Compared to the gasoline engine, the diesel engine has the
advantage of being more efficient and hence achieving a reduction
of CO₂ levels. Unfortunately, particulate matter (PM) and nitrogen
oxides (NOx) emissions from diesel engines are high. To
overcome these drawbacks, several new combustion concepts have been
developed, including the PCCI (Premixed Charge Compression
Ignition) combustion mode. This strategy allows a simultaneous
reduction of NOx and soot emissions through the
reduction of local combustion temperatures and the enhancement of
the fuel/air mixing. In spite of PCCI benefits, the concept is
characterized by its high combustion noise levels. Currently, a
promising way to improve the PCCI disadvantages is being
investigated. It is related with the use of low cetane fuels such
as gasoline and diesel-gasoline blends.
In this paper an experimental study is carried out focusing on
evaluating emissions, performances and combustion noise in PCCI
conditions when using diesel-gasoline blends. For this purpose, a
parametrical study has been performed varying injection timing and
fuel type in a High Speed Direct Injection (HSDI) diesel
engine.
Results show how increasing the gasoline percentage in the fuel
blend results in an enlarged ignition delay, therefore achieving an
extended mixing time between the End of Injection (EoI) and the
Start of Combustion (SoC). As a consequence, lower local
equivalence ratios are achieved and therefore lower soot emissions
are reached. Additionally, performances and the sound quality of
combustion noise are improved. By contrast, NOx levels
are slightly increased.