Abstract
A combined experimental and numerical investigation has been performed in order to evaluate the influence of physical properties of biodiesel on the injection process in a common-direct injection system with second generation solenoid injectors. For that purpose, after a complete characterization of the system, which involved mechanical and hydraulical characterization, a one-dimensional model has been obtained with the commercial code Amesim, which has been extensively validated. Simulations have then been performed with a standard Diesel and a 100% of Rapessed Methyl Ester (RME) biodiesel which allowed a comparison and analyse of the dynamic response of the injector to be done. Different injection strategies involving main injection and main plus post-injection has been used to explore the impact of the use of biodiesel on the performance and stability of solenoid injectors.
As far as the dynamic response of the injector is concerned, the results obtained have clearly shown that the use of biodiesel affects the dynamic response of the needle, especially at low injection pressures. As reported in the paper, this different behavior is explained as a consequence of the higher viscosity of biodiesel compared to the standard fuel. With regard to the results at stationary conditions (at full needle lift), the mass flow rate obtained for a given injection condition from the biodiesel was slightly higher than that obtained for the standard Diesel. In this case, not only the different value of density between fuels is at the origin of this different behavior, but also the different flow regime in the nozzles orifices, which in turn affects the discharge coefficient of the injector nozzle.
The behavior of the system under multi-injection strategies (main and post injection) has been also evaluated determining for different operating conditions (injection pressures and backpressures) the minimum dwell time between injections to assure a stable behavior in the injection process (mass flow rate). No important differences have been found between biodiesel and standard diesel in this critical parameter.
KEYWORDS: injection, modelling, biodiesel