Environmental health awareness has elevated in recent years alongside the evidence that supports the need to mitigate harmful greenhouse gas (GHG) emissions
from non-renewable energy resources. The transportation sector alone significantly
contributes to the pollutants on a global scale. Although it is commonly used for
its superior energy-density and fuel efficiency, diesel engines are a significant portion
of the transportation sector that contributes to these pollutants. As a result, this
motivates novel research to simultaneously drive fuel efficiency improvements and
emissions reductions. <div><br></div><div>The aftertreatment system for a diesel engine is critical in reducing the amount of
harmful tailpipe emissions. Efficient operation of these aftertreatment systems generally requires elevated temperatures of 250◦C or above. In this effort, a flexible valvetrain will be utilized to demonstrate fuel-efficient strategies via intake valve closure
(IVC) modulation at elevated speeds and loads. In addition, thermal management
strategies will be demonstrated at low-to-moderate loads via cylinder deactivation
(CDA), cylinder cutout, exhaust valve opening (EVO) modulation, and high-speed
idle operation.</div><div><br></div><div>At elevated engine speeds, late intake valve closure (LIVC) enables improved
cylinder filling via a dynamic charging effect. It is experimentally and analytically
demonstrated that LIVC at 2200 RPM and 7.6 bar to 12.7 bar BMEP can be used to
increase the volumetric efficiency and enable higher exhaust gas recirculation fractions
without penalizing the air-to-fuel ratio. As a result, efficiency improving injection advances are implemented to achieve 1.2% and 1.9% fuel savings without sacrificing NOx penalties. In order to implement the LIVC benefits on a cammed engine,
production-viable valve profile solutions were investigated. It is demonstrated that
lost-motion-enabled and/or added-motion-enabled boot shape profiles are capable of
improving volumetric efficiency at elevated engine speeds and loads. These profiles
were also considered for one (of two) -valve modulation and two-valve modulation.
Nearly 95% of the volumetric efficiency benefits are possible using production-viable
boot or phase profiles, while 80% of the benefits are possible for single-valve modulation. </div><div><br></div><div>At curb idle, CDA and cylinder cutout operation realize stay-warm aftertreatment
thermal management improvements by leveraging their impact on the gas exchange
process. Specifically, cylinder cutout demonstrates 17% fuel savings, while CDA
demonstrates 40% fuel savings, over the conventional six-cylinder thermal calibration. Additionally, the performance of cylinder cutout is subject to the geometry of
the exhaust manifold, location of the EGR loop, and ability to control the exhaust
manifold pressure. </div><div><br></div><div>Elevating the idle speed, while maintaining the same idle load, enables improved
aftertreatment warm-up performance with engine-out NOx and PM levels no higher
than a state-of-the-art thermal calibration at conventional idle operation. Elevated
idle speeds of 1000RPM and 1200 RPM, compared to conventional idle at 800 RPM,
realized 31% to 51% increase in exhaust flow and 25◦C to 40◦C increase in engine-out
temperature, respectively. Additional engine-out temperature benefits are experimentally demonstrated at all three idle speeds considered (800, 1000, and 1200 RPM),
without compromising the exhaust flow rates or emissions, by modulating the EVO
timing. </div><div><br></div><div>At low-to-moderate loads modern diesel engines manipulate exhaust manifold
pressures to drive EGR and thermally manage the aftertreatment. In these engines
exhaust manifold pressure control is typically achieved via either a valve after the turbine, a variable geometry turbine, or wastegating. It is experimentally demonstrated that valvetrain flexibility enables efficient engine and aftertreatment operation without requiring exhaust manifold pressure control. Specifically, IVC modulation and
CDA at elevated engine speeds, along with EVO modulation, CDA, and internal EGR
at low engine speeds can match, or improve, efficiency and thermal management performance compared to a stock thermal calibration that requires exhaust manifold
pressure control.<br></div>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/8214728 |
| Date | 02 August 2019 |
| Creators | Kalen Vos (6787271) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Utilizing_Valvetrain_Flexibility_to_Influence_Gas_Exchange_and_Reduce_Reliance_on_Exhaust_Manifold_Pressure_Control_for_Efficient_Diesel_Engine_Operation/8214728 |
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