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Effusion cooling in gas turbine combustors is complicated by swirling flows for anchoring flame, whereas miniature effusion cooling jets are highly directional. This work aims at understanding the ...

Atomization plays an important role in the gasification or combustion of bio-oils, where the atomizer parameters need to be properly controlled to efficiently atomize a highly viscous liquid at elevated pressures with imparting the least amount of kinetic energy to the discharged droplets because of evaporation and chemical reaction constraints. With a focus on bio-oil deployments in microgas turbines (MGTs), an aqueous surrogate of a preheated bio-oil, injected from an original equipment manufacturer (OEM) twin-fluid atomizer, is used in the present study for spray size and velocity measurements at elevated pressures. The experiments were conducted in High Pressure Spray Facility of the National Research Council of Canada (NRC) using various optical diagnostics including laser sheet imaging (LSI), phase Doppler anemometry (PDA), and laser diffraction (LD). A scaling strategy was adopted to conserve the ranges of gas-to-liquid momentum flux ratio, M, at different working pressures, P. Over the range of conditions studied, it is found out that the cone angle of sprays is insensitive to P, but they decrease with increasing M. For a constant value of M, droplet mean diameters increase and their corresponding velocities decrease with increasing P, attributed to the effect of gas-to-liquid density ratio on the primary breakup of a liquid jet in a coaxial gas stream. Therefore, to estimate the Sauter mean diameter of spray droplets, D32, a correlation previously reported in the literature is modified by including the effect of system air density at elevated pressures, and a novel correlation is proposed based on four dimensionless groups, namely, gas Weber number and gas-to-liquid momentum flux ratio, density ratio, and viscosity ratio. The detailed results obtained in the present study could be used to define the optimal parameters required for twin-fluid atomization of high viscosity liquids with various atomization gases under realistic operating conditions and to enhance the capabilities of their numerical simulations.

An experimental study was conducted for evaluating the feasibility of using silica aerogel as thermal insulator for combustor liners. Aerogels are a superior material for minimizing heat flux to the metal structure of the combustion liner due to their low thermal conductivity. In this study, a conical natural gas fired swirling-flame combustor was utilized for reproducing the combustion environment. The silica aerogel blanket was attached to the inner side of a perforated combustor liner. Temperature distribution on the outer side of the combustion liner was measured using a calibrated IR camera. To create a protective cooling film over the aerogel surface, cooling air was supplied from the back side of the perforated metal liner and was allowed to penetrate the silica aerogel blanket to be discharged to the combustor. As the combustor was operated at a fixed equivalence ratio of 0.83, cooling air flow rates were varied to evaluate the effectiveness of transpiration cooling on the aerogel blanket as various cooling flow rates. The measured evolution of temperature distribution confirmed thermal equilibriums for every test condition with transpiration cooling. The measured temperature distribution of metal liner demonstrated superior thermal insulation of aerogel blanket under the protection of cooling film with a temperature difference as high as 1580 K between combustion products temperature and the metal liner temperature on the back side. In addition, silica aerogel samples were examined before and after the combustion tests to understand their material degradation exposing to a typical gas turbine combustor environment using high-resolution scanning electron microscope (SEM). Test results suggest multiple degradation mechanisms to the silica aerogel blanket samples from the combustion tests. Improvements can be made to the silica aerogel blankets for a more resilient thermal insulator, for example, by replacing glass fibers in silica aerogels.

This study examines the feasibility of using fast pyrolysis bio-oil (FPBO) made from non-food woody biomass in a micro-gas turbine with a unique burner design, motivated by the recent surge in the development of renewable carbon-neutral biomass-derived liquids in energy applications. The study is comprehensive and covers FPBO production and applications, physicochemical properties and spray characteristics, and combustion performance. The effects of fuel spray formation and preparation on the combustion of FPBO, ethanol (EtOH) and diesel fuel were investigated using two twin-fluid nozzles with distinct atomization mechanisms, externally- and internally-mixed, and a premixer tube. In contrast to diesel fuel and EtOH, reaching a stable flame using 100% FPBO was impossible because of the fuel polymerization (or coking) when impinging on the high-temperature inner wall of the premixer tube. EtOH addition was, therefore, used to address the problem by improving the FPBO's volatility. The FPBO spray flame generated by the internally-mixed nozzle exhibited less gas- and solid-phase emissions than the externally-mixed one and required less EtOH addition for stabilization. While this study shows the feasibility for deployment of FPBO in the present micro-gas turbine design, injector modification or fuel upgrading are necessary prior to it being used to replace fossil oils.

Effusion cooling is a method found in modern aeroengine combustors which produces a protective cooling film over the inner surface of combustor liners combined with heat removal from the metal liner as cooling air passes effusion holes. A complication to effusion cooling in gas turbine combustors is that swirling flows are usually utilized for anchoring flame whereas miniature effusion cooling jets emanating from effusion cooling holes are highly directional. A direct consequence of swirling flow pattern is varying angles between the main flow and cooling jets. This work aims at understanding the directional effects of effusion cooling by studying the effectiveness of cooling film as a function of the offset flow angle (β) between the main flow and effusion cooling jets. The cooling film effectiveness is investigated with the effusion cooling miniature jets at a range of angles between parallel and perpendicular to the main flow at 30° intervals, namely at offset angles of 0°, 30°, 60° and 90°. The cooling film effectiveness is determined by invoking the heat/mass transfer analogy using Pressure Sensitive Paint (PSP) that is sensitive to the oxygen partial pressure at the paint surface. An experimental setup is designed and fabricated based on a low-speed wind tunnel at the National Research Council Canada’s Aerospace Research Center. Experimental results indicate that offset angles (β) have a strong effect on the cooling film effectiveness. At lower coolant mass flow rates an offset angle increases the uniformness of the cooling film, as the flow from each individual hole coalesces together to form the protective film. At higher coolant mass flow rates the cooling film effectiveness is less sensitive to the offset angles (β). This is believed to be caused by the coolant flow lifting off the surface and dissipating more easily in the mainstream flow., AIAA Scitech 2021 Forum, January 11-15, 2021, Virtual Event

There exists more than 280 communities in Canada that are not connected to North American electric grid due to geographic limitations. This work studies the efficiency gains from an engineering perspective as well as the potential economic benefits from complementing a Micro Gas Turbine (MGT) based micro grid with Battery Energy Storage System (BESS) to form a hybrid energy system to meet the power need, and potentially the heat need, of these geographically isolated communities. A yearly averaged profile of power demand from a typical Canadian household with 5-min resolution was adopted to represent the end users of the micro grid. The Capstone C30 of a nominal power rating of 30 KWe is the base MGT power unit assumed for this study. Considering only one cold start of the MGT per day, it was found that an operating strategy to start the MGT between 8 and 10 am minimizes the size of the battery system with an imposed restriction of operating the MGT above 90 percent of its base load; the minimum engine load requirement is designed to achieve the best system efficiency. The minimum size of the usable storage capacity of the BESS is estimated for meeting the energy storage needs for the aforementioned operating strategy. Finally, the economy of a MGT-based hybrid system is assessed by estimating the unit energy price., AIAA Propulsion and Energy 2020 Forum, Virtual Event

One solution to achieving a large scale distribution, transportation and storage of renewable energy is methanol production from renewable-based power plants integrated with hydrogenation. In this study, a novel non-combustion heat-carrier biomass gasifier system is proposed, coupled with a large-scale solar power plant and alkaline water electrolysis system, for methanol production from syngas, water and carbon dioxide. Aspen Plus, MATLAB and TRNSYS are used to simulate and assess the performance of each component of the proposed system, under different climatic conditions of Toronto, Canada, and Crotone, Italy. In both localities, the best energy performance that minimizes the grid energy interaction factor is obtained with a photovoltaic station of 50.4 MW coupled to biomass gasification, which leads to 0.60 kWh and 0.57 kWh, respectively, in Toronto and Crotone, of electricity sent to or drawn from the grid for each kWh required by the electrolyser. However, higher profitability may be achieved in both localities with a single biomass gasification system which brings an enhanced benefit of 0.56 M€ in Toronto and 0.44 M€ in Crotone for each kW installed. It is expected that the developed modelling approach and these four newly formulated dimensionless indicators, i.e., the satisfied load fraction, utilization factor, grid energy interaction factor, and grid economic interaction value can be used to evaluate large-scale integrated renewable-based power systems.

Inherent fuel flexibility of micro gas turbine (MGT) makes the engine a promising energy solution to remote Canadian communities that are not connected to the North American electricity grid, where bio-oils derived from locally available bio-mass may be utilized to meet local power and heat demands to reduce fossil fuel consumption. The switch to bio-oils enabled by MGTs reduces not only carbon footprints but also operating expenses due to high transportation costs of fossil fuels. However, MGT efficiencies are greatly reduced at partial loads. This work investigates the feasibility of addressing MGT efficiency drops at partial loads by incorporating MGT with a Battery Energy Storage System (BESS) to form a hybrid system so that the MGT can be operated at near full power at all times for better efficiencies. In this study, a daily power demand profile of a typical Canadian household is adopted for optimizing battery size and MGT operating strategies. By optimizing MGT daily start time and the engine's threshold partial load factor, the specific fuel consumption and battery size can be minimized for a specific number of households on a micro-grid supported by the MGT-based hybrid power system.

Air-assisted atomization of the sprays produced by injecting different types of highly viscous pyrolysis oils are studied. Different breakup and atomization regimes are characterized using the long distance microscopic imaging technique. The high resolution imaging reveals detailed underlying two-phase interactions in pyrolysis oil injection that are found unlike other conventional liquid fuels. Several cases of droplet size characterization are carried out using the Malvern’s laser diffraction measurements under variable liquid flow rates, atomizing air flow rates and oil preheating temperatures. The time-averaged and high resolution instantaneous images reveal that the highly viscous nature of pyrolysis oils prevent the instability mechanisms from efficiently atomizing the liquid. The present broad set of measured data suggest that the atomization quality of pyrolysis oils can be optimized by applying a combination of liquid preheating and air-assisted atomization. The flow visualizations reveal the transition from ligament-dominated two-phase flow field into fully atomized sprays when proper oil preheating temperatures and sufficient atomizing air flow rates are provided. Visualized observations are quantitatively verified using the droplet size distribution measurements as well as the Sauter mean diameter (SMD) values for several measurement conditions.

The influence of atomization on spray, combustion, and gas- and solid-phase emissions was investigated experimentally for a fast pyrolysis bio-oil (FPBO), also known as bio-oil or pyrolysis oil, in a 10 kW swirl burner. Two different single-hole twin-fluid nozzles, namely externally-mixed and internally-mixed, with the same equivalent exit diameter were studied for applications in micro gas turbine engines. Over the range of air-to-liquid mass flow ratio, 0.25 A L R 0.65 , the spray generated by the internally-mixed nozzle comprised finer droplets with approximately 50% smaller diameter than the externally-mixed one. Two empirical correlations were modified for the prediction of Sauter mean diameter (SMD) of the droplets generated by each nozzle. The combustion tests showed that while reaching a 100% FPBO stable flame was possible using the internally-mixed nozzle, 10% by volume fraction ethanol (EtOH) was needed when using the externally-mixed one to improve the volatility and subsequent ignition characteristics of the larger size fuel droplets generated by this nozzle. The quantitative pollutant emissions measurements also demonstrated that, using 90/10 FPBO/EtOH as a fuel and at the same ALR, the spray flame generated by the internally-mixed nozzle had less pollutant emissions than the externally-mixed one due to the atomization effects. Conducting combustion tests in conjunction with spray testing showed that, while the spray SMD plays a critical role in the ignition and combustion of FPBO, other flow-field characteristics such as near nozzle shear-forces and hot-zone residence times of droplets are also important in generating a stable 100% FPBO flame with minimum emissions.

This article provides a comprehensive review of the spray combustion of fast pyrolysis bio-oil (FPBO, also called bio-oil, pyrolysis oil or pyrolysis liquid biofuel), which is widely regarded as one of the most economically feasible renewable resources to facilitate the replacement of fossil oils. The utilization of FPBO as a fuel is challenging due to its unique atomization and combustion characteristics but it is important given the need to develop a more sustainable energy infrastructure. Significant efforts have been made in utilizing FPBO as a practical alternative fuel and the first FPBO facilities for heat and/or power generation have been brought online in recent years. FPBO-fueled burners, boilers, and furnaces are ready from a technical perspective for large-scale industrial use, and even small-scale systems show excellent flame stability, low emissions, and minimal requirements for secondary fuel usage. FPBO applications in gas turbine and compression-ignition engines are technically more challenging, currently having had only limited successes in larger-scale units and for short time intervals in smaller ones. With recent research and technological advances, however, FPBO use in small-scale combustion engines appears to be technically feasible. In the literature, extensive research efforts have been dedicated to this topic either as a fuel itself or its utilization for practical applications. Nonetheless, inadequate considerations have been given to the critical role of FPBO atomization and its subsequent fuel/air mixing, which in turn controls the combustion efficiency and emission characteristics of a system. Understanding the spray combustion properties of FPBO is especially important because of the fuel's unfavorable properties compared to fossil oils including low energy density, high viscosity, high water content, containing suspended solid particulates and non-volatile residue, chemical instability, and an incompatibility with conventional fossil oils. The information presented herein, therefore, focuses on understanding the challenges and constraints that are unique to FPBO applications, along with proposing several strategies to properly atomize and combust this fuel in order to enhance combustion efficiency and reduce pollutant emissions in practical systems. Although substantial progress has been made in understanding the FPBO spray combustion as revealed by this review, better standardization of FPBO properties, more efficient techniques for optimizing atomization and combustion for different applications, and more studies to understand the long-term reliability of devices running on FPBO are needed.

Hydrogen peroxide (H 2 O 2 ) and hydroperoxy (HO 2 ) reactions present in the H 2 O 2 thermal decomposition system are important in combustion kinetics. H 2 O 2 thermal decomposition has been studied behind reflected shock waves using H 2 O and OH diagnostics in previous studies (Hong et al. (2009) [9] and Hong et al. (2010) [6,8]) to determine the rate constants of two major reactions: H 2 O 2 + M → 2OH + M ( k 1 ) and OH + H 2 O 2 → H 2 O + HO 2 ( k 2 ). With the addition of a third diagnostic for HO 2 at 227 nm, the H 2 O 2 thermal decomposition system can be comprehensively characterized for the first time. Specifically, the rate constants of two remaining major reactions in the system, OH + HO 2 → H 2 O + O 2 ( k 3 ) and HO 2 + HO 2 → H 2 O 2 + O 2 ( k 4 ) can be determined with high-fidelity. No strong temperature dependency was found between 1072 and 1283 K for the rate constant of OH + HO 2 → H 2 O + O 2 , which can be expressed by the combination of two Arrhenius forms: k 3 = 7.0 × 10 12 exp(550/ T ) + 4.5 × 10 14 exp(−5500/ T ) [cm 3 mol −1 s −1 ]. The rate constants of reaction HO 2 + HO 2 → H 2 O 2 + O 2 determined agree very well with those reported by Kappel et al. (2002) [5]; the recommendation therefore remains unchanged: k 4 = 1.0 × 10 14 exp(−5556/ T ) + 1.9 × 10 11+ exp(709/ T ) [cm 3 mol −1 s −1 ]. All the tests were performed near 1.7 atm.

High-temperature 3-pentanone pyrolysis and oxidation studies were performed behind reflected shock waves using laser-based species time-history measurements (3-pentanone, CH 3 , CO, C 2 H 4 , OH and H 2 O) and ignition delay time measurements. The overall 3-pentanone decomposition rate coefficient was inferred from the measured 3-pentanone and CH 3 time-histories during pyrolysis at temperatures of 1070–1530 K and a pressure of 1.6 atm., and yielded a mathematical expression for k tot = 4.383 × 10 49 T −10 exp(−44,780/T) s −1 with an uncertainty of ±35% over 1070–1330 K. The measured species time-histories and ignition delay times were also compared to simulations from a detailed kinetic mechanism of Serinyel et al. (2010) [14] . The measured k tot was approximately 3.5 times faster than the value used by Serinyel et al. Additionally, the absence of a methyl ketene decomposition reaction was identified as the cause of a deficiency in the O-atom balance of the measured 3-pentanone and CO time-histories. Using the revised overall 3-pentanone decomposition rate coefficient and an additional methyl ketene decomposition pathway, the modified mechanism was able to successfully simulate all six species time-histories, and showed a significant improvement in the predictions of ignition delay times. Finally, a comparison of ignition delay times and OH species time-histories during 3-pentanone, 2-pentanone and acetone oxidation found that 3-pentanone was the most reactive of the three ketones.

HO 2 and CH 3 are major intermediate species presented during the oxidation of natural gas at intermediate temperatures and high pressures. Previous theoretical calculations have identified several product channels for HO 2 and CH 3 reactions, with CH 3 + HO 2 → CH 3 O + OH and CH 3 + HO 2 → CH 4 + O 2 being the dominant reaction pathways. Both reaction pathways play an important role in the kinetics of CH 4 oxidation as CH 3 + HO 2 → CH 3 O + OH is a chain-branching reaction whereas CH 3 + HO 2 → CH 4 + O 2 a chain termination reaction. H 2 O 2 /CH 4 /Ar mixtures were shock-heated to a temperature between 1054 and 1249 K near 3.5 atm to initiate the reaction. OH radicals yielded from H 2 O 2 thermal decomposition react with H 2 O 2 and CH 4 respectively to produce HO 2 and CH 3 in the reacting system. Using laser absorption spectroscopy, time-histories of H 2 O, OH and HO 2 were measured behind reflected shock waves. The rate constant of reaction CH 3 + HO 2 → CH 3 O + OH was determined to be 6.8 × 10 12 cm 3 mol −1 s −1 with an uncertainty factor of 1.4. The rate constant of the competing CH 3 + HO 2 → CH 4 + O 2 reaction was determined to be 4.4 × 10 12 cm 3 mol −1 s −1 , with an uncertainty factor of 2.1. In addition, the rate constants of two other major reactions of the reacting system, H 2 O 2 (+M) → 2OH (+M) and OH + CH 4 → CH 3 O + OH, were found to have excellent agreement with values recommended in literature.

Absorption coefficient data are presented for molecular oxygen at temperatures between 1100 and 2000 K and discrete wavelengths between 211 and 235 nm. Measurements were made behind reflected shock waves using broad-linewidth ultraviolet laser radiation generated from a frequency-quadrupled, tunable, pulsed Ti:Sapphire laser. Test mixtures consisting of 15% O 2 , 15% He and balance Ar were used to minimize the influence of vibrational relaxation on the reflected shock temperature. The experimental results are in good agreement with theoretical calculations and confirm that discrete features from the Schumann–Runge system dominate between 211 and 235 nm at temperatures higher than 1100 K.

Ignition delay times were measured behind reflected shock waves for cyclohexane, methylcyclohexane, and n-butylcyclohexane at 1.5 and 3 atm, equivalence ratios near 1 and 0.5, and temperatures between 1280 and 1480 K. The observed ignition delay times can be summarized as follows: methylcyclohexane > n-butylcyclohexane ≈ cyclohexane. Several reasons are suggested to explain the ordering of the ignition delay times for these three naphthenes. We believe that this work provides the first set of ignition delay time data for n-butylcyclohexane. In addition, H2O and OH time-histories were recorded during the oxidation of cyclohexane, methylcyclohexane, n-butylcyclohexane, iso-octane and n-heptane under similar test conditions. OH time-histories near time zero are distinctive for each type of fuel studied, and these early-time OH profiles provides critical insight into the influence of molecular structures on ignition behavior, particularly in the case of the cycloalkanes. Comparisons of measured time-histories with simulations from recent cycloalkane oxidation mechanisms are also presented.

An updated H2/O2 reaction mechanism is presented that incorporates recent reaction rate determinations in shock tubes from our laboratory. These experiments used UV and IR laser absorption to monitor species time-histories and have resulted in improved high-temperature rate constants for the following reactions: H + O 2 = OH + O H 2 O 2 ( + M ) = 2 OH ( + M ) OH + H 2 O 2 = HO 2 + H 2 O O 2 + H 2 O = OH + HO 2 The updated mechanism also takes advantage of the results of other recent rate coefficient studies, and incorporates the most current thermochemical data for OH and HO2. The mechanism is tested (and its performance compared to that of other H2/O2 mechanisms) against recently reported OH and H2O concentration time-histories in various H2/O2 systems, such as H2 oxidation, H2O2 decomposition, and shock-heated H2O/O2 mixtures. In addition, the mechanism is validated against a wide range of standard H2/O2 kinetic targets, including ignition delay times, flow reactor species time-histories, laminar flame speeds, and burner-stabilized flame structures. This validation indicates that the updated mechanism should perform reliably over a range of reactant concentrations, stoichiometries, pressures, and temperatures from 950 to greater than 3000 K.

Species concentration time-histories were measured during oxidation for the large, normal-alkane, diesel-surrogate component n -hexadecane. Measurements were performed behind reflected shock waves in an aerosol shock tube, which allowed for high fuel loading without pre-test heating and possible decomposition and oxidation. Experiments were conducted using near-stoichiometric mixtures of n -hexadecane and 4% oxygen in argon at temperatures of 1165–1352 K and pressures near 2 atm. Concentration time-histories were recorded for five species: C 2 H 4 , CH 4 , OH, CO 2 , and H 2 O. Methane was monitored using DFG laser absorption near 3.4 μm; OH was monitored using UV laser absorption at 306.5 nm; C 2 H 4 was monitored using a CO 2 gas laser at 10.5 μm; and CO 2 and H 2 O were monitored using tunable DFB diode laser absorption at 2.7 and 2.5 μm, respectively. These time-histories provide critically needed kinetic targets to test and refine large reaction mechanisms. Comparisons were made with the predictions of two diesel-surrogate reaction mechanisms (Westbrook et al. [1] ; Ranzi et al. [9] ) that include n -hexadecane, and areas of needed improvement in the mechanisms were identified. Comparisons of the intermediate product yields of ethylene for n -hexadecane with those found for other smaller n -alkanes, show that an n -hexadecane mechanism derived from a simple hierarchical extrapolation from a smaller n -alkane mechanism does not properly simulate the experimental measurements.

The rate coefficient of the reaction H + O2 → OH + O was determined using tunable diode laser absorption of H2O near 2.5 μm behind reflected shock waves over the temperature range 1100–1530 K, at approximately 2 atm. Detailed kinetic analysis of the recorded H2O temporal profiles yielded the rate coefficient expression: k = (1.12 ± 0.08) × 1014 exp [(−7805 ± 90)/T] cm3 mol−1 s−1, with estimated uncertainties of ±4.6% at 1500 K and ±8.8% at 1100 K. Excellent agreement between this study and that of Masten et al. (1990) was found in the overlapping temperature range. By combining the results of these two studies, the reaction rate coefficient over the range 1100–3370 K was found to be described well by: k = ( 1.04 ± 0.03 ) × 10 14 exp [ ( - 7705 ± 40 ) / T ] cm 3 mol - 1 s - 1 .

Shock tube measurements of ignition delay times with high activation energies are strongly sensitive to variations in reflected shock temperatures. At longer shock tube test times, as are needed at low reaction temperatures, small gradual increases in pressure (and simultaneous increases in temperature) that result from incident shock wave attenuation and boundary layer growth can significantly shorten measured ignition delay times. To obviate this pressure increase, we made use of a recently developed driver-insert method of Hong et al. [8] that allows generation of near-constant-volume test conditions for reflected shock measurements. Using this method, we have measured propane ignition delay times in a lean mixture (0.8% C 3 H 8 /8% O 2 /Ar) over temperatures between 980 and 1400 K and nominal pressures of 6, 24 and 60 atm, under both conventional shock tube operation (with post-shock fractional pressure variation d P 5 /d t ∼ 1–7%/ms) and near-constant-volume operation (with d P 5 /d t ∼ 0%/ms). The near-constant-volume ignition delay times provide a database for low-temperature propane model development that is independent of non-ideal fluid flow and heat transfer effects. Comparisons of these near-constant-volume measurements with predictions using the JetSurF v1.0 mechanism of Sirjean et al. [10] and the Curran et al. mechanism of NUI Galway [5] were performed. Ignition delay times measured with d P 5 /d t ∼ 1–7%/ms were found to be significantly shorter (about 1/3 of the near-constant-volume values) at the lowest temperatures and highest pressures studied. However, these ignition times are successfully simulated using the JetSurF v1.0 mechanism when an appropriate gasdynamic model that accounts for changes in pressure and temperature is used.

Reaction rates of hydroxyl (OH) radicals with ethylene (C₂H₄) and propene (C₃H₆) were studied behind reflected shock waves. OH + ethylene → products (rxn 1) rate measurements were conducted in the temperature range 973-1438 K, for pressures from 2 to 10 atm, and for initial concentrations of ethylene of 500, 751, and 1000 ppm. OH + propene → products (rxn 2) rate measurements spanned temperatures of 890-1366 K, pressures near 2.3 atm, and initial propene concentrations near 300 ppm. OH radicals were produced by shock-heating tert-butyl hydroperoxide, (CH₃)₃-CO-OH, and monitored by laser absorption near 306.7 nm. Rate constants for the reactions of OH with ethylene and propene were extracted by matching modeled and measured OH concentration time-histories in the reflected shock region. Current data are in excellent agreement with previous studies and extend the temperature range of OH + propene data. Transition state theory calculations using recent ab initio results give excellent agreement with our measurements and other data outside our temperature range. Fits (in units of cm³/mol/s) to the abstraction channels of OH + ethylene and OH + propene are k₁ = 2.23 × 10⁴ (T)(2.745) exp(-1115 K/T) for 600-2000 K and k₂ = 1.94 × 10⁶ (T)(2.229) exp(-540 K/T) for 700-1500 K, respectively. A rate constant determination for the reaction TBHP → products (rxn 3) was also obtained in the range 745-1014 K using OH data from behind both incident and reflected shock waves. These high-temperature measurements were fit with previous low-temperature data, and the following rate expression (0.6-2.6 atm), applicable over the temperature range 400-1050 K, was obtained: k₃ (1/s) = 8.13 × 10⁻¹² (T)(7.83) exp(-14598 K/T).

Concentration time-histories were measured behind reflected shock waves during n -heptane oxidation for five species: n -heptane, C 2 H 4 , OH, CO 2 , and H 2 O. Experiments were conducted at temperatures of 1300–1600 K and a pressure of 2 atm using a mixture of 300 ppm n -heptane and 3300 ppm oxygen ( ϕ = 1) in argon. n -Heptane and ethylene were monitored using IR gas laser absorption at 3.39 and 10.53 μm, respectively; OH was monitored using UV laser absorption at 306.5 nm; and CO 2 and H 2 O were monitored using tunable IR diode laser absorption at 2.7 and 2.5 μm, respectively. These time-histories provide kinetic targets to test and refine large reaction mechanisms for n -heptane and demonstrate the potential of this type of data for validation of large reaction mechanisms. Comparisons are made with the predictions of several recently developed reaction mechanisms.

The rate constant of the reaction OH + HO(2) --> H(2)O + O(2) (1) can be inferred at high temperatures from measurements of the rate of its reverse reaction H(2)O + O(2) --> OH + HO(2) (-1). In this work, we used laser absorption of both H(2)O and OH to study the reverse reaction in shock-heated H(2)O/O(2)/Ar mixtures over the temperature range 1600-2200 K. Initial H(2)O concentrations were determined using tunable diode laser absorption near 2.5 microm, and OH concentration time-histories were measured using UV ring dye laser absorption near 306.7 nm. Detailed kinetic analysis of the OH time-history profiles yielded a value for the rate constant k(1) of (3.3 +/- 0.9) x 10(13) [cm(3) mol(-1) s(-1)] between 1600 and 2200 K. The results of this study agree well with those reported by Srinivasan et al. (Srinivasan, N.K.; Su, M.-C.; Sutherland, J.W.; Michael, J.V.; Ruscic, B. J. Phys. Chem. A 2006, 110, 6602-6607) in the temperature regime between 1200 and 1700 K. The combination of the two studies suggests only a weak temperature dependence of k(1) above 1200 K. Data from the current study and that of Keyser (Keyser, L.F. J. Phys. Chem. 1988, 92, 1193-1200) at lower temperatures can be described by the k(1) expression proposed by Baulch et al. (Baulch, D.L.; Cobos, C.J.; Cox, R.A.; Esser, C.; Frank, P.; Just, Th.; Kerr, J.A.; Pilling, M.J.; Troe, J.; Walker, R.W.; Warnatz, J. J. Phys. Chem. Ref. Data 1992, 21, 411), k(1) = 2.89 x 10(13) exp(252/T) [cm(3) mol(-1) s(-1)]. However, it should be noted that some previous studies suggest a k(1) minimum around 1250 K (Hippler, H.; Neunaber, H.; Troe, J. J. Chem. Phys. 1995, 103, 3510-3516) or 1000 K (Kappel, C.; Luther, K.; Troe, J. Phys. Chem. Chem. Phys. 2002, 4, 4392-4398).

Ignition delay time data for higher n-alkanes are required for the development and refinement of jet fuel surrogate mechanisms; similar data for oxygen-carrying species are also required for the development of oxygenate fuel mechanisms. To fill this need, ignition delay times were measured using pressure and OH * emission diagnostics behind reflected shock waves for a series of higher n-alkanes and for several simple oxygenates. Reflected shock conditions covered temperatures of 1150―1550 K and pressures of 1―4 atm (0.1―0.4 MPa). Fuel mixtures tested include the four n-alkanes: n-pentane, n-hexane, n-octane, and n-nonane; and the four oxygenates: acetone, n-butanal, methyl butanoate, and 3-pentanone. All fuels were tested in oxygen/argon mixtures with equivalence ratios of 0.5 to 2.0. The ignition data were compared with current models and a new n-butanal reaction mechanism, based on previous studies, was used to model the n-butanal and methyl butanoate data.

There is a strong environmental interest in blending diesel fuels with oxygenates to reduce soot emissions. To investigate the influence of oxygenates on diesel soot emissions, soot formation in fuel-rich n-heptane/oxygen mixtures with added dimethyl ether, acetone, butanal, or 3-pentanone was investigated behind reflected shock waves at pressures from 20 to 30 atm and temperatures from 1600 to 1900 K. Soot formation histories were observed by simultaneously measuring the soot-induced laser light extinction at 633 nm and the light emission by soot particles at 670 nm. Uniform reflected shock conditions over the long test times needed to form soot were achieved by using a new driver insert method to modify shock tube performance. In measurements made under these uniform conditions, the soot formation window near 1700 K was found to be narrower than previously measured. A significant reduction in the overall soot yield was found with the addition of small quantities of oxygenates as well. On a per oxygen-mass basis, butanal was found to be the most effective additive in reducing soot among the oxygenates studied, consistent with the smoke point tests of Pepiot-Desjardins et al. [Pepiot-Desjardins P, Pitsch H, Malhotra R, Kirby SR, Boehman AL. Structural group analysis for soot reduction tendency of oxygenated fuels. Combust Flame 2008;154:191–205]. It was also found that normal alkyl-group chain length in oxygenates has little impact on soot reduction.

The contact surface tailoring conditions normally used for shock tubes do not apply to shock tubes with different driver and driven section diameters. A theoretical model is presented that predicts the contact surface tailoring condition for a convergent shock tube, designed to have a larger driver cross-section area than the driven section. The tailoring condition previously developed for shock tubes with uniform driver and driven diameters can be recovered from this model. Representative on- and off-model performance is verified experimentally in a high-pressure convergent shock. Tailoring conditions calculated with the model are also given for commonly used driven gases (Ar, N2 and air) and He–N2 driver mixtures as a function of driver/driven area ratio.

Non-ideal shock tube facility effects, such as incident shock wave attenuation, can cause variations in the pressure histories seen in reflected shock wave experiments. These variations can be reduced, and in some cases eliminated, by the use of driver inserts. Driver inserts, when designed properly, act as sources of expansion waves which can counteract or compensate for gradual increases in reflected shock pressure profiles. An algorithm for the design of these inserts is provided, and example pressure measurements are presented that demonstrate the success of this approach. When these driver inserts are employed, near- ideal, constant-volume performance in reflected shock wave experiments can be achieved, even at long test times. This near-ideal behavior simplifies the interpretation of shock tube chemical kinetics experiments, particularly in experiments which are highly sensitive to temperature and pressure changes, such as measurements of ignition delay time of exothermic reactions.

Ignition delay times and OH concentration time-histories were measured during n-dodecane oxidation behind reflected shocks waves using a heated, high-pressure shock tube. Measurements were made over temperatures of 727–1422 K, pressures of 15–34 atm, and equivalence ratios of 0.5 and 1.0. Ignition delay times were measured using side-wall pressure and OH∗ emission diagnostics, and OH concentration time-histories were measured using narrow-linewidth ring-dye laser absorption near the R-branchhead of the OH A–X (0, 0) system at 306.47 nm. Shock tube measurements were compared to model predictions of four current n-dodecane oxidation detailed mechanisms, and the differences, particularly in the low-temperature negative-temperature-coefficient (NTC) region where the influence of non-ideal facility effects can be significant, are discussed. To our knowledge, the current measurements provide the first gas-phase shock tube ignition delay times (at pressures above 13 atm) and quantitative OH concentration time-histories for n-dodecane oxidation under practical engine conditions, and hence provide benchmark validation targets for refinement of jet fuel detailed kinetic modeling, since n-dodecane is widely used as the principal representative for n-alkanes in jet fuel surrogates.

Ignition delay times were measured for gas-phase methylcyclohexane (MCH)/O2/argon and MCH/air mixtures behind reflected shock waves. Initial postshock conditions covered temperatures of 795−1560 K, pressures of 1−50 atm, fuel concentrations of 0.25−2%, and equivalence ratios (ϕ) of 0.5−2.0. Ignition delay times were measured using side-wall pressure and CH* and OH* emission measurements. Current measurements complement past high-pressure rapid compression machine results, are in good agreement with past low-pressure shock tube data, and significantly extend the pressure range of available shock tube ignition time data. Detailed comparisons of experimental data with predictions of available MCH mechanisms are presented, and comparisons of shock tube MCH ignition delay times to those of other important jet fuel surrogates and cyclo-alkanes are discussed.

In the present work, an atmospheric pressure combustor using a modern aviation gas turbine fuel nozzle was used to demonstrate active combustion control. The combustor exhibited a low-frequency dynamics mode under fuel-rich conditions. A fast-response fuel valve was adapted as an in-line valve upstream of the nozzle for fuel modulation. Large fuel modulation amplitudes were achieved with the combination of the valve and the engine nozzle at frequencies exceeding 200 Hz. Open-loop flame response to fuel modulation was first examined when the instability mode was absent; for a range of inlet air temperatures, fuel flow rates, and combustor pressure drops. Simple open-loop control at discrete off-resonance frequencies was found ineffective in suppressing the instability mode. An advanced, fast algorithm was developed to enable closed-loop control. In this scheme, the entire fuel supply to the combustor was modulated with the control valve and injected through the fuel nozzle. The control algorithm commanded the fuel injector to produce a steady fuel flow, when the combustion was stable, or to modulate the fuel when the level of pressure oscillations in the combustion chamber became unacceptable. With an optimized control algorithm, an 88% reduction in the amplitude of the low-frequency dynamics mode was achieved.Copyright © 2012 by ASME

The rate constants of the reactions: (1) H2O2+M-->2OH+M, (2) OH+H2O2-->H2O+HO2 were measured in shock-heated H(2)O(2)/Ar mixtures using laser absorption diagnostics for H(2)O and OH. Time-histories of H(2)O were monitored using tunable diode laser absorption at 2550.96 nm, and time-histories of OH were achieved using ring dye laser absorption at 306 nm. Initial H(2)O(2) concentrations were also determined utilizing the H(2)O diagnostic. On the basis of simultaneous time-history measurements of OH and H(2)O, k(2) was found to be 4.6 x 10(13) exp(-2630 K/T) [cm(3) mol(-1) s(-1)] over the temperature range 1020-1460 K at 1.8 atm; additional measurements of k(2) near 1 atm showed no significant pressure dependence. Similarly, k(1) was found to be 9.5 x 10(15) exp(-21 250 K/T) [cm(3) mol(-1) s(-1)] over the same temperature and pressure range.

There is a critical need for accurate kinetic targets to test and refine large reaction mechanisms for jet fuel, and other practical fuels and surrogates mixtures. To this end, concentration time-histories for four species: C2H4, OH, CO2, and H2O, were measured behind reflected shock waves during n-the oxidation of n-heptane, an important normal alkane fuel surrogate component. Experiments were conducted at temperatures of 1300 to 1600 K and a pressure of 2 atm using a mixture of 300 ppm n-heptane in stoichiometric oxygen (φ=1) in argon. Ethylene was monitored using IR gas laser absorption at 10.53 microns; OH was monitored using UV laser absorption at 306.5 nm; and CO2 and H2O were monitored using tunable IR diode laser absorption at 2.7 and 2.5 microns, respectively. These time-histories provide kinetic targets to test and refine reaction mechanisms for nheptane and also serve to demonstrate the potential of this type of data for validation of reaction mechanisms. Comparisons are made with the predictions of the Sirjean et al./JetSurF 1.0 (2009) reaction mechanism for n-alkanes.

The thermal decomposition of hydrogen peroxide was measured behind reflected shock waves in hydrogen peroxide/inert gas mixtures using a sensitive laser diagnostic for water vapor. In these mixtures, the formation rate of water is predominantly controlled by the decomposition rate of hydrogen peroxide. Rate determinations were made over a temperature range of 1000-1200 K and a pressure range of 0.9-3.2 atm for both argon and nitrogen carrier gases. Good detection sensitivity for water was achieved using tunable diode laser absorption of water at 2550.96 nm within its v(3) fundamental band. Hydrogen peroxide decomposition rates were found to be independent of pressure at 0.9 and 1.7 atm and showed only slight influence of pressure at 3.2 atm. The best fit of the current data to the low-pressure-limit rate for H(2)O(2) dissociation in argon bath gas is k(1,0) = 10(15.97+/-0.10) exp(-21 220 +/- 250 K/T) [cm(3) mol(-1) s(-1)] (1000-1200 K). Experiments conducted in a nitrogen bath gas show a relative collision efficiency of argon to nitrogen of 0.67.