Direct Numerical Simulation of Preignition and Knock in Engine Conditions

Abstract

Theoretical framework and high-fidelity direct numerical simulations (DNS) on preignition and knock encountered in internal combustion (IC) engines are briefly reviewed in this chapter. The theoretical framework is presented first, and systematically followed by one-dimensional and multi-dimensional simulations. A number of high-fidelity simulations under realistic IC-engine conditions were used to demonstrate the super-knock mechanism in the presence of the complex chemistry-turbulence interaction. The ratio of ignition delay time to eddy-turnover time, τ ig /τ t , and the ratio of the most energetic length scale of turbulence and temperature fluctuations, l t /l T , affect the knock intensities are discussed. Different statistical metrics extracted from the multi-dimensional simulations to predict knock intensity are also presented. The quantitative determination of strong and weak ignition modes using the predicted Sa-based metrics is also cover in this chapter.

Optical study of knocking phenomenon in a spark-ignition engine by using high-speed OH* chemiluminescence imaging: A multiple ignition sites approach

“…3 Traditionally, the knock phenomenon has been described by two theories: autoignition and detonation. [4][5][6] Auto-ignition is a result of the ignition of so-called hot spots in the unburned end gas caused by non-uniformities in temperature or concentration. Before the unburned gas is ignited, it is compressed by the expanding burned gas, compressed or expanded by the moving piston, heated by radiation from the flame front, and heated by the surrounding boundaries.…”

Knock propensity in a thermally inhomogeneous DME/air mixture: a DNS study

“…Modern internal combustion (IC) engines operate under elevated pressure enabled by downsized boosted technologies to achieve higher thermal efficiency, higher power-density output per volume, and ultra-low emission. However, being operated at elevated pressure and high-load conditions leads to a higher propensity of undesired preignition, knock, and even superknock [1][2][3][4][5][6][7][8]. Superknock is characterized as a developing detonation process featuring excessive pressure oscillations and extremely high-pressure amplitudes that can damage combustion-chamber components [7,[9][10][11][12][13][14][15][16][17][18][19][20]20].…”

“…Superknock is characterized as a developing detonation process featuring excessive pressure oscillations and extremely high-pressure amplitudes that can damage combustion-chamber components [7,[9][10][11][12][13][14][15][16][17][18][19][20]20]. Improved understandings of the superknock propensity and a reliable criterion to predict it are needed to prevent destructive operation of combustion devices [2,4,5,7,[21][22][23][24][25][26][27]. Therefore, first-principle high-fidelity direct numerical simulations (DNS) with the capability of fully resolving all temporal and spatial scales and the complex interaction of thermochemistry and turbulence under extreme high-load operating conditions are employed to unravel the mechanism of abnormal combustion phenomena in combustion devices such as IC engines, shock tubes, and rapid compression machines (RCM) [2,3].…”

“…The 𝜉 − 𝜀 diagram has been widely adopted in one-dimensional (1-D) DNS studies [11,14,[35][36][37][38][39][40][41][42][43][44][45], while a few multi-dimensional DNS studies have been conducted due mainly to computational expense [2][3][4][46][47][48].…”