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Journal Article

Detailed Modeling and Simulation of High-Pressure Fuel Injection Processes in Diesel Engines

This paper provides an analysis of high-pressure phenomena and its potential effects on the fundamental physics of fuel injection in Diesel engines. In particular, we focus on conditions when cylinder pressures exceed the thermodynamic critical pressure of the injected fuel and describe the major differences that occur in the jet dynamics compared to that described by classical spray theory. To facilitate the analysis, we present a detailed model framework based on the Large Eddy Simulation (LES) technique that is designed to account for key high-pressure phenomena. This framework is then used to perform a thermodynamic analysis of the flow. We focus on the experiments being conducted in the high-pressure combustion vessel at Sandia National Laboratories using n-heptane as a reference fuel. The calculations are performed by rigorously treating the experimental geometry and operating conditions, with detailed treatment of relevant thermophysical mixture properties.
Journal Article

Effects of Real-Fluid Thermodynamics on High-Pressure Fuel Injection Processes

This paper first summarizes a new theoretical description that quantifies the effects of real-fluid thermodynamics on liquid fuel injection processes as a function of pressure at typical engine operating conditions. It then focuses on the implications this has on modeling such flows with emphasis on application of the Large Eddy Simulation (LES) technique. The theory explains and quantifies the major differences that occur in the jet dynamics compared to that described by classical spray theory in a manner consistent with experimental observations. In particular, the classical view of spray atomization as an appropriate model at some engine operating conditions is questionable. Instead, non-ideal real-fluid behavior must be taken into account using a multicomponent formulation that applies to hydrocarbon mixtures at high-pressure supercritical conditions.
Journal Article

Large Eddy Simulation of Autoignition Transients in a Model Diesel Injector Configuration

Developing an improved understanding of transient mixing and combustion processes inherent in diesel injection is an important element in the design of advanced engines. This paper provides a detailed analysis of these processes using an idealized benchmark configuration designed to facilitate precise comparisons between different models and numerical methods. The computational domain is similar to the Engine Combustion Network ( Spray-A injector with n-dodecane as the fuel. Quantified idealizations are made in the treatment of boundary conditions to eliminate ambiguities and unknowns associated with the actual injector(s) used in the experiment. These ambiguities hinder comparisons aimed at understanding the accuracy of different models and the coupled effects of potential numerical errors.
Technical Paper

Large Eddy Simulation of a Transient Air Jet with Emphasis on Entrainment during Deceleration

Recent experiments of diesel injection processes have demonstrated that mixing accelerates after the end of injection (EOI). This finding has significant implications for low-temperature combustion (LTC) diesel engines. Previous simulations using a one-dimensional model of a single-pulsed air jet, which is analogous in many aspects to diesel jets, suggest that the rapid mixing after EOI in diesel jets is due to a temporary increase in the entrainment rate as the jet decelerates. In the present study, we performed a high-fidelity large eddy simulation (LES) of an unsteady air jet identical to that used for the one-dimensional model. The LES calculation agrees well with available experimental data and provides both spatially and temporally resolved details of the three-dimensional transient mixing field. Results show that entrainment increases during deceleration.