Abstract
Accurate predictions of low-temperature heat release (LTHR) are critical for modeling auto-ignition processes in internal combustion engines. While LTHR is typically obscured by deflagration, extremely late ignition phasing can lead to LTHR prior to the spark, a behavior known as pre-spark heat release (PSHR). In this research, PSHR in a boosted direct-injection spark-ignition engine was studied using 3-D computational fluid dynamics (CFD) and detailed chemical kinetics. The turbulent combustion was modeled via a hybrid approach that incorporates the G-equation model for tracking the turbulent flame front, and the well-stirred reactor model with detailed chemistry for assessing the low-temperature reactions in unburnt gas. Simulations were conducted using Co-Optima alkylate and E30 fuels at operating conditions characterized by different PSHR intensities. The predicted in-cylinder pressure and heat release rate were found to agree well with experiments. It was found the estimate of previous-cycle trapped residuals is of utmost importance for capturing PSHR correctly. A simulation best practice was developed which keeps the detailed chemistry solver active throughout the entire simulation, allowing to track the evolution of intermediate species from one cycle to the next. Following the validation, the dynamics of PSHR were analyzed in detail employing the pressure-temperature (P-T) trajectory framework. It was shown that PSHR correlated with the first-stage ignition delay of the fuel, hence showing close relation to the in-cylinder P-T trajectory and the chemical kinetics. Besides, it was indicated that LTHR is a self-limiting process that has the effect of attenuating the thermal stratification in the combustion chamber. Furthermore, it was observed the occurrence of PSHR caused the P-T trajectory of end-gas to overlap with the negative temperature coefficient region of the fuel’s ignition-delay maps. This effect was more significant in the fuel-rich regions where engine knock tendency would be generally higher, with potential implications on knock control and mitigation.
| Original language | English |
|---|---|
| Pages (from-to) | 3-15 |
| Number of pages | 13 |
| Journal | International Journal of Engine Research |
| Volume | 24 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jan 2023 |
Funding
The authors wish to thank Kevin Stork, Gurpreet Singh, and Michael Weismiller, program managers at DOE, for their support; Zongyu Yue at Tianjin University (previously at Argonne) for the help with initiating this work; Krishna Kalvakala and Pinaki Pal at Argonne for their help with the 0-D simulations; Joonsik Hwang at Mississippi State University and Lyle Pickett at Sandia National Laboratories for providing the experimental spray data; LCRC cluster facilities at Argonne for the computing resources on the Bebop cluster; Convergent Science Inc. for providing the CONVERGE CFD software licenses. The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The submitted manuscript has been created by Argonne National Laboratory managed by UChicago Argonne, LLC, under contract DE-AC02-06CH11357, and by Oak Ridge National Laboratory managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. This research was conducted as part of the Co-Optimization of Fuels and Engines (Co-Optima) initiative sponsored by the US Department of Energy Office of Energy Efficiency and Renewable Energy and Bioenergy Technologies and Vehicle Technologies Offices. The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The submitted manuscript has been created by Argonne National Laboratory managed by UChicago Argonne, LLC, under contract DE-AC02-06CH11357, and by Oak Ridge National Laboratory managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. This research was conducted as part of the Co-Optimization of Fuels and Engines (Co-Optima) initiative sponsored by the US Department of Energy Office of Energy Efficiency and Renewable Energy and Bioenergy Technologies and Vehicle Technologies Offices.
Keywords
- Pre-spark heat release
- auto-ignition
- low-temperature heat release
- pressure-temperature trajectory
- spark ignition