<div class="section abstract"><div class="htmlview paragraph">The current research octane number (RON) and motor octane number (MON) gasoline
tests are inadequate for describing the auto-ignition reactivity of fuels in
homogeneous charge compression ignition (HCCI) combustion. Intake temperature
and engine speed are two important parameters when trying to understand the fuel
auto-ignition reactivity in HCCI combustion. The objective of this study was to
understand the effect of high intake temperature (between 100 and 200 °C) and
engine speed (600 and 900 rpm) on the auto-ignition HCCI reactivity ratings of
fuels using an instrumented Cooperative Fuel Research (CFR) engine. The fuels
used for this study included blends of iso-octane/n-heptane, toluene/n-heptane,
ethanol/n-heptane, and gasolines with varying chemical compositions and octane
levels. The CFR engine was operated at 600 and 900 rpm with an intake pressure
of 1.0 bar and an excess air ratio (lambda) of 3. It was found that the relative
HCCI reactivity ranking of the gasolines with a RON of 98 was constant at both
engine speeds and high intake temperatures (150 °C and 200 °C). This implied
that for HCCI fuel ratings, there exists a threshold intake temperature beyond
which further increases in temperature do not change the relative rankings of
the fuel’s HCCI reactivity. At these high intake air temperatures, changes in
engine speed between 600 and 900 rpm did not affect the HCCI ratings of the
RON98 gasolines either. However, the effects of intake temperature (between 150
and 200 °C) and engine speed (600 and 900 rpm) did become apparent when
additional gasoline octane levels and chemical compositions were
investigated.</div></div>