knock. / QC 20120626 / Diesel Dual Fuel

Le plasma hors-équilibre est l’un des outils les plus attrayants et prometteurs pour de nombreuses applications assistées par plasma. La production d’espèces actives (espèces excitées, radicaux, photons de hautes énergies couvrant les spectres UV et IR) est importante pour le contrôle des gaz polluants, le traitement de surface, les actionneurs de plasma en aérodynamique, certaines applications biomédicales et, plus récemment, en médecine du plasma. Pour des densités de gaz atmosphérique et élevée, les applications des plasmas non-thermiques sont essentiellement l’allumage des mélanges combustibles ou, soi-disant, l’Allumage Assistée par Plasma (AAP). Les Décharges à Barrière Diélectrique de Surface (DBDS), largement utilisées pour le contrôle de l’écoulement aérodynamique, ont été récemment suggérées comme déclencheur de la combustion distribué dans différents systèmes. La possibilité d’utiliser les DBDS, comme allumeurs à des pressions allant jusqu’à plusieurs dizaines de bar, a été démontrée au cours des 4-5 dernières années. Au début de la thèse, l’ensemble des données expérimentales sur la décharge et l’allumage des combustibles par DBDS était assez pauvre, et insuffisant pour une analyse détaillée. Par conséquent, l’étude expérimentale de la DBDS à des densités atmosphérique et élevée de gaz, ainsi que l’étude du déclenchement de la flamme par DBDS nanoseconde (DBDSn) ont fait l’objet de cette thèse. Les résultats de la thèse sont présentés en trois parties. Dans la première partie, la DBDSn en mode mono-pulse est étudiée. Pour cela, l’analyse du dépôt d’énergie, du courant de la décharge, de la distribution de l’intensité et de la libération d’énergie qui en découle est effectuée. Les impulsions à polarités positive et négative sont utilisées pour générer la décharge surfacique, et la physique des streamers à polarités positive et négative y est discutée. Pour les deux polarités, la densité électronique et le champ électrique réduit sont estimés puis comparés avec des calculs et/ou des résultats obtenus par modélisation 2D. La deuxième partie est consacrée à l’étude des DBDSn à pression élevée (jusqu’à 12 bar) dans différents mélanges de gaz : N2, air, N2:CH4, N2:H2, Ar:O2, etc. Deux aspects morphologiquement différents de la DBDSn sont considérés : une DBD streamer « classique » à des pressions et tensions relativement basses, et une DBD filamentaire à des pressions et/ou tensions élevées. Les données quantitatives sur la décharge à haute pression (de 1 à 12 bar) sont obtenues par spectroscopie d’émission. Une description possible de la nature de cette filamentation est donnée. Enfin, la troisième partie présente les expériences d’allumage assistée par plasma utilisant des DBDSn à haute pression. Les morphologies de la décharge dans les mélanges combustibles pauvres (H2:air) et de l’allumage engendré sont étudiées. Puis, la comparaison entre allumage par décharge filamentaire et par streamer à la pression 1-6 bar est effectuée. Les données expérimentales sont analysées grâce à une modélisation de la cinétique de l’allumage assisté par plasma dans des champs électriques typiques des DBDSn (E/N = 100 Td). Une étude complexe des décharges à pression atmosphérique, à haute pression et de l’allumage permet d’obtenir une description détaillée de l’allumage à haute pression, distribué dans l’espace par le plasma hors-équilibre. / Non–equilibrium plasma is one of the most attractive and promising tool for many plasma–assisted applications. Production of active species (excited species, radicals, high energetic photons covering UV and IR spectral range) is important for gas pollution control, surface treatment, plasma actuators for aerodynamics application, biomedical applications and more recently the field of plasma medicine. For atmospheric and elevated gas densities the mainstream of the non–thermal plasma applications is the ignition of combustible mixtures or so–called Plasma–Assisted Ignition (PAI). Surface dielectric barrier discharges (SDBD), widely used for aerodynamic flow control, were recently suggested as distributed initiators of combustion in different systems. A principal possibility of using the SDBD ignitors at as high pressure as tens of bars has been demonstrated during the last 4-5 years. At the moment of the beginning of the thesis, the set of experimental data on the discharge and of ignition of fuels with SDBD was quite poor and insufficient for detailed analysis. Therefore, the experimental study of the surface DBD at atmospheric and elevated gas densities and the study of flame initiation with nanosecond SDBD were the object of the presented thesis. The results in the Thesis are presented in three parts. In the first part the nSDBD in a single shot regime at atmospheric air is investigated. The analysis of energy deposition, discharge current, intensity distribution and consequent energy release is performed. The positive and negative polarity pulses are used to produce surface discharge. The physics of anode and cathode–directed streamers is discussed. For both polarities of the applied pulses the electron density and reduced electric field are estimated and compared with calculations and/or 2D modeling results. The second part is devoted to the study of nSDBD at elevated pressures, up to 12 bar, in different gas mixtures ( N2, air, N2:CH4, N2:H2, Ar:O2, etc.). Two morphologically different forms of the nSDBD are considered: a “classical” streamer DBD at relatively low pressures and voltages, and a filamentary DBD at high pressures and/or voltages. The emission spectroscopy is used to obtain quantitative data about the discharge at high pressures (1-12 bar). The possible nature of the discharge filamentation is described. Finally, the third part describes the experiments of plasma–assisted ignition with nanosecond SDBD at elevated pressures. The discharge morphology in lean combustible ( H2:air) mixtures and following ignition of the mixtures are studied. The comparison of ignition by filamentary and streamer discharge at the pressures 1-6 bar is performed. Kinetic modeling of plasma assisted ignition for the electric fields typical for nSDBD, E/N = 100 − 200 Td is used for analysis of experimental data. Complex study of the discharges at atmospheric pressure, discharge at high pressures and ignition allow detailed description of the high-pressure distributed in space ignition by non--equilibrium plasma.

Indiana University-Purdue University Indianapolis (IUPUI) / Ignition by a jet of hot combustion product gas injected into a premixed combustible mixture from a separate pre-chamber is a complex phenomenon with jet penetration, vortex generation, flame and shock propagation and interaction. It has been considered a useful approach for lean, low-NOx combustion for automotive engines, pulsed detonation engines and wave rotor combustors. The hot-jet ignition constant-volume combustor (CVC) rig established at the Combustion and Propulsion Research Laboratory (CPRL) of the Purdue School of Engineering and Technology at Indiana University-Purdue University Indianapolis (IUPUI) is considered for numerical study. The CVC chamber contains stoichiometric methane-hydrogen blends, with pre-chamber being operated with slightly rich blends. Five operating and design parameters were investigated with respect to their eff ects on ignition timing. Di fderent pre-chamber pressure (2, 4 and 6 bar), CVC chamber fuel blends (Fuel-A: 30% methane + 70% hydrogen and Fuel-B: 50% methane + 50% hydrogen by volume), active radicals in pre-chamber combusted products (H, OH, O and NO), CVC chamber temperature (298 K and 514 K) and pre-chamber traverse speed (0.983 m/s, 4.917 m/s and 13.112 m/s) are considered which span a range of fluid-dynamic mixing and chemical time scales. Ignition delay of the fuel-air mixture in the CVC chamber is investigated using a detailed mechanism with 21 species and 84 elementary reactions (DRM19). To speed up the kinetic process adaptive mesh refi nement (AMR) based on velocity and temperature and multi-zone reaction technique is used. With 3D numerical simulations, the present work explains the e ffects of pre-chamber pressure, CVC chamber initial temperature and jet traverse speed on ignition for a speci fic set of fuels. An innovative post processing technique is developed to predict and understand the characteristics of ignition in 3D space and time. With the increase of pre-chamber pressure, ignition delay decreases for Fuel-A which is the relatively more reactive fuel blend. For Fuel-B which is relatively less reactive fuel blend, ignition occurs only for 2 bar pre-chamber pressure for centered stationary jet. Inclusion of active radicals in pre-chamber combusted product decreases the ignition delay when compared with only the stable species in pre-chamber combusted product. The eff ects of shock-flame interaction on heat release rate is observed by studying flame surface area and vorticity changes. In general, shock-flame interaction increases heat release rate by increasing mixing (increase the amount of deposited vorticity on flame surface) and flame stretching. The heat release rate is found to be maximum just after fast-slow interaction. For Fuel-A, increasing jet traverse speed decreases the ignition delay for relatively higher pre-chamber pressures (6 and 4 bar). Only 6 bar pre-chamber pressure is considered for Fuel-B with three di fferent pre-chamber traverse speeds. Fuel-B fails to ignite within the simulation time for all the traverse speeds. Higher initial CVC temperature (514 K) decreases the ignition delay for both fuels when compared with relatively lower initial CVC temperature (300 K). For initial temperature of 514 K, the ignition of Fuel-B is successful for all the pre-chamber pressures with lowest ignition delay observed for the intermediate 4 bar pre-chamber pressure. Fuel-A has the lowest ignition delay for 6 bar pre-chamber pressure. A speci fic range of pre-chamber combusted products mass fraction, CVC chamber fuel mass fraction and temperature are found at ignition point for Fuel-A which were liable for ignition initiation. The behavior of less reactive Fuel-B appears to me more complex at room temperature initial condition. No simple conclusions could be made about the range of pre-chamber and CVC chamber mass fractions at ignition point.

Thesis: M.S., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1976 / Includes bibliographical references. / by Gordon D. Marsh. / M.S. / M.S. Massachusetts Institute of Technology, Department of Mechanical Engineering

Wastes have a real potential as being players in the energy mix of tomorrow. They can have a high heating value depending on their composition, which makes them good candidates to be converted into liquid fuel via pyrolysis. Among the different types of wastes, automotive residues are expected to rocket due to the increasing number of cars and the tendency to build cars with more and more polymers. Moreover, the existing regulations concerning the recycling of end-of-life vehicles become more and more stringent. Unconventional fuels such as those derived from automotive shredder residues (ASR) have a particular composition which tends to increase the amount of pollutants comparing with conventional fuels. Relying on alternative combustion modes, such as reactivity controlled compression ignition (RCCI), is a solution to cope with these pollutants. In RCCI, two types of fuels are burned simultaneously, namely a light fraction with a low reactivity, and a heavy fraction with a high reactivity. The heavy fraction governs the ignition as it is injected directly in the cylinder close to the end of compression. A variation of its ignition delay could impact the quality of the combustion. Nevertheless, this issue can be tackled by adjusting the injection timing. As long as the low reactivity fuel is concerned, such a solution cannot be adopted as its reactivity depends on the initial parameters (equivalence ratio, inlet temperature, exhaust gas recirculation ratio). However, if the fuel is too reactive, it could create knock that have a dramatic impact on the engine, leading to damages. Thus, being able to predict its features is a key aspect for a safe usage. Predicting methods exist but had never been tested yet with fuels derived from automotive residues. With petroleum products, usual prediction methods stand at three different levels: the chemical composition, the properties, and the reactivity in an appliance. The fuel is studied at these three levels. First, the structure gives a good overview of the fuel auto-ignition. For instance, aromatics tend to have higher ignition delay time (IDT) than paraffins. Second, the octane numbers are good indicators of the fuel IDT and of the resistance toward knock. Precisely, the octane numbers depict the resistance of a fuel towards an end-gas auto-ignition. Last, the IDT was studied in a rapid compression machine and a surrogate fuel was formulated. Surrogate fuels substitute real fuels during simulations because real fuels cannot be modelled by kinetic mechanisms due to their complexity.The existing methods to estimate the composition were updated to predict the n-paraffin, iso-paraffin, olefin, napthene, aromatic and oxygenate(PIONAOx) fractions. A good accuracy was achieved compared with the literature. This new method requires the measurement of the specific gravity, of the distillation cut points, of the CHO atom fractions, of the kinematic viscosity and of the refractive index.Two methods to predict the octane numbers were developed based on Bayesian inference, principal component analysis (PCA) and artificial neural network (ANN). The first is a Bayesian method which modifies the pseudocomponent (PC) method. It introduces a correcting factor which corrects the existing formulation of the PC method to increase its accuracy. A precision of more than 2% is achieved. The second method is based on PCA and ANN. 41 properties are studied among which reduced set of principal variables are selected to predict the octane numbers. 10 properties calculated only with the distillation cut points, the CHO atom fraction and the specific gravity were selected to accurately predict the octane numbers.Measurements of the IDT in a rapid compression machine (RCM) of a fuel produced from ASR were realized. They are the first measurements insuch a machine ever made. This provide experimental data to the literature. Moreover, these experimental data were used to formulate a surrogate fuel. Surrogate fuels can be used to realize simulations under specific conditions. The current thesis investigates fuels derived from ASR. It was showed that this fuel can be burnt in engines as long as their properties are carefully monitored. Among others, the IDT is particularly important. Nevertheless, additional experimental campaigns and simulations in engine are required in order to correctly assess all of the combustion features of such a fuel in an engine. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

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.

Wildland fire research has been extensive and on going since before 1950. The motivation behind this research is to prevent loss of property and lives. In spite of this research, the heat transfer of fuel ignition and flame spread is not well understood. This dissertation seeks to fill gaps in this understanding through modeling and also by experimentation. The effect of water vapor on the transmission of thermal radiation from the flame to the fuel was investigated. The Spectral Line Weighted-sum-of-gray-gases approach was adopted for treating the spectral nature of the radiation. The study reveals that water vapor has only a moderate effect even at 100 percent humidity. Experiments were conducted wherein wood shavings and Ponderosa pine needles in quiescent air were subjected to an imposed radiant heat flux. The internal temperature of these particles was measured and compared to steady-state model predictions. Excellent agreement was observed between the model predictions and the experimental data. Exercise of the model led to the conclusion that ignition of the fuel element by radiation heating alone is unlikely. Time-resolved radiation and convection heat flux were measured in a series of experimental laboratory fires designed to explore heat transfer behavior during combustion of discontinuous fuel beds. Convection heat flux was shown to fluctuate between positive and negative values during flame engulfment, indicating the presence of alternating packets of hot combustion gas and cool ambient air within the flame. Rapid temporal fluctuations were observed in both radiation and convection. Spectral analysis revealed content at frequencies as high as 150 to 200 Hz. Time-resolved radiation and convection heat flux histories were also collected on fourteen controlled burns and wildfires. The data reveal significant temporal fluctuations in both radiation and convection heat flux. Spectral analysis using a Fast Fourier Trans-form (FFT) revealed content as high as 100 Hz using data sets that were sampled at 500 Hz. The role of the higher frequency convective content in fuel thermal response was explored using a one-dimensional transient conduction model with a convective boundary condition. It was shown that high-frequency (i.e., short-duration) convective pulses can lead to fine fuel ignition.

This dissertation documents the building of computational propellant/ingredient models toward predicting AP/HTPB/Al cookoff events. Two computer codes were used to complete this work; a steady-state code and a transient ignition code Numerous levels of verification resulted in a robust set of codes to which several propellant/ingredient models were applied. To validate the final cookoff predictions, several levels of validation were completed, including the comparison of model predictions to experimental data for: AP steady-state combustion, fine-AP/HTPB steady-state combustion, AP laser ignition, fine-AP/HTPB laser ignition, AP/HTPB/Al ignition, and AP/HTPB/Al cookoff. A previous AP steady-state model was updated, and then a new AP steady-state model was developed, to predict steady-state combustion. Burning rate, temperature sensitivity, surface temperature, melt-layer thickness, surface species at low pressure and high initial temperature, final flame temperature, final species fractions, and laser-augmented burning rate were all predicted accurately by the new model. AP ignition predictions gave accurate times to ignition for the limited experimental data available. A previous fine-AP/HTPB steady-state model was improved to predict a melt layer consistent with observation and avoid numerical divergence in the ignition code. The current fine-AP/HTPB model predicts burning rate, surface temperature, final flame temperature, and final species fractions for several different propellant formulations with decent success. Results indicate that the modeled condensed-phase decomposition should be exothermic, instead of endothermic, as currently formulated. Changing the model in this way would allow for accurate predictions of temperature sensitivity, laser-augmented burning rate, and surface temperature trends. AP/HTPB ignition predictions bounded the data across a wide range of heat fluxes. The AP/HTPB/Al model was based upon the kinetics of the AP/HTPB model, with the inclusion of aluminum being inert in both the solid and gas phases. AP/HTPB/Al ignition predictions bound the data for all but one source. AP/HTPB/Al cookoff predictions were accurate when compared to the limited data, being slightly low (shorter time) in general. Comparisons of AP/HTPB/Al ignition and cookoff data showed that the experimental data might be igniting earlier than expected.

The average intensity and frequency of wildland fires have been on the rise over the years, leading to an increase in the risk to homes located in the Wildland-Urban Interface (WUI). Fire suppression is the most used method of wildland fire control, but this suppression can cause wildland fires to become more frequent and devastating. Increased development in the WUI also puts these homes at greater risk. Current methods of passive fire protection are effective, but these methods are expensive, time consuming to set up, and not fully effective. This research proposes a permanent passive fire protection system that is built into the structure. A flame- resistant material would be attached to the sheathing with the roofing and siding attached over the material. This system would allow the easily replaceable exterior components of the structure to burn, and the interior of the structure would be protected. This system protects the structural supports of the building, so the house does not collapse, and the exterior components can be replaced. To test this permanent passive fire protection system 21 small-scale specimens were constructed with five different flame-resistant materials and three different types of siding. The flame-resistant materials include structural wrap, Kaowool, ceramic fiber insulation, Pyrogel, and intumescent paint. The sidings include wood siding, vinyl siding, and hardie board. The testing took place in a burn room to simulate the conditions of a wildland fire. Post-burn charring evaluations and temperature analyses were conducted to determine which type of material and siding were most effective at protecting the small-scale models. The charring evaluation included determining the percent charring of the OSB face of the specimens, and the temperature analysis included determining the percent difference between the internal and external temperatures of the specimens. The performance, cost and installation, constructability, and replaceability of each of the materials were considered in deciding which materials were most effective. Overall, the Pyrogel outperformed the other materials, but this material is by far the most expensive. The ceramic fiber material was overall the second most effective flame-resistant material, and this material could be as effective as the Pyrogel if used in conjunction with the other materials tested. Further testing of material combinations is required to determine if different flame-resistant material combinations could be as effective as the Pyrogel material on its own. The results of this project did prove the feasibility of a permanent passive fire protection system, but further testing of large-scale specimens is required to test the effectiveness of the system in more complex circumstances.

Autoignition and oxidation of two Methane (CH4) and Dimethyl Ether (CH3OCH3 or DME) mixtures in air were studied in shock tubes over a wide range of equivalence ratios at elevated temperatures and pressures. These experiments were conducted in the reflected shock region with pressures ranging from 0.8 to 35.7 atmospheres, temperatures ranging from 913 to 1650 K, and equivalence ratios of 2.0, 1.0, 0.5, and 0.3. Ignition delay times were obtained from shock-tube endwall pressure traces for fuel mixtures of CH4/CH3OCH3 in ratios of 80/20 percent volume and 60/40 percent volume, respectively. Close examination of the data revealed that energy release from the mixture is occurring in the time between the arrival of the incident shock wave and the ignition event. An adjustment scheme for temperature and pressure was devised to account for this energy release and its effect on the ignition of the mixture. Two separate ignition delay correlations were developed for these pressure- and temperature-adjusted data. These correlations estimate ignition delay from known temperature, pressure, and species mole fractions of methane, dimethyl ether, and air (0.21 O2 + 0.79 N2). The first correlation was developed for ignition delay occurring at temperatures greater than or equal to 1175 K and pressures ranging from 0.8 to 35.3 atm. The second correlation was developed for ignition delay occurring at temperatures less than or equal to 1175 K and pressures ranging from 18.5 to 40.0 atm. Overall good agreement was found to exist between the two correlations and the data of these experiments. Findings of these experiments also include that with pressures at or below ten atm, increased concentrations of dimethyl ether will consistently produce faster ignition times. At pressures greater than ten atmospheres it is possible for fuel rich mixtures with lower concentrations of dimethyl ether to give the fastest ignition times. This work represents the most thorough shock tube investigation for oxidation of methane with high concentration levels of dimethyl ether at gas turbine engine relevant temperatures and pressures. The findings of this study should serve as a validation for detailed chemical kinetics mechanisms.