Abstract: A heavy-duty flame propagation engine has control systems and exhaust aftertreatment systems adapted to provide ultra-low emissions relative to Diesel engines while achieving comparable fuel consumption at reduced emission levels. The control systems include exhaust gas circulation, variable valve actuation, cylinder deactivation, pilot fuel injection, high energy ignition systems and combinations thereof to provide substantially stoichiometric combustion conditions over an entire load range of the engine. In one embodiment, the engine has direct in-cylinder fuel injection, is adapted for lean air-fuel mixture operation, and includes an oxidation catalyst and a lean NOx adsorber.

Abstract: The system for controlling the fuel/air mixture supplied to a lean burn engine when operating on natural gas, gasoline, hydrogen, alcohol, propane, butane, diesel or any other fuel as desired. As specific humidity of air supplied to the lean burn engine increases, the oxygen concentration of exhaust gas discharged by the engine for a given equivalence ratio will decrease. Closed loop fuel control systems typically attempt to maintain a constant exhaust gas oxygen concentration. Therefore, the decrease in the exhaust gas oxygen concentration resulting from increased specific humidity will often be improperly attributed to an excessive supply of fuel and the control system will incorrectly reduce the amount of fuel supplied to the engine. Also, the minimum fuel/air equivalence ratio for a lean burn engine to avoid misfiring will increase as specific humidity increases. A relative humidity sensor to allow the control system to provide a more enriched fuel/air mixture at high specific humidity levels.