The Experts below are selected from a list of 114 Experts worldwide ranked by ideXlab platform
Zoltan Jozefik - One of the best experts on this subject based on the ideXlab platform.
-
constant volume n heptane autoignition using one dimensional turbulence
Combustion and Flame, 2018Co-Authors: A Juan M Medina, Heiko Schmidt, Fabian Mauss, Zoltan JozefikAbstract:Abstract Constant volume premixed lean n-Heptane/air autoignition at high pressure is investigated using the One-Dimensional Turbulence (ODT) model. The configuration consists of a 1D fixed volume domain with a prescribed velocity spectrum and Temperature fluctuations superimposed on an Initial uniformly elevated scalar field. The sensitivity of the heat release rate and pressure evolution to the Initial Temperature Distribution is studied by imposing different Initial Temperature fields while holding the mean, RMS and integral length scale of the field constant. Three detailed chemical mechanisms are employed for the prediction of autoignition and heat release rate. To mitigate the high computational cost associated with the calculation of the chemical source terms in the stiff complex mechanisms, an approach based on the Strang-Splitting method is presented. Finally, a study of the ODT model uncertainty is carried out. For validation, ODT results are compared to 2D DNS data from Yoo et al. (2011) for the temporal evolution of heat release rate, pressure and density-weighted displacement speed. Ensemble averaged ODT results show good agreement with the DNS data. ODT results generated from varying the Initial Temperature fields show that the ignition delay time is highly sensitive to the Initial Temperature field. The ODT model uncertainty study shows that dispersion due to the stochastic nature of the model is considerably smaller than the dispersion resulting from varying the Initial Temperature field. Overall, this study demonstrates that ODT accurately captures the evolution of complex chemistry reactive flows in constant volume autoignition simulations and that once validated, ODT is an efficient tool that can be used to carry out parametric studies not feasible by DNS.
E U Schlunder - One of the best experts on this subject based on the ideXlab platform.
-
study of the analytical solution to the heat transfer problem and surface Temperature in a semi infinite body with a constant heat flux at the surface and an Initial Temperature Distribution
Heat and Mass Transfer, 1995Co-Authors: J R Zhuang, K Werner, E U SchlunderAbstract:In many practical cases, one heats a semi-infinite solid with a constant heat flux source. For such an unsteady heat transfer problem, if the body has a uniform Initial Temperature, the analytical solution has been given by Carslaw and Jaeger. The surface Temperature of the semi-infinite body follows the $$\sqrt t $$ -rule, that is, the surface Temperature changes in proportion to square root of heating time. But if, instead of the uniform Initial Temperature, the body has a Temperature Distribution at the beginning of heating, the analytical solution has not yet been developed. Analytical solutions to the same problem with an exponential or a linear Initial Temperature Distribution are obtained in this paper. It is shown, that in the case of a linear Initial Temperature Distribution the surface Temperature also changes according to $$\sqrt t $$ -rule Approximating the Initial Temperature Distribution near the surface by its tangent at the surface, it is found that the surface Temperature within a short time after the start of heating should also satisfy the $$\sqrt t $$ -rule, in spite of an arbitrary Initial Temperature Distribution. The experimental data support this argument. Furthermore, the constant heat flux can be calculated after relationship between the surface Temperature and heating time according to the equation derived in this paper, if the Initial Temperature Distribution or its first-order derivative at the surface is known.
-
study of the analytical solution to the heat transfer problem and surface Temperature in a semi infinite body with a constant heat flux at the surface and an Initial Temperature Distribution
Wärme- und Stoffübertragung, 1995Co-Authors: J R Zhuang, K Werner, E U SchlunderAbstract:In many practical cases, one heats a semi-infinite solid with a constant heat flux source. For such an unsteady heat transfer problem, if the body has a uniform Initial Temperature, the analytical solution has been given by Carslaw and Jaeger. The surface Temperature of the semi-infinite body follows the √t-rule, that is, the surface Temperature changes in proportion to square root of heating time. But if, instead of the uniform Initial Temperature, the body has a Temperature Distribution at the beginning of heating, the analytical solution has not yet been developed. Analytical solutions to the same problem with an exponential or a linear Initial Temperature Distribution are obtained in this paper. It is shown, that in the case of a linear Initial Temperature Distribution the surface Temperature also changes according to √t-rule. Approximating the Initial Temperature Distribution near the surface by its tangent at the surface, it is found that the surface Temperature within a short time after the start of heating should also satisfy the √t-rule, in spite of an arbitrary Initial Temperature Distribution. The experimental data support this argument. Furthermore, the constant heat flux can be calculated after relationship between the surface Temperature and heating time according to the equation derived, if the Initial Temperature Distribution or its first-order derivative at the surface is known
Ramanan Sankaran - One of the best experts on this subject based on the ideXlab platform.
-
analytical model for auto ignition in a thermally stratified hcci engine
Combustion Science and Technology, 2007Co-Authors: Ramanan Sankaran, John C HewsonAbstract:The characteristics of auto-ignition in HCCI engines in the presence of charge stratification is studied theoretically using activation energy asymptotics. The analysis accounts for the effects of pressure rise due to piston motion and heat release, and the consequent compression-heating of the charge. The chemical kinetics are approximated using a single reaction step with a large activation energy and the compression-heating effects are accounted for through an entropy variable. The resultant model is simple and suitable for extensive parametric studies of HCCI engine combustion. Some preliminary results on the effects of mixture and composition stratification on the duration of burning are presented using a presumed Gaussian PDF for the Initial Temperature Distribution. The effects of mixture stratification on the feasible operating conditions is demonstrated using simple criteria to delineate the knocking and incomplete end-gas combustion regimes.
-
the effects of non uniform Temperature Distribution on the ignition of a lean homogeneous hydrogen air mixture
Proceedings of the Combustion Institute, 2005Co-Authors: Ramanan Sankaran, Evatt R Hawkes, Jacqueline H ChenAbstract:Abstract To characterize the ignition process in homogeneous charge compression ignition engines, high fidelity simulations are performed to study the effects of different Initial Temperature Distributions on the autoignition of a turbulent homogeneous mixture at high pressure. The effects of the Initial Temperature Distribution on the ignition and subsequent heat release are studied by comparison of simulations with three Initial random Temperature fields having different skewness. It is found that the scalar mixing and turbulence have a significant influence on the Initial location and further evolution of the ignition kernels. A comparison of the integrated heat release rates shows that the presence of a hot core leads to early ignition and increased duration of burning, while a cold core leads to a dormant end gas, which is consumed by slow combustion. The extent of flame fronts is quantified by a Temperature gradient cut-off, revealing distinct behavior in the appearance of flame fronts for the three cases. Finally, two distinct ignition regimes, namely the spontaneous propagation and the deflagration regimes, are identified, and a predictive criterion is defined based on the spontaneous propagation speed and deflagration speed at the local mixture conditions. The predictions are found to be consistent with the observed results, suggesting a potential strategy in the modeling of HCCI combustion process.
Jacqueline H Chen - One of the best experts on this subject based on the ideXlab platform.
-
the effects of non uniform Temperature Distribution on the ignition of a lean homogeneous hydrogen air mixture
Proceedings of the Combustion Institute, 2005Co-Authors: Ramanan Sankaran, Evatt R Hawkes, Jacqueline H ChenAbstract:Abstract To characterize the ignition process in homogeneous charge compression ignition engines, high fidelity simulations are performed to study the effects of different Initial Temperature Distributions on the autoignition of a turbulent homogeneous mixture at high pressure. The effects of the Initial Temperature Distribution on the ignition and subsequent heat release are studied by comparison of simulations with three Initial random Temperature fields having different skewness. It is found that the scalar mixing and turbulence have a significant influence on the Initial location and further evolution of the ignition kernels. A comparison of the integrated heat release rates shows that the presence of a hot core leads to early ignition and increased duration of burning, while a cold core leads to a dormant end gas, which is consumed by slow combustion. The extent of flame fronts is quantified by a Temperature gradient cut-off, revealing distinct behavior in the appearance of flame fronts for the three cases. Finally, two distinct ignition regimes, namely the spontaneous propagation and the deflagration regimes, are identified, and a predictive criterion is defined based on the spontaneous propagation speed and deflagration speed at the local mixture conditions. The predictions are found to be consistent with the observed results, suggesting a potential strategy in the modeling of HCCI combustion process.
A Juan M Medina - One of the best experts on this subject based on the ideXlab platform.
-
constant volume n heptane autoignition using one dimensional turbulence
Combustion and Flame, 2018Co-Authors: A Juan M Medina, Heiko Schmidt, Fabian Mauss, Zoltan JozefikAbstract:Abstract Constant volume premixed lean n-Heptane/air autoignition at high pressure is investigated using the One-Dimensional Turbulence (ODT) model. The configuration consists of a 1D fixed volume domain with a prescribed velocity spectrum and Temperature fluctuations superimposed on an Initial uniformly elevated scalar field. The sensitivity of the heat release rate and pressure evolution to the Initial Temperature Distribution is studied by imposing different Initial Temperature fields while holding the mean, RMS and integral length scale of the field constant. Three detailed chemical mechanisms are employed for the prediction of autoignition and heat release rate. To mitigate the high computational cost associated with the calculation of the chemical source terms in the stiff complex mechanisms, an approach based on the Strang-Splitting method is presented. Finally, a study of the ODT model uncertainty is carried out. For validation, ODT results are compared to 2D DNS data from Yoo et al. (2011) for the temporal evolution of heat release rate, pressure and density-weighted displacement speed. Ensemble averaged ODT results show good agreement with the DNS data. ODT results generated from varying the Initial Temperature fields show that the ignition delay time is highly sensitive to the Initial Temperature field. The ODT model uncertainty study shows that dispersion due to the stochastic nature of the model is considerably smaller than the dispersion resulting from varying the Initial Temperature field. Overall, this study demonstrates that ODT accurately captures the evolution of complex chemistry reactive flows in constant volume autoignition simulations and that once validated, ODT is an efficient tool that can be used to carry out parametric studies not feasible by DNS.