Vaporization effects on transient diesel spray structure
Date
2011
Authors
Bajaj, C.
Abraham, J.
Pickett, L.
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Journal article
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Atomization and Sprays, 2011; 21(5):411-426
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Chetan Bajaj, John Abraham and Lyle M. Pickett
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Abstract
This paper examines how the penetration, spreading rate, and entrainment of a vaporizing spray differ from those of a nonvaporizing spray under diesel engine operating conditions, when the injected mass and momentum flow rates are the same for both. Correlations for these parameters derived for nonvaporizing sprays from measurements in a constant-volume chamber are often employed to explain the behavior of vaporizing sprays in diesel engines. In fact, they appear to explain results rather well. Furthermore, vapor jets injected with the same mass and momentum flow rates as the vaporizing sprays have been shown to give penetration and spreading rates which are comparable to those of the sprays, although the latent heat of vaporization has not been included in specifying the internal energy of the vapor. Why? These questions are addressed by carrying out computations in a constant-volume chamber for the Sandia baseline n-heptane spray (http://www.ca.sandia.gov/ecn). This spray has been the subject of a prior study by the authors. Details of vaporizing and nonvaporizing sprays, and corresponding vapor jets, are examined in order to provide insight into the physics whose effects are ultimately reflected in the global parameters such as penetration and spreading. The role that vaporization plays in determining these parameters is a focus of the paper. The influence of drop size and ambient conditions on the conclusions is critically evaluated. The interplay of changes in temperature and density in the core of the spray with momentum exchange and entrainment is discussed as part of the explanation of the observed results.
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© Begell House Inc. 2011