The disintegration process of liquid fuel within combustion chambers is one of the most important parameters for
efficient and stable combustion. Especially for high pressures exceeding the critical value of the injected fluids
the mixing processes are not fully understood yet. Recently, different theoretical macroscopic models have been
introduced to understand breakdown of the classical two phase regime and predict the transition from evaporation to
a diffuse-mixing process. In order to gain deeper insight into the physical processes of this transition, a parametric
study of free-falling n-pentane droplets in an inert nitrogen atmosphere is presented. Atmospheric conditions varied
systematically from sub- to supercritical values with respect to the fluid properties. An overlay of a diffuse lighted
image with a shadowgram directly in the optical setup (front lighted shadowgraphy) was applied to simultaneously
detect the presence of a material surface of the droplet as well as changes in density gradients in the surrounding
atmosphere. The experimental investigation illustrates, that the presence of a material surface cannot be shown
by a direct shadowgram. However, reflections and refractions caused by diffuse ambient illumination are able to
indicate the presence of a material surface. In case of the supercritical droplet injections in this study, front lighted
shadowgraphy clearly revealed the presence of a material surface, even when the pre-heated droplets are released
into a supercritical atmosphere. This detection of the droplet interface indicates, that the droplet remains subcritical
in the region of interest, even though it is injected into a supercritical atmosphere. Based on the adiabatic mixing
assumption recent Raman-scattering results in the wake of the droplet are re-evaluated to compute the temperature
distribution. Presented experimental findings as well as the re-evaluation of recent Raman scattering results are
compared to thermodynamic models to predict the onset of diffuse-mixing and supercritical disintegration of the
droplet. Additionally, a one dimensional evaporation model is used to evaluate the validity of the adiabatic mixing
assumption in the estimation of the droplet temperature. The presented findings contribute to the understanding of
recent theoretical models for prediction of spray and droplet disintegration and the onset of diffuse-mixing processes.
%0 Generic
%1 steinhausen2017experimental
%A Steinhausen, Christoph
%A Lamanna, Grazia
%A Weigand, Bernhard
%A Stierle, Rolf
%A Gross, Joachim
%A Preusche, Andreas
%A Dreizler, Andreas
%D 2017
%K myown from:rolfstierle rstierle from:rstierle itt jgross critical-point
%R 10.4995/ILASS2017.2017.4635
%T Experimental Investigation of Droplet Injections in the Vicinity of the Critical Point: A comparison of different model approaches
%U http://dx.doi.org/10.4995/ILASS2017.2017.4635
%X The disintegration process of liquid fuel within combustion chambers is one of the most important parameters for
efficient and stable combustion. Especially for high pressures exceeding the critical value of the injected fluids
the mixing processes are not fully understood yet. Recently, different theoretical macroscopic models have been
introduced to understand breakdown of the classical two phase regime and predict the transition from evaporation to
a diffuse-mixing process. In order to gain deeper insight into the physical processes of this transition, a parametric
study of free-falling n-pentane droplets in an inert nitrogen atmosphere is presented. Atmospheric conditions varied
systematically from sub- to supercritical values with respect to the fluid properties. An overlay of a diffuse lighted
image with a shadowgram directly in the optical setup (front lighted shadowgraphy) was applied to simultaneously
detect the presence of a material surface of the droplet as well as changes in density gradients in the surrounding
atmosphere. The experimental investigation illustrates, that the presence of a material surface cannot be shown
by a direct shadowgram. However, reflections and refractions caused by diffuse ambient illumination are able to
indicate the presence of a material surface. In case of the supercritical droplet injections in this study, front lighted
shadowgraphy clearly revealed the presence of a material surface, even when the pre-heated droplets are released
into a supercritical atmosphere. This detection of the droplet interface indicates, that the droplet remains subcritical
in the region of interest, even though it is injected into a supercritical atmosphere. Based on the adiabatic mixing
assumption recent Raman-scattering results in the wake of the droplet are re-evaluated to compute the temperature
distribution. Presented experimental findings as well as the re-evaluation of recent Raman scattering results are
compared to thermodynamic models to predict the onset of diffuse-mixing and supercritical disintegration of the
droplet. Additionally, a one dimensional evaporation model is used to evaluate the validity of the adiabatic mixing
assumption in the estimation of the droplet temperature. The presented findings contribute to the understanding of
recent theoretical models for prediction of spray and droplet disintegration and the onset of diffuse-mixing processes.
@conference{steinhausen2017experimental,
abstract = {The disintegration process of liquid fuel within combustion chambers is one of the most important parameters for
efficient and stable combustion. Especially for high pressures exceeding the critical value of the injected fluids
the mixing processes are not fully understood yet. Recently, different theoretical macroscopic models have been
introduced to understand breakdown of the classical two phase regime and predict the transition from evaporation to
a diffuse-mixing process. In order to gain deeper insight into the physical processes of this transition, a parametric
study of free-falling n-pentane droplets in an inert nitrogen atmosphere is presented. Atmospheric conditions varied
systematically from sub- to supercritical values with respect to the fluid properties. An overlay of a diffuse lighted
image with a shadowgram directly in the optical setup (front lighted shadowgraphy) was applied to simultaneously
detect the presence of a material surface of the droplet as well as changes in density gradients in the surrounding
atmosphere. The experimental investigation illustrates, that the presence of a material surface cannot be shown
by a direct shadowgram. However, reflections and refractions caused by diffuse ambient illumination are able to
indicate the presence of a material surface. In case of the supercritical droplet injections in this study, front lighted
shadowgraphy clearly revealed the presence of a material surface, even when the pre-heated droplets are released
into a supercritical atmosphere. This detection of the droplet interface indicates, that the droplet remains subcritical
in the region of interest, even though it is injected into a supercritical atmosphere. Based on the adiabatic mixing
assumption recent Raman-scattering results in the wake of the droplet are re-evaluated to compute the temperature
distribution. Presented experimental findings as well as the re-evaluation of recent Raman scattering results are
compared to thermodynamic models to predict the onset of diffuse-mixing and supercritical disintegration of the
droplet. Additionally, a one dimensional evaporation model is used to evaluate the validity of the adiabatic mixing
assumption in the estimation of the droplet temperature. The presented findings contribute to the understanding of
recent theoretical models for prediction of spray and droplet disintegration and the onset of diffuse-mixing processes.},
added-at = {2020-01-21T11:34:31.000+0100},
author = {Steinhausen, Christoph and Lamanna, Grazia and Weigand, Bernhard and Stierle, Rolf and Gross, Joachim and Preusche, Andreas and Dreizler, Andreas},
biburl = {https://puma.ub.uni-stuttgart.de/bibtex/2047aecfdd6cea2704ed14fbf1e769e58/itt},
doi = {10.4995/ILASS2017.2017.4635},
interhash = {335ec8b360ccdd523dc286b0352236a4},
intrahash = {047aecfdd6cea2704ed14fbf1e769e58},
keywords = {myown from:rolfstierle rstierle from:rstierle itt jgross critical-point},
timestamp = {2023-06-29T10:17:09.000+0200},
title = {Experimental Investigation of Droplet Injections in the Vicinity of the Critical Point: A comparison of different model approaches},
url = {http://dx.doi.org/10.4995/ILASS2017.2017.4635},
year = 2017
}