Abstract
The influence of thermal stratification on autoignition at constant volume and high pressure is studied by direct numerical simulation (DNS) with detailed hydrogen/air chemistry with a view to providing better understanding and modeling of combustion processes in homogeneous charge compression-ignition engines. Numerical diagnostics are developed to analyze the mode of combustion and the dependence of overall ignition progress on initial mixture conditions. The roles of dissipation of heat and mass are divided conceptually into transport within ignition fronts and passive scalar dissipation, which modifies the statistics of the preignition temperature field. Transport within ignition fronts is analyzed by monitoring the propagation speed of ignition fronts using the displacement speed of a scalar that tracks the location of maximum heat release rate. The prevalence of deflagrative versus spontaneous ignition front propagation is found to depend on the local temperature gradient, and may be identified by the ratio of the instantaneous front speed to the laminar deflagration speed. The significance of passive scalar mixing is examined using a mixing timescale based on enthalpy fluctuations. Finally, the predictions of the multizone modeling strategy are compared with the DNS, and the results are explained using the diagnostics developed.
| Original language | English |
|---|---|
| Pages (from-to) | 128-144 |
| Number of pages | 17 |
| Journal | Combustion and Flame |
| Volume | 145 |
| Issue number | 1-2 |
| DOIs | |
| State | Published - Apr 2006 |
| Externally published | Yes |
Funding
Sandia National Laboratories (SNL) is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94-AL85000. The work at SNL was supported by the Division of Chemical Sciences, Geosciences and Biosciences, the Office of Basic Energy Sciences, the U.S. Department of Energy. Calculations were performed at SNL and at the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract DE-AC03-76SF00098. The High Performance Computing and Networking department at SNL provided access to a 256 processor Infiniband testbed. The authors acknowledge fruitful discussions with Drs. John Hewson, John Dec, and Magnus Sjöberg. The work at UM was supported by the Consortium on HCCI Engine Research directed by the UM and funded by the Department of Energy, and also by Department of Energy, Office of Basic Energy Sciences, SciDAC Computational Chemistry Program.
| Funders | Funder number |
|---|---|
| Consortium on HCCI | |
| U.S. Department of Energy | DE-AC04-94-AL85000 |
| Office of Science | DE-AC03-76SF00098 |
| Basic Energy Sciences | |
| Sandia National Laboratories | |
| Chemical Sciences, Geosciences, and Biosciences Division |
Keywords
- Direct numerical simulation
- HCCI
- Ignition
- Multizone model