Effects of application of variable valve timing on the exhaust gas temperature improvement in a low-loaded diesel engine

Approximately 30% of the fuel consumed during typical heavy-duty vehicle operation occurs at elevated speeds with low-to-moderate loads below 6.5 bar brake mean effective pressure. The fuel economy...

Utilizing low airflow strategies, including cylinder deactivation, to improve fuel efficiency and aftertreatment thermal management:

In response to strict emissions regulations, engine manufacturers have implemented aftertreatment technologies to reduce the tailpipe emissions from diesel engines. The effectiveness of most of these systems is limited when exhaust temperatures are below 250°C. This is problematic during cold start and at low-load engine operation when the exhaust gas temperature is too low to keep the aftertreatment working effectively. The implementation of variable valve actuation strategies, including early exhaust valve opening, has been proposed as a means to elevate exhaust temperatures. Early exhaust valve opening results in hotter exhaust gas; however, more fueling is needed to maintain brake power output. This article outlines an analysis of the impact of early exhaust valve opening on exhaust temperature (measured at the turbine outlet) and the required fueling. An experimentally validated model is developed, which relates fueling increase with the timing of exhaust valve opening. This model is used to generate...

Modeling the impact of early exhaust valve opening on exhaust aftertreatment thermal management and efficiency for compression ignition engines

Diesel engine cylinder deactivation (CDA) can be used to reduce petroleum consumption and greenhouse gas (GHG) emissions of the global freight transportation system. Heavy duty trucks require complex exhaust aftertreatment (A/T) in order to meet stringent emission regulations. Efficient reduction of engine-out emissions require a certain A/T system temperature range, which is achieved by thermal management via control of engine exhaust flow and temperature. Fuel efficient thermal management is a significant challenge, particularly during cold start, extended idle, urban driving, and vehicle operation in cold ambient conditions. CDA results in airflow reductions at low loads. Airflow reductions generally result in higher exhaust gas temperatures and lower exhaust flow rates, which are beneficial for maintaining already elevated component temperatures. Airflow reductions also reduce pumping work, which improves fuel efficiency. The fuel economy and thermal management benefits of one-third engine CDA, half-engine CDA and two-third engine CDA have been studied at key operating conditions. CDA improves the fuel efficiency at steady state loaded idle operation by 40% with similar engine out temperatures and lower exhaust flow rates compared to conventional thermal management strategies as demonstrated with an inline six (I6) cylinder medium duty diesel engine used in this study. The lower exhaust f low rates due to CDA help maintain elevated A/T temperatures via reduced heat transfer losses. At elevated engine speeds, CDA provides a 5% 32% BTE improvement in fuel economy, increased rate of A/T warm-up, higher temperatures steady state temperatures, and allow for active diesel particulate filter regeneration without hydrocarbon dosing of the diesel oxidation catalyst. During highway cruise, half-engine CDA and two-third engine CDA can be used to reach engine outlet temperatures of 520 to 570° C, a 170 to 220° C increase compared to normal operation. Full engine CDA enables 78% reduction in motoring torque at an engine speed of 2100 rpm and thus could help save fuel and keep the A/T warm during vehicle coast.

Cylinder Deactivation for Increased Engine Efficiency and Aftertreatment Thermal Management in Diesel Engines

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 technologie...

Diesel engine aftertreatment warm-up through early exhaust valve opening and internal exhaust gas recirculation during idle operation:

Most diesel engines meet today’s strict NOx and particulate matter emission regulations using after-treatment systems. A major drawback of these after-treatment systems is that they are efficient in reducing emissions only when their catalyst temperature is within a certain range (typically between 250  °C and 450 °C). At lower engine loads this is a major problem as the exhaust temperatures are usually below 250 °C. The primary objective of this study was to analyze “cylinder throttling” via both delayed and advanced intake valve closure timing. The effect of cylinder throttling on exhaust gas temperatures, fuel consumption, in-cylinder combustion and emissions is outlined. A significant increase in turbine outlet temperature accompanied by a decrease in fuel consumption, NOx, and particulate matter emissions was observed. Both delayed and advanced intake valve closure timings were equally effective. The increase in exhaust gas temperatures was attributed to a drop in air flow through the engine, which r...

Fuel-efficient exhaust thermal management using cylinder throttling via intake valve closing timing modulation:

Advanced combustion modes, such as PCCI, operate near the system stability limits. In PCCI, the combustion event begins without a direct combustion trigger in contrast to traditional spark-ignited gasoline engines and direct-injected diesel engines. The lack of a direct combustion trigger necessitates the usage of model-based controls to provide robust control of the combustion phasing. The nonlinear relationships between the control inputs and the combustion system response often limit the effectiveness of traditional, non-model-based controllers. Accurate knowledge of the system states and inputs is required for implementation of an effective nonlinear controller. A nonlinear controller is developed and implemented to control the engine combustion timing during diesel PCCI operation by targeting desired values of the in-cylinder oxygen concentration, pressure, and temperature during early fuel injection.

A nonlinear model-based controller for premixed charge compression ignition combustion timing in diesel engines

Control-Oriented Gas Exchange Model for Diesel Engines Utilizing Variable Intake Valve Actuation

Cylinder deactivation (CDA) is a technology that can improve the fuel economy and exhaust thermal management of compression ignition engines (diesel and natural gas), especially at low loads and engine idling conditions. The reduction in engine displacement during CDA improves fuel efficiency at low loads primarily through a reduction in pumping work. During deactivation of a given cylinder the drop in pres- sure inside the cylinder could possibly lead to the transport of oil from the crankcase into the cylinder owing to the reduced pressure difference between the crankcase and the cylinder. In addition, cylinder deactivation might inhibit the first fire readiness of a reactivating cylinder as a result of reduced wall, head, and piston temperatures. Both of these potential issues are quantitatively studied in this paper. This paper describes a strategy to estimate in-cylinder oil accumulation during CDA, and first fire readiness following CDA, through comparison of individual heat realease profiles before and after CDA. Cylinder cool-down and oil accumulation dur- ing deactivation could possibly result in misfire or degraded combustion upon an at- tempt to reactivate a given cylinder. Fortunately, experiments described in this paper demonstrate no cases of misfire at any speed/load conditions for the CDA durations tested, specifically, 100 ft-lb load at 800 rpm and 1200 rpm with deactivation intervals of 0.5, 5, 10 and 20 minutes. Although pilot heat release in the reactivated cylinders was delayed by approximately 1 CAD after 5 minutes of CDA, the main heat release was very similar to the heat release of a continuously activated cylinder. As such, results show no first fire readiness issues at the conditions tested. The duration of time the engine could be operated in CDA mode without significant oil accumulation, and other methods to minimize oil accumulation during CDA have also been proposed.

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Oil Accumulation and First Fire Readiness Analysis of Cylinder Deactivation

Piezo electric injectors provide a means to lower emissions, noise and fuel consumption in advanced IC engines, by providing the capability to allow for tightly spaced injections and rate shaping. With a focus on generating a control design amenable model capturing the injector needle dynamics, the effort described here includes a model simplification and reduction strategy of an experimentally validated, physics-based 13 state model of a direct acting piezo electric injector. The resulting reduced order model for needle dynamics is validated for both single and multi pulse conditions.Copyright © 2011 by ASME

Greg Shaver

Papers

Fuel-efficient exhaust thermal management using cylinder throttling via intake valve closing timing modulation:

A nonlinear model-based controller for premixed charge compression ignition combustion timing in diesel engines

Control-Oriented Gas Exchange Model for Diesel Engines Utilizing Variable Intake Valve Actuation

Oil Accumulation and First Fire Readiness Analysis of Cylinder Deactivation

Control Design Amenable Model of Needle Position for a Direct Acting Piezoelectric Fuel Injector