The main objective of this work is to study combustion characteristics of the reacting high pressure liquid sprays and compression ignition Diesel engines under conventional and low temperature operating modes by development of a robust computational framework. This has been done under RANS turbulence modeling methodology and Lagrangian Droplet Eulerian Flow formulations of multi-dimensional computational fluid dynamics modeling perspective. Initially, Conical and Spray Oriented grids were introduced for non-reacting liquid spray simulations and noticeable enhancement of air-fuel mixing process and better representation of the scalar dissipation rates were depicted. It was shown that a reliable non-reacting simulation is the perquisite of accurate results for reacting liquid spray simulations. In this regard, uncertainties from the liquid spray simulations should be minimized. For instance, it was shown that occurrence of cavitation while injecting of the liquid fuel can highly alter the spray properties, breakup, evaporation, air-fuel mixing, and subsequent combustion. It was discussed that for the fuels that are more prone to cavitation care must be taken both in experimental observation and measurements and numerical model selection and application. Attention then was given to the reactive simulations of the Engine Combustion Network Spray A and Spray B configurations. Two well known combustion closures, models based on well-mixed assumption and flamelet concept, with enhanced applicability were selected. After extensive validations over wide range of operating conditions in case of ambient temperature, density, oxidizer level, and injection pressures, a detailed combustion phasing analysis and mathematical reasoning of observed model-to-model differences were made. Detailed discussions were carried out on how embedded Turbulence Chemistry Interactions (TCI) can enhance the ignition delay times and flame lift-off length and alter the combustion phasing mechanism compared to the closures without considering TCI. Lastly, study was focused on modeling of Partially Premixed Compression Ignition (PPCI) engines as an advanced Low Temperature Combustion (LTC) mode. It was discussed that how air-fuel mixture stratification levels can modify the history of pressure and heat release rate. Negative Temperature Coefficient times tend to reduce by further moving to high fuel stratification levels. This can introduce much better control over PPCI combustion heat release once the engine needed thermal load was provided. All the computational efforts in this work were implemented within the OpenFOAM R framework, as a contribution to the library Lib-ICE, developed by the Internal Combustion Engine Group of the Energy Department of Politecnico di Milano.
|Qualification||Doctor of Philosophy|
|Award date||11 Apr 2017|
|Place of Publication||Milano|
|Publication status||Published - 2017|