A multi-physics simulation approach to Investigating the underlying mechanisms of Low-Speed Pre-Ignition

As part of the effort to improve thermal efficiency, engines are being significantly downsized. A common issue in gasoline engines which limits thermal efficiency and is further exacerbated by downsizing, is low speed pre ignition (LSPI). This thesis uses a Multiphysics approach, initially using a validated 1D engine performance model of a GTDI engine, to define realistic boundary conditions. A strong emphasis on validating each simulation methodology as much as possible is maintained at each stage. A hydrodynamic model of the ring-liner and Lagrangian CFD model are used to investigate the impact of engine oil fluid properties on the mass of oil transported from the crevice volume to the combustion chamber. A heat transfer and evaporation model of a single droplet inside an engine environment was developed for alkanes of chain lengths representing the extremes of the chain lengths present in engine oil. It was found the droplet generally evaporates at a crank angle which is close to the point where LSPI is observed. The hydrocarbon study ends with a CFD constant volume simulation to understand why engine oil like hydrocarbons ignite in rig tests but not in an engine. This research then proceeds to develop a single particle detergent model in an engine environment, to initially understand why ignition occurs when a calcium Ca based detergent is present but not in the case of a magnesium Mg detergent. It was found from simulation that the common theory of calcium oxide CaO resulting from thermal degradation from the previous cycle then reacting with Carbon dioxide CO2 late in the compression stroke is unlikely. There is a stronger case for the CaO particle causing ignition as it is present in fresh engine oil sprayed onto the liner. As predicted by the hydrocarbon evaporation model the oil will cover and protect the CaO particle until late in the compression stroke when the oil will evaporate, exposing the CaO particle to CO2

Optical spectroscopy of HMX reaction regimes

A detailed study on the visible light emission from multiple granular HMX reactions has been completed. New techniques for measuring the reaction properties were devised, both directly and indirectly from the results gained from using optical spectroscopy. Two different impact initiated deflagration reactions were performed. Improvements were made to the fallhammer sensitivity test to allow for more quantitative measurements, and the Split Hopkinson Pressure Bar (SHPB) was used for the first time to purposely initiate deflagration, providing better measurements of the energy present during initiation. Using the greybody emission, the temperatures of these reactions were measured as 3900 ± 400 K and 2900 ± 200 K respectively. Building a time-dependent pyrometer showed a constant temperature throughout the main reaction period. The significant difference between the two temperatures inspired the addition of a mass spectrometer to investigate the products from each reaction. The results showed the two reactions did not resemble variants of an ‘ideal’ deflagration reaction, and so identical chemistry should not be assumed to be present in both. Optical spectroscopy also showed the existence of a spectral peak in deflagration due to emissive sodium impurities. The peak was red-shifted under the pressures of the reaction, and the calibration curve of the red-shift was calculated. The functional form of the shift has a dependence on pressure and temperature in agreement with Lindholm-Foley collisional theory, allowing the pressure to be calculated optically from position of the shift. This was achieved with a streak spectrometer, where time-dependent measurements of the temperature (using greybody emission) and pressure (using the sodium peak) from the same source of light were made. Finally, detonation of HMX was examined. The detonation pressure and velocity were measured as a function of initial density, and found consistent with models of shock conservation and Group Interaction Modelling. High temperatures of 7000 K were recorded from the greybody emission, with the light emitted from mechanical high pressure void collapse dominating over the heat produced from the chemical reaction. These temperatures were not affected by the density of the HMX bed, but instead the size of the voids present. Larger particles increased the size of the voids, leading to higher temperatures and decreased light scattering, with the inclusion of sodium absorption features.Emmanuel college Avik Chakravarty Memorial fun

Studies on the Impact Initiation and Kinetics of Condensed Phase Reactives with Application to the Shock Induced Reaction Synthesis of Cubic Boron Nitride

Shock induced reaction synthesis is a complex, scientifically rich field with the potentially to produce novel materials with unique properties. This work seeks to understand the processes governing shock induced reaction synthesis. Particular emphasis is placed on the reaction kinetics of condensed phase reactives under various mechanical and thermal heating rates. This understanding was then applied to the synthesis of cubic boron nitride through shock induced reaction synthesis. Mechanical initiation of reactions in powder systems involve complex interactions that can yield unexpected results. Two materials that exhibit similar thermal responses can behave very differently under the same loading conditions due to differences in their mechanical properties. Reactive composite powders with small characteristic dimensions can exhibit short ignition delays and reduced thermal ignition thresholds; however, a full understanding of the response of these powders to rapid mechanical loading is still unclear. This work seeks to clarify the role of mechanical properties in impact induced ignition by considering the response of nanolaminate (NL) powders and high energy ball milled (HEBM) Ni-Al powders subjected to impact loading. The powders were placed into a windowed enclosure and mechanically loaded using a light gas gun, which allowed the resulting reactions to be observed using high-speed imaging. Even though the thermal ignition temperatures for the two powders are within 30 °C of each other, it was observed that the NL powders reacted on the microsecond timescale, immediately following the compaction wave for a short distance before decoupling from the compaction front. In contrast, the HEBM powders reacted after a several millisecond delay and clearly propagated as a deflagration front. Microindentation showed that the HEBM powders are much more ductile than those of NL. This suggests that the primary difference between the behavior of these materials on impact results from the ability and degree of the material to fracture, illustrating that the mechanical properties of a reactive material can have a dramatic effect on ignition during impact loading. By using the jump equations to understand compaction events, it is easy to think about the compaction wave as a discontinuity, with no structure. In practice this is not the case. Both shock waves and compaction events have been observed to have a structure with a finite thickness. Studies of the propagation of shocks through monolithic solids have shown that the strain rate, which is directly related to the shock width, scales with the pressure rise to the fourth power. Studies of dynamic compaction of porous materials have shown that this relationship is closer to linear. This work seeks to study the effect that increasing the crush strength of the compact has on the width of the compaction wave. Ball milling is used to produce strain hardened powders that are then pressed to form a porous compact. Plate impact experiments are performed to evaluate the equation of state and measure the shock width of both milled and unmilled powders. The results show that a Mie-Gruneisen equation of state accurately predicts the response of all materials tested; however, the compaction width is found to change with milling condition. For all materials tested, the compaction width is found to decrease with increase pressure rise; however, the unmilled material is found to have a longer rise time compared to the ball milled material. This results in a reduction in apparent viscosity with increased crush strength. It is suggested that stress waves percolating ahead of the compaction front (since the velocity of the compaction wave is below the acoustic velocity of the parent material) and their interaction defines the compaction width. In a weaker material, a weaker stress is required to begin compaction, resulting in a broader front compared to a stronger material and an increased viscosity. Despite their widespread use, the reaction pathways of thermite (reduction-oxidation) reactions are relatively unknown. Multilayer thin films produced through magnetron sputtering provide a highly controlled geometry and direct contact between reactives, making them an ideal platform to study atomic-scale processes underlying thermite reactions. This work utilizes the multilayer thin film geometry to study the combustion and reaction pathway of equimolar Al-NiO. The low heating rate kinetics and product phase growth are studied through hot-stage X-ray diffraction and differential scanning calorimetry. The results indicate significant product formation beginning as low as 180°C, and results in the formation of nickel aluminum intermetallic phases. Hot-plate ignition experiments show that ignition occurs in the solid state for fine bilayer thicknesses, with a transition to melt dependent reaction for multilayers with larger bilayer thicknesses. Laser ignition and self-propagating reactions are observed to exhibit a similar length scale dependence in reaction behavior. The activation energy determined from the hot-plate ignition experiments was found to be less than that for the laser ignition experiments, indicating a heating rate dependent response. This work culminates with the direct synthesis of cubic boron nitride through shock loading of 3B+TiN composite particles. It was found that reduction of the diffusion distance through high energy ball milling before loading was critical for success, with unmilled powders showing no evidence of reaction after recovery. The results show the possibility of rapid reaction occurring in a condensed phase system at microsecond timescales. As a results, optimization of this process may provide a route for the fabrication and discovery of other advanced compounds

Indexes of the Proceedings for the Ten International Symposia on Detonation 1951-93

The Proceedings of the ten Detonation Symposia have become the major archival source of information of international research in explosive phenomenology, theory, experimental techniques, numerical modeling, and high-rate reaction chemistry. In many cases, they contain the original reference or the only reference to major progress in the field. For some papers, the information is more complete than the complementary article appearing in a formal journal; yet for others, authors elected to publish only an abstract in the Proceedings. For the large majority of papers, the Symposia Proceedings provide the only published reference to a body of work. This report indexes the ten existing Proceedings of the Detonation Symposia by paper titles, topic phrases, authors, and first appearance of acronyms and code names

Nanoenergetic Materials

This highly informative and carefully presented book discusses the preparation, processing, characterization and applications of different types of nanoenergetic materials, as well as the tailoring of their properties. It gives an overview of recent advances of outstanding classes of energetic materials applied in the fields of physics, chemistry, aerospace, defense, and materials science, among others. The content of this book is relevant to researchers in academia and industry professionals working on the development of advanced nanoenergetic materials and their applications

Fire performance of residential shipping containers designed with a shaft wall system

seven story building made of shipping containers is planned to be built in Barcelona, Spain. This study mainly aimed to evaluate the fire performance of one of these residential shipping containers whose walls and ceiling will have a shaft wall system installed. The default assembly consisted of three fire resistant gypsum boards for vertical panels and a mineral wool layer within the framing system. This work aimed to assess if system variants (e.g. less gypsum boards, no mineral wool layer) could still be adequate considering fire resistance purposes. To determine if steel temperatures would attain a predetermined temperature of 300-350ºC (a temperature value above which mechanical properties of steel start to change significantly) the temperature evolution within the shaft wall system and the corrugated steel profile of the container was analysed under different fire conditions. Diamonds simulator (v. 2020; Buildsoft) was used to perform the heat transfer analysis from the inside surface of the container (where the fire source was present) and within the shaft wall and the corrugated profile. To do so gas temperatures near the walls and the ceiling were required, so these temperatures were obtained from two sources: (1) The standard fire curve ISO834; (2) CFD simulations performed using the Fire Dynamics Simulator (FDS). Post-flashover fire scenarios were modelled in FDS taking into account the type of fuel present in residential buildings according to international standards. The results obtained indicate that temperatures lower than 350ºC were attained on the ribbed steel sheet under all the tested heat exposure conditions. When changing the assembly by removing the mineral wool layer, fire resistance was found to still be adequate. Therefore, under the tested conditions, the structural response of the containers would comply with fire protection standards, even in the case where insulation was reduced.Postprint (published version