"Alex Esplin" <[EMAIL PROTECTED]> writes:
>
> Here's the deal. Your ECM is monitoring the gas exiting the cylinders
> of the engine. This is how the efficiency is monitored. The ECM has
> no way of knowing and doesn't care what the torque and horsepower are.
> If you improve the efficiency of the explosion by more completely
> burning the fuel that enters the cylinder, the ECM detects this and
> alters the amount of fuel entering the cylinder. What you get is a
> constant amount of energy generated with each ignition, but that
> energy is created by burning more of less gas entering the cylinder.
> Your ECM knows what to give you based on the relative position of the
> throttle. If you have the pedal all the way on the floor, it's
> pumping in as much gas as you want. If you are cruising, it's just
> pumping in enough gas to maintain RPM. If you are using water
> injection, NOS, or any other explosion-additive, that "enough to
> maintain RPM" is much less than a normal, less-efficient
> configuration.
Yes, the computer monitors the O2 sensors, which inform it as to how
complete the combustion is and allow it to modify its ignition timing
and fuel injection maps. But the primary inputs to the map are RPM
and air flow, as measured by an airflow meter or manifold absolute
pressure sensor. Until recently, most computers only know what the
throttle pedal is doing by the amount of air that gets sucked in.
And, by saying sucked in, I mean to suggest that an engine is
primarily an air pump. The size of the cylinders directly determines
the amount of air that gets sucked in via the intake stroke. Thus the
'liter' measurement of engines, which determines the intake volume of
the cylinders. More air means more combustion and more power.
The throttle pedal on a car is connected to a flap that sits in front
of the intake manifold. At idle, the flap is completely closed and
all the incoming air has to get sucked through a small, generally
screw-adjustable valve. That gives the engine just enough air to
generate enough power to keep the engine and its accessories turning
smoothly.
When you push on the pedal, it pulls on a cable that directly actuates
the flap. As the flap opens, the engine is able to suck more air into
the intake, and the vacuum level inside the engine decreases. The
computer detects the extra air, injects enough fuel to compensate, and
the power output increases. At wide-open throttle, intake pressure at
the end of the intake stroke is equal to atmospheric pressure, i.e. no
vacuum at all.
Superchargers (belt drive, electric drive, or exhaust turbine driven,
which are more commonly known as turbochargers) work by further
increasing the air volume inside the cylinders by creating
greater-than-atmospheric pressure in the intake system. They're
basically auxiliary air pumps to supplement the air-pumping ability of
the engine. Higher than ambient pressures can require different fuel
mixtures to stave off detonation, since the more compressed the oxygen
gets the easier it is to pre-ignite. Thus the need for higher octane
gas (which has greater resistance to combustion) in high-compression
and supercharged engines. Water injection also works well here to
stave off pre-detonation, since you can then rely on the water to
prevent pre-detonation instead of extra fuel that won't be burnt
anyway.
--Levi
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