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An electronic fuel/air mixture controller has been developed which is designed to reduce exhaust emissions on small utility engines. Lean Power Corporation has conducted a field study using this controller in cooperation with the United States Postal Service. Additional laboratory testing was performed in cooperation with the U.S. Environmental Protection Agency using the SAE J1088 test procedure. In this study, electronic air/fuel mixture controllers were installed and exhaust emissions evaluated on a sample of lawnmowers and engines. A significant reduction was achieved in Carbon Monoxide and the sum of Hydrocarbons plus Oxides of Nitrogen with the electronic mixture controller.

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.

Automotive engineers have recognized the fuel economy advantage of elevated coolant temperatures for many years. Evaporative engine cooling is a well established technology which maintains the engine coolant at its boiling temperature regardless of operating conditions. By assuring that the coolant entering the engine is at nearly the same temperature as that leaving the engine, overcooling is avoided. Excellent temperature uniformity is assured throughout the engine, permitting coolant temperatures to be raised without raising peak metal temperatures. Evaporative cooling allows engine coolant to boil freely at atmospheric pressure, taking advantage of the inherently high heat transfer rates obtained with boiling and condensing. The benefits derived from evaporative cooling are faster warm-up, reduced friction, (which contribute toward fuel economy) greater engine durability, and safe, low pressure operation.