Blending gasoline with oxygenates like ethanol, MTBE or ETBE has
a proven potential to increase the thermodynamic efficiency by
enhancing knock resistance.
The present research focuses on assessing the capability of a 2-
and tert-butanol mixture as a possible alternative to
state-of-the-art oxygenates. The butanol mixture was blended into a
non-oxygenated reference gasoline with a research octane number
(RON) of 97. The butanol blending ratios were 15% and 30% by mass.
Both the thermodynamic potential and the impact on emissions were
investigated.
Tests are performed on a highly boosted single-cylinder gasoline
engine with high load capability and a direct injecting fuel system
using a solenoid-actuated multi-hole injector. The engine is
equipped with both intake and exhaust cam phasers. The engine has
been chosen for the fuel investigation, as it represents the SI
technology with a strongly increasing market share.
The blended gasoline-butanol mixtures showed a distinct increase
in RON and MON numbers as well as in heat of vaporization. As a
consequence, high and full load efficiency could be improved by
earlier ignition timing and hence a more favorable center of
combustion could be attained. The indicated mean effective pressure
(IMEP) could be increased by more than 20% in comparison to the
reference gasoline at an equivalent level of coefficient of
variance (COV) of IMEP. The gain in knock resistance could
contribute to a significant reduction in CO₂ emissions when
compression ratio is increased or when engine downsizing is
realized. At low and medium loads, identical or slightly improved
performance regarding thermodynamics and emissions could be
detected.
With the ongoing discussion on the limitation of particulate
emission from gasoline engines, the observed capability of butanol
blends to reduce soot particle mass and number especially at cold
engine conditions can be regarded as a positive impact of the
butanol blends when compared to the non-oxygenated gasoline.
This study underlines the high potential of the investigated 2-
and tert-butanol mixtures to serve as oxygenates for blending into
gasoline in order to achieve higher fuel quality levels.
Furthermore, detailed investigations including multi-cylinder
engine experiments are planned for part 2.
