Investigation of the injection process in a research CR diesel engine using different blends of propane-diesel fuel

Blends of propane-diesel fuel can be used in direct injection diesel
engines to improve the air-fuel mixing and the premixed combustion
phase, and to reduce pollutant emissions. The potential benefits of
usinf propane in diesel engines are both environmental and economic;
furthermore, its use does not require changes to the compression ratio
of conventional diesel engines. The present paper describes an
experimental investigation of the injection process for different liquid
preformed blends of propane-diesel fuel in an optically accessible
Common Rail diesel engine. Slight modifications of the injection
system were required in order to operate with a blend of propanediesel
fuel. Pure diesel fuel and two propane-diesel mixtures at
different mass ratios were tested (20% and 40% in mass of propane
named P20 and P40). First, injection in air at ambient temperature
and atmospheric pressure were performed to verify the functionality
of the modified Common Rail injection system. Second, injection
process was investigated within the engine. In both configurations,
images of the injection process were recorded; in particular, the
in-cylinder process was visualized through a sapphire window in the
piston bowl. The experimental investigation was performed at four
engine operating points of the NEDC (New European Driving Cycle).
Results show that the penetration of the blend fuel is as long as the
diesel one in the first phase of the injection and is shorter than the
diesel fuel at the end of the injection. The cone angle of the blend fuel
is always higher than diesel because of the sudden evaporation of
propane exiting from the nozzle hole. For these reasons, the use of
propane-diesel blends in a diesel engine could allow a better
homogenization of the air-fuel mixture