CFD Prectictions of Electrohydrodynamics in Model DISI Engines 2007-01-1419

A concept combustion chamber, in which an electrospray interacts with electrostatic forces applied on the boundaries, is used to simulate the mixture preparation in a Direct Injection Spark Ignition (DISI) engine. The study is made in a 2D axisymmetric enclosure, which reflects a motored engine operating with an electrostatic atomizer previously investigated for application in fuel burners [1]. Using a rewritten version of a research CFD code [2], the transition injection mode has been chosen given that it integrates the two basic modes of operation of DISI engines [3]. Three pulses of 5 mg each are made at crank angles of 80, 150 and 300 °ATDC of the intake, these falling within the intervals for stable combustion of either early or late injection modes of operation of DISI engines. Over the half engine cycle simulated, the effects of charge are qualitatively studied with use of an uncharged spray as the benchmark. The comparisons are based on droplet dispersion, gas velocity vectors and the profiles of axial and radial mean velocities and turbulence kinetic energy. Two diametrical planes cutting through the axial positions of 10 and 20 mm downstream of the nozzle exit are selected for temporal evaluation of the behaviour of two interesting/peculiar recirculation zones identified in the vicinity of the cylinder roof. The in-cylinder Coulomb forces acting on the injected electrospray are found to effectively control the spray dispersion and deposition, hence making the proposed system an alternative method to minimize the spray wall impingement in DISI engine in-cylinder flows.