Impact of Cylinder Deactivation and Cylinder Cutout via Flexible Valve Actuation on Fuel Efficient Aftertreatment Thermal Management at Curb Idle

Abstract

Cylinder deactivation (CDA) and cylinder cutout are different operating strategies for diesel engines. CDA includes the deactivation of both the valve motions and the fuel injection of select cylinders, while cylinder cutout incorporates only fuel injection deactivation in select cylinders. This study compares diesel engine aftertreatment thermal management improvements possible via CDA and cylinder cutout at curb idle operation (800 RPM and 1.3 bar BMEP). Experiments and analysis demonstrated that both CDA and cylinder cutout enable improved fuel efficient "stay warm" thermal management compared to a stock thermal calibration on a Clean Idle Certified engine. At curb idle, this stock calibration depends on elevated exhaust manifold pressure to increase the required fueling (for thermal management) and to drive EGR. The study described here demonstrates that CDA does not require an elevated exhaust manifold pressure for thermal management or EGR delivery control, whereas cylinder cutout does. In addition to achieving engine-out NOx levels no higher than the stock thermal calibration, both cylinder cutout and CDA enable up to 55 and 80% reductions in particulate matter (PM), respectively. Cylinder cutout demonstrates 17% fuel savings, while CDA demonstrates 40% fuel savings, over the stock six-cylinder thermal calibration. These fuel efficiency improvements primarily result from reductions in pumping work via reduced air flow through the engine. Cylinder cutout reduces the air flow rate via elevated amounts of recirculated gases which are also required to regulate engine-out NOx, resulting in a larger delta pressure across the engine and consequently more pumping work than CDA. CDA reduces the air flow rate by deactivating cylinders, which reduces the charge flow rate and enables a small delta pressure between the intake and exhaust manifolds, resulting in less pumping work by the cylinders. As a result, CDA is more efficient than cylinder cutout. Furthermore, the thermal merits of cylinder cutout require high exhaust manifold pressures, and are subject to the configuration of the exhaust manifold and the exhaust gas recirculation (EGR) path.

Strategies for using valvetrain flexibility instead of exhaust manifold pressure modulation for diesel engine gas exchange and thermal management control

“…, using CDA and cylinder cutout at 800 r/min and 1.3 bar BMEP, per Figure 19. 20 One such CDA strategy has two (of six) CF and does not depend on exhaust manifold pressure control for improved stay-warm performance. The cylinder cutout strategy utilizes three (of six) CF, while the remaining cylinders transmit non-combusted charge gas, and requires exhaust manifold pressure control for improved stay-warm performance and EGR delivery control.…”

“…Exhaust gas-to-catalyst heat transfer rate plots, where the exhaust flow corresponds to the steepness of the slope and the crossing of the zero heat transfer rate axis represents the TOT. Figure data are at 800 r/min, 1.3 bar BMEP, and corresponds to effort described in Vos et al 20 …”

“…Cylinder cutout reduced the air flow rate via elevated amounts of recirculated gases that were required to regulate engine-out NOx, which resulted in a large pressure difference between the manifolds. 20 As a result, CDA is a more fuel-efficient stay-warm strategy than cylinder cutout and the Stock Thermal Cal. , while not depending on exhaust manifold pressure control for its performance.…”

“…2,18,19 Compared to a state-of-the-art thermal calibration, several of the authors have demonstrated the ability to maintain elevated aftertreatment temperatures while improving fuel efficiency by 40% using CDA at idle operation. 20…”

Implementing variable valve actuation on a diesel engine at high-speed idle operation for improved aftertreatment warm-up

“…Previous studies by several of the authors, and others, have demonstrated the ability to raise exhaust temperatures for more efficient aftertreatment thermal management (TM) by utilizing various strategies such as maximally closing a variable geometry turbine (VGT), cylinder deactivation (CDA), intake valve modulation, and exhaust valve modulation. 2,10–17…”