High Power Discharge Combustion Effects on Fuel Consumption, Emissions, and Catalyst Heating
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Copyright 2014 SAE International. A key element to achieving vehicle emission certification for most light-duty vehicles using spark-ignition engine technology is prompt catalyst warming. Emission mitigation largely does not occur while the catalyst is below its "light-off temperature", which takes a certain time to achieve when the engine starts from a cold condition. If the catalyst takes too long to light-off, the vehicle could fail its emission certification; it is necessary to minimize the catalyst warm up period to mitigate emissions as quickly as possible. One technique used to minimize catalyst warm up is to calibrate the engine in such a way that it delivers high temperature exhaust. At idle or low speed/low-load conditions, this can be done by retarding spark timing with a corresponding increase in fuel flow rate and / or leaning the mixture. Both approaches, however, encounter limits as combustion stability degrades and / or nitrogen oxide emissions rise excessively. Such limits are inevitable but also seem to be influenced by the type of ignition technology. One ignition technology that may improve the limits of advanced ignition timing and leaned mixture for low-load catalyst warming is pulsed energy ignition technology. In other studies, this technology is shown to improve engine fuel consumption and combustion stability at low load and idle conditions. Further, with controlled combustion bomb studies, the technology shows shorter ignition and flame development periods, thus suggesting the possibility to ignite "more difficult" combustion mixtures (such as low-turbulent kinetic energy or lean mixtures). Such data supported the pursuit of the current study, which has the objectives to determine the potential improvement in combustion stability, exhaust heat flow, and emissions during low-load catalyst warming operation of a spark-ignition engine. This article highlights the study and provides data showing combustion stability, emissions, and exhaust heat flux behavior as ignition timing and fuel mixture strength vary for two different plugs: a conventional spark plug and a pulsed energy plug. The study reveals the pulsed energy ignition technology can increase exhaust heat flux by 6% for similar combustion stability criterion (less than 15% IMEP-COV for catalyst heating strategy) with marginal penalty in fuel consumption and unburned hydrocarbon emissions when compared to conventional spark plug technology.
