Riassunto analitico
During the last years, the 3D internal combustion engine models were developed and analyzed using gasoline mono-component, based on the multiple components present in reality. This method of analysis may be considered rapid and for simple applications, but not sufficiently close to reality. The components differ between them, as a property and as behavior. For example, they vary in volatility, specific heat, density in liquid and solid phases, heat of vaporization, ecc…. without forgetting their combination in mass in mixture.
These properties can vary the stratification inside the cylinder, compared with the mono component models, with some of the less volatile components that are not homogeneously mixed with air in the cylinder for their difficulty to pass in their gas phase, or with the more volatile components that pass almost immediately in the gas phase.
Distinguishing various components allows predicting the possible formation of deposits of liquid on the walls, with subsequent formation of scale and diffusive combustion, not typical for petrol GDI high performance engines.
In this thesis project, a turbocharged petrol GDI high performance engine is taken as the basic model, on which different kind of analysis is done, especially:
- Liquid film activation
- Multi component fuel modelling
- Combination of these effects
Gasoline may not be modeled in all its real components, but must be simplified, so as to obtain a good compromise between the detail provided by the multi-component modeling and a not so high computational cost. The composition of the fuel is given by Shell, already simplified in 14 components. some researches has been made in the literature and in chemical databases (i.e. NIST) to assess and identify as many properties as possible, so to put a further and final simplification. In fact, the software CD-STAR by CD-Adapco allows analyzing only gasoline made up of maximum 10 components with liquid film activated. All this models lead to different results, which are best analyzed in the fully document.It was made possible, through usercoding, written from scratch, to monitor the mixing especially around the spark plug, so as to predict the quality of the mixture in the chamber just before and during the combustion process. After some detailed analyzes reported in the full document, some further analysis have been made on the model with multi-component liquid film, with the aim of reducing the liquid film attached on the internal cylinder walls. It is made by actively changing the start of injection angle, assessing the overall effects. As expected, the amount of the liquid film produced decreases by increasing the delay of the instant of injection. Further detailed analysis within the document, then confirmed by the experimental data provided, assert that this trend, although positive, causes other problems related to the stratification in the chamber. It results not optimal by excessively delaying the SOI, therefore causing high cycle variability and some unstable combustion.
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Abstract
During the last years, the 3D internal combustion engine models were developed and analyzed using gasoline mono-component, based on the multiple components present in reality. This method of analysis may be considered rapid and for simple applications, but not sufficiently close to reality. The components differ between them, as a property and as behavior. For example, they vary in volatility, specific heat, density in liquid and solid phases, heat of vaporization, ecc…. without forgetting their combination in mass in mixture.
These properties can vary the stratification inside the cylinder, compared with the mono component models, with some of the less volatile components that are not homogeneously mixed with air in the cylinder for their difficulty to pass in their gas phase, or with the more volatile components that pass almost immediately in the gas phase.
Distinguishing various components allows predicting the possible formation of deposits of liquid on the walls, with subsequent formation of scale and diffusive combustion, not typical for petrol GDI high performance engines.
In this thesis project, a turbocharged petrol GDI high performance engine is taken as the basic model, on which different kind of analysis is done, especially:
- Liquid film activation
- Multi component fuel modelling
- Combination of these effects
Gasoline may not be modeled in all its real components, but must be simplified, so as to obtain a good compromise between the detail provided by the multi-component modeling and a not so high computational cost. The composition of the fuel is given by Shell, already simplified in 14 components. some researches has been made in the literature and in chemical databases (i.e. NIST) to assess and identify as many properties as possible, so to put a further and final simplification. In fact, the software CD-STAR by CD-Adapco allows analyzing only gasoline made up of maximum 10 components with liquid film activated. All this models lead to different results, which are best analyzed in the fully document.It was made possible, through usercoding, written from scratch, to monitor the mixing especially around the spark plug, so as to predict the quality of the mixture in the chamber just before and during the combustion process. After some detailed analyzes reported in the full document, some further analysis have been made on the model with multi-component liquid film, with the aim of reducing the liquid film attached on the internal cylinder walls. It is made by actively changing the start of injection angle, assessing the overall effects. As expected, the amount of the liquid film produced decreases by increasing the delay of the instant of injection. Further detailed analysis within the document, then confirmed by the experimental data provided, assert that this trend, although positive, causes other problems related to the stratification in the chamber. It results not optimal by excessively delaying the SOI, therefore causing high cycle variability and some unstable combustion.
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