Development of Thermal Management Strategies Using Cylinder Deactivation for Low-Load Operation in Heavy-Duty Diesel Trucks

Abstract

Cylinder deactivation (CDA) has been used in gasoline engines, for decades, as a strategy for fuel consumption reduction. The idea of CDA in the heavy-duty diesel (HDD) engine sector has gained traction as a pathway to fuel efficient thermal management strategy. Oxides of nitrogen (NOx) control has been a major focus over the last decade and maintaining conducive aftertreatment temperatures is a major design aspect. HDD original equipment manufacturers (OEM) have developed a variety of thermal management strategies which almost all revolve around large fuel penalties. The goal of all of these strategies is for thermal management of the diesel particulate filter (DPF) and the selective catalytic reduction (SCR) systems. Low-load duty cycles are a target area of thermal management due to insufficient SCR temperatures for NOx conversion after extended time in these operating regions. Operation inside of this low temperature window include: stop and go, creep mode, downhill coasting and extended idle. In these load scenarios, typical operation is below 30% rated torque of the engines. Studies have shown that reduction in brake-specific fuel consumption (BSFC) results in small exhaust temperature increase. Significant turbine outlet temperature (TOT) increases have been demonstrated with little to no BSFC penalty. Implementation of a cost-effective CDA system, developed by Jacobs Vehicle Systems, has been implemented onto a 6-cylinder 15 L HDD engine platform. Each cylinder has individual control capabilities. The project is focused on reducing fuel penalties associated with thermal management strategies while improving SCR activity. Low-load operation, below 30% power curve, was targeted due to significant SCR substrate cooling when exhaust gases are below the SCR temperature. By increasing the TOT temperature with CDA, the cooling rate of the SCR will reduce, and in some operating conditions, will add heat to the SCR. Steady-state testing observed an increase for all turbine outlet and SCR inlet temperatures using CDA. Each 10% load point resulted in a 1%-14% increase in brake thermal efficiency. Additionally, the fuel benefit varied from a reduction of 8.5% to an increase of 0.9% for operating points tested in the CDA window. While cooling effects of motoring were analyzed, total time to cool the SCR increased by 99% with three cylinders deactivated while motoring the engine.