In this study, a strategy for MCCI combustion of a novel alcohol fuel is
demonstrated. The novel fuel, “GrenOl”, is the result of the catalytic upgrade
of sustainable ethanol into alcohols of higher molecular weight. The composition
of GrenOl includes approximately 70% 1-butanol, 15% 1-hexanol, and 5% 1-octanol
by mass, resulting in a cetane number around 18.
In order to achieve mixing-controlled compression ignition with GrenOl, an
exhaust rebreathing strategy is employed. In this strategy, the exhaust valve
reopens for a part of the intake stroke, inducting hot exhaust into the cylinder
and preheating the fresh air. This study investigates the feasibility of
operating with such a valve strategy from idle to peak torque. At idle, the
primary challenge is ensuring stable combustion by inducting adequate exhaust to
achieve ignition. Under load, when cylinder temperatures are higher, the primary
challenge is ensuring sufficient air is inducted to achieve the target
torque.
It was found that a modest exhaust rebreathing valve strategy could ensure stable
combustion with diesel-like emissions and efficiency from idle to peak torque.
Coefficient of variation of IMEP as low as 2% was achieved at idle, matching
diesel idle stability despite the very low cetane number of the fuel. At medium
load, indicated specific fuel consumption was as low as 235 g/kWh, and
engine-out indicated specific NOx emissions were as low as 4 g/kWh. Peak torque
was attained despite the volumetric efficiency penalty imposed by exhaust
rebreathing.
These results demonstrate the feasibility of operating a diesel engine on neat,
sustainable, ethanol-derived fuel over the entire engine operating map with
minimal well-defined design modifications. Future work should extend these
findings to multicylinder engines and challenging cold start conditions.
