Evaluation of engine performance and emissions in an optical DISI engine with various spark plug designs and gaps

Tawfik Badawy, James W.G. Turner, Hongming Xu*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


This study aims to assess how spark-ignition engine performance and emissions are affected by both the design of the spark plug and the size of its electrode gap. Two distinct spark plug configurations (BUGAETS and NGK) with varying spark gap sizes of 1, 1.2, and 1.4 mm were used. Experiments were performed in an optical constant volume chamber as well as an optical direct injection spark ignition engine. At various equivalence ratios, the effects of both spark plugs on flame propagation, in-cylinder pressure, mass fraction burnt, and emissions for gasoline fuel were explored. For all spark plug gaps and equivalence ratios tested, the constant volume experimental results showed that the flame propagation area with the BUGAETS spark plug is faster than that with the NGK spark plug. According to the engine results, BUGAETS can produce an IMEP up to 2.4 % higher with a significant reduction in both cyclic variability and fuel consumption when compared to NGK. BUGAETS electrode consistently produces higher in-cylinder pressure and heat release rate than the NGK spark plug. When compared to NGK, the BUGAETS spark plug emits more NOx while emitting less hydrocarbon and particulate emissions. In terms of NGK electrode gaps, a comparison revealed that a gap size of 1.4 mm resulted in the most optimal engine performance and the lowest exhaust emissions. On the other hand, when it came to BUGAETS' spark plug, a gap size of 1.2 mm delivered the best engine performance and emissions out of all the tested gap sizes for the BUGAETS electrode.

Original languageEnglish (US)
Article number129900
StatePublished - Feb 1 2024


  • Combustion
  • Emissions
  • Flame development area
  • GDI engine
  • Particulate number
  • Spark plug gap

ASJC Scopus subject areas

  • General Chemical Engineering
  • Fuel Technology
  • Energy Engineering and Power Technology
  • Organic Chemistry


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