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Although an engine's lean limit fuel-air ratio may be easily found experimentally, it is difficult to predict accurately due to the influence of speed, load, ambient conditions, ignition characteristics, fuel chemistry, engine wear, etc. This paper will describe a new closed loop feedback control which adaptively tracks the engine's instantaneous lean limit using only one engine sensor. Test data is presented which indicates the control system response to changes in ignition timing, fuel chemistry, speed, and load. Results from laboratory and field tests indicate a significant improvement over programmed fuel-air scheduling systems, both in fuel economy and exhaust emissions.

A fuel control system has been developed which allows fuels of various stoichiometries to be used interchangably, without suffering a fuel consumption penalty, allowing a more efficient use of the combustion energy. This Adaptive Lean Limit Control system uses a single, digital sensor and an electronic circuit to detect lean limit engine operation, and feeds back information to the fuel system to maintain the best economy mixture, regardless of the fuel blend being used. This paper will describe the hardware, and include the results of extensive vehicle testing, using 20 percent and 50 percent ethanol-gasoline blends.