Evaluation of Electric Heater Performance in Exhaust Aftertreatment Systems

Abstract

Increasingly stringent vehicle emission standards call for improved performance of exhaust aftertreatment systems. A common problem is emissions during cold starts when the exhaust temperature is not sufficient to heat up the catalysts to operating conditions. Traditionally, this challenge is met by supplying additional exhaust heat using engine-based thermal management techniques by injecting additional fuel or decreasing engine efficiency. However, these techniques come with penalties such as increased fuel consumption and noise. An alternate solution is to use an electric heater to heat up the exhaust gases flowing into the catalysts. This can provide a large amount of heat close to the catalyst to enable them to reach operating temperatures quickly. This study investigates the performance of an electric heater installed upstream of the silencer in a 380 hp 13-liter heavy-duty diesel engine. Tests in an air flow rig, an engine test cell were complemented with 1D simulations to evaluate catalyst heating performance, reduction of nitrogen oxides and energy consumed by the heater in steady and transient cycles. A major finding in this study was the effect of flow maldistribution limiting the effectiveness of the heater and the aftertreatment system. 1D models were found to be useful in testing different test cases but are challenged by flow maldistribution into the aftertreatment system. The results show that a 10 kW heater works to improve nitrogen oxide emissions but need to be used in combination with engine modes that have low nitrogen oxide emissions. The performance of the system was also found to be significantly affected by the installation by heat losses in the exhaust flow.