EBS' strategy
starts with a gas engine that would be smaller than a diesel or gas
engine designed for the same power application. So a V-8 becomes a
small V-6 or even a four-cylinder. A monster 11-liter diesel engine
usually found in an 18-wheeler would become a 7.0-liter gas engine.
"The
technology applies across the board," Cohn said. "It
works with higher rpm motors as well."
The smaller engine provides better fuel economy during normal operation,
is less expensive to produce and reduces vehicle weight.
These small engines are designed with high compression (12:1 or 13:1)
and turbocharged, with boost pressures around 35psi to provide power
when needed. Normally that combination is a grenade waiting for the pin
to be pulled; such a design leads to massive detonation under most loads,
and certainly at wide-open throttle, even with premium 91-octane fuel.
Detonation
occurs in the cylinder when abnormal combustion leads to an instantaneous
and unwanted spike in cylinder pressure. Basically, there’s an
explosion of the air-fuel mixture — often setting
off at different places in the cylinder — instead of a controlled
burn or combustion. When these separate pressure waves collide — especially
if the piston is forced backward against its will on the compression
stroke — they create a sonic symphony of metallic chatter referred
to as "knocking" or "pinging."
Higher-octane
fuels reduce knocking because their burn properties help control or
challenge abnormal combustion. Powertrain engineers can also address
knocking with a lower compression ratio or by backing off the ignition
timing, all of which can reduce power. A traditional pre-treatment
remedy was an injection of water mixed with ethanol, or methanol, into
the intake manifold. Water in the air-fuel mixture helped cool the
cylinder, and the ethanol/methanol increased the fuel’s octane
rating to reduce knocking. This solution is very maintenance-heavy,
though, because the water/ethanol bottle had to be refilled often because
there was no precise injection strategy.
EBS discovered
that injecting ethanol directly into the cylinder allows a higher cylinder
pressure to produce torque and horsepower when needed, but without
the detonation. The engine-management computer uses sensors to monitor
the knock level, then injects only as much ethanol as needed to cool
the cylinder and increase the gasoline’s octane for that
particular rpm and load.
Cohn estimates
that ethanol consumption during normal driving would be about 3 percent
to 5 percent of gasoline consumption because full power isn’t
needed for cruising or light city driving.
