The arising environmental concerns make emission reduction from combustion devices one of the greatest challenges of the century. Modern dry low-NOx emission combustion systems often operate under lean premixed turbulent conditions. In order to design and operate these systems efficiently, it is necessary to have a thorough understanding of combustion process in these devices. In premixed combustion, flame speed determines the conversion rate of fuel. The flame speed under highly turbulent conditions is defined as turbulent flame speed. Turbulent flame speed depends on laminar flame speed, which is a property of the combustible mixture. The goal of this thesis is to estimate laminar flame speed and NOx emissions under certain conditions for specific industrial gas turbines. For this purpose, an in-house one-dimensional code, GENE-AC, is used. At first, a data validation is performed in order to select an optimized chemical reaction mechanism which can be used safely with the fuels of interest in gas turbines. Results show that GRI-Mech 3.0 performs well in most cases. This mechanism is selected for further simulations. Secondly, laminar flame speed is calculated using GRI-Mech 3.0 at SGT-800 conditions. Results show that at gas turbine conditions, increasing ambient temperature and fuel to air ratio enhances flame speed, mainly due to faster reaction rates. Moreover, laminar flame speed is highly affected by fuel composition. In particular, adding hydrogen to a fuel changes chemical processes significantly, because hydrogen is relatively light and highly diffusive. Calculations are conducted over a range of equivalence ratios and hydrogen fractions in methane at atmospheric as well as gas turbine operating conditions. Results reveal some trends for changes in laminar flame speed, depending on hydrogen content in the mixture. The final part of the thesis involves the development of a reactor network model for the SGT-700 combustor in order to predict NOx emissions. The network model is built in GENE-AC based on results from available computational fluid dynamics (CFD) simulations of the combustor. The model is developed for full load conditions with variable pilot fuel ratios. The NOx emissions are predicted using GRI-Mech 3.0 mechanism. A parametric study shows the dependency of NOx emissions on equivalence ratio and residence time. For SGT-700 running on natural gas, NOx emissions are fitted to measurement data by tuning equivalence ratio and residence time. The model is then tested for a range of ambient temperatures and fuel compositions. It is found that, although the model can correctly predict the trends of ambient temperature and fuel effects on NOx emissions, these effects are to some extent over-estimated. Using future engine tests and amending calibration can improve the results.

The focus of the present work is on the empirical characterization and modeling of ignition trends of ternary blends of three distinct hydrocarbon classes, namely a methyl ester (C9H18O2), a linear alkane (n-C9H20), and a cycloalkane (MCH). Numerous surrogate biofuel formulations have been proposed in the literature, yet specific blending of these species has not been studied. Moreover, the effects of blending biofuel compounds with conventional hydrocarbons are not widely studied and a further point is the lack of studies paying specific attention to the effects of fuel variation within a given blended biofuel. To this end, a statistical Design of Experiments L9 array, comprised of 4 parameters (%MO, %MCH, pressure, and equivalence ratio) with 3 levels of variation, constructed in order to systematically study the effects of relative fuel concentrations within the ternary blend enabled variations in fuel concentration for methyl octanoate and MCH of 10% - 30% and 20% - 40%, respectively. Variation in pressure of 1 atm, 5 atm, and 10 atm and in equivalence ratio of 0.5, 1.0, and 2.0 were used, respectively. The fuel-volume percentage of n-nonane varied from 30% - 70%. In total, 10 ternary blends were studied. Ignition delay times for the ternary blends and for the three constituents were obtained by monitoring excited-state OH or CH transitions, A2Epsilon+ -> X2Pi or A2Delta -> X2Pi, respectively, behind reflected shock waves using a heated shock tube facility. Dilute conditions of 99% Ar (vol.) were maintained in all shock tube experiments with the exception of a separate series of n-nonane and MCH experiments under stoichiometric conditions which used 4% oxygen (corresponding to ~ 95% Ar dilution). Temperatures behind reflected shock waves were varied over the range 1243 < T (K) < 1672. From over 450 shock tube experiments, empirical ignition delay time correlations were constructed for all three pure fuels and a master correlation equation for the blended fuels. Ignition experiments conducted on the pure fuels at 1.5 atm indicated the following ignition delay time order, from shortest to longest: methyl octanoate < n-nonane < MCH. With increased pressure to 10 atm (nominal) the order remained, in general, consistent. Under fuel-lean conditions, ignition trends between methyl octanoate and n-nonane exhibited overlap at temperatures below 1350 K, below which the trends diverged with methyl octanoate having shorter ignition delay times. Similar behavior was observed under fuel-rich conditions, yet with the overlap occurring above 1450 K. Stoichiometric ignition trends did not display overlapping behavior under either 1.5 atm or 10 atm pressure. Laminar flame speed measurements were performed at 1 atm and an initial temperature of 443 K on the pure fuel constituents. Additional flame speed measurements of MCH were conducted at 403 K to compare with literature values and were shown to agree strongly with experiments conducted in a constant-volume apparatus. The experiments conducted herein, for the first time, measure laminar flame speeds methyl octanoate. A detailed chemical kinetics mechanism was compiled from three independent, well-validated models for the constituent fuels, where the sub-mechanisms for methyl octanoate and MCH were extracted for integration into a base n-nonane model. The compiled mechanism in the present study (4785 reactions and 1082 species) enables modeling of oxidation processes of the ternary fuel blends of interest. Calculations were performed using the compiled model relative to the base models to assess the impact of utilizing different base chemistry sets. In general, results were reproduced well relative to base models for both n-nonane and MCH, however results for methyl octanoate from both the compiled model and the base model are in disagreement with the results measured herein. Ignition delay times of the fuel blends are well-predicted for several conditions, specifically for blends at lean/high-pressure and stoichiometric/high-pressure conditions, however are not accurately modeled at fuel-rich, high-pressure conditions.

Research with heterogeneous mixtures involving solid particulate in closed, constant-volume bombs is typically limited by the powder dispersion technique. This work details the development of an experimental apparatus that promotes ideal conditions, namely a quiescent atmosphere and uniform particle distribution, for measuring laminar, heterogeneous flame propagation. In this thesis, two methods of dispersing particles are investigated. In the first, heterogeneous mixtures are made in a secondary vessel that is connected to the main experiment. Particles are dispersed into the secondary vessel by adapting a piston-driven particle injector, which has been shown to produce uniform particle distributions. The heterogeneous mixture is then transferred to the main bomb facility and ignited after laminar conditions are achieved. In the second method of dispersion, particles are directly injected into the main experimental facility using a strong blast of compressed air. As with the first approach, enough time is given (~4 minutes) for the mixture to become quiescent before ignition occurs. An extinction diagnostic is also applied to the secondary mixing vessel as well as the primary experimental facility (for both dispersion methods) to provide a qualitative understanding of the dispersion technique. To perform this diagnostic a 632.8-nm, 5-mW Helium-Neon (HeNe) laser was employed. Aluminum nano-particles with an average diameter of 100 nm were used in this study. It was found that for typical dust loadings produced with both dispersion techniques, a pure dust-air system would not ignite due to the current spark ignition system. Thus, a hybrid mixture of Al/CH4/O2/N2 was employed to achieve the project goal of demonstrating a system for controlled laminar flame speed measurements in aerosol mixtures. With the hybrid mixture, the combustion characteristics were studied both with and without the presence of nano-Al particles. Based on the experimental results, the simplicity of the "direct-injection" methodology compared to that of the "side-vessel" is desirable and will be further investigated as a viable alternative, or improvement, to the side-vessel technology.

Iso-octane, n-heptane, ethanol and their blends were tested in a constant volume combustion chamber to measure laminar burning velocities. The experimental apparatus was modified from the previous version to an automatically-controlled system. Accuracy and speed of data acquisition were improved by this modification. The laminar burning velocity analysis code was also improved for minimized error and fast calculation. A large database of laminar burning velocities at elevated temperatures and pressures was established using this improved experimental apparatus and analysis code. From this large database of laminar burning velocities, laminar flame speeds were extracted. Laminar flame speeds of iso-octane, n-heptane and blends were investigated and analysed to derive new correlations to predict laminar flame speeds of any blending ratio. Ethanol and ethanol blends with iso-octane and/or n-heptane were also examined to see the role of ethanol in the blends. Generally, the results for iso-octane and n-heptane agree with published data. Additionally, blends of iso-octane and n-heptane exhibited flame speeds that followed linear blending relationships. A new flame speed model was successfully applied to these fuels. Ethanol and ethanol blends with iso-octane and/or n-heptane exhibited a strongly non-linear blending relationship and the new flame speed model was not applied to these fuels. It was shown that the addition of ethanol into iso-octane and/or n-heptane accelerated the flame speeds. / text

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.

The combustion of petroleum-based fuels leads to the formation of several pollutants. Among them, soot particles are particularly harmful due to their severe consequences on human health. Over the past decades, strict regulations have been placed on automotive and aircraft engines to limit these particulate matter emissions. This work is primarily focused on understanding the fundamental behaviour of soot particles and their formation. Though the focus of this work is on soot formation and growth pathways, the study of the gas-phase combustion process was also an integral part to validate the mechanism. A reduced mechanism is developed with retaining the larger PAH species till coronene from KAUST-ARAMCO mechanism. Counterflow diffusion flames had emphasized the simulation of canonical configuration where the reduced mechanism is validated and the soot growth pathways are evaluated. The importance of the significant contribution of larger PAH species on the soot growth pathways in both SF and SFO flames is evident in this analysis. The sensitivity of these flames with respect to strain rates, dilution, and at higher pressures are analysed. Direct Numerical Simulation (DNS) of two-dimensional counterflow diffusion flames is conducted to understand the impact of vortex interactions on soot characteristics. The results indicate that the larger PAH species contributes to the soot formation in the air-side perturbation regimes, whereas the soot formation is dominated by the soot transport in fuel-side perturbation. The study is extended to simulate and compare coflow laminar flame using different statistical moment methods MOMIC, HMOM and CQMOM.

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.

Following stringent mandates from environmental regulatory authorities worldwide, various steps are being implemented to ensure clean combustion with minimum emissions, including fuel dilution, mild combustion and additives. Due to the need to understand combustion characteristics in primary applications (engines and turbines) with minimum emissions, the laminar burning velocity of natural gas has been measured with CO2 dilution and a wide range of blends with higher hydrocarbons. And because it has improved anti-knock quality to reduce greenhouse gas emissions (GHGE), the demand for oxygenated gasoline is now worldwide, making a compelling case for determining combustion behavior of oxygenated gasoline doped with hydrogen, ozone and carbon monoxide. The first section of this dissertation discusses dilution of methane with CO2 at elevated pressures, providing insight into comparative laminar burning characteristics in a wide range of equivalence ratios, particularly significant at elevated initial pressure. Utilizing CHEMKIN, a detailed kinetic study has been performed that explains the varying dependence on dilution ratio controlled by initial pressure. The second phase of this work reports the laminar burning velocity measurement of commercial gasoline. A TPRFE surrogate was used here to investigate burning characteristics and to provide detailed kinetic analysis of gasoline doped with additives (hydrogen, carbon monoxide and ozone). A study was also made of the behavior of gasoline with these additives in practical applications like engine and turbines. For this purpose, laminar burning velocity was measured at elevated pressures and temperatures, by varying the concentrations of synthetic EGR, and followed by measuring turbulent burning velocity at two turbulent intensities.

No description available.

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>