Cycle-to-cycle variability in spark-assisted compression ignition engines near optimal mean combustion phasing

Stoichiometric spark-assisted compression ignition (SACI) combustion with exhaust gas recirculation (EGR) dilution has demonstrated higher part-load thermal efficiencies compared to spark-ignited engines, while maintaining ultra-low tailpipe emissions. However, SACI is often characterized by high cyclic variability in heat release or torque output, which poses a challenge to its implementation in light-duty vehicles. This paper presents an experimental investigation of cyclic variability in stoichiometric SACI combustion under EGR-dilute conditions, while maintaining mean combustion phasing (θ₅₀) near optimal timing for thermal efficiency. The present work focuses on SACI conditions where the flame-based heat release fraction is between approximately 10% and 40% of the overall heat release, and therefore contributes significantly to the combustion process. For the SACI conditions examined, the variability in θ₅₀ was driven by variability in autoignition timing, which in turn correlated with the start of measurable heat release (θ₀₂). High variability in θ₅₀ caused unstable work output due to very late combustion with poor or no end-gas autoignition. The use of a high ignition energy dual-coil offset ignition system had negligible impact in reducing θ₅₀ variability. Analysis of experimental data from close to 1000 operating conditions showed that the magnitude of θ₅₀ variability correlates with the flame-based heat release fraction (xB,θAI), for a large range of intake pressures, spark timings and exhaust gas recirculation levels. For the SACI conditions examined, combustion phasing variability was largely determined by flame-based combustion and particularly the initial flame formation (θign₋₀₂), and minimally by the end-gas autoignition heat release. The analysis also demonstrated that θ₅₀ variability is amplified as the contribution of the flame to the overall heat release increases.

• Record URL:
  https://doi.org/10.1177/14680874211053061
• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/issn/14680874
• Supplemental Notes:
  • © IMechE 2021.
• Authors:
  • Triantopoulos, Vassilis
  • 0000-0002-5318-5606
  • Bohac, Stanislav V
  • Sterniak, Jeff
  • Lavoie, George
  • 0000-0003-1265-7889
  • Boehman, André L
  • 0000-0002-0965-9288
  • Assanis, Dennis N
  • Martz, Jason B
• Publication Date: 2023-2

Language

• English

Media Info

• Media Type: Digital/other
• Features: Appendices; Figures; References; Tables;
• Pagination: pp 420-436
• Serial:
  • International Journal of Engine Research
  • Volume: 24
  • Issue Number: 2
  • Publisher: Sage Publications, Incorporated
  • ISSN: 1468-0874
  • EISSN: 20413149

Subject/Index Terms

• TRT Terms: Combustion; Compression ignition engines; Engine cycle; Exhaust gas recirculation; Ignition; Spark plugs
• Subject Areas: Highways; Vehicles and Equipment;

Filing Info

• Accession Number: 01876841
• Record Type: Publication
• Files: TRIS
• Created Date: Mar 23 2023 10:20AM