Fig. 1: Experimental setup.
In particular, the ICCD camera was used and Experimental apparatus coupled with narrow filters corresponding to λ=310
The optically accessible engine used during ex- nm for OH, λ=330 nm for HCO* and λ=431nm for
periments was a single cylinder, direct injection, CH, respectively. The second CCD was sensible in
four-stroke, diesel engine, with EURO IV multi the visible. Moreover, two colour pyrometry method
valves production head. The engine used a classic was applied by using an “ad hoc” filter in order to
extended piston with piston crown window (46 mm evaluate soot temperature and concentration [
Two different CCD cameras, with a different the injection pressure, even if higher quantities for
capability, were used. The first (ICCD) had high the engine operation with RME fuel because of its
sensibility both in the UV and visible range. The lower energy content. It can be noted that the rates
intensifier-gate duration of 41 µs was used in order of heat release have typical shape of HCCI
comto have a good accuracy in the timing of the onset bustion with two well resolvable peaks not
correof the combustion process. Previous investigations lated with the injection strategy investigated. The
showed the presence of characteristics radicals first is characteristic of low temperature reactions
during the low temperature and premixed combus- that occur in the chamber at autoignition; and the
tion development [
UV images were recorded by means a filter (bandwidth 10nm) at the characteristic emission wavelength of OH (310 nm). In figure 3, the OH images and the relative maximum intensity at the lower left corner are reported. -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40
]° g ][rraesesbu4300 115000 /l[tkJkaeeseaeR rrepnd20 fHO ly10 50 tae i C R 0 0 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40
Fig. 2: Combustion pressure, rate of heat release and drive current at 2000 rpm for REF (up) and RME (down) fuels at several injection pressures.
To examine the temporal and spatial evolution
of HCCI combustion digital imaging measurements
from UV to visible were performed. In figure 3 the
images of visible combustion and the soot KL
factor are reported. They are related to RME fuel, the
engine speed of 2000 rpm and an injection
pressure of 500 bar. In figure 3, the first column shows
the flame evolution, it can be noted the presence
of luminous spots randomly distributed in the bowl.
Increasing the crank angle, the luminous spots
move in the cylinder, due to the air swirl motion,
and increase their density in the whole chamber.
These bright spots are distributed not only in the
bowl but also in the space between the engine
head and the top of the piston [
Previous analysis of extinction and
chemiluminescence measurements showed that the
premixed combustion process is widely dominated by
the presence of OH radical [
They show very low emission because only 15% of incident light passed through the filter. The OH radical is detected close to the bowl wall at the start of combustion, then it fills the whole chamber, and it shows maximum intensity at 4° BTDC, three crank angle degrees later than the heat release peak.
400 500 600 700
In figure 4 the integral OH measured in the
combustion chamber at 2000 rpm and for several
injection pressures are reported. The integral
concentrations were computed for both REF and RME
fuels. It can be noted that increasing the injection
pressure the OH intensity decreases for both fuels
and the lowest intensity is detected for RME at 700
bar. Previous paper showed that OH radical was
responsible of the soot oxidation in the chamber
[
In conclusion, the use of oxygenated fuel helps to keep low the production and emission of HC with consequently positive effect on the emission of particulate matter.
Acknowledgments
The authors wish to thank Mr. Carlo Rossi and Bruno Sgammato for maintaining the experimental apparatus and for their precious help. 4.E+07 4.E+07 ] 3.E+07 .. u a [n 3.E+07 o iilrssm2.E+07 e a tge 2.E+07 n i H O1.E+07 5.E+06 0.E+00 ] 5 3 m / g 4 m [ PM3 8 7 6 2 1 0 400 500 600 700