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FUEL 6 SMADST CONTROL S?STEK <br />. The fuel air rations that are supplied to the engine are <br /> kept in a very narrow window on both sides of stoichiometric. <br /> This is accomplished regardless of the composition of the gas in <br /> the well. This strategy was chosen because of the three-way <br /> catalytic converter (TWC) whose conversion efficiency is at a <br /> maximum if the fuel air ratio is held very close to stoichiometric. <br /> This task is accomplished by the use of a specially designed <br /> mixture control unit (MCU) , air/fuel mixer and a computer, which <br /> is fed information by an oxygen sensor in the exhaust. This <br /> automotive type oxygen sensor measures the amount of excess oxygen <br /> in the exhaust relative to that in the air. When the exhaust varies <br /> from rich to lean, the oxygen sensor produces a signal which is <br /> used to control the MCU. <br /> If the calorific value of the gas in the well is high enough <br /> to support combustion in the engine at stoichiometric, the system <br /> will use only well gas. If the calorific value of the well is <br /> too low to support stoichiometric combustion, the system will <br /> instantly blend propane gas with the well gas to bring the calorific <br /> value to a suitable level. <br /> The system also uses a specially designed water separating <br /> device in the well gas line to keep large amounts of water vapor <br /> from migrating into the MCU and engine. When the water level begins <br /> to build in the separator, a red warning light is lit on the instru- <br /> ment panel which signals water accumulation in the separator. If <br /> the water is not drained at this point, approximately one and one- <br /> half gallons of additional collection water will cause the computer <br /> to shut down the engine. <br /> The effect of humidity in the intake charge has virtually <br /> no effect on Co and HC emissions. However, it does have a dramatic <br /> effect on NOx production, as the steam generated will cool the <br /> peak combustion temperatures, which in turn drops the HOx level. <br /> The RPM is controlled by an electronic governing device which <br /> is operated by the process link computer. <br />