Modeling combusting diesel jets: The wall jet regime.

摘要

In this work, the structures of turbulent non-reacting jets and laminar reacting jets which impinge on walls are studied. The laminar jet studies are carried out to understand the structure of laminar diffusion flames which interact with walls.; A study of mass entrainment rates in wall-impinging jets and comparison of the rates with those in radial and round jets show that the increase in entrained mass in the fully developed wall-impinging jet is slower than that in the fully developed round and radial jets. These results are supported by computational studies.; Detailed chemical kinetics are employed in the reacting jet computations. As this approach is computationally time-consuming, several methods to accelerate the chemistry calculations are explored. It is shown that parallelizing the chemical kinetics computations using the Message Passing Interface algorithm can achieve a close to linear speed-up for chemistry calculations. An in-situ adaptive tabulation method is shown to give a significant speed-up but is not suitable during the early stage of jet development and ignition. Computations of transient reacting laminar wall jets show that minor species distribution in the wall jet is affected by wall heat transfer. NO formation in the transient wall-impinging jet is reduced relative to a free jet. A significant fraction of the soot that is formed deposits on the wall as a result of thermophoresis. Wall heat transfer decreases soot formation and oxidation rates. Radiative heat transfer also reduces the soot formation and oxidation rates.; A wall-modified interactive flamelet model which includes the effects of wall heat transfer is developed and implemented in a multidimensional code. In this model, several flamelets representing different levels of heat loss to the wall are calculated. The averaged flame profile is interpolated between the flamelets according to the energy defect due to wall heat loss. Computations carried out in a heavy-duty Diesel engine and comparisons with measured results in the engine show that the wall-modified flamelet model is able to improve the predictions of NO emissions relative to a more widely employed local equilibrium characteristic time model.