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Author: Yi Cao Publisher: ISBN: Category : Languages : en Pages :
Book Description
As alternatives to traditional petroleum-based fuels are increasingly sought after, the National Jet Fuel Combustion Program (NJFCP) was established to streamline the evaluation and certification of these fuels. The current mandate is for the replacements of traditional fuels to be equally safe and to provide better environmental performance [1]. These so-called "drop-in" jet fuels refer to hydrocarbon fuels that deliver identical combustion performance and are produced from non-petroleum sources [2]. Following the mandate delivered by the NJFCP for alternative fuels, this study aims to improve the traditionally phenomenological understanding of combustion performance by making connections between fuel properties and the chemical composition of fuels. The ignition delay time is an important measure of the combustion performance of fuels, as it is an integrated measure of the fuels' physical and chemical properties, such as volatility, diffusivity, and chemical reactivity. Consequently, it is a very useful validation target in chemical kinetic modeling and has implications in practical aviation phenomena such as, among others, lean blowout, cold-start ignition and altitude relight. Shock tubes are well-suited for ignition delay time measurements, as they provide a well-defined time zero and a quasi-constant temperature and pressure test region behind the reflected shocks. All experiments in this thesis were performed on the Stanford Flexible Application Shock Tube (FAST). Reactive gas mixtures were prepared with equivalence ratios of 1 ± 0.05, and mixed in the shock tube driven section to avoid fuel loss attributed to non-idealities in the jet fuel vapor. Changes in the fuel mole fraction during mixing and ignition were monitored using laser absorption diagnosis at 3.39 μm. The ignition delay time is defined in this study by the onset of emission from electronically excited OH radicals at 306 nm. Ignition delay times were measured in the temperature range of 1200-1500 K and at 4 atm pressure for five distillate jet fuels from refineries around the US (termed geographical fuels), and for six synthetic jet fuels with varying cetane numbers ranging from 30-55 (termed CN fuels). The ignition delay times for A1-3 and C1-9 jet fuels were also measured at 1300 K and at 4 atm. The dependence of combustion properties on fuel chemical composition were investigated using the ignition delay times for these fuels. In particular, the key role that the degree of branching in the jet fuel molecular structure plays in the combustion kinetics and performance is discussed.
Author: Yi Cao Publisher: ISBN: Category : Languages : en Pages :
Book Description
As alternatives to traditional petroleum-based fuels are increasingly sought after, the National Jet Fuel Combustion Program (NJFCP) was established to streamline the evaluation and certification of these fuels. The current mandate is for the replacements of traditional fuels to be equally safe and to provide better environmental performance [1]. These so-called "drop-in" jet fuels refer to hydrocarbon fuels that deliver identical combustion performance and are produced from non-petroleum sources [2]. Following the mandate delivered by the NJFCP for alternative fuels, this study aims to improve the traditionally phenomenological understanding of combustion performance by making connections between fuel properties and the chemical composition of fuels. The ignition delay time is an important measure of the combustion performance of fuels, as it is an integrated measure of the fuels' physical and chemical properties, such as volatility, diffusivity, and chemical reactivity. Consequently, it is a very useful validation target in chemical kinetic modeling and has implications in practical aviation phenomena such as, among others, lean blowout, cold-start ignition and altitude relight. Shock tubes are well-suited for ignition delay time measurements, as they provide a well-defined time zero and a quasi-constant temperature and pressure test region behind the reflected shocks. All experiments in this thesis were performed on the Stanford Flexible Application Shock Tube (FAST). Reactive gas mixtures were prepared with equivalence ratios of 1 ± 0.05, and mixed in the shock tube driven section to avoid fuel loss attributed to non-idealities in the jet fuel vapor. Changes in the fuel mole fraction during mixing and ignition were monitored using laser absorption diagnosis at 3.39 μm. The ignition delay time is defined in this study by the onset of emission from electronically excited OH radicals at 306 nm. Ignition delay times were measured in the temperature range of 1200-1500 K and at 4 atm pressure for five distillate jet fuels from refineries around the US (termed geographical fuels), and for six synthetic jet fuels with varying cetane numbers ranging from 30-55 (termed CN fuels). The ignition delay times for A1-3 and C1-9 jet fuels were also measured at 1300 K and at 4 atm. The dependence of combustion properties on fuel chemical composition were investigated using the ignition delay times for these fuels. In particular, the key role that the degree of branching in the jet fuel molecular structure plays in the combustion kinetics and performance is discussed.
Author: Subith Vasu Sumathi Publisher: ISBN: Category : Languages : en Pages :
Book Description
Fossil-based hydrocarbon fuels account for over 80% of the primary energy consumed in the world - it is still expected to be about 70% in year 2050 - and nearly 60% of that amount is used in the transport sector. The basis for globalization is transportation and a driving force has been the growth in global air traffic. The current climate crisis magnifies the need for improving the performance of jet engines by introducing scientific designs in which the use of chemical kinetics will be essential and critical for better performance and reducing pollutant emissions. Most aviation fuels are jet fuels originating from crude oil and there are major gaps in our knowledge of the high-temperature chemistry of real liquid carbon-based fuels. There is a critical need for experimental kinetic databases that can be used for the validation and refinement of jet fuel surrogate mechanisms. To fill this need, experiments were performed using shock tube and laser absorption methods to investigate jet fuel and surrogate oxidation systems under engine-relevant conditions. Ignition times and OH species time-histories were measured and low-uncertainty measurements of the reactions of OH with several stable intermediates were carried out. The work presented in this study can be broken into three categories: 1) jet fuel oxidation, 2) surrogate oxidation, and 3) OH radical reactions with several stable combustion intermediates. Ignition delay times were measured for gas-phase jet fuel oxidation (Jet-A and JP-8) in air behind reflected shock waves in a heated high-pressure shock tube. Initial reflected shock conditions were as follows: temperatures of 715-1229 K, pressures of 17-51 atm, equivalence ratios (phi) of 0.5 and 1, and oxygen concentrations of 10 and 21 % in synthetic air. Ignition delay times were measured using sidewall pressure and OH* emission at 306 nm. The new experimental results were modeled using several kinetic mechanisms using various jet fuel surrogate mixtures. Normal and cyclo alkanes are the two most important chemical classes found in jet fuels. Ignition delay time experiments were conducted during high-pressure oxidation of two commonly used representative components for normal and cyclo alkanes in jet fuel surrogates, i.e., n-dodecane and methylcyclohexane (MCH), respectively. Fuel/air ignition was studied for the following shock conditions: temperatures of 727-1177 K, pressures of 17-50 atm, phi's of 0.5 and 1. OH concentration time-histories during high-pressure n-dodecane, n-heptane and MCH oxidation were measured behind reflected shock waves in a heated, high-pressure shock tube. Experimental conditions covered temperatures of 1121 to 1422 K, pressures of 14.1-16.7 atm, and initial fuel concentrations of 500 to 1000 ppm (by volume), and an equivalence ratio of 0.5 with O2 as the oxidizer in argon as the bath gas. OH concentrations 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. Detailed comparisons of these data with the predictions of various kinetic mechanisms were made. Sensitivity and pathway analyses for these reference fuel components were performed, leading to reaction rate recommendations with improved model performance. Reactions of OH radical with two alkenes (ethylene and propene) and a diene (1,3-butadiene) were studied behind reflected shock waves. Measurements were conducted in the range of temperatures from 890-1438 K and pressures from 1.99-10.18 atm for three initial concentrations of fuels (500ppm, 751.1ppm and 1000ppm). OH radicals were produced by shock-heating tert-butyl hydroperoxide, (CH3)3-CO-OH, and monitored by narrow-line width ring dye laser absorption of the well characterized R1(5) line of the OH A-X (0, 0) band near 306.7 nm. OH time-histories were modeled by using a modified oxidation mechanism and rate constants for the reactions of OH with ethylene, propene, and 1,3-butadiene were extracted by matching modeled and measured OH concentration time histories in the reflected shock region. Detailed error analyses yielded an uncertainty estimate of " 22.8% (OH+ethylene at 1201 K), "16.5% (OH+propene at 1136 K), and "13% (OH+1,3-butadiene at 1200K). Canonical and variational transition state theory calculations using recent ab initio results gave excellent agreement with our experimental measurements and data outside our range and hence the resulting expressions can be used directly in combustion models. In the current studies, a rate measurement for the decomposition of TBHP has been obtained in the range 745-1014 K using both incident and reflected OH data.
Author: Ritu Gaur Publisher: GRIN Verlag ISBN: 3346061124 Category : Technology & Engineering Languages : en Pages : 22
Book Description
Research Paper (postgraduate) from the year 2019 in the subject Engineering - Chemical Engineering, , course: M.TECH, language: English, abstract: This work is an experimental study for the measurement of ignition delay characteristics of burning fuel sprays in cylindrical combustion chambers. It is carried out on hot air and high pressure. The objective of the study is to investigation the effect of hot air temperature and a well as high pressure on ignition delay of diesel fuel sprays. The effect of blending of n-Pentane with pure diesel was investigated. An experimental set up was design for this purpose with the emphasis on optical method for measurement of ignition delay at various pressures. The results presented here show that ignition delay of diesel fuel spray decreases with increase in the temperature and pressure of hot air. Results also show the effect of methyl group being more dominant at low ignition temperatures and that of alkyl group being more dominant at higher temperature. Blending of n-pentane with diesel fuel, increase its ignition delay at low ignition temperatures. However, as the concentration of blending fuel was increased beyond 30%, the ignition temperature increase. Ignition temperature for 40% pentane blends is much higher that the pure diesel.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Abstract : The U.S. Army and many NATO affiliates have adopted a 'one fuel forward fuel policy' (OFF). The goal of the OFF policy is reducing the logistics and cost involved with providing fuel for military vehicles. With this policy, the logical choice fuel is military grade jet petroleum, JP-8, because of the fuel constraints of turbo-jet engines. This requirement has made it necessary to run military compression ignited engines on JP-8. To reduce the Army's reliance on petroleum based fuels an alternative fuel, synthetic JP-8, derived from coal and made in the Fischer-Tropsch production method is allowed to be blended up to 50% with JP-8. The two fuels have varying cetane numbers of for 43.1 for JP-8 and 25 for the synthetic JP-8 which influence combustion characteristics. Therefore, the goal of the current work is to characterize the ignition characteristics of synthetic JP-8 as compared to the reference JP-8 under the same test conditions. A JP-8 surrogate fuel is also developed and compared against the baseline fuel in terms of both ignition behavior and liquid penetration. Testing is conducted in an optically accessible combustion vessel sweeping ambient temperatures and densities of 800 - 1100 K and 7.3 - 30.2 kg/m3, respectively. The resultant data is used in comparison of all three fuels in ignition delay and steady state liquid penetration characteristics. Correlations are also developed for calculating the ignition delay of both the JP-8 and the synthetic JP-8 fuel and is used to compare to the surrogate fuel and to compare to a pool of data from past work on JP-8. Results of these comparisons show a 50% increase in the ignition delay and a 10% shorter steady state liquid penetration of the low cetane value synthetic JP-8 over the baseline JP-8 fuel sample. Findings also show the surrogate matches the baseline fuel to within 10% for ignition delays but it over penetrates the baseline fuel by around 30% for liquid penetration.
Author: Rui Xu (Mechanical engineer) Publisher: ISBN: Category : Languages : en Pages :
Book Description
Real fuels usually contain hundreds to thousands of hydrocarbon components. Over a wide range of combustion conditions, large hydrocarbon molecules undergo thermal decomposition first to form a small set (usually less than 10 species) of low molecular weight products, followed by the oxidation of those products, which is usually rate limiting. Hence, the composition of the decomposed products determines the overall global combustion properties. For conventional distillate fuels, the pyrolysis products comprise ethylene (C2H4), hydrogen (H2), methane (CH4), propene (C3H6), 1-butene (1-C4H8), iso-butene (i-C4H8), benzene (C6H6) and toluene (C7H8). From a joint consideration of thermodynamics and chemical kinetics, it is shown that the composition of the thermal decomposition products is a weak function of the thermodynamic condition, the equivalence ratio and the fuel composition within the range of temperatures relevant to high temperature combustion phenomena. In this dissertation study, I demonstrate a hybrid chemistry (HyChem) approach to modeling the high-temperature oxidation of real, liquid fuels. In this approach, the kinetics of fuel pyrolysis is modeled using experimentally derived, lumped reaction steps, while the oxidation of the pyrolysis fragments is described by a detailed foundational fuel chemistry model. A wide range of modeling results are provided to support the approach, including three conventional aviation fuels (JP-8 POSF10264, Jet A POSF10325, JP-5 POSF10289), two rocket fuels (RP2-1 POSF7688, RP2-2 POSF5433), and a bio-derived alternative jet fuel (Gevo alcohol-to-jet fuel, C1 POSF11498). The HyChem models of those fuels were developed using advanced speciation data obtained from shock tubes and a flow reactor, and the models were subsequently tested against global combustion properties, including ignition delay time, laminar flame speed, and flame extinction strain rates across a wide range of pressure, temperature and reactant mixture conditions. Sensitivity analysis of the model predictions with respect to the measurement uncertainties and rate parameter uncertainties of foundational fuel chemistry model is assessed. In this dissertation, the HyChem modeling approach was also extended to three key aspects critical to modeling fuel combustion over an even wider range of condition. First, a modified HyChem model was formulated for capturing the physics in negative temperature coefficient (NTC) and low-temperature oxidation regimes. Sensitivity test and suggestions on future NTC enabled HyChem model development are presented. Second, the HyChem approach was applied to modeling the blend of a conventional Jet A fuel and an alternative, alcohol-to-jet synthetic fuel. The pyrolysis as well as the combustion properties of several blended fuels were predicted by a simple combination of the HyChem models of the two individual fuels, thus demonstrating that the HyChem models for two jet fuels of very different compositions can be "additive" as far as high-temperature properties are concerned. Lastly, I will discuss a case study in which the HyChem model of Jet A is extended to NOx prediction after combining it with a recently updated reaction model of nitrogen chemistry. The combined reaction model is shown to predict NOx formation in premixed stretched-stabilized Jet A flames satisfactorily.
Author: Yi Cao
Author: Yi Cao
Author: Subith Vasu Sumathi
Author: Ritu Gaur
Author: Alexander Burcat
Author: Dan G. Dimitriu
Author: Dan G. Dimitriu
Author: 
Author: 
Author: British Standards Institute Staff
Author: Rui Xu (Mechanical engineer)