The concept of hot surface assisted compression ignition (HSACI) was previously
shown to allow for control of combustion timing and to enable combustion beyond
the limits of pure homogeneous charge compression ignition (HCCI) combustion.
This work investigates the potential of HSACI to extend the operating limits of
a naturally aspirated single-cylinder natural gas fueled HCCI engine.
A zero-dimensional (0D) thermo-kinetic modeling framework was set up and coupled
with the chemical reaction mechanism AramcoMech 1.3. The results of the 0D study
show that reasonable ignition timings in the range 0-12°CA after top dead center
(TDC) in HCCI can be expressed by constant volume ignition delays at TDC
conditions of 9-15°CA. Simulations featuring the two-stage combustion in HSACI
point out the capability of the initial heat release as a means to shorten
bulk-gas ignition delay.
Engine trials were conducted to map the operating limits in HCCI and HSACI mode
for an engine speed of 1400 1/min as a function of intake air temperature
(148-173°C) and relative air-fuel ratio (λ = 2.0-3.0). Results show that HSACI
extends the lean limit by more than ∆λ = 0.4 and reduces the minimum required
intake temperature by at least 5 K compared to HCCI. Comparative experiments of
HCCI and HSACI reveal that HSACI benefits from higher engine load, lower ringing
intensity and lower NOx emissions without deteriorating efficiency.
Experimental data concerning the occurrence of instable combustion in HCCI and
the role of initial heat release in HSACI agree with the trends predicted by the
0D models.
