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Investigation of the Early Flame Development in Spark Assisted HCCI Combustion Using High Speed Chemiluminescence Imaging

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Author

  • Håkan Persson
  • Anders Hultqvist
  • Bengt Johansson
  • Alfredo Remon

Summary, in English

Auto-ignition with SI-compression ratio can be achieved by replacing some of the fresh charge by hot residuals. In this work an engine is run with a negative valve overlap (NVO) trapping hot residuals. By increasing the NVO, thus raising the initial charge temperature it is possible to investigate the intermediate zone between SI and HCCI as the amount of residuals is increased. Recent research has shown the potential of using spark assistance to aid gasoline HCCI combustion at some operating conditions, and even extend the operating regime into regions where unsupported HCCI combustion is impossible. In this work the influence of the spark is studied in a single cylinder operated engine with optical access. Combustion is monitored by in-cylinder pressure and simultaneous high speed chemiluminescence imaging. It is seen that even for large NVO and thus high residual fractions it is a growing SI flame that interacts with, and governs the subsequent HCCI combustion. Using the spark timing it is possible to phase the combustion timing even when the major part of the released heat is from HCCI combustion. The flame expansion speed is decreases for higher NVO, but prevails also for high residual fractions. A higher spark advance is found to compensate for the slower flame expansion up to a point. The auto-ignition process is found to be stratified for both spark assisted HCCI as well as for pure HCCI. For pure HCCI the initial front spreading velocity is found to be in the same order of magnitude as for the expansion speed of the SI flame. Calculations to estimate the crank angle of auto-ignition are performed based on cylinder pressure information providing good statistics on how the proportion of SI to HCCI behaves for different operating conditions.

Department/s

Publishing year

2007

Language

English

Publication/Series

SAE Special Publications

Document type

Conference paper

Publisher

Society of Automotive Engineers

Topic

  • Other Mechanical Engineering

Keywords

  • chemiluminescence
  • early flame
  • high speed imaging
  • spark assistance
  • combustion
  • hcci
  • engine
  • SACI

Conference name

SAE World Congress, 2007

Conference date

2007-04-16 - 2007-04-19

Conference place

Detroit, United States

Status

Published

Project

  • Competence Centre for Combustion Processes

ISBN/ISSN/Other

  • ISBN: 978-0-7680-1890-5
  • SAE Technical Paper 2007-01-0212