Cylinder Deactivation for Diesel Engines

Hannu Jääskeläinen

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• Introduction
• Hardware
• Benefits
• Challenges
• Effect on Catalyst Light-Off

Introduction

Cylinder deactivation (CDA) is emerging as an important technology to manage exhaust temperature in diesel engines. While cylinder deactivation has been commercially applied to Otto cycle engines for several decades to reduce throttling losses, its use in diesel engines has been very limited. Since diesel engines are unthrottled, benefits have been more challenging to realize. However, with continued efforts to further reduce NOx from diesel engines, the need to manage exhaust temperatures after a cold start, at idle, and low load conditions to ensure NOx aftertreatment devices warm up quickly and remain active has become more critical. Using conventional thermal management techniques such as retarded combustion phasing and fuel dosing over a DOC would simply increase the fuel penalty. Cylinder deactivation, often when combined with other engine measures, can achieve the required exhaust temperature at these challenging low load conditions while keeping the fuel consumption penalty at a minimum. Very simply, by deactivating some of the cylinders, the remaining cylinders in a diesel engine then operate at a higher BMEP and lower air fuel ratio to yield higher exhaust temperatures and lower exhaust flow rates.

Application of CDA to some heavy-duty diesel applications is thought to be possible as early as 2021 for the US EPA GHG limits. The EPA/CARB ultra-low NOx standards proposed for 2024/2027 may see a wider adoption of the technology.

Hardware

Cylinder deactivation can be implemented with a variety of valvetrain hardware options that include collapsible elements such as hydraulic lash adjusters and roller lifers, switchable rocker arms or finger followers and camshaft shifting based systems that switch to no-lift cam profiles when cylinder deactivation is required. Actuation can be either electro-hydraulic or electro-mechanical.

For heavy-duty engines, electro-hydraulic approaches are considered sufficient. Common approaches that are being considered include collapsible elements such as Jacobs’ collapsing valve bridge system for overhead camshaft engines and collapsing pushrod system for cam-in-block engines as well as Eaton’s Deactivating Hydraulic Lash Adjuster (DHLA).

For light duty engines, electro-hydraulic and electro-mechanical systems could be used. Electro-hydraulic approaches include switchable rocker arms or finger followers such as those by Delphi, and Eaton. Schaeffler’s eRocker system is an example of an electro-mechanically actuated finger follower system that could also be used.

Benefits

Overview

Figure 1 illustrates the principal benefit of CDA over the first 400 s of the cold start US HD FTP cycle for a heavy-duty diesel demonstration targeting the proposed EPA/CARB 2027 NOx limit of 0.02 g/bhp-hr [4592]. The baseline condition illustrates the stock calibration for a 2017 heavy-duty Cummins X15 engine.

Due to the low exhaust temperature resulting from the combination of cold start and relatively long periods of idle over this portion of the FTP cycle, little urea dosing for the SCR catalyst would be possible and SCR catalyst activity (even for a close-coupled SCR catalyst) would be insufficient to provide any significant NOx reduction until after about 400 s for the baseline engine. By modifying the warm-up strategy using measures such as increased idle speed, increased EGR, modified air handling and multiple injections [4801], the exhaust temperature can be maintained above 200°C during engine idle but with a 4.0% CO₂ penalty over the cold start heavy-duty FTP cycle (+0.5% over the composite FTP). Alternatively, by combining CDA with a modified calibration, even higher exhaust temperature during idle is possible while reducing the CO₂ penalty over the cold start heavy-duty FTP to 1.3% (+0.2% over the composite FTP). In this example, the higher exhaust temperature at idle while the engine is warming up enables the use of a close-coupled light-off SCR (LO-SCR) catalyst that can provide NOx reduction much sooner than would be possible with the main SCR catalyst located after the DPF. Even after the engine has warmed up, CDA can still be used to keep idle and low load exhaust temperatures sufficiently high to avoid SCR catalyst light-out; i.e., the condition where the catalyst temperature drops to a point where urea dosing needs to be turned off and catalyst activity stops.

Earlier work with CDA for diesel engines considered its possible use as a means to control AFR for NOx adsorber regeneration. Temperature increases on the order of 300°C were noted at part load conditions above 3 bar BMEP [1494].

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