Reduction of cold start emissions with microwave heated catalytic converters

Authors

Viola Papetti, Panayotis Dimopoulos Eggenschwiler, Daniel Schreiber, Empa, Swiss Federal Laboratories for Materials Science and Technology Automotive Powertrain technologies

Year

2019

Summary

Emissions of Euro-6 gasoline powertrains at normal operating temperatures are almost zero. On the contrary, during cold starts, characterized by low temperatures for the catalytic converters, CO and unburned hydrocarbon (HC) emissions are 2-3 orders of magnitude higher than during cruise operating conditions [1]. The situation is even more severe with hybrid powertrains. Here the intermittent engine operation often leads to numerous cold starts. In parallel, the steadily increasing efficiency of modern engines has dramatically lowered exhaust gas temperatures, both in gasoline and diesel engines (first law of thermodynamics). All near-future engine concepts will face increasing difficulties conflicting with the fuel saving imperative in providing the necessary heat for the pollutant aftertreatment. Depending on the application, load conditions and aftertreatment technology, sometimes “artificial” supply of energy to the catalytic converter is required in order to meet emission limits. One potential solution was the utilization of electrically heated catalytic converters. Electrical Heated Catalysts (EHC) that uses mechanical energy from the engine to generate the electrical energy to heat up the exhaust gas upstream the catalytic converter is proposed in [2, 3, 4, 5].
In literature, microwave heating is often applied to chemical reactions: [6] discusses different designs for microwave field applied to Small-Scale Chemical Processing. In the exhaust aftertreatment field, microwaves have been used for initiating active regeneration of particle filters [7], as well as for sensing the urea level in an SCR catalytic converter [8, 9].
In this study, we describe a microwave heating system applied to catalytic converters for automotive applications and we show its relevant contribution in emissions reduction during cold start conditions. Experiments with synthetic exhaust gas and inflow gas temperature of 20°C have shown conversions of more than 60%. A vehicle size system mounted at the end of the tailpipe of a gasoline vehicle achieved a reduction of 15% of cumulative emissions in the first 600s after cold start. Further optimizations related to higher microwave power, substitution of conventional honeycomb (HC) with additive manufactured polyhedral catalytic converters and to improved layout
have the potential to further increase cold start emission conversions.

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