Optical studies of spray development and combustion characterization of oxygenated and Fischer-Tropsch fuels

Optical studies of combusting diesel sprays were doneon three different alternative liquid fuels and compared toSwedish environmental class 1 diesel fuel (MK1). Thealternative 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 HighPressure High Temperature spray rig under conditionssimilar to those prevailing in a direct-injected dieselengine prior to injection. High speed shadowgraphs wereacquired to measure the penetration of the continuousliquid phase, droplets and ligaments, and vaporpenetration. Flame temperatures and relative sootconcentrations were measured by emission based, lineof-sight, optical methods. A comparison betweenprevious engine tests and spray rig experiments wasconducted in order to provide a deeper explanation of thecombustion phenomena in the engine tests.Results pertaining to spray behavior show that highviscosity fuels have wider spray cone angles, smallerdischarge coefficients (Cd) and shorter vapor penetrationthan low viscosity fuels. Continuous liquid phasepenetration is related to differences in surface tension,viscosity and density; while the penetration of dropletsand ligaments is related to volatility, their penetration isshort for highly volatile fuels and long for low-volatilityfuels.Engine tests show that particle matter (PM) emissionsare generally lower when these alternative fuels areused, but the use of RME leads to increased NOxemissions correlating with elevated flame temperatures