Gasoline turbocharged direct injection (GTDI) engines, such as
EcoBoost™ from Ford, are becoming established as a high value
technology solution to improve passenger car and light truck fuel
economy. Due to their high specific performance and excellent
low-speed torque, improved fuel economy can be realized due to
downsizing and downspeeding without sacrificing performance and
driveability while meeting the most stringent future emissions
standards with an inexpensive three-way catalyst.
A logical and synergistic extension of the EcoBoost™ strategy
is the use of E85 (approximately 85% ethanol and 15% gasoline) for
knock mitigation. Direct injection of E85 is very effective in
suppressing knock due to ethanol's high heat of vaporization -
which increases the charge cooling benefit of direct injection -
and inherently high octane rating. As a result, higher boost levels
can be achieved while maintaining optimal combustion phasing giving
high thermal efficiency. However, due to their different
properties, optimization of a combustion system for both regular
grade (91 RON) gasoline and E85 is non-trivial.
This paper describes the initial design and development of a new
combustion system for a flexible fuel (gasoline and E85)
turbocharged direct injection engine. The development process
utilized a boosted single-cylinder engine in conjunction with a
second boosted single-cylinder engine with optical access which was
used to provide insight into fuel/air interactions and resultant
combustion performance. Using this approach a robust combustion
system was developed to meet targets for both gasoline and E85
operation before multi-cylinder hardware was available.
