This content is not included in your SAE MOBILUS subscription, or you are not logged in.
Evaluation of Fast Warm-Up Strategies for a Light-duty Gasoline Compression Ignition(GCI) Engine
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on April 14, 2020 by SAE International in United States
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 heater. The aftertreatment system is comprised of an oxidation catalyst, followed by a particulate filter and an SCR catalyst. A detailed GT-Power model of the GCI engine system was developed for 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 470 degree C and 10 kW, respectively at the catalyst inlet. In the second work phase, measure 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 quantified using fast thermocouples and heat probes located at the turbine entry and exit. The measured steady-state and transient temperature profiles were then input in the 1-D model to calibrate the heat-loss characteristics of the turbine assembly. 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 thickness. Overall, the effectiveness of the strategies to raise both exhaust temperature and enthalpy, as well as the implementation challenges are discussed. Finally, a sequence of cold start strategies is recommended for a faster catalyst light-off.