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The study aims to approach the performance of fuel injection system of diesel engines when using biodiesel as an alternative fuel. Mathematical model is proposed to simulate the fuel path through the injection system taking into consideration the compressibility effect, pressure waves in the pipeline, fuel properties and the leakage through clearance of moving parts. The model is compared with another experimental work for validation. The effect of biodiesel properties and its blends on the injection system behavior are examined. The results indicate that, when using biodiesel as an alternative fuel, the pressure waves propagating through the line diminished rapidly compared with conventional diesel oil. The results indicate also that, when using biodiesel, the leakage decreased because of its higher viscosity. As a result, the rate of pressure rise increases and the beginning of injection becomes earlier. It is important in this case to retard the injection timing to optimize the engine performance. On the other hand, the study shows that, the same atomization degree can be obtained when transformed to biodiesel by raising the injection pressure with certain ratios. These ratios depend on biodiesel blend percentage and compression ratio of the engine.

The Effervescent atomizer, which is a type of internal-mixing twin-fluid atomizer, has been showed to work well with biofuels in terms of lower droplets size at relatively low injection pressure. The two phase flow inside the atomizer was numerically simulated using the volume of fluid model. Validation with experimental work was performed. The present results showed that the gas to liquid mass ratio (GLR) is one of the major contributory factors affecting the atomizer performance. The two phase flow was identified as slug flow in the discharge passage at low GLR (.08%). The flow evolved to slug-annular flow at GLR= 0.5%. At relatively high GLR (0.8%) the annular flow was distinguished. The mixing between phases was augmented with increasing GLR. Finally the liquid film thickness at the atomizer outlet was calculated and compared with the conventional aviation Jet-A1 fuel. The results showed that the liquid film thickness almost remains unchanged at low GLRs, though the higher biofuel viscosity, order of four. But, for higher GLRs, the liquid film thickness slightly changed. Finally, the results unveil the superiority of effervescent atomizer with Jatropha biofuel.

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In the present work, a complete simulation of reactive flow in the combustion chamber of a rocket motor equipped with convergent-divergent nozzle has been introduced. The model describes the combustion process inside the combustion chamber considering a steady premixed reactant gas injected through side porous walls of the combustion chamber. The products flow through a convergent-divergent nozzle with adiabatic impermeable walls. The reactants are treated as two-dimensional, multi-components, turbulent compressible flow. The local properties of the mixture are calculated and updated during the solution process. At the boundary of the combustion chamber, a constant mass flux and predefined properties are considered. The proposed model employs the basic conservation equations of continuity, momentum and energy as well as the finite rate of reaction and species transport equations. Finite volume method is used to solve the basic nonlinear partial differential equations numerically. The details of the numerical scheme, structure of the used grids, numerical accuracy and stability are introduced. The effect of grid resolution as well as the validity of the results is included. The results showed fair agreement with other models in the literature; specially the reaction zone depth, temperature contours and species concentration along the entire space of the combustion chamber.