In this paper we report how optical techniques were applied in
the cylinder of an optically accessible engine equipped with
latest-generation EURO V diesel engine head. The injection strategy
with high percentage of EGR, characteristic of real engine
operating point, was adopted. In particular, the combustion
behavior at 1500 rpm\2 bar BMEP was investigated. Alternative
diesel fuels were used. In particular, rapeseed methyl ester (RME)
and gas to liquid (GTL) were selected as representative of 1st and
2nd generation alternative diesel fuel, respectively.
Combustion analysis was carried out in the engine combustion
chamber by means of visible digital imaging. These measurements
helped to analyze the chemical and physical events occurring during
the mixture preparation and the combustion development. Ultraviolet
(UV) digital imaging was also performed and the presence of
characteristic radical, like OH, in the various phases of
combustion was detected as well. OH spatial distribution and
temporal evolution were computed and compared to soot volume
fraction measured in the combustion chamber by means of the two
color pyrometry methods. The effect of fuels on the combustion
process and pollutants formation was evaluated.
The GTL fuel showed better performance in terms of indicated
mean effective pressure (IMEP) with respect to the diesel reference
fuel with different effects on particulate matter (PM) and gaseous
emissions. On the other hand, the RME fuel showed a decrease in
IMEP that can be adjusted with a little increase of fuel injected
quantity, and very low production of soot in the cylinder and PM at
the exhaust compared to the diesel reference fuel.