Emission Optimization of the Cold Start Behavior of a CNG Engine with Electrically Heated Catalyst and Secondary Air Injection

Decarbonization and a continuous reduction in exhaust emissions from combustion engines are key objectives in the further development of modern powertrains. In order to address both aspects, the DE4LoRa research project is developing an innovative hybrid powertrain that is characterized by the highly flexible combination of two electric motors with a monovalent compressed natural gas (CNG) engine. This approach enables highly efficient driving in purely electric, parallel and serial operating modes. The use of synthetic CNG alone leads to a significant reduction in CO₂ emissions and thus in the climate impact of the drivetrain. With CNG-powered engines in particular, however, methane and other tailpipe emissions of climate gases and pollutants must also be minimized. This is possible in particular through efficient exhaust gas aftertreatment and an effective operating strategy of the powertrain. This publication presents measurement results that examine the critical aspect of cold starts. The engine is operated with a three-way catalyst with a coating specially tailored to CNG as well as an electrically heated disk and secondary air injection. The powertrain operating strategy makes it possible to preheat the catalyst when the engine is not running, which enables the catalyst to reach higher temperatures prior to the engine start, thus effectively reducing methane slip and other emissions during cold start. The combination of electrical heating power, secondary air mass flow and pre-heating duration are three of the factors in the optimization carried out here. Added to this is an analysis of the most efficient and low-emission engine start using a serial operating mode.