Combined Effects of Spark Discharge Pattern and Tumble Level on Cycle-to-Cycle Variations of Combustion at Lean Limits of SI Engine Operation

Paper #:
  • 2017-01-0677

Published:
  • 2017-03-28
Abstract:
Well-mixed lean or dilute SI engine operation can provide efficiency improvements relative to that of traditional well-mixed stoichiometric SI operation. However, the realized gains depend on the ability to ensure stable, complete and fast combustion. This work examines the use of two methods for improving the stability of lean operation, multiple spark discharge and high tumble flow. These two methods are compared to standard SI operation using single spark discharge without high tumble flow. High octane gasoline is the fuel chosen for this study. The multiple spark discharge is performed by the ignition system which can generate 5 bursts of 2 ignition coils while adjusting interval time between each discharge. For high tumble flow, a custom intake adapter is applied in the intake port. Performance testing shows that lean operation with a combination of multiple spark discharge and high tumble flow enables a 21% improvement of thermal efficiency at ϕ = 0.5, relative to that of stoichiometric operation. Especially, 5 discharges of 2 coils with interval time of 0.25us offers most stable ultra-lean operation, with IMEPn variability less than 5% down to even for ϕ = 0.5. The ability to operate stably at such lean conditions is attributed to a more stable flame initiation offered by both the multiple spark discharge and the high tumble flow that allows a later spark timing due to the decreased burn duration of initial combustion.
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