Optical studies of spray development and combustion characterization of oxygenated and Fischer-Tropsch fuels
Paper in proceeding, 2008
Optical studies of combusting diesel sprays were done
on three different alternative liquid fuels and compared to
Swedish environmental class 1 diesel fuel (MK1). The
alternative fuels were Rapeseed Oil Methyl Ester (RME),
Palm Oil Methyl Ester (PME) and Fischer-Tropsch (FT)
fuel.
The studies were carried out in the Chalmers High
Pressure High Temperature spray rig under conditions
similar to those prevailing in a direct-injected diesel
engine prior to injection. High speed shadowgraphs were
acquired to measure the penetration of the continuous
liquid phase, droplets and ligaments, and vapor
penetration. Flame temperatures and relative soot
concentrations were measured by emission based, lineof-
sight, optical methods. A comparison between
previous engine tests and spray rig experiments was
conducted in order to provide a deeper explanation of the
combustion phenomena in the engine tests.
Results pertaining to spray behavior show that high
viscosity fuels have wider spray cone angles, smaller
discharge coefficients (Cd) and shorter vapor penetration
than low viscosity fuels. Continuous liquid phase
penetration is related to differences in surface tension,
viscosity and density; while the penetration of droplets
and ligaments is related to volatility, their penetration is
short for highly volatile fuels and long for low-volatility
fuels.
Engine tests show that particle matter (PM) emissions
are generally lower when these alternative fuels are
used, but the use of RME leads to increased NOx
emissions correlating with elevated flame temperatures.