The dissertation discusses the details of the four following items: 1) design, assembly, and testing of a shock tube setup as well as a laser diagnostics apparatus for studying ignition characteristics of fuels and associated reaction rates, 2) measurements of methane and propanal infrared spectra at room and high temperatures using a Fourier Transformed Infrared Spectrometer (FTIR) and a shock tube , 3) measurements of ignition delay times and reaction rates during propanal thermal decomposition and ignition, and 4) investigation of ignition characteristics of methane during its combustion in carbon-dioxide diluted bath gas. The main benefit and application of this work is the experimental data which can be used in future studies to constrain reaction mechanism development.

This thesis describes a new facility and method of experimentation, which can be used to study the combustion chemistry of low-volatility fuels in the gas phase. Two main goals are described: first, the development of the aerosol shock tube and procedures; and second, a demonstration of its capabilities. There is a lack of high-quality, accurate chemical kinetics data for the oxidation of large hydrocarbons, which are important for modeling diesel, rocket, or jet engines among other combustion systems. While conventional shock tubes are very effective reactor vessels for low-molecular-weight gaseous fuels (n-alkanes up to five carbon atoms), larger fuel molecules exist as low-volatility liquids/solids, and the vapor-pressures of these fuels are not large enough for high or even moderate fuel loadings. Heating the shock tube has extended the use of shock tubes to carbon numbers of 10 to 12, but beyond that, the high temperatures prior to the shock initiation can decompose the fuel, and (for fuel mixtures like diesel) can cause fractional distillation. The question is then: how can we study low-vapor-pressure fuels in a shock tube? The solution presented here, which avoids the problems associated with heating, is called the aerosol shock tube. In the aerosol shock tube, the fuel is injected as an aerosol of micron-size droplets. Then a series of shock waves first evaporate the fuel and subsequently raise the resultant purely gas-phase mixture to combustion-relevant temperatures. With proper selection of the shock strength and timing, this process effectively decouples the mass and heat transfer processes associated with evaporation from the chemical mechanism of combustion. This enables the study of extremely low-volatility fuels, never before studied in a purely gas-phase form in a shock tube. The first application of this new facility was to measure the ignition delay time for many previously inaccessible fuels in the gas-phase. In this thesis, we have measured ignition delay times for the pure surrogate fuel components n-decane, n-dodecane, n-hexadecane, and methyl decanoate as well as for multi-component fuels such as JP-7 and multiple different blends of diesel fuel. Taken over a range of conditions, these measurements provide sensitive validation targets for their respective chemical mechanisms. These data showed agreement with past heated shock tube experiments for fuels in which premature fuel decomposition is not an issue (n-decane and low concentration n-dodecane). However, when comparing heated and aerosol shock tube ignition delay times for fuels that require significant heating, like n-hexadecane, the existing heated shock tube data demonstrated evidence of premature decomposition. The second application to the study of chemical kinetics was to measure the concentration of important species during the decomposition and oxidation of select low-vapor-pressure fuels. These species time-histories provide much more information for kinetic mechanism refinement. Experiments were performed to measure the important OH radical and the stable intermediate C2H4 for both n-hexadecane and diesel. The number of important low-vapor-pressure fuels that require high-quality validation targets is large, and our new method for providing this data has proven very effective. This work enables the development of the next generation of accurate chemical mechanisms and will be essential to their success.

We report results of high-temperature shock tube research aimed at improving knowledge of the combustion behavior of diesel, jet and related fuels. Research was conducted in four Stanford shock tube facilities and focused on the following topics: (1) development of the aerosol shock tube; (2) ignition delay time measurements of gaseous jet fuels (JP-8 and Jet-A) and surrogate components at high pressures and low temperatures; (3) laser absorption measurements of species time-histories for OH radicals and alkanes; (4) ignition delay times of n-dodecane, jet fuel and diesel using the aerosol shock tube technique; and (5) improving shock tube performance and modeling.

Experimental data for ignition delay times and species time-histories (CH4) were obtained in mixtures diluted with CO2. Experiments were performed behind reflected shockwaves from temperatures of 1200 to 2000 K for pressures ranging from 1 to 11 atm. Ignition times were obtained from emission and laser absorption measurements. Current experimental data were compared with the predictions of detailed chemical kinetic models (available from literature) that will allow for accurate design and modeling of combustion systems.

H2O time-histories were studied within the H2/O2 system using a tunable diode laser system and a pressure-driven shock tube. Stoichiometric H2/O2 mixtures were prepared in high amounts of argon dilution. The mixtures were heated using a shock tube with a driver length of 3.04 m, a driven length of 6.78 m, and an inner diameter of 16.2 cm. A tunable diode laser (TDL) was used to measure H2O concentration near the endwall region of the shock tube after the passage of the reflected shock wave, 1.6 cm from the endwall. Both the incident and transmitted beam intensities were measured using IR photodetectors. The laser was tuned to access the H2O transition at 7204 cm−1. Experiments in the H2/O2 system were performed from 1100 to 1500 K and at an average pressure of 2.8 atm. The experimental results were compared with a mechanism from Hong et al. (2011). Preliminary results show good agreement in ignition delay time between experiment and model. A computer routine was created to modify the absorption coefficient as a function of temperature to account for the temperature variation during the experiment due to the chemical reaction. After rescaling, the corrected H2O profiles showed excellent agreement with the chemical kinetics model. Topics related to mechanism validation, the potential effects of impurities, and measurement accuracy are also addressed in the thesis. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155232

Ignition times and OH radical concentration time histories were measured behind reflected shock waves in iso-octane/O2/Ar mixtures. Initial reflected shock conditions were in the ranges 1177 to 2009 K and 1.18 to 8.17 atm, with fuel concentrations of 100 ppm to 1% and equivalence ratios from 0.25 to 2. Ignition times were measured using endwall emission of CH and sidewall pressure. OH concentrations were measured using narrow-linewidth ring-dye laser absorption of the R1(5) line of the OH A-X (0,0) band at 306.5 nm. The ignition time data and OH concentration time history measurements were compared to model predictions of four current iso-octane oxidation mechanisms, and the implications of these comparisons are discussed. To our knowledge, these data provide the first extensive measurements of low fuel-concentration ignition times and OH concentration time histories for iso-octane auto-ignition, and hence provide a critical contribution to the database needed for validation of a detailed mechanism for this primary reference fuel.

This dissertation focuses on the development of two experimental approaches for the study of low-temperature combustion kinetics in a shock tube: a combined laser absorption spectroscopy-gas chromatography (LAS-GC), fast-sampling speciation diagnostic, and a method for measuring laminar flame speeds in a shock tube at previously unexplored temperature conditions. The combined LAS-GC speciation technique was developed in three stages. First, an endwall sampling system was developed to provide species yield measurements in conventional shock tube experiments. The diagnostic was paired with an in situ ethylene laser absorption diagnostic and used to study ethylene pyrolysis at conditions ranging from 1200-2000 K at 5 atm. A methodology for accurately comparing species-yield sampling results with laser and model results is also presented. In the second stage of GC fast-sampling technique development, the endwall sampling system was used to study low-temperature n-heptane oxidation. Quasi-time-resolved endwall samples were extracted and used to quantify intermediate species present between first- and second-stage n-heptane ignition. Three laser diagnostics were simultaneously employed to measure temperature, carbon dioxide, water, and ethylene. Laser-measured ignition delay times indicate an overestimation of three primary RO2 isomerization reactions in the kinetic model used for comparison. In the third stage of technique development, long test-time shock tube experiments were conducted to allow for three consecutive, 10-ms samples to be extracted from the reacting shock tube gas before the arrival of the expansion fan. This time-resolved, fast-sampling technique was applied to the study of cyclohexene pyrolysis (980-1150 K, 7.3 atm) and ethane pyrolysis (1060-1153 K, 6.9 atm). A time-resolved ethylene laser diagnostic was simultaneously used to provide truly time-resolved, in situ results. A discrepancy between late-time GC and laser/model results was found to be caused by endwall thermal boundary layer growth. In addition to the combined LAS-GC experimental approach, a new shock tube technique was developed for measuring high-temperature (> 500 K) laminar flame speeds. Shock-heated gas mixtures are ignited via laser-induced spark-ignition and high-speed, endwall emission imaging is used to capture flame propagation in time. The technique was validated by measuring stoichiometric methane/air and propane/air flame speeds at 1 atm and unburned gas temperatures below 600 K. Stoichiometric, 1-atm, propane/modified-air flame speeds were then recorded at unburned gas temperatures exceeding 750 K, representing the highest-temperature propane laminar flame speed data available to date. Next, single line-of-sight laser absorption diagnostics were deployed in the flame speed experiments, allowing for the simultaneous measurement of laminar flame speed, temperature, species, and pressure in high-temperature, spherically expanding ethane/air flames (449-537 K, 1 atm). The burned gas, equilibrium temperature and species measurements, as well as the flame speed measurements, show close agreement with model results.