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.