Biofuel spray injection modelling

Project Details


Depletion of fossil fuels and the need to reduce carbon dioxide emissions, contributing to climate changes, have stimulated the development of alternative fuels for internal combustion engines. As an alternative to Diesel fuel biodiesel fuels have been developed. The term ‘biodiesel’ typically refers to “a fuel comprised of mono-alkyl esters of long-chain fatty acids derived from vegetable oils or animal fats”. Sometimes it is used to refer to as “fatty acid methyl or ethyl esters made from vegetable oils or animal fats, whose properties are good enough to be used in diesel engines”.

Biodiesel is produced from vegetable oil or animal fat through the process known as transesterification. Most studies of biodiesel fuels have been focused on rapeseed, soybean and palm oil biodiesels. The dominant oils for production of these fuels are rapeseed oil in Europe, soybean oil in the USA, and palm oil in Asia. The term ‘second-generation biodiesel’ refers to biodiesel derived from inedible oil or algae.

This project looked into the developments of a new model for biofuel spray penetration in diesel engines, based on the COFM-model - the application of the quasi-discrete model for droplet heating and evaporation to Biofuel droplets.

Biodiesel fuel droplet heating and evaporation was investigated using the previously developed models, taking into account temperature gradient, recirculation, and species diffusion within droplets.

The analysis was focused on four types of biodiesel fuels: Palm Methyl Ester, Hemp Methyl Esters, Rapeseed oil Methyl Ester, and Soybean oil Methyl Ester. These fuels contain up to 15 various methyl esters and possibly small amounts of unspecified additives, which are treated as methyl esters with some average characteristics.

Calculations were performed using two approaches: (1) taking into account the contribution of all components of biodiesel fuels (up to 16); and (2) assuming that these fuels can be treated as a one component fuel with averaged transport and thermodynamic coefficients.

It is pointed out that for all types of biodiesel fuel the predictions of the multi-component and single component models are rather close (the droplet evaporation times predicted by these models differ by less than about 5.5%).

This difference is much smaller than observed in the case of Diesel and gasoline fuel droplets, and is related to the fact that in the case of Diesel and gasoline fuel droplets the contribution of components in a wide range of molar masses and enthalpies of evaporation needs to be taken into account, while in the case of biodiesel fuels the main contribution comes from the components in a narrow range of molar masses, boiling temperatures and enthalpies of evaporation. As in the case of Diesel and gasoline fuel droplets, the multi-component model predicts higher droplet surface temperature and longer evaporation times than the single component model.

Key findings

The previously suggested model for droplet heating and evaporation, taking into account temperature gradient and recirculation inside droplets and species diffusion within them, has been applied to the analysis of biodiesel fuel droplet heating and evaporation in realistic Diesel engine-like conditions. In contrast to most commonly used models to take into account these effects, our model is based on the analytical solutions to the heat transfer and species diffusion equations inside droplets.
Effective start/end date1/10/1231/05/13


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