Butanol Blending - a Promising Approach to Enhance the Thermodynamic Potential of Gasoline - Part 1 2011-01-1990

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.