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Ethanol Autoignition Characteristics and HCCI Performance for Wide Ranges of Engine Speed, Load and Boost
Abstract:
The characteristics of ethanol autoignition and the associated
HCCI performance are examined in this work. The experiments were
conducted over wide ranges of engine speed, load and intake boost
pressure (Piⁿ) in a single-cylinder HCCI research engine
(0.98 liters) with a CR = 14 piston.
The data show that pure ethanol is a true single-stage ignition
fuel. It does not exhibit low-temperature heat release (LTHR), not
even for boosted operation. This makes ethanol uniquely different
from conventional distillate fuels and offers several benefits: a)
The intake temperature (Tiⁿ) does not have to be
adjusted much with changes of engine speed, load and intake boost
pressure. b) High Piⁿ can be tolerated without running
out of control authority because of an excessively low
Tiⁿ requirement.
However, by maintaining true single-stage ignition
characteristics, ethanol also shows a relatively low
temperature-rise rate just prior to its hot ignition point.
Therefore, ethanol does not tolerate as much combustion-phasing
retard as fuels that exhibit LTHR and/or pronounced
intermediate-temperature heat release. Since combustion retard is
important for avoiding excessive pressure-rise rates, the distinct
single-stage ignition characteristic of ethanol can be considered a
drawback when reaching for higher loads. Nonetheless, an
IMEPg of 11.3 bar was demonstrated for Piⁿ =
247 kPa.
Finally, the latest ethanol chemical-kinetics mechanism from the
National University of Ireland - Galway was evaluated against the
experimental engine data using a multi-zone model. Overall, the
mechanism performs very well over wide ranges of operating
conditions.