The objective of this study is to increase fundamental
understanding of the effects of fuel composition and properties on
low temperature combustion (LTC) and to identify major properties
that could enable engine performance and emission improvements,
especially under high load conditions.
A series of experiments and computational simulations were
conducted under LTC conditions using 67% EGR with 9.5% inlet O₂
concentration on a single-cylinder version of the General Motors
Corporation 1.9L direct injection diesel engine. This research
investigated the effects of Cetane number (CN), volatility and
total aromatic content of diesel fuels on LTC operation. The values
of CN, volatility, and total aromatic content studied were selected
in a DOE (Design of Experiments) fashion with each variable having
a base value as well as a lower and higher level. Timing sweeps
were performed for all fuels at a lower load condition of 5.5 bar
net IMEP at 2000 rpm using a single-pulse injection strategy.
Selected fuels were also run under a higher load condition of 10
bar net IMEP at 2000 rpm with roughly 90 dB combustion noise using
a split injection strategy.
For this engine and the operating conditions tested, at 5.5 bar
net IMEP, results show that increasing CN reduces CO and UHC,
improves ISFC and reduces combustion noise due to more favorable
combustion phasing. The results at higher load with split injection
indicate that the two injection timings and respective fuel
quantity delivered in each injection must be varied significantly
to reach optimum conditions for fuels with different CN. Numerical
simulation results also demonstrate the effects of fuel property
differences on combustion. In-cylinder flow fields and
distributions of temperature and species depict the reasons for
different combustion performance of the fuels considered in the
study.