Search Results

Computational models widely employed for predicting the dispersion of fuel sprays in combustion engines suffer from well-known drawbacks associated with the utilization of case-dependent empirical phase-change models, describing the conversion of liquid into vapour during fuel injection. The present work couples the compressible Navier-Stokes and energy conservation equations with a thermodynamic closure approximation covering pressures from 25 to 2000bar and temperatures that expand from compressed liquid, vapor-liquid equilibrium to trans/supercritical mixing, and thus, cover the whole range of P-T values that diesel fuel undergoes during its injection into combustion engines. The model assumes mechanical and thermal equilibrium between the liquid, vapour and surrounding air phases and thus, it avoids utilization of case-dependent empirical phase-change models for predicting in-nozzle cavitation and vaporization of fuels.

Optimization of geometric and operating parameters controlling the fuel injection rate of in-line pump-based fuel injection system for small-sized industrial DI diesel engines can be obtained using computer models simulating simultaneously the flow inside the fuel injection system and the subsequent spray development. Empirical sub-models accounting for the effect of injection hole cavitation both on hole exit velocity and on the atomization of the injected liquid have been included in order to enhance model predictions. Validation of the FIE model s performed by comparing model predictions against experimental data for the pumping chamber pressure, delivery valve lift, line pressure, needle lift and injection rate for various pump designs and for a wide range of pump operating conditions. The results confirm that the FIE simulation model is capable of predicting the flow characteristics inside the fuel injection system for all cases investigated.

Rail pressures of modern diesel fuel injection systems have increased significantly over recent years, greatly improving atomisation of the main fuel injection event and air utilisation of the combustion process. Continued improvement in controlling the process of introducing fuel into the cylinder has led to focussing on fluid phenomena related to transient response. High-speed microscopy has been employed to visualise the detailed fluid dynamics around the near nozzle region of an automotive diesel fuel injector, during the opening, closing and post injection events. Complementary computational fluid dynamic (CFD) simulations have been undertaken to elucidate the interaction of the liquid and gas phases during these highly transient events, including an assessment of close-coupled injections.