Investigation of HCCI Combustion in a DI Diesel Engine for Various Injection Timings – A CFD Study

Abstract

Homogeneous charge compression ignition engines have the potential for low
emissions and better efficiency. This benefit is due to its low temperature constant volume
combustion where the diesel cycle moves closer to Otto cycle for the same compression ratio.
Numerical investigations are carried out on a direct injection diesel engine for different HCCI
modes and the results are compared with the engine operating on standard mode. Since control
of fuel injection is one of the methods of obtaining controlled auto ignition, three injection
modes viz., very early injection (during the start of compression) late injection (middle of
compression) and injection just before the end of the compression (conventional injection) are
investigated. The earliest injection timing of SOI during the start of compression stroke
produced lowest levels of pollutants. But it suffers from poor evaporation of injected fuel and
lowest pressure rise and hence poor fuel economy. The injection during the middle of
compression stroke produced steep rise in pressure coupled with highest NOx emission level.
This indicates that this timing more or less is a typical diesel combustion. The conventional
injection timing of SOI 20° bTDC produced pressures which are comparable with experimental
data and highest soot emission. Hence it is concluded that injection timing control alone is not
sufficient to produce a reliable HCCI combustion.
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