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.
Highlights
Diesel engine emissions are strictly regulated in the U.S to 0.2 g/hp-hr oxides of nitrogen (NOx), 0.01 g/hp-hr particulate matter (PM), and 0.14 g/hp-hr unburnt hydrocarbons (UHC) (United States Environmental Protection Agency, 2010)
Fuel-efficient (FE) low load operation, which includes curb idle, generally does not produce engine-out temperatures that are high enough to support effective selective catalytic reduction (SCR) NOx reduction. It will be experimentally demonstrated at curb idle that both Cylinder deactivation (CDA) and Cylinder Cutout are capable of achieving desirable engine-out temperatures in a more fuel efficient manner than a state-of-the-art thermal calibration
A six-cylinder Clean Idle Certified Cummins diesel engine equipped with a camless variable valve actuation (VVA) system was utilized to perform the experiments described in this effort
Summary
Diesel engine emissions are strictly regulated in the U.S to 0.2 g/hp-hr oxides of nitrogen (NOx), 0.01 g/hp-hr particulate matter (PM), and 0.14 g/hp-hr unburnt hydrocarbons (UHC) (United States Environmental Protection Agency, 2010). Modern diesel engine aftertreatment systems include a diesel oxidation catalyst (DOC), diesel particulate filter (DPF), and selective catalytic reduction (SCR) system. Ramesh et al demonstrated 5–25% fuel savings while simultaneously improving the rate of warm-up of the aftertreatment system at elevated engine speeds and low engine loads via CDA (Ramesh et al, 2017). Previous work has shown up to 26% fuel savings via Cylinder Cutout operation in a medium speed diesel-gas dual fuel engine with exhaust throttling capability at low-load conditions without demanding any major changes to the engine setup (Konrad et al, 2018). Yang demonstrated an improvement of 1–13% in fuel efficiency using Cylinder Cutout operation on an excavator’s diesel engine (Yang et al, 2012). Mo demonstrated in Mo et al (2013) that Cylinder Cutout has significantly higher pumping losses than CDA
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