Optimization of a Diesel Engine with Variable Exhaust Valve Phasing for Fast SCR System Warm-Up

A large fraction of diesel engine tailpipe NOx emissions are emitted before the aftertreatment components reach effective operating temperatures. As a result, it is essential to develop technologies to accelerate initial aftertreatment system warm-up. This study investigates the use of early exhaust valve opening (EEVO) and its combination with negative valve overlap to achieve internal exhaust gas recirculation (iEGR), for aftertreatment thermal management, both at steady state loaded idle operation and over a heavy-duty federal test procedure (HD-FTP) drive cycle. The results demonstrate that implementing EEVO with iEGR during steady state loaded idle conditions enables engine outlet temperatures above 400 °C, and when implemented over the HD-FTP, is expected to result in a 7.9% reduction in tailpipe-out NOx.

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Exhaust valve phasing controllers for cold start NOx emissions reduction in heavy duty diesel engines

International Journal of Engine Research ◽

10.1177/1468087421996514 ◽

2021 ◽

pp. 146808742199651

Author(s):

Rasoul Salehi ◽

Robert J Middleton

Keyword(s):

Operating Conditions ◽

Exhaust Valve ◽

Emissions Reduction ◽

Drive Cycle ◽

Test Drive ◽

Rule Based ◽

Warm Up ◽

Model Based ◽

Predictive Controller ◽

Scr System

In this paper, early exhaust valve opening (EVO) is applied to a diesel engine for fast warm up of the selective catalytic reduction (SCR) system with the ultimate goal of tailpipe NOx emissions reduction. By advancing EVO from top dead center, the exhaust gas temperature increases and the exhaust flow reduces, influencing the enthalpy available to warm up the SCR, and the engine-out NOx emissions increase or decrease depending on the engine’s operating conditions. Therefore, proper management of EVO is required to ensure that (1) engine-out NOx emissions do not increase when the SCR catalyst is cold; (2) heat transfer to the SCR increases and it warms up faster than the baseline operation (without EVO phasing); and (3) fuel consumption increase is minimal. A novel model predictive controller (MPC) is proposed for this application, assuming a limited preview of the drive cycle is available. For the MPC, an optimization objective function is applied such that a sequential warm up strategy can be implemented for the aftertreatment system catalysts. Using this technique, the prediction horizon for effective thermal management of the slow SCR system is reduced. In addition, a rule-based logic is offered as an alternative to the predictive controller to calculate the EVO trajectory with less computational power. Observations based on optimization problems solved by dynamic programing (DP) were used to develop the rule-based controller. Both the rule-based logic and model-based MPC are tested with a detailed high fidelity one-dimensional model in a model-in-the-loop simulator. Results indicate the potential of an EVO phasing system with the proposed controllers to reduce tailpipe NOx by 10% and 25% for the world harmonized transient cycle (WHTC) and federal test procedure (FTP), respectively. The rule-based controller has been found to be sensitive to the test drive cycle while the model based MPC shows a consistent performance, that is, independent of the test trajectory.

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Exhaust valve profile modulation for improved diesel engine curb idle aftertreatment thermal management

International Journal of Engine Research ◽

10.1177/1468087420969101 ◽

2021 ◽

pp. 146808742096910

Author(s):

Mrunal C Joshi ◽

Dheeraj Gosala ◽

Gregory M Shaver ◽

James McCarthy ◽

Lisa Farrell

Keyword(s):

Diesel Engine ◽

Fuel Consumption ◽

Thermal Management ◽

Exhaust Valve ◽

Outlet Temperature ◽

Exhaust Manifold ◽

Warm Up ◽

Valve Opening ◽

Active Regeneration ◽

Negative Valve Overlap

Rapid warm-up of a diesel engine aftertreatment system (ATS) is a challenge at low loads. Modulating exhaust manifold pressure (EMP) to increase engine pumping work, fuel consumption, and as a result, engine-outlet temperature, is a commonly used technique for ATS thermal management at low loads. This paper introduces exhaust valve profile modulation as a technique to increase engine-outlet temperature for ATS thermal management, without requiring modulation of exhaust manifold pressure. Experimental steady state results at 800 RPM/1.3 bar BMEP (curb idle) demonstrate that early exhaust valve opening with negative valve overlap (EEVO+NVO) can achieve engine-outlet temperature in excess of 255°C with 5.7% lower fuel consumption, 12% lower engine out NOx and 20% lower engine-out soot than the conventional thermal management strategy. Late exhaust valve opening with internal EGR via reinduction (LEVO+Reinduction) resulted in engine-outlet temperature in excess of 280°C, while meeting emission constraints at no fuel consumption penalty. This work also demonstrates that LEVO in conjunction with modulation of exhaust manifold pressure results in engine-outlet temperature in excess of 340°C while satisfying desired emission constraints. Aggressive use of LEVO can result in engine-outlet temperatures of 460°C, capable of active regeneration of DPF at curb idle, without the significant increase in engine-out soot emissions seen in previously studied strategies.

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Ammonium-Salt Formation and Catalyst Deactivation in the SCR System for a Marine Diesel Engine

Catalysts ◽

10.3390/catal9010021 ◽

2018 ◽

Vol 9 (1) ◽

pp. 21 ◽

Cited By ~ 5

Author(s):

Yuanqing Zhu ◽

Qichen Hou ◽

Majed Shreka ◽

Lu Yuan ◽

Song Zhou ◽

...

Keyword(s):

Diesel Engine ◽

Decomposition Reaction ◽

Marine Diesel Engine ◽

Exhaust Gas ◽

Gas Temperature ◽

Scr Catalyst ◽

Marine Diesel ◽

Fast Scr ◽

Exhaust Gas Temperature ◽

Scr System

Due to the low temperature and complex composition of the exhaust gas of the marine diesel engine, the working requirements of the selective catalytic reduction (SCR) catalyst cannot be met directly. Moreover, ammonium sulfate, ammonium nitrate, and other ammonium deposits are formed at low temperatures, which block the surface or the pore channels of the SCR catalyst, thereby resulting in its reduction or even its loss of activity. Considering the difficulty of the marine diesel engine bench test and the limitation of the catalyst sample test, a one-dimensional simulation model of the SCR system was built in this paper. In addition, the deactivation reaction process of the ammonium salt in the SCR system and its influencing factors were studied. Based on the gas phase and the surface reaction kinetics, the models of the urea decomposition, the surface denitrification, the nitrate deactivation, and the sulfate deactivation were both constructed and verified in terms of accuracy. Moreover, the formation/decomposition reaction pathway and the catalytic deactivation of ammonium nitrate and ammonium bisulfate, as well as the composition concentration and the exhaust gas temperature range were correspondingly clarified. The results showed that within a certain range, the increase of the NO2/NOx ratio was conducive to the fast SCR reaction and the NH4NO3 formation’s reaction. Increasing the exhaust gas temperature also raised the NO2/NOx ratio, which was beneficial to both the fast SCR reaction and the NH4NO3 decomposition reaction, respectively. Furthermore, the influence of the SO2 concentration on the denitrification efficiency decreased with the increase of the exhaust gas temperature because of increasing SCR reaction rate and reversibility of ammonia sulfate formation, and when the temperature of the exhaust gas was higher than 350 °C, the activity of the catalyst was almost unaffected by ammonia sulfate.

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INFLUENCE OF THERMAL RADIATION FROM THE BURNED ZONE ON HEAT TRANSFER IN THE EXHAUST VALVE OF DIESEL ENGINE

Proceeding of International Heat Transfer Conference 11 ◽

10.1615/ihtc11.4510 ◽

1998 ◽

Cited By ~ 1

Author(s):

Piotr Furmanski ◽

Jerzy Banaszek ◽

Tomasz S. Wisniewski ◽

Marek Rebow

Keyword(s):

Heat Transfer ◽

Diesel Engine ◽

Thermal Radiation ◽

Exhaust Valve

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

International Journal of Engine Research ◽

10.1177/1468087419880639 ◽

2019 ◽

Vol 21 (7) ◽

pp. 1134-1146

Author(s):

Kalen R Vos ◽

Gregory M Shaver ◽

Mrunal C Joshi ◽

James McCarthy

Keyword(s):

Particulate Matter ◽

High Speed ◽

Exhaust Valve ◽

Exhaust Gas ◽

Warm Up ◽

Aftertreatment System ◽

Idle Speed ◽

Variable Valve Actuation ◽

Brake Mean Effective Pressure ◽

Valve Opening

Aftertreatment thermal management is critical for regulating emissions in modern diesel engines. Elevated engine-out temperatures and mass flows are effective at increasing the temperature of an aftertreatment system to enable efficient emission reduction. In this effort, experiments and analysis demonstrated that increasing the idle speed, while maintaining the same idle load, enables improved aftertreatment “warm-up” performance with engine-out NOx and particulate matter levels no higher than a state-of-the-art thermal calibration at conventional idle operation (800 rpm and 1.3 bar brake mean effective pressure). Elevated idle speeds of 1000 and 1200 rpm, compared to conventional idle at 800 rpm, realized 31%–51% increase in exhaust flow and 25 °C–40 °C increase in engine-out temperature, respectively. This study also demonstrated additional engine-out temperature benefits at all three idle speeds considered (800, 1000, and 1200 rpm, without compromising the exhaust flow rates or emissions, by modulating the exhaust valve opening timing. Early exhaust valve opening realizes up to ~51% increase in exhaust flow and 50 °C increase in engine-out temperature relative to conventional idle operation by forcing the engine to work harder via an early blowdown of the exhaust gas. This early blowdown of exhaust gas also reduces the time available for particulate matter oxidization, effectively limiting the ability to elevate engine-out temperatures for the early exhaust valve opening strategy. Alternatively, late exhaust valve opening realizes up to ~51% increase in exhaust flow and 91 °C increase in engine-out temperature relative to conventional idle operation by forcing the engine to work harder to pump in-cylinder gases across a smaller exhaust valve opening. In short, this study demonstrates how increased idle speeds, and exhaust valve opening modulation, individually or combined, can be used to significantly increase the “warm-up” rate of an aftertreatment system.

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EGR cylinder deactivation strategy to accelerate the warm-up and restart processes in a Diesel engine operating at cold conditions

International Journal of Engine Research ◽

10.1177/14680874211039587 ◽

2021 ◽

pp. 146808742110395

Author(s):

José Galindo ◽

Vicente Dolz ◽

Javier Monsalve-Serrano ◽

Miguel Angel Bernal Maldonado ◽

Laurent Odillard

Keyword(s):

Steady State ◽

Diesel Engine ◽

Internal Combustion Engines ◽

Cold Start ◽

Pollutant Emissions ◽

Oxidation Catalyst ◽

Maximum Efficiency ◽

Warm Up ◽

Cylinder Deactivation ◽

The Impact

The aftertreatment systems used in internal combustion engines need high temperatures for reaching its maximum efficiency. By this reason, during the engine cold start period or engine restart operation, excessive pollutant emissions levels are emitted to the atmosphere. This paper evaluates the impact of using a new cylinder deactivation strategy on a Euro 6 turbocharged diesel engine running under cold conditions (−7°C) with the aim of improving the engine warm-up process. This strategy is evaluated in two parts. First, an experimental study is performed at 20°C to analyze the effect of the cylinder deactivation strategy at steady-state and during an engine cold start at 1500 rpm and constant load. In particular, the pumping losses, pollutant emissions levels and engine thermal efficiency are analyzed. In the second part, the engine behavior is analyzed at steady-state and transient conditions under very low ambient temperatures (−7°C). In these conditions, the results show an increase of the exhaust temperatures of around 100°C, which allows to reduce the diesel oxidation catalyst light-off by 250 s besides of reducing the engine warm-up process in approximately 120 s. This allows to reduce the CO and HC emissions by 70% and 50%, respectively, at the end of the test.

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