Increasingly stringent emissions regulations in automotive applications are driving advancements in after-treatment technology and emissions control strategies. Fast warm-up of the after-treatment system during the engine cold-start is essential to meet future emissions targets. In this study, a range of strategies were evaluated on a 2.2L, four cylinder, light-duty Gasoline Compression Ignition (GCI) engine with geometric compression ratio 17. The GCI engine has a single stage turbocharger and low-pressure exhaust gas recirculation (EGR) with EGR cooler bypass. For cold-start assist, the engine is equipped with a 2.5kW electric intake air heater. The aftertreatment system is comprised of an oxidation catalyst, followed by a particulate filter and an SCR catalyst. A GT-Power model of a light-duty diesel engine was modified to represent the GCI engine system setup for catalyst light-off strategies evaluations.
In the first work phase, the individual and combined benefit of the engine-based strategies, such as flare speed, load, retarded CA50, intake air heater and backpressure valve throttling were evaluated for ambient cold-start. The cumulative benefit of the strategies produced estimated exhaust temperature and exhaust enthalpy of 450 degree C and 11.3 kW, respectively at the catalyst inlet.
In the second work phase, measures to conserve heat such as turbine-bypass, thermal barrier coating (TBC), air-gap manifold insulation, and cylinder-deactivation were investigated individually as well as combined with the strategies in the first phase. For turbine bypass, the turbocharger thermal inertia was not quantified. The effects of the thermal barrier coating on the piston and valve surfaces exposed to the hot gas were simulated by imposing the temperature swing profiles representing the coating material characteristics. The analysis predicted ~40-70 °C rise in exhaust temperature depending on the material coating type and thickness. Overall, the effectiveness of the strategies to raise both exhaust temperature and enthalpy, as well conserve exhaust heat were discussed. Finally, a cold start strategy is recommended for fast catalyst light-off.