Effect of Timing and Location of Hotspot on Super Knock during Pre-ignition

Paper #:
  • 2017-01-0686

Published:
  • 2017-03-28
Abstract:
Pre-ignition in SI engine is a critical issue that needs addressing as pre-ignition may lead to engine knocking events that may damage engine catastrophically. It is widely accepted that pre-ignition event emanates from hot spot(s) inside the combustion chamber. The pre-ignition event can be anywhere inside the combustion chamber. The location of pre-ignition is expected to influence the knock intensity that may result from the pre-ignition event. In this study, we vary the location of the hot spot inside the cylinder using numerical simulations. The simulation is performed using a three-dimensional computational fluid dynamics (CFD) code (CONVERGETM). We simulate the full 3-D engine cycle coupled with chemistry, turbulence and moving structures (valves, piston). Gasoline direct injection (GDI) spray is represented by Kelvin-Helmholtz/Rayleigh-Taylor spray breakup model with rng k-epsilon turbulence model to describe the internal flow field. G-equation model for flame tracking coupled with multi-zone model to capture auto-ignition (knock) is utilized to solve gas phase kinetics. A parametric study on CAD of pre-ignition and location of pre-ignition location inside the combustion chamber is performed. The simulation results show great sensitivity to the pre-ignition location, and the influence of local temperature gradients is noted to be significant. The CAD of pre-ignition and location of pre-ignition that influences subsequent knock in engines is analyzed. In case of early hot spot timings of -180 CAD, the pre-ignition event did not lead to super knock. Nevertheless, late hot spot timings were crucial in that super knock was realized. The location of hot spot depends on the geometry of the combustion chamber and has little effect on the transition of pre-ignition event to super knock.
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