As powertrains and IC engines continue to grow in complexity, many vehicle manufacturers (OEMs) are turning to simulation in an effort to reduce design validation and calibration costs. Ultimately, their aim is to complete this process entirely within the virtual domain, without the need for any physical testing. Practical simulation techniques for the prediction of knock in spark ignition (SI) engines rely on empirical ignition delay correlations (IDCs). These IDCs are used to approximate the complex ignition delay characteristics of real and surrogate fuel compositions with respect to temperature, pressure and mixture composition. Over the last 40 years, a large number of IDCs have been put forward in the literature, spanning a broad range of fuels, operating conditions and calibration methods. However, the applicability of these tools has yet to be verified at the high brake mean effective pressure (BMEP) operating conditions relevant to highly boosted, downsized engines. Here, the applicability of 16 gasoline-relevant IDCs for predicting knock onset at high loads (BMEP > 30bar) has been investigated by comparing the knock predictions from each IDC against experimentally measured knock onset times. Firstly, a detailed investigation into cylinder pressure data processing techniques was performed to determine which knock detection and angle of knock onset (aKO) measurement methods were most appropriate at high loads. A method based on the maximum amplitude pressure oscillation (MAPO) during knock-free operation best estimated cycle classifications, whilst Shahlari’s Signal Energy Ratio technique [1] most accurately predicted knock onset. To the author’s knowledge, this is the first time that such a comprehensive study on the accuracy of these techniques at such high loads has been conducted. Importantly, these findings represent a valuable framework to inform other researchers in the field of knocking combustion on which techniques are needed to extract accurate and relevant information from measured cylinder pressure records. Secondly, the data processing techniques derived were applied to experimental data collected across a wide range of high BMEP operating conditions (up to a maximum of 32 bar) using a 1.6 litre, 4-cylinder SI engine. Trapped charge composition and temperature were predicted using a calibrated 1D model of the engine, whilst the temperature of a hypothetical hotspot in the unburned zone was estimated separately by assuming adiabatic compression from a point after intake valve closing and by mapping γ (the ratio of specific heat capacities) as a function of temperature. This revealed that none of the IDCs tested performed well at conditions relevant to modern, downsized engines. The IDC that achieved the best overall balance between aKO accuracy and cycle-classification agreement was the “cool-flame” correlation for iso-octane proposed by Ma [2]. However, this had an unacceptably high average aKO error of ±3.5° compared to the ±2°CA limit observed within the literature, and its average cycle-classification accuracy was below 60%. The main reason for this relatively modest accuracy was a large number of false-positive cycle classifications, which mainly occurred in slow or late burning cycles. Further work should therefore focus on methods to reduce the number of false positive classifications obtained with this correlation, which could be achieved using empirical correlations to describe the latest point in the cycle for which knock would be permitted to occur in terms other measureable combustion parameters. Overall, this research has generated a unique insight into combustion at very high loads, as well as an extensive dataset that can be used for future research to improve the accuracy of empirical knock modelling techniques. Furthermore, this work has demonstrated that for the purposes of virtual spark timing calibration and the avoidance of knock, the current crop of practical simulation tools is not accurate enough at the conditions relevant to modern SI engines and has provided a better understanding of their limitations. These findings represent a major contribution to the field from both a research perspective and for industrial applications.

The problem of self-heating of combustible dusts accumulated on hot surfaces has caused several fires and dust explosions. The current test standards (ASTM E 2021, EN50281-2-1) used to ensure safe environment for a given dust, define a safe temperature of the flat hot surface for certain dust layer thickness. Since in these standards, measurement of temperature is taken along the centerline, they mainly represent a simplified scenario of one-dimensional heat transfer. A need to investigate behavior of spontaneous ignition in dust deposits in complex geometries forms the motivation of this work. The effect of hot surface geometry is experimentally studied by devising wedge-shaped configurations having angles of 60o and 90o. Results show that ignition always occurred around the top region in the case of 60o wedge, and in the top and middle regions in the case of 90o wedge. These trends are explained by investigating three parameters affecting the ignition behavior, namely, the heat transfer from the hot plate to the dust, the rate of heat transfer between different regions within the dust and the minimum volume of dust required to produce sufficient heat release. A mathematical method has been proposed to predict the ignition behavior of dust deposit subjected to any boundary conditions arising due to geometrical confinement. Further, numerical simulations have been carried out to simulate the conjugate heat transfer in the interface of dust surface and air. Both analyses, mathematical and numerical, compare well with the experimental data. Furthermore, in the standard test method, ASTM E- 2021, a metal ring is used to contain the sample dusts. It is observed from experimental and numerical simulations that the resultant temperature field is not one-dimensional as desired since the corner part ignites first due to heat transfer from both the bottom plate and the metal ring, which is at almost same temperature as that of bottom plate. Theories those describe the thermal ignition in these standard tests, use the assumption that the heat flow is unidirectional. Therefore, a better substitute to the metal ring has been proposed as a ring made out of an insulating material (having low thermal conductivity). This makes the heat transfer to the dust layer phenomenally one-dimensional. Another leg of the experiments have been carried out to investigate the effect of weathering of combustible dusts on their spontaneous ignition process. Two types of weathering methods, heat- and moisture-weathering are used. Sample preparation and weathering quantification methods follow the standard test procedure. Thermogravimetric analysis has been employed to understand the variation in weight loss of fresh, heat-weathered and moisture-weathered samples of coal and organic dusts. Preliminary results show that heat weathering increases the hazard level for organic (wheat) dust. In summary, the current research work mainly involves modification of the standard test method such as ASTM E-2021 to include an insulated ring instead of a metal ring to ensure one-dimensional heat transfer and extending the test method to include wedge-shaped geometries. The spontaneous ignition of combustible dust in the new setups is investigated thoroughly. Furthermore, mathematical and numerical models have been proposed to simulate the experimental tests. Finally, the effect of two types of weathering processes on the characteristics of spontaneous ignition has been studied. In all the cases, results are thoroughly discussed with the explanation of the physics involved.

Hybrid rockets motors provide distinct safety advantages when compared to traditional liquid or solid propellant systems, due to the inherent stability and relative inertness of the propellants prior to established combustion. As a result of this inherent propellant stability, hybrid motors have historically proven dicult to ignite. State of the art hybrid igniter designs continue to require solid or liquid reactants distinct from the main propellants. These ignition methods however, reintroduce to the hybrid propulsion system the safety and complexity disadvantages associated with traditional liquid or solid propellants. The results of this study demonstrate the feasibility of a novel direct electrostatic arc ignition method for hybrid motors. A series of small prototype stand-alone thrusters demonstrating this technology were successfully designed and tested using Acrylonitrile Butadiene Styrene (ABS) plastic and Gaseous Oxygen (GOX) as propellants. Measurements of input voltage and current demonstrated that arc-ignition will occur using as little as 10 watts peak power and less than 5 joules total energy. The motor developed for the stand-alone small thruster was adapted as a gas generator to ignite a medium-scale hybrid rocket motor using nitrous oxide /and HTPB as propellants. Multiple consecutive ignitions were performed. A large data set as well as a collection of development 'lessons learned' were compiled to guide future development and research. Since the completion of this original groundwork research, the concept has been developed into a reliable, operational igniter system for a 75mm hybrid motor using both gaseous oxygen and liquid nitrous oxide as oxidizers. A development map of the direct spark ignition concept is presented showing the ow of key lessons learned between this original work and later follow on development.

Conventionally, metal halide lamps were ignited by striking the lamp electrodes several times with high voltage pulses. Such a starting scenario causes uncomfortable light strobes to users. To solve this problem, this thesis attempts to ignite small-wattage metal halide lamps with a single pulse strike. At first, the forms of the high voltage pulses required for breaking down the electrodes are investigated. After being broken down, a continuous current is critical for sustaining the lamp arc. With conventional electronic ballasts, however, the lamp current tends to resonate to zero resulting in break of the lamp arc. This problem can be solved by adding an extra switch to remove the capacitor of the output filter during the ignition stage. An electronic ballast is designed and tested on 70 W metal halide lamps with an associated switch for single pulse striking. Experiments have demonstrated that the proposed ignition criteria can start up the lamps successfully with a single-pulse high voltage.

Stemming from a continuing demand for fuel surrogates, composed of only a few species, combustion of high-molecular-weight hydrocarbons (>C5) is of scientific interest due to their abundance in petroleum-based fuels, which contain hundreds of different hydrocarbon species, used for military, aviation, and transportation applications. Fuel surrogate development involves the use of a few hydrocarbon species to replicate the physical, chemical, combustion, and ignition properties of multi-component petroleum-based fuels, enabling fundamental studies to be performed in a more controlled manner. Of particular interest are straight-chained, saturated hydrocarbons (n-alkanes) due to the high concentration of these species in diesel and jet fuels. Prior to integrating a particular hydrocarbon into a surrogate fuel formulation, its individual properties are to be precisely known. n-Nonane (n-C9H20) is found in diesel and aviation fuels, and its combustion properties have received only minimal consideration. The present work involves first measurements of n-C9H20 oxidation in oxygen (O2) and argon (Ar), which were performed under dilute conditions at three levels of equivalence ratio (phi = 0.5, 1.0, and 2.0) and fixed pressure near 1.5 atm using a shock tube. Utilizing shock waves, high-temperature, fixed-pressure conditions are created within which the fuel reacts, where temperature and pressure are calculated using 1D shock theory and measurement of shock velocity. Of interest were measurements of ignition times and species time-histories of the hydroxyl (OH*) radical intermediate. A salient pre-ignition feature was observed in fuel-lean, stoichiometric, and fuel-rich OH* species profiles. The feature at each equivalence ratio was observed above 1400 K with the time-of-initiation (post reflected-shock) showing dependence on phi as the initiation time shortened with increasing phi. Relative percentage calculations reveal that the fuel-rich condition produces the largest quantity of pre-ignition OH*. Ignition delay time measurements and corresponding activation energy calculations show that the phi = 1.0 mixture was the most reactive, while the phi = 0.5 condition was least reactive.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

The effect of viscoplastic deformation of the energetic material HMX on the mechanical, thermal, and ignition response of a two-phase (HMX and Estane) polymer bonded explosive (PBX) is analyzed. Specific attention is given to the high strain rate response of the material during the first passage of the stress wave when impacted by a constant velocity piston. PBX microstructures are subjected to impact loading from a constant velocity piston traveling at a rate of 50 to 200 m/s using a 2D cohesive finite element (CFEM) framework. The initial focus is to fully quantify the effect that viscoplastic HMX has on the behavior of a PBX composite, a thorough thermo-mechanical analysis is performed. The thermal response of the PBX specimens having viscoplastic HMX is characterized by a significant reduction in average heating, peak temperature rise, and the number or amount of material experiencing localized heating (hotspots). This reduction in heating is found to be accomplished through the mechanism of greatly reducing the density of fracture in the PBX. The second focus of this work is to evaluate the ignition sensitivity of these materials to determine the effect, if any, of the viscoplastic HMX. Viscoplastic HMX is shown to increase the minimum load duration, mean load duration, and range of critical load durations required for ignition. A 3D crystal plasticity framework is employed to quantify the potential heterogeneities in the stress and temperature field resulting from the inherent crystalline anisotropy of the HMX grains. It is found that in a densely packed HMX, the heterogeneities due to material anisotropy can contribute to increased stress gradients and localized temperature rise. Finally, the 2D framework is used to study a hypothetical composite containing HMX grains suspended in an aluminum matrix. This investigation focuses not on the feasibility of producing such a composite, but on determining whether such an arrangement would be advantageous from a mechanical and ignition sensitivity standpoint. Results indicate that this hypothetical composite would be considerably less sensitive than a similar PBX.

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