skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Parallel methodology to capture cyclic variability in motored engines

Abstract

Numerical prediction of of cycle-to-cycle variability (CCV) in SI engines is extremely challenging for two key reasons: (i) high-fidelity methods such as large eddy simulation (LES) are require to accurately capture the in-cylinder turbulent flowfield, and (ii) CCV is experienced over long timescales and hence the simulations need to be performed for hundreds of consecutive cycles. In this study, a new methodology is proposed to dissociate this long time-scale problem into several shorter time-scale problems, which can considerably reduce the computational time without sacrificing the fidelity of the simulations. The strategy is to perform multiple single-cycle simulations in parallel by effectively perturbing the simulation parameters such as the initial and boundary conditions. It is shown that by perturbing the initial velocity field effectively based on the intensity of the in-cylinder turbulence, the mean and variance of the in-cylinder flowfield is captured reasonably well. Adding perturbations in the initial pressure field and the boundary pressure improves the predictions. It is shown that this new approach is able to give accurate predictions of the flowfield statistics in less than one-tenth of time required for the conventional approach of simulating consecutive engine cycles.

Authors:
 [1];  [2];  [2];  [1]
  1. Argonne National Laboratory, Lemont, IL, USA
  2. General Motors R&,D, Warren, MI, USA
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE) - Office of Vehicle Technology
OSTI Identifier:
1412703
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: International Journal of Engine Research; Journal Volume: 18; Journal Issue: 4
Country of Publication:
United States
Language:
English
Subject:
33 ADVANCED PROPULSION SYSTEMS

Citation Formats

Ameen, Muhsin M., Yang, Xiaofeng, Kuo, Tang-Wei, and Som, Sibendu. Parallel methodology to capture cyclic variability in motored engines. United States: N. p., 2016. Web. doi:10.1177/1468087416662544.
Ameen, Muhsin M., Yang, Xiaofeng, Kuo, Tang-Wei, & Som, Sibendu. Parallel methodology to capture cyclic variability in motored engines. United States. doi:10.1177/1468087416662544.
Ameen, Muhsin M., Yang, Xiaofeng, Kuo, Tang-Wei, and Som, Sibendu. 2016. "Parallel methodology to capture cyclic variability in motored engines". United States. doi:10.1177/1468087416662544.
@article{osti_1412703,
title = {Parallel methodology to capture cyclic variability in motored engines},
author = {Ameen, Muhsin M. and Yang, Xiaofeng and Kuo, Tang-Wei and Som, Sibendu},
abstractNote = {Numerical prediction of of cycle-to-cycle variability (CCV) in SI engines is extremely challenging for two key reasons: (i) high-fidelity methods such as large eddy simulation (LES) are require to accurately capture the in-cylinder turbulent flowfield, and (ii) CCV is experienced over long timescales and hence the simulations need to be performed for hundreds of consecutive cycles. In this study, a new methodology is proposed to dissociate this long time-scale problem into several shorter time-scale problems, which can considerably reduce the computational time without sacrificing the fidelity of the simulations. The strategy is to perform multiple single-cycle simulations in parallel by effectively perturbing the simulation parameters such as the initial and boundary conditions. It is shown that by perturbing the initial velocity field effectively based on the intensity of the in-cylinder turbulence, the mean and variance of the in-cylinder flowfield is captured reasonably well. Adding perturbations in the initial pressure field and the boundary pressure improves the predictions. It is shown that this new approach is able to give accurate predictions of the flowfield statistics in less than one-tenth of time required for the conventional approach of simulating consecutive engine cycles.},
doi = {10.1177/1468087416662544},
journal = {International Journal of Engine Research},
number = 4,
volume = 18,
place = {United States},
year = 2016,
month = 7
}
  • Here we review developments in the understanding of cycle to cycle variability in internal combustion engines, with a focus on spark-ignited and premixed combustion conditions. Much of the research on cyclic variability has focused on stochastic aspects, that is, features that can be modeled as inherently random with no short term predictability. In some cases, models of this type appear to work very well at describing experimental observations, but the lack of predictability limits control options. Also, even when the statistical properties of the stochastic variations are known, it can be very difficult to discern their underlying physical causes andmore » thus mitigate them. Some recent studies have demonstrated that under some conditions, cyclic combustion variations can have a relatively high degree of low dimensional deterministic structure, which implies some degree of predictability and potential for real time control. These deterministic effects are typically more pronounced near critical stability limits (e.g. near tipping points associated with ignition or flame propagation) such during highly dilute fueling or near the onset of homogeneous charge compression ignition. We review recent progress in experimental and analytical characterization of cyclic variability where low dimensional, deterministic effects have been observed. We describe some theories about the sources of these dynamical features and discuss prospects for interactive control and improved engine designs. In conclusion, taken as a whole, the research summarized here implies that the deterministic component of cyclic variability will become a pivotal issue (and potential opportunity) as engine manufacturers strive to meet aggressive emissions and fuel economy regulations in the coming decades.« less
  • This work, which parallels a recent study of cyclohexane and methylcyclohexane by the authors, concerns the oxidation chemistry of methylcyclopentane (MCP), 1,2,3,4-tetrahydronaphthalene (tetralin), and decahydronaphthalene (decalin) in a motored engine at low to intermediate temperatures. The experiment is conducted with variable compression ratio from 4 to 15 at equivalence ratio of 0.25 and fixed intake temperature. Results show dramatically different reactivity in low temperature oxidation for the three compounds. MCP and tetralin show little low temperature reaction prior to autoignition, while decalin shows significant low temperature reactivity. Detailed product analysis showed that conjugate olefins, the olefin having the identical structuremore » with the reactant except the only C=C bond, account for over 70% of the products from MCP and an even higher percentage of the products from tetralin. Tetralin oxidation under the present conditions is essentially oxidative dehydrogenation with little oxygenated cyclic compound being formed. Hydronaphthalenes with various degrees of unsaturation are detected in the products from decalin, but are not as prevalent as in the case of MCP and tetralin, because of the high selectivity toward low temperature chain branching. The ring-opening paths in decalin oxidation are discussed, suggesting that breaking the common C-C bond of the two rings is more likely than opening the two rings one after the other. Methyl substitution on the ring was found to significantly promote the formation of propene relative to ethene. Reaction mechanisms are proposed to explain the major products formed from each compound. (author)« less
  • Simulations that require solutions of block tridiagonal systems of equations rely on fast parallel solvers for runtime efficiency. Leading parallel solvers that are highly effective for general systems of equations, dense or sparse, are limited in scalability when applied to block tridiagonal systems. This paper presents scalability results as well as detailed analyses of two parallel solvers that exploit the special structure of block tridiagonal matrices to deliver superior performance, often by orders of magnitude. A rigorous analysis of their relative parallel runtimes is shown to reveal the existence of a critical block size that separates the parameter space spannedmore » by the number of block rows, the block size and the processor count, into distinct regions that favor one or the other of the two solvers. Dependence of this critical block size on the above parameters as well as on machine-specific constants is established. These formal insights are supported by empirical results on up to 2,048 cores of a Cray XT4 system. To the best of our knowledge, this is the highest reported scalability for parallel block tridiagonal solvers to date.« less
  • Spark assist appears to offer considerable potential for increasing the speed and load range over which homogeneous charge compression ignition (HCCI) is possible in gasoline engines. Numerous experimental studies of the transition between conventional spark-ignited (SI) propagating-flame combustion and HCCI combustion in gasoline engines with spark assist have demonstrated a high degree of deterministic coupling between successive combustion events. Analysis of this coupling suggests that the transition between SI and HCCI can be described as a sequence of bifurcations in a low-dimensional dynamic map. In this paper, we describe methods for utilizing the deterministic relationship between cycles to extract globalmore » kinetic rate parameters that can be used to discriminate multiple distinct combustion states and develop a more quantitative understanding of the SI-HCCI transition. We demonstrate the application of these methods for indolene-containing fuels and point out an apparent HCCI mode switching not previously reported. Our results have specific implications for developing dynamic combustion models and feedback control strategies that utilize spark assist to expand the operating range of HCCI combustion.« less