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

Abstract

Pre-ignition in SI engine is a critical issue that needs addressing as it may lead to super knock event. It is widely accepted that pre-ignition event emanates from hot spot(s) that can be anywhere inside the combustion chamber. The location and timing of hotspot is expected to influence the knock intensity from a pre-ignition event. In this study, we study the effect of location and timing of hot spot inside the combustion chamber using numerical simulations. The simulation is performed using a three-dimensional computational fluid dynamics (CFD) code, CONVERGE™. We simulate 3-D engine geometry coupled with chemistry, turbulence and moving structures (valves, piston). G-equation model for flame tracking coupled with multi-zone model is utilized to capture auto-ignition (knock) and solve gas phase kinetics. A parametric study on the effect of hot spot timing and location inside the combustion chamber is performed. The hot spot timing considered are -180 CAD, -90 CAD and -30 CAD and the locations of the hot spots are in the center and two edges of the piston surfaces. Simulation results for normal combustion cycle are validated against the experimental data. The simulation results show great sensitivity to the hot spot timing, and the influence of local temperature gradient is noted to be significant. In case of early hot spot timing of -180 CAD, the pre-ignition event did not lead to super knock. Nevertheless, at late hot spot timing, super knock was realized. On the other hand, the effect of hot spot location on pre-ignition event depends on the geometry of the combustion chamber.

Multidimensional Numerical Simulations of Knocking Combustion in a Cooperative Fuel Research Engine

“…The laminar flame speed in Eq. (3) is generally calculated using empirical correlations [24][25][26]40]. However, a major limitation of these correlations is that they are valid for only simple fuels, such as iso-octane, ethanol, methanol and their blends.…”

“…This model was further extended for knock prediction by including chemical kinetics calculation ahead of the flame front [21][22][23]. More recently, Ali et al [24] used this hybrid approach to investigate the effect of pre-ignition on the likelihood of super knock in a direct-injection SI engine. In these previous works [19,[21][22][23][24], the fuel laminar flame speed, an input to the G-equation model, was calculated using empirical correlations [25,26], which are available and valid for simple fuels only, such as iso-octane, thereby precluding the study of more complex multicomponent fuels or fuel blends with this type of modeling approach.…”

Probabilistic Approach to Predict Abnormal Combustion in Spark Ignition Engines

“…Our previous study [9] emphasized the importance of the temperature, mixture stratification, and low-temperature reactivity in end-gas on super-knock. The location of the hotspot that initiates preignition front is found to be of paramount importance in determining the intensity of super-knock.…”

Model-Based Pre-Ignition Diagnostics in a Race Car Application

“…When the measured ignition delay becomes significantly smaller than that modeled, it means that ignition has been activated by a hot spot instead of the spark plug. In this case, the presented approach, implemented in the electronic control unit (ECU) that manages the whole hybrid power unit, detects a pre-ignition event and corrects the injection pattern to avoid the occurrence of further abnormal combustion.Energies 2019, 12, 2277 2 of 12 applications), end-gas knock is successfully controlled through proper spark advance/retarding (except in the case of runaway knock [9][10][11]), which reduce pressure and temperature during the combustion process. To maximize engine power and avoid reliability issues, an accurate cycle-by-cycle knock detection strategy is necessary; this can be based on the analysis of several kinds of signals, such as in-cylinder pressure (often used as a reference for the calibration of detection strategies) [12], engine block acceleration [13], ion currents [14], acoustic emissions [15,16], or innovative low-cost piezo-electric sensing devices [17].…”