PIV Investigation of High Swirl Flow on Spray Structure and its Effect on Emissions in a Diesel-Like Environment 2011-01-1286

The paper presents results of an experimental investigation of the fluid dynamic processes during the air/fuel mixture formation period between an evaporating diesel spray and swirl air flow under realistic engine conditions. Particle Image Velocimetry (PIV) experiments have been carried out using an optically accessible prototype 2-stroke diesel engine equipped with a swirled combustion chamber. The flow within the chamber assumes a well structured swirl motion, similar to that developing in a real diesel engine, operating at high swirl ratio. The engine has been equipped with a common rail injection system and a solenoid-controlled injector, in use on automotive engines for the European market, able to manage multiple injection strategies. Two injector nozzles have been tested: a micro-sac 5-hole nozzle, 0.13 mm diameter, 150° spray angle and a 7-hole, 0.141 mm diameter, 148° spray angle. Tests have been carried out for three injection strategies: two single at the injection pressure of 100 and 120 MPa and a triple strategy at 71 MPa, representing low load engine conditions.

First, the air flow field was investigated, without fuel injection, by applying the 2D Mie-scattering PIV technique estimating the velocity of fuel droplets tracers sprayed within the combustion chamber and assumed to follow accurately the air flow. The air/fuel spray interaction has been also explored by the PIV technique to provide global information on the fuel jet evolution, in terms of liquid spray morphology, tip penetration and velocity vector distribution of the liquid fuel droplets within the combustion chamber, under evaporating conditions. The behavior of the two nozzles and injection strategies on fuel droplets vector velocity distribution and gaseous engine out emissions has been evaluated.