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Fokion N. Egolfopoulos - One of the best experts on this subject based on the ideXlab platform.
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laminar flame speeds under engine relevant conditions uncertainty quantification and minimization in spherically expanding flame experiments
Combustion and Flame, 2016Co-Authors: Christodoulos Xiouris, Jagannath Jayachandran, Fokion N. EgolfopoulosAbstract:Abstract The spherically expanding flame method is the only approach for measuring laminar flame speeds at thermodynamic states that are relevant to engines. In the present study, a comprehensive evaluation of data obtained under constant pressure and constant volume conditions was carried out through experiments, development of a mathematically rigorous method for uncertainty quantification and propagation, and advancement of numerical models that describe the experiments accurately. The proposed uncertainty characterization approach accounts for parameters related to all measurements, data processing, and finally data interpretation. With the aid of direct numerical simulations, an alternative approach was proposed to derive laminar flame speeds in constant pressure experiments by eliminating the need for using extrapolation equations developed based on simplifying assumptions, which are known to be susceptible to major errors under certain conditions. The propagation of spherical flames under constant volume conditions was investigated through experiments carried out in an entirely spherical chamber and the use of two numerical models. The first involves the solution of the one-dimensional conservation equations of mass, species, and energy while accounting for pressure rise. The second model was developed based on thermodynamics similarly to existing literature, but radiation loss was introduced at the optically thin limit and approximations were made to allow for re-absorption with minimum computational cost. It was shown that neglecting radiation in constant volume experiments could introduce errors as high as 15%. Incorporating the aforementioned techniques, laminar flame speeds were measured and reported with properly quantified uncertainties for flames of synthesis gas for pressures ranging from 3 to 30 atm, and unburned Mixture Temperatures ranging from 298 to 550 K. Selected measurements were carried out as well for methane and propane flames for pressures ranging from 3 to 7 atm, and unburned Mixture Temperature of 298 K. The approaches introduced in this study allow for the determination of laminar flame speeds with notably reduced uncertainties under conditions of relevance to engines, which has major implications for the validation of kinetic models of surrogate and real fuels.
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laminar flame propagation of atmospheric iso cetane air and decalin air Mixtures
Combustion and Flame, 2014Co-Authors: Hai Zhang, Fokion N. EgolfopoulosAbstract:Abstract Laminar flame speeds of iso-cetane/air and decalin/air Mixtures were measured in the counterflow configuration at atmospheric pressure and an elevated unburned Mixture Temperature of 443 K. Axial flow velocities were measured along the stagnation streamline using the digital particle image velocimetry. The laminar flame speeds were determined by determining the variation of a reference flame speed as a function of strain rate and computationally assisted non-linear extrapolations. The data are the first to be reported in the literature, and they were modeled using a recently developed kinetic model that includes 187 species and 6086 elementary reactions. In general, the computed results were found to be in close agreement with the data. In order to get insight into kinetic effects on flame propagation, detailed sensitivity and reaction path analyses were performed using the computed flame structures. The results revealed that at the same equivalence ratio, laminar flame speeds of iso-cetane/air Mixtures are lower than those of n-hexadecane/air Mixtures. Additionally, it was found that the laminar flame speeds of iso-cetane/air and decalin/air Mixtures are sensitive largely to C0–C4 kinetic subset, and that the lower reactivity of iso-cetane compared to n-hexadecane could be attributed to the higher production of relatively stable intermediates.
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an experimental and modeling study of the propagation of cyclohexane and mono alkylated cyclohexane flames
Proceedings of the Combustion Institute, 2011Co-Authors: Chunsheng Ji, Enoch E Dames, Baptiste Sirjean, Hai Wang, Fokion N. EgolfopoulosAbstract:Abstract Laminar flame speeds of cyclohexane/air, methylcyclohexane/air, ethylcyclohexane/air, n -propylcyclohexane/air, and n -butylcyclohexane/air Mixtures were determined in the counterflow configuration at atmospheric pressure, unburned Mixture Temperature of 353 K, and for a wide range of equivalence ratios. The results indicate that cyclohexane/air flames propagate somewhat faster than mono-alkylated cyclohexane/air flames. Flames of mono-alkylated cyclohexane compounds were found to have similar laminar flame speeds, from methylcyclohexane to n -butylcyclohexane, suggesting that the different alkyl groups have a secondary effect on flame propagation. The experiments were modeled using JetSurF (version 1.1) – a detailed kinetic model for the combustion of cyclohexane and its derivatives. Both experiment and model show satisfactory agreement with each other. Based on the analysis of the model results, the somewhat lower rates of mono-alkylated cyclohexane flame propagation are attributed to the greater production of propene and allyl and the increased H-atom scavenging by these C 3 intermediates. Though these fuel-specific reaction kinetic features do not limit the overall oxidation rates, the distribution of the cracked products do exert influences on flame propagation, leading to the subtle differences in the laminar flame speeds observed experimentally.
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flame propagation of Mixtures of air with binary liquid fuel Mixtures
Proceedings of the Combustion Institute, 2011Co-Authors: Fokion N. EgolfopoulosAbstract:Abstract The laminar flame speeds of Mixtures of air with 80% n -dodecane + 20% methylcyclohexane and 80% n -dodecane + 20% toluene, on a per volume basis, were determined in the counterflow configuration over a wide range of equivalence ratio, at atmospheric pressure and 403 K unburned Mixture Temperature. The choice of the fuel blends was dictated by their anticipated compositions in jet fuels surrogates. Phenomenological analysis shows that the laminar flame speeds of binary fuels Mixtures can be estimated using the laminar flame speeds and adiabatic flame Temperatures of the neat components. The propagation rates of various binary fuels blends were computed using detailed descriptions of chemical kinetics and molecular transport and were found to be in good agreement with the estimations. Although the fuel initial consumption pathways and the resulting intermediates and radicals may be different for each neat component, the propagation of flames of binary fuels is mostly sensitive to the flame Temperature through its influence on the main branching reaction H + O 2 → OH + O. Thus, kinetic couplings resulting from the presence of two different fuels, appear to have minor effect on flame propagation.
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flame propagation of butanol isomers air Mixtures
Proceedings of the Combustion Institute, 2011Co-Authors: Peter S Veloo, Fokion N. EgolfopoulosAbstract:Abstract An experimental and computational study was conducted on the propagation of flames of saturated butanol isomers. The experiments were performed in the counterflow configuration under atmospheric pressure, unburned Mixture Temperature of 343 K, and for a wide range of equivalence ratios. The experiments were simulated using a recent kinetic model for the four isomers of butanol. Results indicate that n-butanol/air flames propagate somewhat faster than both sec-butanol/air and iso-butanol/air flames, and that tert-butanol/air flames propagate notably slower compared to the other three isomers. Reaction path analysis of tert-butanol/air flames revealed that iso-butene is a major intermediate, which subsequently reacts to form the resonantly stable iso-butenyl radical retarding thus the overall reactivity of tert-butanol/air flames relatively to the other three isomers. Through sensitivity analysis, it was determined that the mass burning rates of sec-butanol/air and iso-butanol/air flames are sensitive largely to hydrogen, carbon monoxide, and C1–C2 hydrocarbon kinetics and not to fuel-specific reactions similarly to n-butanol/air flames. However, for tert-butanol/air flames notable sensitivity to fuel-specific reactions exists. While the numerical results predicted closely the experimental data for n-butanol/air and sec-butanol/air flames, they overpredicted and underpredicted the laminar flame speeds for iso-butanol/air and tert-butanol/air flames respectively. It was demonstrated further that the underprediction of the laminar flame speeds of tert-butanol/air flames by the model was most likely due to deficiencies of the C4-alkene kinetics.
Sudarshan Kumar - One of the best experts on this subject based on the ideXlab platform.
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effects of co2 n2 dilution on laminar burning velocity of stoichiometric dme air Mixture at elevated Temperatures
Journal of Hazardous Materials, 2017Co-Authors: Abdul Naseer Mohammed, Sudarshan Kumar, Khalid A Juhany, Ratna V Kishore, Akram MohammadAbstract:Abstract The laminar burning velocity of CO2/N2 diluted stoichiometric dimethyl ether (DME) air Mixtures is determined experimentally at atmospheric pressure and elevated Mixture Temperatures using a mesoscale high aspect-ratio diverging channel with inlet dimensions of 25 mm × 2 mm. In this method, planar flames at different initial Temperatures (Tu) were stabilized inside the channel using an external electric heater. The magnitude of burning velocities was acquired by measuring the flame position and initial Temperature. The mass conservation of the Mixture entering the inlet and the stationary planar flame front is applied to obtain the laminar burning velocity. Laminar burning velocity at different initial Mixture Temperatures is plotted with Temperature ratio ( T u / T u , o ) , where a reference Temperature (Tu,o) of 300 K is used. Enhancement in the laminar burning velocity is observed with Mixture Temperature for DME-air Mixtures with CO2 and N2 dilutions. A significant decrease in the burning velocity and slight increase in Temperature exponent of the stoichiometric DME-air Mixture was observed with dilution at same Temperatures. The addition of CO2 has profound influence when compared to N2 addition on both burning velocity and Temperature exponent.
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effect of co2 n2 dilution on laminar burning velocity of liquid petroleum gas air Mixtures at elevated Temperatures
Energy, 2016Co-Authors: Aswathy K Nair, Ratna Kishore Velamati, Sudarshan KumarAbstract:Abstract The present experimental study reports the effect of CO 2 /N 2 dilution on laminar burning velocity of premixed LPG (liquid-petroleum-gas)-air Mixtures at elevated Temperatures using a preheated mesoscale diverging channel technique. The experiments were carried out for a range of equivalence ratios varying from 0.8 2 varying from 10% 2 varying from 10% 2 /N 2 leads to an increase in Temperature exponent (α). The increase in Temperature exponent due to CO 2 dilution is more pronounced as compared to N 2 dilution case. A flame structure study has been carried out to understand the effect of Mixture Temperature and diluent using USC (University of Southern California) Mech II reaction mechanism.
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effect of co2 n2 dilution on laminar burning velocity of liquid petroleum gas air Mixtures at elevated Temperatures
Energy, 2016Co-Authors: Aswathy K Nair, Ratna Kishore Velamati, Sudarshan KumarAbstract:The present experimental study reports the effect of CO2/N2 dilution on laminar burning velocity of premixed LPG (liquid-petroleum-gas)-air Mixtures at elevated Temperatures using a preheated mesoscale diverging channel technique. The experiments were carried out for a range of equivalence ratios varying from 0.8 < Φ < 1.3 with percentage dilution of the fuel component by volume (β) for CO2 varying from 10% < β < 30% and N2 varying from 10% < β < 40%. A power–law correlation has been obtained for the present experimental data as a function of percentage dilution, Mixture Temperature and equivalence ratio. It has been observed that an increase in dilution with CO2/N2 leads to an increase in Temperature exponent (α). The increase in Temperature exponent due to CO2 dilution is more pronounced as compared to N2 dilution case. A flame structure study has been carried out to understand the effect of Mixture Temperature and diluent using USC (University of Southern California) Mech II reaction mechanism.
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laminar burning velocity of methane air Mixtures at elevated Temperatures
Energy & Fuels, 2013Co-Authors: Mohammad Akram, Priyank Saxena, Sudarshan KumarAbstract:The measured and computed laminar burning velocities of methane–air Mixtures at higher Mixture Temperatures are reported in this paper. The experiments and computations were performed for a wide range of Mixture Temperatures and equivalence ratios. The unburned Mixture Temperature ranges from 370 to 650 K. Computational predictions of burning velocities were carried out with GRI-Mech 3.0, San Diego mechanism, and Konnov mechanism for methane–air Mixtures. The measured burning velocities match very well with the numerical predictions for all Mixture Temperatures and existing experimental results for Mixtures at ambient Temperature. Another contribution of the present work is the variation of the measured power-law Temperature exponent with Mixture equivalence ratios. The maximum burning velocity (even at high Mixture Temperatures) and minimum Temperature exponent magnitudes were observed to exist for slightly richer Mixtures.
Gregory B Rieker - One of the best experts on this subject based on the ideXlab platform.
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broadband dual frequency comb spectroscopy in a rapid compression machine
Optics Express, 2019Co-Authors: Anthony D Draper, Ryan K Cole, Amanda S Makowiecki, Jeffrey Mohr, Andrew Zdanowicz, Anthony J Marchese, Nazanin Hoghooghi, Gregory B RiekerAbstract:We demonstrate fiber mode-locked dual-frequency comb spectroscopy for broadband, high-resolution measurements in a rapid compression machine (RCM). We apply an apodization technique to improve the short-term signal-to-noise-ratio (SNR), which enables broadband spectroscopy at combustion-relevant timescales. We measure the absorption on 24345 individual wavelength elements (comb teeth) between 5967 and 6133 cm−1 at 704 µs time resolution during a 12 ms compression of a CH4-N2 Mixture. We discuss the effect of the apodization technique on the absorption spectra, and apply an identical effect to the spectral model during fitting to recover the Mixture Temperature. The fitted Temperature is compared against an adiabatic model, and found to be in good agreement with expected trends. This work demonstrates the potential of DCS to be used as an in situ diagnostic tool for broadband, high-resolution measurements in engine-like environments.
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broadband dual frequency comb spectroscopy in a rapid compression machine
arXiv: Applied Physics, 2018Co-Authors: Anthony D Draper, Ryan K Cole, Amanda S Makowiecki, Jeffrey Mohr, Anthony J Marchese, Nazanin Hoghooghi, Andrew Zdanawicz, Gregory B RiekerAbstract:We demonstrate fiber mode-locked dual frequency comb spectroscopy for broadband, high resolution measurements in a rapid compression machine (RCM). We apply an apodization technique to improve the short-term signal-to-noise-ratio (SNR), which enables broadband spectroscopy at combustion-relevant timescales. We measure the absorption on 24345 individual wavelength elements (comb teeth) between 5967 and 6133 cm-1 at 704 microsecond time resolution during a 12-ms compression of a CH4-N2 Mixture. We discuss the effect of the apodization technique on the absorption spectra, and apply an identical effect to the spectral model during fitting to recover the Mixture Temperature. The fitted Temperature is compared against an adiabatic model, and found to be in good agreement with expected trends. This work demonstrates the potential of DCS to be used as an in situ diagnostic tool for broadband, high resolution, measurements in engine-like environments.
Anthony D Draper - One of the best experts on this subject based on the ideXlab platform.
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broadband dual frequency comb spectroscopy in a rapid compression machine
Optics Express, 2019Co-Authors: Anthony D Draper, Ryan K Cole, Amanda S Makowiecki, Jeffrey Mohr, Andrew Zdanowicz, Anthony J Marchese, Nazanin Hoghooghi, Gregory B RiekerAbstract:We demonstrate fiber mode-locked dual-frequency comb spectroscopy for broadband, high-resolution measurements in a rapid compression machine (RCM). We apply an apodization technique to improve the short-term signal-to-noise-ratio (SNR), which enables broadband spectroscopy at combustion-relevant timescales. We measure the absorption on 24345 individual wavelength elements (comb teeth) between 5967 and 6133 cm−1 at 704 µs time resolution during a 12 ms compression of a CH4-N2 Mixture. We discuss the effect of the apodization technique on the absorption spectra, and apply an identical effect to the spectral model during fitting to recover the Mixture Temperature. The fitted Temperature is compared against an adiabatic model, and found to be in good agreement with expected trends. This work demonstrates the potential of DCS to be used as an in situ diagnostic tool for broadband, high-resolution measurements in engine-like environments.
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broadband dual frequency comb spectroscopy in a rapid compression machine
arXiv: Applied Physics, 2018Co-Authors: Anthony D Draper, Ryan K Cole, Amanda S Makowiecki, Jeffrey Mohr, Anthony J Marchese, Nazanin Hoghooghi, Andrew Zdanawicz, Gregory B RiekerAbstract:We demonstrate fiber mode-locked dual frequency comb spectroscopy for broadband, high resolution measurements in a rapid compression machine (RCM). We apply an apodization technique to improve the short-term signal-to-noise-ratio (SNR), which enables broadband spectroscopy at combustion-relevant timescales. We measure the absorption on 24345 individual wavelength elements (comb teeth) between 5967 and 6133 cm-1 at 704 microsecond time resolution during a 12-ms compression of a CH4-N2 Mixture. We discuss the effect of the apodization technique on the absorption spectra, and apply an identical effect to the spectral model during fitting to recover the Mixture Temperature. The fitted Temperature is compared against an adiabatic model, and found to be in good agreement with expected trends. This work demonstrates the potential of DCS to be used as an in situ diagnostic tool for broadband, high resolution, measurements in engine-like environments.
Rolf D Reitz - One of the best experts on this subject based on the ideXlab platform.
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an investigation of thermodynamic states during high pressure fuel injection using equilibrium thermodynamics
International Journal of Multiphase Flow, 2015Co-Authors: Lu Qiu, Rolf D ReitzAbstract:Abstract A numerical investigation of mixing processes between an injected fuel (an n-alkane) and a chamber inert gas (nitrogen) was carried out for high-pressure fuel injection. The objective is to determine conditions for the coexistence of both liquid and gas phases under the typical ambient conditions encountered in diesel engines. A phenomenological investigation was built by coupling phase stability analysis with the energy conservation equation. Phase changes (including separation and combination) are predicted to occur so as to yield the lowest Gibbs free energy. It is also shown that predicted states without considering phase transitions can be very different from the corresponding thermodynamically correct states. By comparing four n-alkane/nitrogen Mixtures it is shown that the lower limit of the two-phase region occurs at similar Temperatures. However, heavy n-alkane/nitrogen Mixtures have a larger upper limit, and phase separation occurs at higher Temperatures. The present model predicts the existence of multiple phases locally in the dense spray jet under high Temperature and pressure ambient conditions due to the significant reduction of the Mixture Temperature caused by vaporization and cooling.
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in cylinder fuel blending of gasoline diesel for improved efficiency and lowest possible emissions on a multi cylinder light duty diesel engine
SAE 2010 Powertrains Fuels & Lubricants Meeting, 2010Co-Authors: Scott Curran, Vitaly Y Prikhodko, Scott C Sluder, James E Parks, Robert M Wagner, Sage L Kokjohn, Rolf D ReitzAbstract:In-cylinder fuel blending of gasoline/diesel fuel is investigated on a multi-cylinder light-duty diesel engine as a potential strategy to control in-cylinder fuel reactivity for improved efficiency and lowest possible emissions. This approach was developed and demonstrated at the University of Wisconsin through modeling and single-cylinder engine experiments. The objective of this study is to better understand the potential and challenges of this method on a multi-cylinder engine. More specifically, the effect of cylinder-to-cylinder imbalances, heat rejection, and in-cylinder charge motion as well as the potential limitations imposed by real-world turbo-machinery were investigated on a 1.9-liter four-cylinder engine. This investigation focused on one engine condition, 2300 rpm, 4.2 bar brake mean effective pressure (BMEP). Gasoline was introduced with a port-fuel-injection system. Parameter sweeps included gasoline-to-diesel fuel ratio, intake air Mixture Temperature, in-cylinder swirl number, and diesel start-of-injection phasing. In addition, engine parameters were trimmed for each cylinder to balance the combustion process for maximum efficiency and lowest emissions. An important observation was the strong influence of intake charge Temperature on cylinder pressure rise rate. Experiments were able to show increased thermal efficiency along with dramatic decreases in oxides of nitrogen (NOX) and particulate matter (PM). However, indicated thermal efficiency for themore » multi-cylinder experiments were less than expected based on modeling and single-cylinder results. The lower indicated thermal efficiency is believed to be due increased heat transfer as compared to the model predictions and suggest a need for improved cylinder-to-cylinder control and increased heat transfer control.« less
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analysis of mixing and thermal effects on low Temperature combustion in ic engine operation
Combustion Science and Technology, 2009Co-Authors: Youngchul Ra, Rolf D Reitz, Ramachandra DiwakarAbstract:The effects of thermal and mixing conditions of the in-cylinder charge in internal combustion (IC) engines on emissions in low-Temperature combustion (LTC) regimes are analyzed numerically. In the analysis, concepts of an equilibrium Temperature (Teq), peak Temperature (Tpeak), and anticipated emissions (AE) are introduced. Also, Mixture condition representations in Temperature (T) vs. Temperature (T) space (called T − T plot) and anticipated emissions (AE) vs. Temperature (T) space (called AE − T plot) are proposed to represent the in-cylinder Mixture quality and emission characteristics of the combustion. Five combustion pathways are identified using a Tpeak − Teq plot, and it is applied to describe both HCCI and DI engine combustion. An optimal Temperature window and an optimal mixing window are defined and demonstrated in LTC engine operation. The results show that stratification of Mixture Temperature due to evaporation cooling and wall heat transfer significantly affects UHC/CO emissions of LTC engi...