Comparison of Long-Chain Alcohol Blends, HVO and Diesel on Spray Characteristics, Ignition and Soot Formation

Journal article, 2019

Spray characteristics of fossil Diesel fuel, hydrotreated
vegetable oil (HVO) and two oxygenated fuel blends
were studied to elucidate the combustion process. The
fuels were studied in an optically accessible high-pressure/
high-temperature chamber under non-combusting (623 K,
4.59 MPa) and combusting (823 K, 6.04 MPa) conditions. The
fuel blends contained the long-chain alcohol 2-ethylhexanol
(EH), HVO and either 20 vol.% Diesel or 7 vol.% rapeseed
methyl ester (RME) and were designed to have a Diesel-like
cetane number (CN). Injection pressures were set to 120 MPa
and 180 MPa and the gas density was held constant at 26 kg/m3.
Under non-combusting conditions, shadow imaging revealed
the penetration length of the liquid and vapor phase of the
spray. Under combusting conditions, the lift-off length and
soot volume fraction were measured by simultaneously
recording time-resolved two-dimensional laser extinction,
flame luminosity and OH* chemiluminescence images. The
ignition delay and start of soot formation were also recorded.
Under non-combusting conditions at both injection pressures,
the liquid penetration length was higher for the blends and
HVO compared to Diesel, whereas the vapor penetration
length was similar for all fuels. Under combusting conditions,
the liquid penetration length of all the tested fuels was similar.
Despite different CNs, the ignition delay was similar for Diesel
and HVO. The EH blends had an increased ignition delay
compared to Diesel, despite having the same CN. The lift-off
length was found to be highest for the blend containing the
highest share of EH. In agreement with previously published
scaling relations, the lift-off length increased with increasing
injection pressure. The soot volume fraction was found to
be lower for the blends, in agreement with engine studies.