No description available.

Electrical control over propellant combustion has the opportunity to improve the functionality and performance of various propulsion systems. In solid rocket motors, active burn rate modulation has the potential to enable throttling. In spacecraft propulsion systems, electrolysis of propellants may provide a means to reduce energy requirements and eliminate the need for expensive catalysts. The work presented in this thesis is concerned with fundamental science related to propellant electrolysis and the performance of rocket propulsion systems using electrolytic ignition. Specifically, the present research is concerned with the effect of conductive and energetic additives on the ignition, combustion, and extinction characteristics of lithium perchlorate-based propellants. Particular attention is paid to the relative importance of electrochemistry and ohmic heating during ignition and steady-state combustion as well as the relative influence of pressure and voltage during steady combustion. Research into the development of an electrically initiated propellant and its integration into a rocket motor is presented as well. This work focused primarily on surveying propellants based on ammonium perchlorate, lithium perchlorate, and hydroxylammonium nitrate for use in a small rocket motor. The decomposition processes of propellants based on ionic liquids and gel polymer electrolytes are detailed. Finally, data from motor firings is presented and parameters influencing the motor's performance and consistency are identified for future improvement. / Master of Science / The principal disadvantage of solid rocket motors is the lack of an active throttling and restart capability. Put simply, once a motor is ignited, it will burn until all of the propellant is consumed and there currently isn't a good method to speed up or slow down a solid rocket on command after it has been launched. As a result, the situations in which solid rocket motors can be used are limited. For example, solid rockets are not used in satellite propulsion because satellites need periodic adjustments to attitude and altitude, not a single boost. But solid rockets are relatively cheap, simple, and reliable and so various means of throttling solid propellants are being investigated. The method relevant to this work is throttling by using an electrical stimulus. By applying voltage across a propellant, the propellant can be ignited and the burning rate can be changed. The research here investigates what materials can be added to these propellants to make them ignite and burn faster as well as the development of novel propellants for applications in a small rocket motor.

"This paper investigates the thermal conditions at the surface and at depth of 1.8 cm (3/4-inch) maple plywood exposed to heat fluxes between 6 and 15 kW/m2 in the cone calorimeter for up to 8 hours. The minimum heat flux for unpiloted smoldering ignition was 7.5 kW/m2 and compared favorably to classical self-heating theory. The role of self-heating was explored via temperature measurements distributed within the specimens. Elevated subsurface temperature profiles indicated self-heating was an important ignition factor resulting in ignition at depth with smolder propagation to the surface and into the material. The ignition depth was shown to be a function of the heat flux with the depth moving towards the surface as the heat flux increased. Supporting work included sensor calibration testing, mass loss rate analysis, char depth testing and computer modeling. The calibration testing showed optical pyrometer temperature measurements compare favorably to those of surface mounted thermocouples. Mass loss rate analysis was found to be a lagging indicator of smoldering ignition. The char depth tests showed that the rate of change of the temperatures recorded at depth increased around the time the derived char front passed. Computer modeling (HEATING) of a heat flux applied to the plywood for conditions similar to the performed ignition tests compared favorably to experimental data for sub-critical incident heat flux temperature profiles, excepting surface temperatures. For heat fluxes near critical, the model correctly predicted thermal runaway below the sample surface. At higher heat fluxes simulation results indicated surface ignition at times significantly earlier than experimental results."

Le fonctionnement en régime très pauvre ou avec forts taux d'EGR des moteurs à allumage commandé (MAC) permet de réduire efficacement les émissions de CO2 et de Nox ; cependant ces stratégies se heurtent à l'augmentation des variabilités cycliques. Ces dernières sont principalement dues à la phase d'allumage qui devient critique de dilution. Le modèle ECFM-LES actuellement utilisé à IFPEn, basé sur la notion de densité de surface de flamme, est insuffisant pour décrire l'allumage dans ces conditions critiques. Dans ces travaux, l'approche TF-LES est adoptée, l'allumage étant alors décrit par un emballement cinétique des réactions chimiques lors d'une élévations locale de la température. Ces travaux définissent et évaluent une stratégie de simulation pour TF-LES en configuration moteur, qui permette une prédiction fine des allumages critiques et de la propagation turbulente de la flamme, afin de décrire le cycle moteur complet.Dans une première partie, des DNS d'allumages turbulents ont été réalisées, en modélisant la phase d'allumage par un dépôt d'énergie thermique (Lacaze et al., (2009)). Les calculs ont simulé les expériences d'allumage de Cardin et al. (2013), dans lesquelles l'énergie minimum d'allumage (MIE) d'un mélange mtéhane-air a été mesuré, pour différentes richesses pauvres et sous différentes intensités turbulentes. L'objectif principal des simulations a été de déterminer les paramètres numériques et physiques du modèle permettant de reproduire les allumages de l'expérience. Deux types de schémas cinétiques ont été évalués : un schéma simplifié et un schéma analytique (ARC), ce dernier reproduisant et les délais d'auto-allumage et la vitesse de flamme laminaire. Les résultats ont permis de définir des critères d'allumage et de mettre en évidence les différentes prédiction d'allumage avec les deux types de schémas cinétiques. Les résultats ont été également démontré que l'approche choisie permettait de prédire les bons niveaux d'énergie pour les allumages laminaires et à faible nombres de Kalovitz (Ka<10). Aux plus hauts nombres de Karlovitz, il a été montré que le modèle ED était insuffisant pour prédire les énergie d'allumage et qu'une description plus fine du dépôt d'énergie est nécessaire.Dans la seconde partie des travaux, un modèle de plissement dynamique (Wang et al., 2012) a été étudié, afin de décrire le développement hors-équilibre de la flamme dans la phase de propagation turbulente. Des études sur des flammes sphériques laminaires ont d'abord été menées. Ensuite, les premiers tests de configuration moteur ayant révélé des incompatibilités du modèle, des modifications ont été proposées. Le modèle de plissement dynamique modifié a été finalement évalué sur la configuration moteur ICAMDAC. Les résultats obtenus ont été comparés aux résultats obtenus par Robert et al. (2015) avec le modèle ECFM-LES, qui utilise une équation de transport de densité de surface de flamme décrivant le plissement hors-équilibre de la flamme. Les résultats obtenus avec le plissement dynamique sont en très bon accord avec ceux du modèles ECFM-LES, démontrant ainsi la capacité du modèle dynamique à prédire des valeurs de plissement hors-équilibre. D'autre part, le modèle dynamique s'ajustant automatiquement aux conditions de turbulence de l'écoulement, nul besoin n'est d'ajuster la constante de modélisation en fonction du régime moteur, comme c'est le cas pour l'équation de transport de la densité de surface de flamme. / The use of lean equivalence ratios or high EGR rates in spark ignition engines (SIE) enables to optimize CO2 and NOx emissions; however too important dilution rates leads to increased cycle-to-cycle variability. These latter are mostly due to the ignition phase, which becomes critical when dilution rates are important and requires high ignition energy. The ECFM-LES model currently used in IFPEN, which is based on the flame surface density concept, is not sufficient to describe ignition in these critical conditions. The TF-LES approach was chosen in this study, principally because it directly resolved chemistry and can thus model ignition via a local raise of the temperature. The present work defines and evaluates a simulation strategy for TF-LES in SIE configurations, that enables a fine prediction of critical ignitions and of the turbulent flame propagation.In the first part, DNS of turbulent ignition were performed. The ignition phase was modeled using a thermal energy deposit (ED model, Lacaze et al.). Simulations reproduced the ignition experiments of Cardin et al. who determined the minimum ignition energy (MIE) of lean premixed methane/air mixtures, for different turbulence characteristics. The main purpose of the study was to determine the numerical and physical model parameters, which enable to reproduce Cardin et al. experiments. Two types of kinetic schemes were evaluated: a simplified kinetic scheme and an analytical kinetic scheme (ARC), that can predict both the auto-ignition delays and the laminar flame speed, while keeping affordable CPU times. Results analysis enabled to define ignition criteria and to highlight the differences in terms of ignition prediction using the two kinetic schemes. Results also demonstrated that the chosen approach could recover correct levels of ignition energy for laminar and low Karlovitz number cases (Ka<10). For higher Karlovitz number cases, the ED model was found to be insufficient to predict the ignition and a finer description of the energy deposit is required.In the second part, a dynamic wrinkling model (Wang et al., 2012) was studied to describe the out-of-equilibrium behavior of the flame during the propagation phase. Studies on laminar spherical flames were first performed, to assess the laminar degeneration of the model. Then, as first tests in an engine configuration have revealed incompatibilities of the model, modifications were proposed. The modified dynamic model was finally tested in the ICAMDAC engine configuration. Results of the simulations were compared against previous results of Robert et al. obtained with the ECFM-LES model using a transport equation for the flame surface density that can describe the out-of-equilibrium wrinkling of the flame. Results obtained with the dynamic model are in very good agreement with the ones of Robert et al., thus demonstrating the ability of the dynamic model to predict out-of-equilibrium values in the engine configuration. Besides, the dynamic model self-adapts to the turbulence conditions, hence does not require any model parameter adjustment, as is it the case for models based on the flame surface density transport equation.

In this study, an ignition unit was designed and constructed for a new design engine with eight cylinders and sixteen pistons. The ignition coils with two high voltage outputs were used to ignite sixteen spark plugs on the system. They were driven by PIC16F628A based igniter circuits triggered with digital signals. The igniter circuits receive ignition signals in a square wave form from a main control circuit / they open or close primary voltage of the induction coils to ignite spark plugs. This main control circuit is based on PIC16F877A / and there are two of them. The duty of main control circuit is to determine ignition advance according to engine speed and cooling water temperature, and send proper ignition signals to the igniter circuits. This main control circuit receives engine speed from the other main circuit (secondary control circuit) with serial communication and reads cooling water temperature and then it reads advance value from external eeprom memory according to engine speed and temperature. The main control circuit receives cylinder position signals from the secondary control circuit and adds advance value on them to form ignition timing signals which triggers igniter circuits. The secondary control circuit reads engine speed and determines cylinder positions with two magnetic pick-ups and LM2907 circuits on a gear wheel. This gear wheel was used to simulate disks on the crank shaft of the cars, and driven with an electric motor. The ignition unit was tested for different engine speeds, and its proper working was proved.

No description available.

Ignition and combustion enhancement of lean homogeneous mixtures offers the potential to simultaneously lower pollutant emissions and improve the thermal efficiency of internal combustion engines. A single cylinder, high compression ratio (16.5:1), open chamber diesel engine has been converted to operate on homogenously charged compressed natural gas (CNG) with the aim of minimising pollutant emissions such as oxides of nitrogen, particulate matter and carbon dioxide. Three ignition systems were tested to examine how effectively they could ignite lean mixtures of CNG with the ultimate aim of achieving simultaneously high thermal efficiency and low oxides of nitrogen emissions. The ignition systems examined were spark ignition (SI), diesel pilot ignition (DPI) and hydrogen assisted jet ignition (HAJI). Irrespective of ignition system used, the efficiency of the engine operating on CNG was significantly reduced at part load compared to diesel. This was predominantly due to a greater amount of unburnt hydrocarbons, higher cycle-by-cycle variability, slow and partial burns and increased heat transfer to the walls. DPI and HAJI systems were able to extend the lean limit to lambda 2.7 and 3.3 respectively, however this did not result in efficiency gains over SI systems. HAJI proved to be superior to DPI with higher peak efficiency, lower carbon dioxide, carbon monoxide and particulates, and significantly lower oxides of nitrogen in the absence of a locally rich ignition source. (For complete abstract open document)

The main aim of this thesis is the analysis of influence of inlet valve opening length and compression ratio on performance and thermodynamic parameters of Miller cycle using GT-SUITE software. Next step was an optimization of inlet and exhaust valve timing with goal of increasing motor effective power. For chosen option was designed cam shaft with regard of kinematic and dynamic magnitude courses.

No description available.

This thesis investigates the oxidation chemistry and ignition properties of formic acid (FA). The study reports experimental measurements of ignition delay time (IDT) and CO/CO2 time histories during FA oxidation in a shock tube. The initial concentration of FA was measured with a laser to minimize uncertainties arising from its low vapor pressure and tendency to form dimers. Shock tube experiments were carried out at two pressures, around 1.7 and 3.5 bar, and temperatures ranging from 1194 to 1658 K, with two equivalence ratios, 0.72 and 1.47. The results show a noticeable dependence of IDTs on temperature and pressure, while there was insignificant dependence on equivalence ratio. Six kinetic models for FA oxidation available in the literature were tested against the obtained data to evaluate their accuracy and suggest potential improvements. We found that 4 models performed well in predicting IDTs and CO/CO2 profiles with some overprediction at certain conditions. Sensitivity analysis revealed that the IDTs of FA are governed by unimolecular decomposition, H abstraction, and radical consumption (HOCO) reactions. The concentration of HO2 is higher at low temperatures, which is favorable for the system’s reactivity as it makes IDTs more sensitive to the reaction HOCHO + HO2 = H2O2 + HOCO. CO formation is controlled by two reactions: CO + OH = HOCO and HOCHO (+M) = CO + H2O, while the second reaction is more pronounced at high temperatures. Moreover, the dissociation of HOCO is faster at higher pressures, leading to higher initial CO concentrations. The formation of CO2 is determined by CO + OH = CO2 + H, while at higher temperatures, HOCHO (+M) = CO2 + H2 (+M) becomes more important, resulting in higher initial CO2 concentrations.