Performance, gaseous and particle emissions of a small compression ignition engine operating in diesel/methane dual fuel mode

This paper deals with the combustion behavior and exhaust emissions
of a small compression ignition engine modified to operate in diesel/
methane dual fuel mode. The engine is a three-cylinder, 1028 cm3 of
displacement, equipped with a common rail injection system. The
engine is provided with the production diesel oxidation catalyst.
Intake manifold was modified in order to set up a gas injector
managed by an external control unit.
Experiments were carried out at different engine speeds and loads.
For each engine operating condition, the majority of the total load
was supplied by methane while a small percentage of the load was
realized using diesel fuel; the latter was necessary to ignite the
premixed charge of gaseous fuel.
Thermodynamical analysis of the combustion phase was performed
by in-cylinder pressure signal. Gas emissions and particulate matter
were measured at the exhaust by commercial instruments. The sizing
and the counting of the particles were performed by means of an
engine exhaust particle sizer spectrometer. It was found out that dual
fuel combustion reduces the carbon dioxide and nitrogen oxides
emissions while increases the total hydrocarbons and carbon
monoxide. Moreover, it was found out that dual fuel combustion
produces lower particulate matter concentration. The effect of
methane on particle size and number is influenced by the operating
condition. In particular, at high engine speed dual fuel combustion
emits larger amount of particles smaller than 20 nm with respect to
diesel fuel. The use of a catalytic device allows to reduce
considerably the carbon monoxide emissions.