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Title: Understanding the dynamics of spark-assisted HCCI combustion

Abstract

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 global 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.

Authors:
 [1];  [1];  [1];  [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
958828
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: American-Japanese Flame Research Committees International Symposium 2007, Waikoloa, HI, USA, 20071022, 20071026
Country of Publication:
United States
Language:
English
Subject:
33 ADVANCED PROPULSION SYSTEMS; COMBUSTION; COMPRESSION; FEEDBACK; FLAMES; IGNITION; INTERNAL COMBUSTION ENGINES; KINETICS; HCCI; nonlinear controls; combustion

Citation Formats

Edwards, Kevin Dean, Daw, C Stuart, Wagner, Robert M, Green Jr, Johney Boyd, and Glewen, William J. Understanding the dynamics of spark-assisted HCCI combustion. United States: N. p., 2007. Web.
Edwards, Kevin Dean, Daw, C Stuart, Wagner, Robert M, Green Jr, Johney Boyd, & Glewen, William J. Understanding the dynamics of spark-assisted HCCI combustion. United States.
Edwards, Kevin Dean, Daw, C Stuart, Wagner, Robert M, Green Jr, Johney Boyd, and Glewen, William J. Mon . "Understanding the dynamics of spark-assisted HCCI combustion". United States. doi:.
@article{osti_958828,
title = {Understanding the dynamics of spark-assisted HCCI combustion},
author = {Edwards, Kevin Dean and Daw, C Stuart and Wagner, Robert M and Green Jr, Johney Boyd and Glewen, William J},
abstractNote = {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 global 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.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
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  • A heuristic algorithm based on a double Wiebe function is proposed for estimating the relative importance of distinct combustion modes (propagating flame and compression ignition) occurring within individual combustion cycles as an engine is transitioned from conventional spark-ignited (SI) combustion to homogeneous charge compression ignition (HCCI). The proposed algorithm automates the analysis and categorization of pressure measurements from large numbers of individual cycles, providing new insight into the unstable combustion processes occurring during mode transition. Similar techniques could potentially be utilized for on-line diagnostics and control of the balance between SI and HCCI combustion in spark-assisted HCCI.
  • We report experimental observations of cyclic combus-tion variability during the transition between propagating flame combustion and homogeneous charge compres-sion ignition (HCCI) in a single-cylinder, stoichiometri-cally fueled, spark-assisted gasoline engine. The level of internal EGR was controlled with variable valve actua-tion (VVA), and HCCI combustion was achieved at high levels of internal EGR using the VVA system. Spark-ignition was used for conventional combustion and was optionally available during HCCI. The transition region between purely propagating combustion and HCCI was mapped at multiple engine speeds and loads by incre-mentally adjusting the internal EGR level and capturing data for 2800 sequential cycles. Thesemore » measurements revealed a complex sequence of high COV, cyclic com-bustion variations when operating between the propagat-ing flame and HCCI limits. We were able to experimen-tally demonstrate an increase in the zone of acceptable HCCI-like combustion by using the spark assist. A de-tailed analysis of the cyclic variations in the intermediate zone indicates that they are dominated by nonlinear, nonrandom processes. Comparisons with previous studies of lean-limit cyclic variations suggest that nonlin-ear EGR feedback is probably the major source of the observed variations for this engine. The predictable na-ture of this feedback suggests the possibility of develop-ing on-line diagnostics and proactive control algorithms for expanding stable HCCI operation and improving transitions between conventional and HCCI modes.« less
  • Widespread implementation of homogeneous charge compression ignition (HCCI) engines is presently hindered by stability, control, and load range issues. Although the operable HCCI speed/load range is expanding, it is likely that the initial HCCI engines will rely on conventional combustion for part of the operating cycle. In the present study, we have investigated the role of fuel properties and chemistry on the operation of a spark-assisted gasoline HCCI engine. The engine employed is a single cylinder, 500 cc, port fuel injected research engine, operating near lambda = 1.0 and equipped with hydraulic variable valve actuation. HCCI is initiated by earlymore » exhaust valve closing to retain exhaust in the cylinder, thereby increasing the cylinder gas temperature. This is also referred to as a 'negative overlap' strategy. A total of 10 custom blended gasolines and three different batches of indolene from two suppliers were run at 5 speed-load combinations and performance was characterized by timing sweeps. Within the quality of the data set, we can say the all fuels provided equivalent combustion and performance characteristics when compared at the same combustion phasing. The fuels did, however, require different degrees of retained exhaust as measured by exhaust valve closing angle to achieve the same combustion phasing. Fuels with higher octane sensitivity were found to ignite more easily or more quickly and to burn more quickly than fuels with lower octane sensitivity. This is an expected result since the engine is naturally aspirated and operates with high compression temperatures due to the high retained exhaust fraction and recompression.« less