College Park, MD--In theory, an IC engine's efficiency goes up as the amount of air fed into it increases and the amount of fuel decreases--until fuel input hits zero. Practically speaking, the engine emits smoke, fails to respond, and becomes unstable when the mixture becomes too lean. Maximum achievable efficiency is just slightly richer than that "lean limit."
Engineers recently developed a computer chip in a closed-loop feedback system that can operate the engine right at the limit. It adds extra air to the fuel/air mix, which substantially decreases carbon monoxide and hydrocarbon emissions, and increases fuel efficiency.
Maintaining an engine at its lean limit is tricky, according to John Studer, LeanPower's product engineer. To avoid producing a too-lean mixture, the feedback loop must be fast and precise.
On engines that use a carburetor, LeanPower's actuator is an air servo valve, or essentially a computer-controlled intake manifold vacuum leak between the carburetor and the engine, Studer explains. The basic air/fuel mixture is set at stoichiometric, or a little richer. When the engine runs, the signal processor (the Lean 2000 chip) opens the valve, so that air intake increases, and the mixture becomes leaner. Just past the lean limit, the pistons lose regularity and the flywheel, which is very sensitive to engine instability, loses angular velocity.
In the present system, LeanPower's sensor, a magnetic transducer, detects the change in angular velocity by tracking the flywheel ring-gear teeth, and relays it to the signal processor. (A processor now in development receives tachometer input from the ignition system.) The processor assesses the change in engine performance, then decreases the auxiliary air flow, making the mixture richer.
When performance improves, the processor can begin to lean the mixture again. Normally the loop keeps the engine running smoothly right at the lean limit. At full throttle, which a driver might need for passing or climbing hills, the processor allows a richer mixture. "The driver can't tell the difference," Studer says. He and his colleagues use a similar system on engines that employ fuel injection. But in that case, the Lean 2000 chip communicates directly with the fuel injection control system.
Ideally the system should adjust the lean level before the next cycle fires. The entire loop takes less than 2.5 mseconds.
"We offer a low-cost solution," Studer insists. "Retrofitting an old car would cost about $250, and that includes the tuneup." With the new tachometer input now under development, this cost may decrease.
Additional details...Contact Michael Leshner, President, LeanPower, 335 Paint Branch Dr., College Park, MD 20742.