Autoignition characterization of methanol, ethanol, propanol, and butanol over a wide range of operating conditions in LTC/HCCI

Abstract

In this work, the autoignition properties of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, and sec-butanol are studied in HCCI and compared. Experiments were performed, characterizing the sensitivity of these fuels to equivalence ratio, intake temperature, residual fraction, intake pressure, and engine speed. Under all of the low boost pressure operating conditions considered (1.15 bar), the order of reactivity of each fuel from low to high is: isopropanol, sec-butanol, ethanol ≈ n-propanol ≈isobutanol, methanol, n-butanol. n-butanol was less sensitive to changes in intake temperature than the other six fuels at low boost conditions. The required intake temperature to maintain a constant combustion phasing decreased significantly for n-butanol with intake pressure due to emergent intermediate temperature heat release (ITHR). At an intake pressure of 1.95 bar, sec-butanol showed some amount of ITHR which decreased its sensitivity to intake temperature. However, sec-butanol still maintained its high autoignition resistance, unlike n-butanol. Isobutanol did not show any ITHR at this intake temperature, though did show a decrease in intake temperature sensitivity. With the exception of n-butanol, the behavior and sensitivity of each alcohol fuel to the wide array of operating conditions considered were similar, with small differences in autoignition resistance. This means that these six fuels could potentially be blended and used interchangeably with little change to their autoignition characteristics.