An investigation of high speed direct injection (DI) compression
ignition (CI) engine combustion fueled with gasoline injected using
a triple-pulse strategy in the low temperature combustion (LTC)
regime is presented. This work aims to extend the operation ranges
for a light-duty diesel engine, operating on gasoline, that have
been identified in previous work via extended controllability of
the injection process. The single-cylinder engine (SCE) was
operated at full load (16 bar IMEP, 2500 rev/min) and computational
simulations of the in-cylinder processes were performed using a
multi-dimensional CFD code, KIVA-ERC-Chemkin, that features
improved sub-models and the Chemkin library. The oxidation
chemistry of the fuel was calculated using a reduced mechanism for
primary reference fuel combustion chosen to match ignition
characteristics of the gasoline fuel used for the SCE
experiments.
With constraints on a minimum allowable combustion efficiency,
maximum allowable noise level (pressure rise rate) and maximum
allowable NOx and soot emissions, engine operation
ranges were identified as functions of injection timings and the
fuel split ratio (i.e., fraction of total fuel injected in each
pulse) with triple-pulse injections. Parametric variation of the
engine operating ranges were also investigated with respect to
initial (i.e., intake) gas temperature, exhaust gas recirculation
ratio, intake boost pressure and injection system rail pressure.
Following the modeling, engine experiments were performed under
conditions identified through analysis of the numerical results in
order to confirm the effectiveness of gasoline direct injection
compression ignition (GDICI or GCI) operation with triple-pulse
injections at full load.
Based on both computational and experimental results, the role
of each pulse in GDICI operation was identified in terms of
combustion stability, engine performance and emissions. While
maintaining similar emissions characteristics to that of the
double-pulse injection cases (~0.1 g/kg-f of NOx and PM,
and ~173 g/kW-hr of ISFC), the extension of operable conditions
using a triple-pulse injection strategy was successfully
achieved.