Alternative diesel fuels from renewable sources (biodiesels)
have increased significantly interest due to their potential CO₂
emission benefits, capability to reduce unburned hydrocarbons and
particulate matter emissions, biodegradability and
non-toxicity.
Biodiesels undergo ageing effects due to autoxidation processes
of their molecular chains. Ageing leads to a variety of
decomposition products like peroxides, alcohols, aldehydes and
carboxylic acids. They are detectable as alterations of chemical
properties, odor and taste (rancidity).
The characteristics of Rapeseed Methylester (RME), RME aged and
diesel sprays have been analyzed for different injection strategies
in engines. The tests have been performed on a Bosch second
generation common rail solenoid-driven fuel injection system
capable of 160 MPa maximum injection pressure, fitted on EURO5
diesel engine for passenger car applications. Three different flux
number injectors have been adopted at the injection pressures of
40, 80 and 160 MPa with 1.0, 0.6 and 0.3 ms solenoid energizing
time. The characterization of the injection process for the defined
fuels has been carried out in terms both of fuel injection rate as
well as of spatial and temporal fuel distribution in a quiescent
chamber in non-evaporative conditions.
Largest discharging nozzle area produced highest fuel injection
rate while smallest area created longest injection duration at
parity of solenoid exciting time. Digital processing of the spray
images, captured at different instant from the start of injection,
has enabled the characterization of the fuel dispersion in terms of
tip penetration and cone angle. Differentiate behavior of the
injected fuel has been noted for the diverse nozzles at early time
from the start of injection.
Finally, a detailed reconstruction of the jet images, at very
early time from the start of injection, has highlighted repetitive
anomalies in the jet-to-jet propagations. Their absolute values and
stabilizing time depend on the nozzle type and injection pressure.
At late time, the sprays uniform themselves with a homogeneous
pattern in the vessel.