Modelling of Automotive Fuel Droplet Heating and Evaporation (original) (raw)
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Models for droplet heating and evaporation: an application to biodiesel, diesel and gasoline fuels
International Journal of Engineering Systems Modelling and Simulation, 2017
This paper presents our recent progress in the modelling of automotive fuel droplet heating and evaporation processes in conditions close to those in direct-injection internal-combustion engines. Three types of automotive-fuels are considered: biodiesel, diesel and gasoline fuels. Modelling of biodiesel fuel droplets is based on the application of the discrete component (DC) model. A distinctive feature of this model is that it is based on the analytical solutions to the transient heat conduction and species diffusion equations in the liquid phase, taking into account the effects of recirculation. The application of the DC model to fossil fuels (containing potentially hundreds of components), however, is computationally expensive. The modelling of these fuels is based on the recently introduced multi-dimensional quasi-discrete (MDQD) model. This model replaces a large number of components in diesel and gasoline fuels with a much smaller number of quasi-components/components without losing the main features of the original DC model. The MDQD model is shown to accurately predict droplet temperatures and evaporation times and to be much more computationally efficient than the DC model. The main features of these models and their applications to three types of automotive fuel droplets are summarised and discussed.
Modelling of automotive fuel droplet heating and evaporation: mathematical tools and approximations
Journal of Physics: Conference Series, 2016
New mathematical tools and approximations developed for the analysis of automotive fuel droplet heating and evaporation are summarised. The approach to modelling biodiesel fuel droplets is based on the application of the Discrete Component Model (DCM), while the approach to modelling Diesel fuel droplets is based on the application of the recently developed multi-dimensional quasi-discrete model. In both cases, the models are applied in combination with the Effective Thermal Conductivity/Effective Diffusivity model and the implementation in the numerical code of the analytical solutions to heat transfer and species diffusion equations inside droplets. It is shown that the approximation of biodiesel fuel by a single component leads to under-prediction of droplet evaporation time by up to 13% which can be acceptable as a crude approximation in some applications. The composition of Diesel fuel was simplified and reduced to only 98 components. The approximation of 98 components of Diesel fuel with 15 quasi-components/components leads to under-prediction of droplet evaporation time by about 3% which is acceptable in most engineering applications. At the same time, the approximation of Diesel fuel by a single component and 20 alkane components leads to a decrease in the evaporation time by about 19%, compared with the case of approximation of Diesel fuel with 98 components. The approximation of Diesel fuel with a single alkane quasi-component (C14.763H31.526) leads to under-prediction of the evaporation time by about 35% which is not acceptable even for qualitative analysis of the process. In the case when n-dodecane is chosen as the single alkane component, the above-mentioned under-prediction increases to about 44%.
2015
The application of the discrete component model for heating and evaporation to multi-component biodiesel fuel droplets in direct injection internal combustion engines is described. This model takes into account the effects of temperature gradient, recirculation and species diffusion inside droplets. A distinctive feature of the model used in the analysis is that it is based on the analytical solutions to the transient heat transfer and species diffusion equations inside the droplets. The results of applications of the multi-dimensional quasi-discrete model to the analyses of Diesel and gasoline fuel droplet heating and evaporation are summarised. In this model, actual components of the fuel are replaced with a smaller number of components or hypothetical quasi-components. As in the original discrete component model, transient diffusion of these components/quasi-components, temperature gradient and recirculation (due to relative droplet velocities and ambient air) inside droplets are...
Models for automotive fuel droplets heating and evaporation
Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems
The paper presents recent approaches to the modelling of heating and evaporation of automotive fuel droplets with application to biodiesel, diesel, gasoline, and blended fuels in conditions representative of internal combustion engines. The evolutions of droplet radii and temperatures for gasoline, diesel, and a broad range of biodiesel fuels and their selective diesel fuel blends have been predicted using the Discrete Component model (DCM). These mixtures combine up to 112 components of hydrocarbons and methyl esters. The results are compared with the predictions of the case when blended diesel-biodiesel fuel are represented by pure fossil and biodiesel fuels. In contrast to previous studies, it is shown that droplet evaporation time and surface temperature predicted for 100% biodiesel (B100) are not always close to those predicted for pure diesel fuel. Also, the previously introduced MultiDimensional Quasi-Discrete model and its application to these fuels and their mixtures are di...
Modelling of biodiesel and Diesel fuel droplet heating and evaporation
New results of the investigation of biodiesel fuel droplet heating and evaporation, using previously developed models, are presented. Temperature gradient, recirculation and species diffusion within the droplets are taken into account. The results of calculations, taking into account the contribution of all components of biodiesel fuels (up to 16) and assuming that these fuels can be treated as a one component fuel, are discussed. It is pointed out that there are serious problems with the application of the approach, based on the analysis of diffusion of individual components, to the modelling of heating and evaporation of realistic Diesel fuel droplets, as the latter include more than 100 components. In our earlier papers, a new approach to the modelling of heating and evaporation of multi-component droplets, suitable for the case when a large number of components are present in the droplets, was suggested. This approach was based on the introduction of quasi-components, and the model was called the 'quasi-discrete' model. It is pointed out that there are two main problems with the application of the quasi-discrete model to realistic Diesel fuels. Firstly, even if we restrict our analysis to alkanes alone, it appears not to be easy to approximate this distribution with a reasonably simple distribution function. Secondly, the contributions of other hydrocarbon families in addition to alkanes cannot be ignored in any realistic model of Diesel fuels. Some results of the development of the generalised multi-dimensional version of the quasi-discrete model and its application to realistic Diesel fuel droplets are presented.
Multi-dimensional quasi-discrete model taking into account liquid species diffusion in realistic Diesel fuel.The dependence of the properties of components of Diesel fuels on temperature.The modelling of heating and evaporation of Diesel fuel droplets.A new multi-dimensional quasi-discrete model is suggested and tested for the analysis of heating and evaporation of Diesel fuel droplets. As in the original quasi-discrete model suggested earlier, the components of Diesel fuel with close thermodynamic and transport properties are grouped together to form quasi-components. In contrast to the original quasi-discrete model, the new model takes into account the contribution of not only alkanes, but also various other groups of hydrocarbons in Diesel fuels; quasi-components are formed within individual groups. Also, in contrast to the original quasi-discrete model, the contributions of individual components are not approximated by the distribution function of carbon numbers. The formation of quasi-components is based on taking into account the contributions of individual components without any approximations. Groups contributing small molar fractions to the composition of Diesel fuel (less than about 1.5%) are replaced with characteristic components. The actual Diesel fuel is simplified to form six groups: alkanes, cycloalkanes, bicycloalkanes, alkylbenzenes, indanes & tetralines, and naphthalenes, and 3 components C19H34 (tricycloalkane), C13H12 (diaromatic), and C14H10 (phenanthrene). It is shown that the approximation of Diesel fuel by 15 quasi-components and components, leads to errors in estimated temperatures and evaporation times in typical Diesel engine conditions not exceeding about 3.7% and 2.5% respectively, which is acceptable for most engineering applications.
Previously developed droplet heating and evaporation models, taking into account temperature gradient, recirculation, and species diffusion within droplets, and their application to the analysis of commercial automotive fuel droplets are reviewed. It is shown that the most efficient analysis of Diesel fuel droplet heating and evaporation is based on the MDQD (multi-dimensional quasi-discrete) model, taking into account the contribution of all groups of hydrocarbons in automotive fuels. The main features of this model are summarised and its new application to the analysis of droplets in Diesel engine-like conditions, taking into account time-dependent velocities, is described. In the MDQD model, Diesel fuel is approximated by six groups of components: alkanes, cycloalkanes, bicycloalkanes, alkylbenzenes, indanes & tetralines, naphthalenes, and three characteristic components C19H34 (tricycloalkane), C13H12 (diaromatic), and C14H10 (phenanthrene). It is shown that errors in estimated temperatures and evaporation times in typical Diesel engine conditions, using the approximation of Diesel fuel by 15 quasi-components/components compared to the case when all 98 components are taken into account, are up to 1% and 3%, respectively. This is acceptable in most engineering applications. This approximation has also reduced CPU time by about 6 times compared with the case when the contribution of 98 components is taken into account. The approximations of Diesel fuel with n-dodecane (widely used in engineering modelling) and 20 alkane components lead to under-prediction of the evaporation time by over 50% and 22%, respectively.
Modelling of blended Diesel and biodiesel fuel droplet heating and evaporation
The paper presents a new approach to the modelling of heating and evaporation of dual-fuel droplets with a specific application to blends of biodiesel (represented by the widely used soybean methyl ester, SME) and Diesel fuels in conditions representative of internal combustion engines. The original compositions, with up to 105 components of Diesel and biodiesel fuels, are replaced with a smaller number of components and quasi-components using the recently introduced multi-dimensional quasi-discrete (MDQD) model. Transient diffusion of these components and quasi-components in the liquid phase and temperature gradient and recirculation inside droplets are taken into account. The results are compared with the predictions of the case when blended biodiesel/Diesel fuel droplets are represented by pure biodiesel fuel or pure Diesel fuel droplets. It is shown that droplet evaporation time and surface temperature predicted for 100% SME, representing pure biodiesel fuel, are close to those ...
New approaches to the modelling of multi-component fuel droplet heating and evaporation
Journal of Physics: Conference Series, 2015
The previously suggested quasi-discrete model for heating and evaporation of complex multi-component hydrocarbon fuel droplets is described. The dependence of density, viscosity, heat capacity and thermal conductivity of liquid components on carbon numbers n and temperatures is taken into account. The effects of temperature gradient and quasi-component diffusion inside droplets are taken into account. The analysis is based on the Effective Thermal Conductivity/Effective Diffusivity (ETC/ED) model. This model is applied to the analysis of Diesel and gasoline fuel droplet heating and evaporation. The components with relatively close n are replaced by quasi-components with properties calculated as average properties of the a priori defined groups of actual components. Thus the analysis of the heating and evaporation of droplets consisting of many components is replaced with the analysis of the heating and evaporation of droplets consisting of relatively few quasi-components. It is demonstrated that for Diesel and gasoline fuel droplets the predictions of the model based on five quasi-components are almost indistinguishable from the predictions of the model based on twenty quasi-components for Diesel fuel droplets and are very close to the predictions of the model based on thirteen quasi-components for gasoline fuel droplets. It is recommended that in the cases of both Diesel and gasoline spray combustion modelling, the analysis of droplet heating and evaporation is based on as little as five quasi-components.
Modelling of biodiesel fuel droplet heating and evaporation: Effects of fuel composition
A comparative analysis of predictions of several models of biodiesel fuel droplet heating and evaporation in realistic Diesel engine-like conditions is presented. Nineteen types of biodiesel fuels composed of methyl esters are used for the analysis. It is shown that the model, based on the assumption that the diffusivity of species in droplets is infinitely fast and the liquid thermal conductivity is infinitely large, under-predicts the droplet evaporation time compared with the model taking into account the effects of finite diffusivity and conductivity, by up to about 15%. A similar under-predictions of the model in which the transient diffusion of species is ignored and the liquid thermal conductivity is assumed to be infinitely large, is shown to be about 26%. The latter result is not consistent with the earlier finding, based on the analysis of only five types of biodiesel fuels and different input parameters, in which it was shown that the deviations between the evaporation times predicted by these models do not exceed about 5.5%. As in the case of Diesel and gasoline fuel droplets, for biodiesel droplets the multi-component models predict higher droplet surface temperatures at the final stages of droplet evaporation and longer evaporation times than for the single-component models. This is related to the fact that at the final stages of droplet evaporation the mass fraction of heavier species, which evaporate more slowly than the lighter species and have higher boiling temperatures, increases at the expense of lighter species.