Cylinder deactivation improves Diesel aftertreatment and fuel economy for commercial vehicles

Commercial vehicles require continual improvements for meeting fuel emission standards, improving diesel aftertreatment systems and optimizing vehicle fuel economy. Aftertreatment systems are temperature sensitive for removing engine out NOx. Most diesel aftertreatment systems show a marked efficiency improvement above 250°C while efficiency generally improves above 300°C. This poses an efficiency issue for vehicles operated at low load. All commercial vehicles operate in low load operation for a portion of the vehicle duty cycle. Idle temperatures reside in the 100°C to 150°C range while engine torque ratings below 200 Nm (150 ft-lbs) have temperatures below 250°C where the aftertreatment system is below its peak efficiency. Vehicles that spend more time in low load operation need a means to increase the exhaust temperature to enable efficient NOx reduction in the aftertreatment system. Cylinder deactivation (CDA) has been shown to increase diesel engine exhaust temperature by approximately 100°C when operating in half engine mode and more than 100°C with less cylinders. The higher temperature improves aftertreatment NOx reduction performance which offers the potential to save vehicle fuel by increasing engine out NO_x levels where the engine operates more fuel efficiently. Additionally, there are inherent fuel economy benefits up to 140 to 180 Nm (100 to 130 ft-lbs) of torque which is independent of the aftertreatment benefits. These benefits can range between 25% and 40% at near idle conditions while slightly higher speeds showed benefits up to 49%. The benefits converge to nominal fuel economy values for normal engine conditions (all cylinders firing) at or around 180 Nm (130 ft-lbs) of torque. Implementing technologies such as CDA for diesel can be used to improve exhaust thermal management during low load operation, World Harmonized Transient Cycle and US Heavy Duty transient emission cycles. This paper will show the benefits of cylinder deactivation for meeting future emission regulations and improving vehicle fuel economy.