Ignition Delay Time Measurements Research Articles

An experimental and kinetic modeling study of the auto-ignition of natural gas blends containing C1–C7 alkanes

Ignition delay time measurements for multi-component natural gas mixtures were carried out using a rapid compression machine at conditions relevant to gas turbine operation, at equivalence ratios of 0.5–2.0 in ‘air’ in the temperature range 650–1050 K, at pressures of 10–30 bar. Natural gas mixtures comprising C1–C7n-alkanes with methane as the major component (volume fraction: 0.35–0.98) were considered. A design of experiments was employed to minimize the number of experiments needed to cover the wide range of pressures, temperatures and equivalence ratios. The new experimental data, together with available literature data, were used to develop and assess a comprehensive chemical kinetic model. Replacing 1.875% methane with 1.25% n-hexane and 0.625% n-heptane in a mixture containing C1–C5 components leads to a significant increase in a mixture's reactivity. The mixtures containing heavier hydrocarbons also tend to show a strong negative temperature coefficient and two-stage ignition behavior. Sensitivity analyses of the C1–C7 blends have been performed to highlight the key reactions controlling their ignition behavior.

A kinetic investigation on the synergistic low-temperature reactivity, antagonistic RON blending of high-octane fuels: Diisobutylene and cyclopentane

A synergistic effect on low-temperature autoignition reactivity of blending two high-octane compounds, i.e. cyclopentane and diisobutylene, was observed in engine experiments and ignition delay time measurements at 700–880 K and up to 25 bar with a rapid compression machine. Results show that the low-temperature ignition delay and RON of a cyclopentane-diisobutylene blend are inferior to those of its isolated blendstocks, therefore exhibiting an increased reactivity towards ignition at the tested conditions. Sampling and speciation of the reacting mixture during the ignition delay of pure compounds and the most reactive blend was conducted to support discussions focused on the kinetic perspective to this phenomena, which suggest that the separate chain initiation pathways of these potential high-octane blendstocks can interact with each other to help the radical pool growth at the beginning stage of the autoignition chemistry, and finally accelerate the propagation and branching pathways to promote the global reactivity. This result in significant two-stage ignition behavior for the blend, which is not observed at this temperature for both isolated blendstocks. These findings are especially meaningful for designing and blending suitable high-octane fuels for advanced combustion mode engines.

Shock tube ignition delay time measurements for methyl propanoate and methyl acrylate: Influence of saturation on small methyl ester high‐temperature reactivity

AbstractWe report ignition delay time measurements for methyl propanoate (MP) and methyl acrylate (MA), carried out in a high‐pressure shock tube. Experiments were performed behind reflected shock waves across a temperature range of 989‐1 367 K, for fuel‐air mixtures at equivalence ratios of ϕ = 0.5, 1.0, and 2.0, and nominal pressures of 1 and 4 MPa. Ignition delay times were found to decrease with increasing temperature, equivalence ratio, and pressure, and are well described with correlations involving Arrhenius temperature dependence and power‐law dependence on equivalence ratio and pressure. Ignition delay times are compared with model predictions from literature kinetic models, with the models of Zhang et al (Energy & Fuels 2014; 28(11): 7194‐7202) and Bennadji et al (International Journal of Chemical Kinetics 2011; 43(4): 204‐218.) in good agreement with measured ignition delay times for MP and MA, respectively. Kinetic sensitivity analysis shows that the reactions most important for modeling ignition fall into two categories: initiation reactions (ie, decomposition and H‐atom abstraction) and C0‐C1 chemistry controlling the pool of small radicals. The unsaturated MA was observed to have lower reactivity than MP, due to its greater bond strengths for C─C and C─H bonds, resulting in slower rates for initiation reactions.

Evaluation of non-ideal piston stopping effects on the “adiabatic core” and ignition delay time simulation in rapid compression machines

Piston creep and rebound are two non-ideal piston stopping behaviors in the rapid compression machine. Compared to nominal piston stopping, piston rebound/creep will result in a smaller/bigger ‘adiabatic’ core zone volume in the reaction chamber and length/shorten the ignition delay time measurements. However, the ‘adiabatic core’ hypothesis can still be validated under these compressions and ensures the applicability of zero-dimensional method in the model simulation.

High-pressure ignition delay time measurements of a four-component gasoline surrogate and its high-level blends with ethanol and methyl acetate

Ignition delay times of a gasoline surrogate (iso-octane/toluene/n-heptane/1-hexene at 55/25/15/5% by liquid volume, developed in McCormick et al. 2017) with high-level bioblendstock-gasoline surrogate blends (50% and 85% biofuel by liquid volume of each ethanol and methyl acetate) were collected behind reflected shock waves. Post-reflected-shock temperatures ranged from 968 to 1361 K at pressures of about 4, 10, 25, and 50 atm. Data were collected for real fuel–air mixtures at fuel lean and stoichiometric conditions (φ = 0.5, 1.0) with focus on the more-practical, fuel-lean conditions. Ignition delay times were measured from OH* chemiluminescence around 307 nm using an endwall diagnostic. The RON and MON of the surrogate were 90.3 and 84.7, respectively. Ethanol was chosen due to its wide use in flex-fuel vehicles and availability, while also providing an increased octane rating. Methyl acetate was chosen for its especially high octane rating to investigate the effect of an extreme case. To validate the gasoline surrogate, the data are compared to real gasoline (RD387) and several gasoline surrogate experiments from the literature. Using the wide range of pressures studied, the gasoline surrogate’s pressure dependence was quantified to account for test-to-test variations using regression analysis. Similarly, a global correlation for gasoline and its surrogates was developed using all available data from the literature. Two modern chemical kinetics models targeting gasoline and its surrogates are compared to the ignition delay time measurements. These new high-pressure, high-bioblendstock concentration tests provide required chemical kinetic data for optimizing fuel and engine design.

Autoignition studies of NH3/CH4 mixtures at high pressure

Autoignition delay times of NH3/CH4 mixtures with CH4 fractions of 0%, 5%, 10% and 50% were measured in a rapid compression machine at equivalence ratio φ = 0.5, pressures from 20 to 70 bar and temperatures from 930 to 1140 K. In addition, measurements were performed for NH3 mixtures with 10% CH4 at φ = 1.0 and 2.0. Methane shows a strong ignition-enhancing effect on NH3, which levels off at higher CH4 fractions, as the ignition delay time approaches that of pure methane. Autoignition delay times at 10% CH4 at φ = 0.5 and 1.0 are indistinguishable, while an increase of ignition delay times by factor of 1.5 was observed upon increasing φ to 2.0. The experimental data were used to evaluate six NH3 oxidation mechanisms capable of simulating NH3/CH4 mixtures. The mechanism previously used by the authors shows the best performance: generally, it predicts the measured ignition delay times to better than 30% for all conditions, except for 50% CH4 addition for which the differences increase up to 50% at the highest temperature. Sensitivity analysis based on the mechanism used indicates that under lean conditions the reaction CH4 + NH2 = CH3 + NH3 significantly promotes ignition for modest CH4 addition (5% and 10%), but becomes modestly ignition-inhibiting at 50% CH4. Sensitivity and rate-of-production analyses indicate that the ignition-enhancing effect of 50% CH4 addition is closely related to the formation and decomposition of H2O2. Flux analysis for NH3/CH4 mixtures indicates that CH4 + NH2 = CH3 + NH3 contributes substantially to the decomposition of methane early in the oxidation process, while CH3 + NO2 (+M) = CH3NO2 (+M) is a significant reservoir of NO2 at low temperature. Additionally, an anomalous pre-ignition pressure rise phenomenon, which is not reproduced by the simulations, was observed with high reproducibility for the NH3 mixture with 50% CH4 addition.

Ignition delay time and laminar flame speed measurements of mixtures containing diisopropyl-methylphosphonate (DIMP)

Diisopropyl-methylphosphonate (DIMP) is a common surrogate of Sarin for which a detailed kinetics mechanism was developed in 2002 (Glaude et al.— [12]). In the present paper, ignition delay times and laminar flame speeds of DIMP-based mixtures were studied around atmospheric pressure for the first time. Methane and hydrogen were used as baseline fuels, and mixtures of these fuels were doped with DIMP. The DIMP was added at 10% mol. of the fuel concentration for the shock-tube experiments (three equivalence ratios (0.5, 1.0, and 2.0) were investigated with methane). A stoichiometric DIMP/O2 mixture was also studied. For the laminar flame speed experiments, an equivalence ratio sweep was performed, and DIMP was added at 0.1% vol. of the total mixture, although DIMP was added to up to 0.5% vol. for the maximum flame speed condition with H2. Results showed that adding DIMP promotes the ignition of methane but also largely inhibits its laminar flame speed. A decrease in the flame speed with DIMP addition was observed with H2 as well, and the maximum flame speed was found to decrease linearly with the amount of DIMP added. The new results with DIMP were compared to data obtained recently for other Sarin surrogates. The influence of the structure of these surrogates on combustion properties was discussed. The kinetics model for DIMP does not capture the peculiar OH* profiles observed in the shock tube for the DIMP/O2 mixture, and the ignition delay times for the H2-DIMP mixture were very poorly predicted. On the other hand, ignition delay times for the CH4-DIMP mixture were predicted with good-to-fair agreement for most cases. A chemical analysis showed that a sub-mechanism for iso-propanol needs to be added to the mechanism. An updated detailed kinetics model, with a state-of-the-art hydrocarbon chemistry (including iso-propanol chemistry) and updates in the phosphorous chemistry and thermodynamic database was tested. This updated mechanism provides predictions that are less accurate than the original model in most cases, indicating a strong need to revisit the reactions describing the thermal decomposition of DIMP.

Aerosol Shock Tube Designed for Ignition Delay Time Measurements of Low-Vapor-Pressure Fuels and Auto-Ignition Flow-Field Visualization

An aerosol shock tube has been developed for measuring the ignition delay times (tig) of aerosol mixtures of low-vapor-pressure fuels and for visualization of the auto-ignition flow-field. The aerosol mixture was formed in a premixing tank through an atomizing nozzle. Condensation and adsorption of suspended droplets were not observed significantly in the premixing tank and test section. A particle size analyzer was used to measure the Sauter mean diameter (SMD) of the aerosol droplets. Three pressure sensors and a photomultiplier were used to detect local pressure and OH emission respectively. Intensified charge-coupled device cameras were used to capture sequential images of the auto-ignition flow-field. The results indicated that stable and uniform aerosol could be obtained by this kind of atomizing method and gas distribution system. The averaged SMD for droplets of toluene ranged from 2 to 5 μ m at pressures of 0.14–0.19 MPa of dilute gases. In the case of a stoichiometric mixture of toluene/O2/N2, ignition delay times ranged from 77 to 1330 μs at pressures of 0.1–0.3 MPa, temperatures of 1432–1716 K and equivalence ratios of 0.5–1.5. The logarithm of ignition delay times was approximately linearly correlated to 1000/T. In contrast to the reference data, ignition delay times of aerosol toluene/O2/N2 were generally larger. Sequential images of auto-ignition flow-field showed the features of flame from generation to propagation.

A new skeletal mechanism for ethanol using a modified implementation methodology based on directed relation graph (DRG) technique

A different methodology for implementing the standard mechanism reduction technique directed relation graph (DRG) is presented and applied to develop a new skeletal mechanism for ethanol. Two combustion processes, ignition delay time and flame speed, that are mandatory for a mechanism to reproduce are used to calculate the species coupling through DRG index. Based on a detailed mechanism of 57 species among 383 reversible elementary reactions, a skeletal mechanism of 37 species and 184 reactions is obtained, which represents a decrease of 35% in the number of species and almost 52% in the number of reactions. The new mechanism is validated for ignition delay time and flame speed measurements, and also for one-dimensional burner stabilized flat and counterflow flames simulations, which were not considered in the development of the skeletal mechanism. Comparisons with experimental data and with the behaviour of other mechanisms in the literature are also displayed. The methodology presented can be useful and contribute to generate skeletal mechanisms with less effort that can reproduce a more demanding simulation.

Ignition Delay Times of Oxy-Syngas and Oxy-Methane in Supercritical CO2 Mixtures for Direct-Fired Cycles

Abstract The direct-fired supercritical CO2 (sCO2) cycles promise high efficiency and reduced emissions while enabling complete carbon capture. However, there is a severe lack of fundamental combustion kinetics knowledge required for the development and operation of these cycles, which operate at high pressures and with high CO2 dilution. Experiments at these conditions are very challenging and costly. In this study, a shock tube was used to investigate the auto-ignition tendencies of several mixtures under high carbon dioxide dilution and high fuel loading. Individual mixtures of oxy-syngas and oxy-methane fuels were added to CO2 bath gas environments and ignition delay time data were recorded. Reflected shock pressures neared 100 atm, above the critical pressure of carbon dioxide into the supercritical regime. In total, five mixtures were investigated with a pressure range of 70–100 atm and a temperature range of 1050–1350 K. Measured ignition delay times of all mixtures were compared with two leading chemical kinetic mechanisms for their predictive accuracy. The mixtures included four oxy-syngas and one oxy-methane compositions. The literature mechanisms tended to show good agreement with the data for the methane mixture, while these models were not able to accurately capture all behavior for syngas mixtures tested in this study. For this reason, there is a need to further investigate the discrepancies. To the best of our knowledge, we report the first ignition data for the selected mixtures at these conditions. Current work also highlights the need for further work at high pressures to fully understand the chemical kinetic behavior of these mixtures to enable the sCO2 power cycle development.

Experimental and numerical investigation of the Advanced Fuel Ignition Delay Analyzer (AFIDA) constant-volume combustion chamber as a research platform for fuel chemical kinetic mechanism validation

Advanced combustion engine strategies that can offer increased efficiency and reduced emissions are enabled by numerical engine combustion simulations, requiring accurate chemical kinetic mechanism input. The Advanced Fuel Ignition Delay Analyzer (AFIDA) device can perform high quality, repeatable measurements of ignition delay (ID) times using small fuel quantities with high throughput. The AFIDA experiments involve liquid fuel injection into the heated and pressurized constant-volume chamber, producing an autoignition delay resulting from a combination of physical mixing and chemical kinetic processes, a complexity which makes the development of complementary numerical models necessary for the development and validation of chemical kinetic mechanisms. Modeling the device based on a homogenous approximation with reduced primary reference fuel (PRF) mechanism shows up to 75% error in the modeled vs. observed autoignition delay data for n-heptane and iso-octane at 10 bar (ɸ = 1.2–0.8) and 20 bar (ɸ = 0.6–0.4) over 973–648 K, whereas the use of a computational fluid dynamics (CFD) model reduces the discrepancy to within 25%. The homogenous approximation error is greatest for conditions where the observed ignition delay is short and the system is not sufficiently mixed (<30 ms), providing guidance to select a homogenous reactor vs. CFD modeling approach based upon desired accuracy. Experimental 20 bar iso-octane ID results show a larger magnitude of negative temperature coefficient chemistry compared to numerical results, indicating possible deficiencies in the PRF chemical kinetic mechanism. This characterization demonstrates the AFIDA as a capable research platform for chemical kinetic model development and validation.

ETHENE/NITROUS OXIDE MIXTURES AS GREEN PROPELLANT TO SUBSTITUTE HYDRAZINE: REACTION MECHANISM VALIDATION

Reaction mechanism validation for nitrogen-diluted ethane/nitrous oxide mixtures at stoichiometric conditions has been performed using ignition delay time measurements at p = 1, 4, and 16 bar as well as laminar flame speed measurements at p = 1 and 3 bar. The predictive capability of the public domain mechanism GRI 3.0 was improved considerably by adapting some reactions within the nitrogen subsystem and optimizing the most sensitive reactions with respect to selected optimization targets (i.e., ignition delay time and selected laminar flame speed measurements) within the published error bounds.

Ignition delay time measurement and kinetic modeling of furan, and comparative studies of 2,3-dihydrofuran and tetrahydrofuran at low to intermediate temperatures by using a rapid compression machine

The low to intermediate temperature (850–1050 K) auto-ignition characteristics of furan, 2,3-dihydrofurn and tetrahydrofuran have been investigated both experimentally and kinetically. The pressure (18 and 33 bar) and equivalence ratio (0.5, 1.0 and 2.0) effects on the auto-ignition of furan were experimentally examined using a rapid compression machine. Compared with alkylated furans, the ignition delay times of furan show notably insensitivity to equivalence ratio. Comparison on the low to intermediate temperature reactivity of furan, alkylated furans, 2, 3-dihydrofuran, and tetrahydrofuran indicates that saturation degree plays a more dominant role in enhancing reactivity than alkyl substitution. Literature mechanisms were validated against present data. Kinetic analyses revealed the major fuel consuming routes and the causes for the deviation between simulation and experimental results. Furthermore, a modified model of furan, 2, 3-dihydrofuran, and tetrahydrofuran was proposed and validated against the ignition delay times in this study as well as experimental data in literatures.

Auto-ignition of oxymethylene ethers (OMEn, n = 2–4) as promising synthetic e-fuels from renewable electricity: shock tube experiments and automatic mechanism generation

Carbon-neutral synthetic fuels can be produced from renewable electricity by the hydrogenation of carbon dioxide captured from air or exhaust gas. A promising class of these synthetic fuels are long-chain oxymethylene ethers (OMEs), which exhibit good auto-ignition characteristics for compression-ignition engine application. This study aims to investigate the auto-ignition of three oxymethylene ethers (OMEn, n = 2–4) numerically and experimentally. A shock tube is applied to measure ignition delay times over a range of initial conditions and the obtained results serve as the validation and optimization targets for a chemical mechanism of OME2-4 developed in this work. This model is derived first using an automatic reaction class-based mechanism generator. To ensure the chemical validity of the mechanism, the automatic generator applies reaction classes and rate rules consistently for OME2-4, which are adopted from a recently published OME1 mechanism. For improved model prediction accuracy of ignition delay times, the mechanism is then optimized automatically by calibrating these rate rules within their uncertainties using data for all OMEn fuels. It is shown that this highly automated model development process is able to provide accurate chemical mechanisms for large fuel components in a very efficient manner, if accurate prior kinetic knowledge exists for their short-chain counterparts.

High-pressure shock tube study of ethanol oxidation: Ignition delay time and CO time-history measurements

Ethanol oxidation was studied by measuring CO time-histories and ignition delay times behind reflected shockwaves at elevated pressures. In this study, experimental conditions included a temperature range of 960–1580 K, pressure range of 17.8–23.9 atm, and initial fuel concentrations of 6.54% and 0.25% with nitrogen and argon used as bath gasses, respectively. The equivalence ratio for high fuel loading was kept constant at 1.0, and for low fuel loading equivalence ratios were 1.0 and 0.5. For high fuel loading, early heat/energy release was observed in nearly all ignition delay time measurements, indicative of preignition; however, data collected are in good agreement with model predictions. These events are interpreted as a transition from mild to strong ignition. For the low fuel loading cases (ϕ = 1.0 and 0.5), no early heat/energy release was observed. Comparisons of measured CO concentration profiles with the predictions from kinetic mechanisms of Metcalfe et al. (2013), Mittal et al. (2014), and Zhang et al. (2018) were made assuming constant internal energy and volume for the test gas. Such comparisons in addition with performed sensitivity and pathway analyses for CO formation revealed lower temperature sensitivity to the bimolecular reaction of methyl and hydroperoxyl radicals given by CH3 + HO2CH3O + OH, and H-atom abstraction by the hydroperoxyl radical at the alpha site on ethanol given by elementary reaction C2H5OH + HO2sC2H4OH + H2O2. The current study provides important validation targets for ethanol chemical kinetic mechanisms and highlights the benefits of time-history measurements at various temperatures and pressures in a shock tube, which are scare in the literature.

Effects of organic silicon compounds on syngas auto-ignition behavior

Siloxanes are a significant impurity in syngas feedstocks and an important source of silicon in combustion synthesis applications. However, little is known regarding the fundamental combustion chemistry of siloxane compounds. The impact of two organic silicon species with different but related chemical structures, trimethylsilanol (TMSO) and hexamethyldisiloxane (HMDSO), on syngas auto-ignition behavior was investigated in this study using physical and computational experiments. A rapid compression facility (RCF) was used to create temperatures of 1010–1070 K and pressures of 8–10.3 atm for auto-ignition experiments. Experiments with trace concentrations of TMSO (100 ppm, mole basis) or HMDSO (100 ppm) were added to a surrogate syngas blend (CO and H2 with a molar ratio of 2.34:1, air levels of dilution, with molar equivalence ratios of ϕ = 0.1). The measured ignition delay times showed both siloxane species promote ignition behavior with TMSO yielding faster ignition delay times by approximately 37% and HMDSO yielding faster times by approximately 50% compared with the reference syngas mixture which contained no siloxanes. A computational study was conducted to interpret the results of the ignition experiments. Because detailed chemistry does not exist for these organo-silicon compounds, the effects of the addition of CH3, H, and OH radicals to H2 and CO mixtures were explored to simulate the potential rapid decomposition of the siloxanes in the H2 and CO system. Addition of the radicals decreased the predicted ignition delay times when compared with the H2 and CO mixture simulations without the radical species, but the simulations did not fully capture the behavior observed in the experiments, indicating the siloxane chemistry is more complex than providing a rapid source of radicals.

An experimental and modeling study on the reactivity of extremely fuel-rich methane/dimethyl ether mixtures

Chemical reactions in stoichiometric to fuel-rich methane/dimethyl ether/air mixtures (fuel air equivalence ratio ϕ = 1–20) were investigated by experiment and simulation with the focus on the conversion of methane to chemically more valuable species through partial oxidation. Experimental data from different facilities were measured and collected to provide a large database for developing and validating a reaction mechanism for extended equivalence ratio ranges. Rapid Compression Machine ignition delay times and species profiles were collected in the temperature range between 660 and 1052 K at 10 bar and equivalence ratios of ϕ = 1–15. Ignition delay times and product compositions were measured in a shock tube at temperatures of 630–1500 K, pressures of 20–30 bar and equivalence ratios of ϕ = 2 and 10. Additionally, species concentration profiles were measured in a flow reactor at temperatures between 473 and 973 K, a pressure of 6 bar and equivalence ratios of ϕ = 2, 10, and 20. The extended equivalence ratio range towards extremely fuel-rich mixtures as well as the reaction-enhancing effect of dimethyl ether were studied because of their usefulness for the conversion of methane into chemically valuable species through partial oxidation at these conditions. Since existing reaction models focus only on equivalence ratios in the range of ϕ = 0.3–2.5, an extended chemical kinetics mechanism was developed that also covers extremely fuel-rich conditions of methane/dimethyl ether mixtures. The measured ignition delay times and species concentration profiles were compared with the predictions of the new mechanism, which is shown to predict well the ignition delay time and species concentration evolution measurements presented in this work. Sensitivity and reaction pathway analyses were used to identify the key reactions governing the ignition and oxidation kinetics at extremely fuel-rich conditions.

Ignition delay time and species measurement in a rapid compression machine: A case study on high-pressure oxidation of propane

To understand and develop a robust kinetic model for describing the oxidation of a fuel, knowledge of different physicochemical parameters is essential. It can be global parameters like ignition delay times (IDTs) and laminar burning velocities or intrinsic local parameter like species mole fraction profiles. Different facilities have been utilized to provide such measured values from a wide range of conditions that aid in the validation of a detailed chemical kinetic mechanism. In this study, IDT and stable intermediate species mole fractions were obtained for a non-diluted stoichiometric mixture of propane/oxygen/inert gas at compressed pressures of 30 and 50 bar in a rapid compression machine. The species mole fractions during the ignition delay period were obtained at 747 K for 50 bar and 765 K for the 30 bar condition. The species measurement for non-diluted mixtures at such high pressures is vital as there is a change in the sensitivities of the important reactions at these conditions. The non-diluted mixture under this range of pressures represent the application relevant conditions, and the speciation measurement is, for the first time investigated at such conditions in an RCM. This aspect directly highlights the novelty of this study. The work elaborates, in detail, the methodology used for the measurement and simulation of the species mole fraction at the measured conditions with emphasis on the relevant uncertainties. The discussion also includes the significance of sampling from the reaction core and the outcome of the results when sampling from the boundary layer. The IDT measurements are utilized to find a suitable mechanism from the literature that well represents the reactivity both qualitatively and quantitatively in the measured regime. The selected mechanism is used for the simulation and comparison with the measured species mole fractions profiles. The sensitivity and rate of production analysis are performed using the selected mechanism to comprehend the important pathways leading to the formation of the key stable species observed in this experimental work.

Experimental Investigation and Benchmark Study of Oxidation of Methane–Propane–n-Heptane Mixtures at Pressures up to 100 bar

Dual fuel combustion exhibits a high degree of complexity due to the presence of different fuels like diesel and natural gas in initially different physical states and a spatially strongly varying mixing ratio. Optimizing this combustion process on an engine test bench is costly and time consuming. Cost reduction can be achieved by utilizing simulation tools. Although these tools cannot replace the application of test benches completely, the total development costs can be reduced by an educated combination of simulations and experiments. A suitable model for describing the reactions taking place in the combustion chamber is required to correctly reproduce the dual fuel combustion process. This is why in the presented study, four different reaction mechanisms are benchmarked to shock tube (ST) and rapid compression machine (RCM) measurements of ignition delay times (IDTs) at pressures between 60 and 100 bar and temperatures between 671 and 1284 K. To accommodate dual fuel relevant diesel-natural gas mixtures, methane–propane–n-heptane mixtures are considered as the surrogate. Additionally, the mechanisms AramcoMech 1.3, 2.0 and 3.0 are tested for methane–propane mixtures. The influence of pressure and propane/n-heptane content on the IDT based on the measurements is presented and the extent to which the mechanisms can reflect the IDT-changes discussed.

Experimental study of ethanol oxidation behind reflected shock waves: Ignition delay time and H2O laser-absorption measurements

The oxidation of ethanol was investigated in shock tubes by measuring ignition delay times and water time history profiles. A laser absorption technique was used in the latter case. Ignition delay times were investigated for three equivalence ratios, 0.5, 1.0, and 2.0, and for pressures ranging from 1.3 to 53 atm. The fuel concentration and the type of diluent used were also varied. The ignition delay times were in very good agreement with results from the literature for the very few overlapping conditions, and most of the experimental conditions have never been studied before. A high level of accuracy was observed for the predictions of the ignition delay times from detailed kinetics mechanisms. Inhomogeneous ignition events were observed in some specific conditions, validating the notions of thermal diffusivity and flame thickness developed in the literature for the reasons behind such inhomogeneous ignition. The water time-history profiles showed the formation of water in two stages. These profiles were also modeled using well-known detailed kinetic mechanisms from the literature. Severe discrepancies were often observed for laser-absorption measurements, and this was the case with most of the models. A numerical analysis (sensitivity and rate-of-production) was conducted using the two best-performing literature mechanisms (namely, AramcoMech3.0 and CRECK).