Dheeraj B Gosala

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

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 and aftertreatment thermal management of the engine at these conditions can be improved using conventional means as well as cylinder deactivation and intake valve closure modulation. Airflow reductions result in higher exhaust gas temperatures, which are beneficial for aftertreatment thermal management, and reduced pumping work, which improves fuel efficiency. Airflow reductions can be achieved through a reduction of displaced cylinder volume by using cylinder deactivation and through reduction of volumetric efficiency by using intake valve closure modulation. This paper shows that, depending on load, cylinder deactivation and intake valve closure modulation can be used to reduce the fuel consumption between 5% and 25%, increase the rate of warm-up of aftertreatment, maintain higher temperatures, or achieve active diesel particulate filter regeneration without requiring dosing of the diesel oxidation catalyst.

Reducing Diesel Engine Drive Cycle Fuel Consumption through Use of Cylinder Deactivation to Maintain Aftertreatment Component Temperature during Idle and Low Load Operating Conditions

Modern on-road diesel engine systems incorporate flexible fuel injection, variable geometry turbocharging, high pressure exhaust gas recirculation, oxidation catalysts, particulate filters and selective catalytic reduction systems in order to comply with strict tailpipe-out NOx and soot limits. Fuel consuming strategies, including late injections and turbine-based engine exhaust throttling are typically used to increase turbine outlet temperature and flow rate in order to reach the aftertreatment component temperatures required for efficient reduction of NOx and soot. The same strategies are used at low load operating conditions to maintain aftertreatment temperatures. This paper demonstrates that cylinder deactivation (CDA) can be used to maintain aftertreatment temperatures in a more fuel efficient manner through reductions in airflow and pumping work. The incorporation of CDA to maintain desired aftertreatment temperatures during idle conditions is experimentally demonstrated to result in fuel savings of 3.0% over the HD-FTP drive cycle. Implementation of CDA at non-idle portions of the HD-FTP where BMEP is below 3 bar is demonstrated to reduce fuel consumption further by an additional 0.4%, thereby resulting in 3.4% fuel savings over the drive cycle.

Cylinder deactivation during dynamic diesel engine operation

Cylinder deactivation can be implemented at low loads in diesel engines to improve efficiency and aftertreatment thermal management through reductions in pumping work and airflow, respectively. The rate of increase of torque/power during diesel engine transients is limited by the engine’s ability to increase the airflow quickly enough to allow sufficient fuel addition to meet the desired torque/power. The reduced airflow during cylinder deactivation needs to be managed properly so as to not slow the torque/power response. This paper demonstrates that it is possible to operate a diesel engine at low loads in cylinder deactivation without compromising its transient torque/power capabilities, a key finding in enabling the practical implementation of cylinder deactivation in diesel engines.

Comparative study of diesel engine cylinder deactivation transition strategies

Cylinder deactivation is an effective strategy to improve diesel engine fuel efficiency and aftertreatment thermal management when implemented through deactivation of both fueling and valve motion for a set of cylinders. Brake power is maintained by injecting additional fuel into the remaining activated cylinders. The initial deactivation of cylinders can be accomplished in various ways, the two most common options being to trap freshly inducted charge in the deactivated cylinders or to trap combusted gases in the deactivated cylinders. The choice of trapping strategy dictates the in-cylinder pressure characteristics of the deactivated cylinders and has potential to affect torque, oil consumption, and emissions upon reactivation. The effort described here compares these trapping strategies through examination of in-cylinder pressures following deactivation. Proponents of each trapping strategy exist; however, the results discussed here suggest no significant performance differences. As an example, the in-cylinder pressures of both trapping strategies converge as quickly as seven cycles, less than 1 s, after deactivation at curb idle conditions.

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

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.

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

Dynamic cylinder activation in diesel engines

Cylinder deactivation has been recently demonstrated to have fuel savings and aftertreatment thermal management benefits at low to moderate loads compared to conventional operation in diesel engines. This study discusses dynamic cylinder activation as an effective variant to fixed diesel engine cylinder deactivation. The set of inactive and active cylinders varies on a cycle-by-cycle basis during dynamic cylinder activation. This enables greater control over forcing frequencies of the engine, thereby allowing the engine to operate away from the drivetrain resonant frequency at all engine speeds, while maintaining similar fuel savings, thermal management, and emission characteristics as fixed cylinder deactivation. Additional benefits of dynamic cylinder activation include a reduction in the consecutive number of cycles a given cylinder is deactivated, and more even cylinder usage. Enablement of engine operation without exciting drivetrain resonant frequencies at similar fuel efficiency and emissions as fixed cylinder deactivation makes dynamic cylinder activation a strong candidate to augment the benefits already demonstrated for fixed cylinder deactivation.

Reverse breathing in diesel engines for aftertreatment thermal management

Approximately 40% of typical heavy-duty vehicle operation occurs at loaded idle during which time conventional diesel engines are unable to maintain aftertreatment component temperatures in a fuel-efficient manner. Fuel economy and thermal management at this condition can be improved via reverse breathing, a novel method in which exhaust gases are recirculated, as needed, from exhaust to intake manifold via one or more cylinders. Resultant airflow reductions increase exhaust gas temperatures and decrease exhaust flow rates, both of which are beneficial for maintaining desirable aftertreatment component temperatures while consuming less fuel via reduced pumping work. Several strategies for implementation of reverse breathing are described in detail and are compared to cylinder deactivation and internal exhaust gas recirculation operation. Experimental data demonstrate 26% fuel consumption savings compared to conventional stay-warm operation, 60 °C improvement in turbine outlet temperature and 28% reduction in exhaust flow compared to conventional best fuel consumption operation at the loaded idle condition (800 r/min, 1.3 bar brake mean effective pressure). The incorporation of reverse breathing to more efficiently maintain desired aftertreatment temperatures during idle conditions is experimentally demonstrated to result in fuel savings of 2% over the heavy-duty federal test procedure drive cycle compared with conventional operation.