HCCI (Homogeneous Charge Compression Ignition) engine is able to
achieve low NOx and particulate emissions as well as high
efficiency. However, its operation range is limited by the knocking
at high load, which is the consequence of excessively rapid
pressure rises. It has been suggested that making thermal or fuel
inhomogeneities can be used to solve this problem, since these
inhomogeneities have proved to create different auto-ignition
timing zones.
It has also been suggested that EGR (Exhaust Gas Recirculation)
has a potential to reduce pressure rise rate. But according to a
past report, it was concluded that under the same fueling ratio and
CA50 with different initial temperature and EGR ratio, the maximum
PRR is almost constant.
The purpose of this study is to investigate the fundamental
effects of EGR. First, I considered EGR homogeneous charge case. In
this case, the effects of EGR and its components like CO₂, H₂O or
N₂ on HCCI combustion process is argued. When diluted with EGR or
its components, gas composition changes and the ratio of heat
capacity and O₂ concentration become changed. As a consequence, the
histories of pressure and temperature, ignition timing and
temperature, combustion duration and PRR might be changed. So I
checked them with addition of different amounts of EGR and its
components under the same fueling ratio, by using RCM (Rapid
Compression Machine). I used RCM to avoid influences such as
in-cylinder gas temperature and fuel inhomogeneities. Second, I
considered EGR inhomogeneous case. In this case, I checked those
which are mentioned in homogeneous case with addition of same total
amounts of EGR but different amounts of EGR in each zones under the
same fueling ratio by using RCM. In these two cases, additional
numerical calculation with single and multi-zones model is run to
know the potentials of EGR homogeneous and stratified charge, in
order to reduce PRR.