After the restriction of different halogenated fire suppressants by the Montreal Protocol, there is an urgent need to identify environmentally friendlier alternatives. In particular, several efforts have been conducted to find substitutes of Halon 1301 (CF_(3)Br) which was considered the best in its class, not only because of its superior extinguishing performance, but also due to its relatively low toxicity. Different options have been proposed over the last decade. However, no single compound has been found to meet all of the exigent criteria. Further progress in this research requires fundamental combustion knowledge that can help us understand the unique performance of Halon 1301, to prevent this search from becoming a tedious trial-and-error process. To this end, the present work aids in the search of fire suppressants alternatives by improving the flame inhibition mechanism understanding, starting with CF_(3)Br, which serves as a benchmark for new fire suppressants. Then, a case study of two of the most currently used fire suppressants, C_(2)HF_(5) (HFC-125) and C_(2)HF_(7) (HFC-227), is presented and compared with CF_(3)Br performance. For these analyses, a systematic analytical methodology was used to examine the effect of fire suppressants on ignition and laminar flame propagation of C_(1)-C_(3) alkanes premixed mixtures, as good representatives of flammable gas fires (Class B fires). This methodology integrates model formulations and experimental designs in order to examine both chemical kinetics and thermal effects on fire suppressants at different stoichiometric conditions. Modeling predictions were based on a detailed chemical kinetics mechanism which was assembled from a new, well-studied H_(2), C_(0)–C_(5) hydrocarbon mechanism from NUI Galway and recent CF_(3)Br and HFC fire suppressant chemistry from NIST. Experimental study involved the use of a shock tube (for ignition analysis) and a freely expanding flame speed bomb (for laminar flame speed analysis). Most of the experimental data provided in this work are the first measurements of their kind for the compounds and mixtures explored in this thesis. These measurements are extremely valuable since they can be used as a metric for model validation which represents one of the objectives of this work. Current analyses indicate that the combustion properties of halogenated compounds cannot be generalized and depends on different factors. On one hand, the presented results showed that all the tested fire suppressants can decrease the laminar flame speed of the examined C_(1)-C_(3)alkanes premixed flames; however, in some cases they can act as ignition promoters. In order to understand these behaviors, sensitivity analyses were conducted showing that halogenated species, resulting from the fire suppressants decomposition, can participate in both promoting and inhibiting reactions that compete to give a net effect. Identification of the key reaction responsible for such effects was conducted. Then, improvements on the fire suppressant chemistry can be done by modifying the corresponding Arrhenius parameters of such important reactions. This work not only provides fundamental knowledge of halogenated flame inhibition mechanisms, but also serves as the basis for more accurate chemical kinetics mechanisms that can be used for better predictions over a wide range of conditions.

This PhD thesis is an analysis of the chemical kinetics and oxidation behavior of fuel components via experiments and correlations. First, a number of experimental studies of the reactivity of OH radicals with unsaturated hydrocarbons are performed at temperatures ranging from 294 to 1400 K by OH absorption and laser induced fluorescence techniques in two different reactors: shock tube and flow reactor. It is found that OH has a tendency to add to the unsaturated CC bond, forming a relatively stable adduct. The thermal stability of these adducts is vital for a better understanding of the kinetics of olefins, poly-olefins, alkynes and other unsaturated components in real and surrogate fuel blends. In this work, the reaction rate coefficient of the reaction of hydroxyl radical with many olefins (butenes, pentenes, hexenes), di-olefins (butadienes, and pentadienes) and allyl radical are measured. A strong competition between H-abstraction and OH-addition pathways is seen particularly in the intermediate temperature window of ~ 400 to 900 K. All of these measured elementary reactions give new insights into the chemical kinetics of fuels and allow modelers to improve the predictive capability of their models. Second, measurements of the ignition delay times of propene, isobutene, 2-methylhexane and 2-methylbutanol in air are performed using a high-pressure shock tube. Details about multi-stage ignition and ignition delay dependence on various thermodynamic properties is investigated for these four hydrocarbons. We followed this with a correlation study of ignition delay times of fuel blends and real fuel streams. The main requirement of these correlations is that these should be predictive enough to compete with the predictive capabilities of detailed chemical kinetic models but at a much reduced computational cost. The obtained correlation scheme does not only predict ignition timing during CFD simulations but also other combustion properties such as low-temperature heat release timing and resulting temperature and pressure increases due to cool flame. A discussion on the weak dependence of high-temperature ignition delay times on the composition of real fuels is also presented, where universal Arrhenius type expressions of ignition delay times of gasoline, diesel and jet fuels are given.

Energy demand is rapidly increasing due to the increase in population and rising living standards. Petroleum-based fuels account for the main source of energy consumed in the world. However, they are also considered to be the main source of the unwanted emissions to the atmosphere. In this context, chemical kinetic studies of combustion processes are essential for a better understanding of the underlying reactions and to achieve increased combustion efficiency and reduced pollutant emissions. In this study, ignition delay times, a global indicator of fuel reactivity, were measured for promising fuels for use in advanced combustion engines. Also, rate coefficients were measured for promising oxygenated hydrocarbons that can be used as additives to conventional fuels. Ignition delay time measurements of four primary reference fuel (PRF) blends, mixtures considered to be some of the simplest gasoline surrogates, were measured behind reflected shock waves to provide a large experimental dataset to validate PRF chemical kinetic models. The kinetic modeling predictions from four chemical kinetic models were compared with the experimental data. Ignition delay correlations were also developed to reduce the simulation cost of complicated models. Recently, naphtha, a low-octane distillate fuel, has been proposed as a low-cost refinery fuel. Likewise, a mid-octane blend which consists of low-octane (light and heavy naphtha) and high-octane (reformate) distillate fuels has been proposed to power gasoline compression ignition (GCI) engines. In this work, experimental and modeling studies were conducted on low and mid-octane distillate fuels (naphtha and GCI blend) and surrogate candidates to assess their autoignition characteristics for use in advanced internal combustion engines. Oxygenated molecules are considered to be promising additives to conventional fuels. Thermal decomposition of three esters (ethyl levulinate, ethyl propionate and diethyl carbonate ) and a five-member cyclic ketone (cyclopentanone) was investigated in this work. Laser absorption technique was employed to follow the reaction progress by measuring ethylene (C2H4) near 10.532 µm using a CO2 gas laser for the decomposition process of the three esters. The reaction progress of the decomposition of cyclopentanone was followed by monitoring CO formation using a quantum cascade laser at a wavelength near 4.556 µm.

Population growth and increasing standards of living have resulted in a rapid demand for energy. Our primary energy production is still dominated by fossil fuels. This extensive usage of fossil fuels has led to global warming, environmental pollution, as well as the depletion of hydrocarbon resources. The prevailing difficult situation offers not only a challenge but also an opportunity to search for alternatives to fossil fuels. Hence, there is an urgent need to explore environmentally friendly and cost-effective renewable energy sources. Oxygenates (alcohols, ethers) and ammonia are among the potential renewable alternative fuels of the future. This thesis investigates the combustion characteristics of promising alternative fuels and their blends using a combination of experimental and modelling methodologies. The studied fuels include ethanol, diethyl ether, dimethyl ether, dimethoxy methane, γ-valerolactone, cyclopentanone, and ammonia. For the results presented in this thesis, the studies may be classified into three main categories: 1. Ignition delay time measurements of ethanol and its blends by using a rapid compression machine and a shock tube. The blends studied include binary mixtures of ethanol/diethyl ether and ternary mixtures of ethanol/diethyl ether/ethyl levulinate. A chemical kinetic model has been constructed and validated over a wide range of experimental conditions. The results showed that a high-reactivity fuel, diethyl ether, may be blended with a low-reactivity fuel, ethanol, in varying concentrations to achieve the desired combustion characteristics. A ternary blend of ethanol/diethyl ether/ethyl levulinate may be formulated from a single production stream, and this blend is shown to behave similarly to a conventional gasoline. 2. Ignition delay time and flame speed measurements of ammonia blended with combustion promoters by utilizing a rapid compression machine and a constant volume spherical reactor. The extremely low reactivity of ammonia makes it unsuitable for direct use in many combustion systems. One of the potential strategies to utilize ammonia is to blend it with a combustion promoter. In this work, dimethyl ether, diethyl ether, and dimethoxy methane are explored as potential promoters of ammonia combustion. Chemical kinetic models were developed and validated in the high temperature regime by using flame speed data and in the low-to-intermediate temperature regime by using ignition delay time data. The results showed that even a small addition (~ 5 – 10%) of combustion promoters can significantly alter ammonia combustion, and diethyl ether was found to have the highest propensity to enhance ammonia ignition and flame propagation. Blends of combustion promoters with ammonia can thus be utilized in modern downsized turbo-charged engines. 3. Octane boosting and emissions minimization effects of next generation oxygenated biofuels. These studies were carried out using a cooperative fuel research engine operating in a homogenous charge compression ignition (HCCI) mode. The oxygenated fuels considered here include γ-valerolactone and cyclopentanone. The results showed that γ-valerolactone and cyclopentanone can be effective additives for octane boosting and emission reduction of conventional fuels. Overall, the results and outcomes of this thesis will be highly useful in choosing and optimizing alternative fuels for future transportation systems.

Siemens Industrial Turbomachinery AB produce five gas turbines models. The SGT-700 can currently only start on gases which contain low amounts of inert gases. It is therefore of interest to widen the fuel range which the SGT-700, as well as other gas turbines, can start on. This report investigates the maximum limit of inert gases the SGT-700 will be able to start on, but also investigates if it is possible to start on liquid fuel (diesel) by making a few modifications to the gas turbine. To investigate this, the atmospheric combustion rig available at Siemens in Finspång has been used with a standard burner, igniter and ignition unit for the SGT-700. For the liquid fuel, the igniter was replaced by a torch igniter specially made for liquid fuels. Four different gases were evaluated; methane, propane, CO2 and N2 in order to see the effect of both various hydrocarbons and various inert gases. A model was developed for the gaseous experiments to estimate the limit for the maximum amount of inert gases the gas turbine would be able to start on. The model suggested that CO2 would require a larger amount of energy than N2 for the same amount in the composition, but that varying hydrocarbons did not have any effect if looking at the mass % of inert gas in the composition. The model was also extended with ethane and hydrogen but no experiments were performed with these gases. The model gave satisfying results. It overestimated the maximum amount of inert gases which could be mixed with propane, but agreed well when comparing the two inert gases with each other. Other interesting results were that an increased fuel flow decreased the minimum ignition energy and that an increased air flow gave a minor decrease in the maximum amount of inert gases that was possible to ignite. The torch igniter for the liquid fuel worked in a satisfying way. The ignition energy was however too low, so the ignition reliability was low. A new ignition unit with larger energy output therefore needs to be implemented. The igniter was fairly insensitive to variations in burner air flow and the ignition delay was small enough to provide a sustainable flame.

Indiana University-Purdue University Indianapolis (IUPUI) / A chemically reactive turbulent traversing hot-jet issued from a pre-chamber to a relatively long combustion chamber is experimentally investigated. The long combustion chamber represents a single channel of a wave rotor constant-volume combustor. The issued jet ignites the fuel-air mixture in the combustion chamber. Fuel-air mixtures are prepared with different hydrocarbon fuels of different reactivity, namely, methane, propane, methane-hydrogen blend, methane-propane blend and methane-argon blend. The jet acts as a rapid, distributed and moving source of ignition, traversing across one end of the long combustion chamber entrance, induces complex flow structures such as a train of counter rotating vortices that enhance turbulent mixing. In general, a stationary hot-jet ignition process lack these structures due to absence of the traversing motion. The ignition delay of the fuels and fuel blends are measured in order to obtain insights about constant-volume pressure-gain combustion process initiated by a moving source of ignition and also to glean useful data about design and operation of a wave rotor combustor. Reactive hot-jets are useful to ignite fuel-air mixtures in internal combustion engines and novel wave rotor combustors. A reactive hot-jet or puff of gas issued from a suitably designed pre-chamber can act as rapid, distributed and less polluting ignition source in internal combustion engines. Each cylinder of the engine is provided with its own pre-chamber. A wave rotor combustor has an array of circumferentially arranged channels on a rotating drum. Each channel acts as a constant-volume combustor and produces high pressure combustion products. Implementation of hot-jet igniter in a wave rotor combustor offers utilization of available high temperature and high pressure reactive combustion products residing in each of the wave rotor channels as a distributed source of ignition for other channels, thus requiring no special pre-chamber in ultimate implementation. Such reactive products or partially combusted and radical-laden gases can be issued from one or more channels to ignite the fuel-air mixture residing in another channel. Due to the rotation of the rotor channels, the issued hot-jet would have relative motion with respect to one end of the channels and traverse across it. This thesis aims to investigate the effects of jet traverse time experimentally on ignition delay along with other important factors that affect the hot-jet ignition process such as fuel reactivity, fuel-air mixture preparation quality and stratification and equivalence ratio. In this study, the traversing motion of the hot-jet at one end of the main combustion chamber is implemented by keeping the main combustion chamber stationary and rotating a pre-chamber at speeds of 400 RPM, 800 RPM and 1200 RPM. The rotational speeds correspond to jet traverse times of 16.9 ms, 8.4 ms and 5.6 ms respectively. The fuel-air mixture inside the channel is at room temperature and pressure initially and its equivalence ratio is varied from 0.4 to 1.3. The cylindrical pre-chamber is initially filled with a 50%-50% methane-hydrogen blend fuel and air mixture at room pressure and temperature and at an equivalence ratio of 1.1. These conditions were chosen based on prior evidence of ignition rapidity with the jet properties. The hot-jet is issued by rupturing a thin diaphragm isolating the chambers. Using high frequency dynamic pressure transducer pressure histories, the diaphragm rupture moment and onset of ignition is measured. Pressure traces from two transducers are employed to measure the initial rupture shock speed and ignition delay. Schlieren images recorded by a high speed camera are used to identify ignition moment and validate the measured ignition delay times. Ignition delay is defined as time interval from the rupture moment to onset of ignition of fuel-air mixture in the main combustion chamber. The ignition system is designed to produce diaphragm rupture at almost exactly the moment when jet traverse begins. Ignition delay times are measured for methane, propane, methane-hydrogen blends, methane-propane blend and methane-argon blend. The equivalence ratio of the fuel-air mixtures varied from 0.4 to 1.3 in steps of 0.1 for stationary-hot jet ignition experiments and in steps of 0.3 for traversing hot-jet ignition experiments. Hot-jet ignition delay of fuel-air mixtures, for both stationary hot-jet ignition process and traversing hot-jet ignition process, generally increased with increasing equivalence ratio. For stationary hot-jet ignition delay, the minimum ignition delay occurs between Ф = 0.4 to Ф = 0.6 for the tested fuel-air mixtures. Both stationary and traversing hot-jet ignition delay depended on fuel reactivity. In particular, the shortest ignition delay times were observed for a fuel blend containing hydrogen. Among pure fuels propane exhibited slightly shorter ignition delay times, on average, compared to pure methane fuel. The addition of argon to pure methane, intended to control fuel density and buoyancy, increased the ignition delay. The traversing hot-jet ignition delay generally increased with increasing jet traverse times. To explain the variations in the measured hot-jet ignition delay and investigate qualitatively the effect of buoyancy on flame propagation and mixture stratification, the fuel-air mixture inside the main combustion chamber was ignited using a spark plug to generate a propagating laminar flame. The laminar flame propagated within the flammable regions of the channel in ways that sensitively reveal variations in local fuel-air mixture equivalence ratio. Flame luminosity images from a high speed camera and schlieren images revealed the fuel-air mixture being highly stratified depending on the density difference between the fuel and air and provided mixing time (0 s, 10s ,30s for most fuels). The lack of buoyancy-driven spreading caused the fuel to remain in the vicinity of the fuel injector resulting in significant longitudinal stratification of the fuel-air mixture. Lighter fuels stratified to the top of the chambers and heavier fuel stratified to the bottom of the chamber. Increasing the mixing time, which is defined as the time interval from end of fuel injection into the chamber to the triggering of the spark plug, improved the buoyancy-driven spreading and extended the flammable region as evidenced by the schlieren and flame luminosity images. The maximum pressure developed in the combustor for the three ignition processes, namely, stationary hot-jet ignition, traversing hot-jet ignition and spark ignition process in laminar flame propagation experiments were compared. Stationary hot-jet ignition process generally exhibited the highest pressure being developed in the chamber. Variations in heat loss, fuel-air mixture leakage and mass addition mechanisms reduced the maximum pressure for spark ignition and traversing hot-jet ignition process.

This thesis focuses on ignition of diisopropyl ketone (DIPK), a new biofuel candidate that is produced by endophytic conversion. The ignition delay times behind reflected shockwaves were modeled in a high-pressure shock tube. The ignition delay times were compared to other biofuels and gasoline surrogates. Parametric studies of the ignition delay experiments were performed between 1-10 atm and 900 -1200K. An OH optical sensor was developed in conjunction for the ignition delay experiments. The OH optical sensor uses a microwave discharge lamp to generate light at 308 nm that will then be shined through the combustion reaction. Using Beer-Lambert law the concentration of OH can be obtained during ignition and oxidation of hydrocarbon fuels in a shock tube. DIPK ignition delay time experiments are planned in two shock tubes (located at UCF and UF) to provide ignition and OH time-histories data for model validation.

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.

Ignition and oxidation characteristics of CO/H2, H2/O2 and CO/H2/CH4/CO2/Ar fuel blends in air were studied using both experimental and computer simulation methods. Shock-tube experiments were conducted behind reflected shock waves at intermediate temperatures (825 < T < 1400 K) for a wide range of pressures (1 < P < 45 atm). Results of this study provide the first undiluted fuel-air ignition delay time experiments to cover such a wide range of syngas mixture compositions over the stated temperature range. Emission in the form of chemiluminescence from the hydroxyl radical (OH*) transition near 307 nm and the pressure behind the reflected shock wave were used to monitor reaction progress from which ignition delay times were determined. In addition to the experimental analysis, chemical kinetics calculations were completed to compare several chemical kinetics mechanisms to the new experimental results. Overall, the models were in good agreement with the shock-tube data, especially at higher temperatures and lower pressures, yet there were some differences between the models at higher pressures and the lowest temperatures, in some cases by as much as a factor of five. In order to discern additional information from the chemical kinetics mechanisms regarding their response to a wide range of experimental conditions, ignition delay time and reaction rate sensitivity analyses were completed at higher and lower temperatures and higher and lower pressures. These two sensitivity analyses allow for the identification of the key reactions responsible for ignition. The results of the sensitivity analysis indicate that the ignition-enhancing reaction H + O2 = O + OH and hydrogen oxidation kinetics in general were most important regardless of mixture composition, temperature or pressure. However, lower-temperature, higher-pressure ignition delay time results indicate additional influence from HO2- and CO- containing reactions, particularly the well-known H + O + M = HO2 + M reaction and also the CO + O + M = CO2 + M and CO + HO2 = CO2 + OH reactions. Differences in the rates of the CO-related reactions are shown to be the cause of some of the discrepancies amongst the various models at elevated pressures. However, the deviation between the models and the experimental data at the lowest temperatures could not be entirely explained by discrepancies in the current rates of the reactions contained within the mechanisms. Additional calculations were therefore performed to gain further understanding regarding the opposing ignition behavior for calculated and measured ignition delay time results. Impurities, friction induced ionization, static charge accumulation, boundary layer effects, wall reaction effects, and revised chemical kinetics were all considered to be possible mechanisms for the model and measured data disparity. For the case of wall-reaction effects, additional shock-tube experiments were conducted. For the remaining effects listed above, only detailed calculations were conducted. Results from this preliminary anomaly study are at this time inconclusive, but likely avenues for future study were identified. Additional kinetics calculations showed that the large difference between the experimental data and the chemical kinetics models predictions at low temperatures can be explained by at least one missing reaction relevant to low-temperature and high-pressure experimental conditions involving the formation of H2O2, although further study beyond the scope of this thesis is required to prove this hypothesis both theoretically and experimentally.

There is a great interest to develop biomass combustion systems for industrial and utility applications. Improved biomass energy conversion systems are designed to provide better combustion efficiencies and environmental friendly conditions, as well as the fuel flexibility options in various applications. The gas derived from the gasification process of biomass is considered as one of the potential candidates to substitute traditional fuels in a combustion process. However, the gascomposition from the gasification process may have a wide range of variation depending on the methods and fuel sources. The better understanding of the combustion features for the Gasified Biomass Gas(GBG) is essential for the development of combustion devices to be operated efficiently and safely at the user-end. The objective of the current study is therefore aiming to achieve data associated with the combustion features of GBG fuel for improving the efficiency and stability of combustion process. The numerical result is achieved from the kinetic models of premixed combustion with a wide range of operating ranges and variety of gas compositions. The numerical result is compared with experimental data to provide a better understanding of the combustion process for GBG fuel. In this thesis the laminar flame speed and ignition delay time of the GBG fuel are analyzed, using 1-D premixed flame model and constant volume model respectively. The result from different kinetics are evaluated and compared with experimental data. The influences of initial temperature, pressure and equivalence ratio are considered, as well as the variation of gas compositions. While the general agreement is reached between the numerical result and experimental data for laminarflame speed prediction, deviations are discovered at fuel-rich region and increased initial temperature. For the ignition delay time, deviations are found in the low-temperature and low pressure regime. The empirical equations considering the influence of initial temperature,pressure and equivalence ratio are developed for laminar flame speed and ignition delay times. The influence of major compositions such as CO, H2 and hydrocarbons are discussed in details in the thesis. Furthermore, a simplified kinetic model is developed and optimized based on the evaluation of existing kinetics for GBG fuel combustion. The simplified kinetic model is expected to be used for simulating the complexc ombustion process of GBG fuel in future studies. / <p>QC 20150511</p>