A new shock tube targeting low temperature, high pressure, and long test times was designed and installed at the Turbomachinery Laboratory in December of 2008. The single-pulse shock tube uses either lexan diaphragms or die-scored aluminum disks of up to 4 mm in thickness. The modular design of the tube allows for optimum operation over a large range of thermodynamic conditions from 1 to 100 atm and between 600-4000 K behind the reflected shock wave. The new facility allows for ignition delay time, chemical kinetics, high-temperature spectroscopy, vaporization, atomization, and solid particulate experiments. An example series of ignition delay time experiments was made on mixtures of CH4/C2H6/O2/Ar at pressures from 1 to 30.7 atm, intermediate temperatures from 1082 to 2248 K, varying dilutions (between 75 and 98% diluent), and equivalence ratios ranging from fuel lean (0.5) to fuel rich (2.0) in this new facility. The percentage by volume variation and equivalence ratios for the mixtures studied were chosen to cover a wide parameter space not previously well studied. Results are then used to validate and improve a detailed kinetics mechanism which models the oxidation and ignition of methane and other higher order hydrocarbons, through C4, with interest in further developing reactions important to methane- and ethane-related chemistry.

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.

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.

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>

No description available.

Applications of natural gases that contain high levels of hydrogen have become a primary interest in the gas turbine market. For reheat gas turbines, understanding of the ignition delay times of high-hydrogen natural gases is important for two reasons. First, if the ignition delay time is too short, autoignition can occur in the mixer before the primary combustor. Second, the flame in the secondary burner is stabilized by the ignition delay time of the fuel. While the ignition delay times of hydrogen and of the individual hydrocarbons in natural gases can be considered well known, there have been few previous experimental studies into the effects of different levels of hydrogen on the ignition delay times of natural gases at gas turbine conditions. In order to examine the effects of hydrogen content at gas turbine conditions, shock-tube experiments were performed on nine combinations of an L9 matrix. The L9 matrix was developed by varying four factors: natural gas higher-order hydrocarbon content of 0, 18.75, or 37.5%; hydrogen content of the total fuel mixture of 30, 60, or 80%; equivalence ratios of 0.3, 0.5, or 1; and pressures of 1, 10, or 30 atm. Temperatures ranged from 1092 K to 1722 K, and all mixtures were diluted in 90% Ar. Correlations for each combination were developed from the ignition delay times and, using these correlations, a factor sensitivity analysis was performed. It was found that hydrogen played the most significant role in ignition delay time. Pressure was almost as important as hydrogen content, especially as temperature increased. Equivalence ratio was slightly more important than hydrocarbon content of the natural gas, but both were less important than pressure or hydrogen content. Further analysis was performed using ignition delay time calculations for the full matrix of combinations (27 combinations for each natural gas) using a detailed chemical kinetics mechanism. Using these calculations, separate L9 matrices were developed for each natural gas. Correlations from the full matrix and the L9 matrix for each natural gas were found to be almost identical in each case, verifying that a thoughtfully prepared L9 matrix can indeed capture the major effects of an extended matrix.

Indiana University-Purdue University Indianapolis (IUPUI) / Investigations of a constant-volume combustor ignited by a penetrating transient jet (a puff) of hot reactive gas have been conducted in order to provide vital data for designing wave rotor combustors. In a wave rotor combustor, a cylindrical drum with an array of channels arranged around the axis spins at a high rpm to generate high-temperature and high-pressure product gas. The hot-gas jet ignition method has been employed to initiate combustion in the channels. This study aims at experimentally investigating the ignition delay time of a premixed combustible mixture in a rectangular, constant-volume chamber, representing one channel of the wave rotor drum. The ignition process may be influenced by the multiple factors: the equivalence ratio, temperature, and the composition of the fuel mixture, the temperature and composition of the jet gas, and the peak mass flow rate of the jet (which depends on diaphragm rupture pressure). In this study, the main mixture is at room temperature. The jet composition and temperature are determined by its source in a pre-chamber with a hydrogen-methane mixture with an equivalent ratio of 1.1, and a fuel mixture ratio of 50:50 (CH4:H2 by volume). The rupture pressure of a diaphragm in the pre-chamber, which is related to the mass flow rate and temperature of the hot jet, can be controlled by varying the number of indentations in the diaphragm. The main chamber composition is varied, with the use of four equivalence ratios (1.0, 0.8, 0.6, and 0.4) and two fuel mixture ratios (50:50, and 30:70 of CH4:H2 by volume). The sudden start of the jet upon rupture of the diaphragm causes a shock wave that precedes the jet and travels along the channel and back after reflection. The shock strength has an important role in fast ignition since the pressure and the temperature are increased after the shock. The reflected shock pressure was examined in order to check the variation of the shock strength. However, it is revealed that the shock strength becomes attenuated compared with the theoretical pressure of the reflected shock. The gap between theoretical and measured pressures increases with the increase of the Mach number of the initial shock. Ignition delay times are obtained using pressure records from two dynamic pressure transducers installed on the main chamber, as well as high-speed videography using flame incandescence and Schileren imaging. The ignition delay time is defined in this research as the time interval from the diaphragm rupture moment to the ignition moment of the air/fuel mixture in the main chamber. Previous researchers used the averaged ignition delay time because the diaphragm rupture moment is elusive considering the structure of the chamber. In this research, the diaphragm rupture moment is estimated based on the initial shock speed and the longitudinal length of the main chamber, and validated with the high-speed video images such that the error between the estimation time and the measured time is within 0.5%. Ignition delay times decrease with an increase in the amount of hydrogen in the fuel mixture, the amount of mass of the hot-jet gases from the pre-chamber, and with a decrease in the equivalence ratio. A Schlieren system has been established to visualize the characteristics of the shock wave, and the flame front. Schlieren photography shows the density gradient of a subject with sharp contrast, including steep density gradients, such as the flame edge and the shock wave. The flame propagation, gas oscillation, and the shock wave speed are measured using the Schlieren system. An image processing code using MATLAB has been developed for measuring the flame front movement from Schlieren images. The trend of the maximum pressure in the main chamber with respect to the equivalence ratio and the fuel mixture ratio describes that the equivalence ratio 0.8 shows the highest maximum pressure, and the fuel ratio 50:50 condition reveals lower maximum pressure in the main chamber than the 30:70 condition. After the combustion occurs, the frequency of the pressure oscillation by the traversing pressure wave increases compared to the frequency before ignition, showing a similar trend with the maximum pressure in the chamber. The frequency is the fastest at the equivalence ratio of 0.8, and the slowest at a ratio of 0.4. The fuel ratio 30:70 cases show slightly faster frequencies than 50:50 cases. Two different combustion behaviors, fast and slow combustion, are observed, and respective characteristics are discussed. The frequency of the flame front oscillation well matches with that of the pressure oscillation, and it seems that the pressure waves drive the flame fronts considering the pressure oscillation frequency is somewhat faster. Lastly, a feedback mechanism between the shock and the flame is suggested to explain the fast combustion in a constant volume chamber with the shock-flame interactions.