Evaluation of an Unsteady Flamelet Progress Variable Model for Autoignition and Flame Lift-Off in Diesel Jets

Abstract

An unsteady flamelet progress variable (UFPV) model is evaluated for modeling autoignition and flame lift-off in diesel jets. Changes in injection pressure, orifice diameter, ambient temperature, density, and O₂ concentration are considered. In implementing the model in a Reynolds-averaged Navier–Stokes (RANS) code, a look-up table of reaction source terms is generated as a function of mixture fraction Z, stoichiometric scalar dissipation rate χ_st and progress variable C_st by solving the unsteady flamelet equations. It is assumed that the probability density functions (pdfs) of Z, χ_st, and C_st are statistically independent, and presumed functions are employed for the pdfs. Comparisons with experimental results show that the model is able to predict ignition delay and flame lift-off with reasonable accuracy in the RANS simulations. The quantitative agreement between computed and measured results depends on the definitions employed to quantify autoignition time and lift-off height, but, in general, the agreement is within 25%.

Keywords:

• Diesel autoignition
• Diesel flame lift-off
• Multidimensional modeling
• Unsteady flamelets

ACKNOWLEDGMENTS

The authors thank Professor Vinicio Magi for his help with the code and useful discussions related to this work. They also thank the Rosen Center for Advanced Computing at Purdue University and the National Center for Supercomputing Applications (NCSA) for providing the computing resources for this work. Financial support for this work was provided by Caterpillar, Inc.

Notes

^a Estimatedvalue: This value is for diesel fuel injected at 432 K.