The Effect of In-Cylinder Temperature on the Ignition Initiation Location of a Pre-Chamber Generated Hot Turbulent Jet 2018-01-0184

Ignition location is one of the important factors that affect the thermal efficiency, exhaust emissions and knock sensitivity in premixed-charge ignition engines. However, the ignition initiation locations of pre-chamber generated turbulent jet ignition, which is a promising ignition enhancement method, are not clearly understood due to the complex physics behind it. Motivated by this, the ignition initiation location of a transient turbulent jet in a constant volume combustor is analyzed by the use of computational fluid dynamics (CFD) simulations. In the CFD simulations of this work, commercial codes KIVA-3 V release 2 and an in-house-developed chemical solver with a detailed mechanism for H₂/air mixtures are used. Comparisons are performed between simulated and experimental ignition initiation locations, and they agree well with one another. A detailed parametric study of the influence of in-cylinder temperature on the ignition initiation location is also performed. As the temperature increases, the ignition initiation location significantly moves toward the exit of the orifice. When the mixture reaches the temperatures of 600 and 700 K, large amounts of OH and H radicals are observed in the orifice exit zone. The chemical reaction time scales decrease with increasing temperature, leading to a short time duration requirement for the reactant consumption for high temperature cases. In addition, low stream-wise Damköhler number zone shortens with rising temperature, and ignition occurs within zones where Damköhler number is close to one. These results demonstrate that the increase of temperature causes the reduction of chemical reaction time scales, and in turn leads to ignition initiation location moving upstream from the jet where mixing is high.