Experimental study on electrically heated catalyst coupling strategies for ultra-low emissions and energy-efficient thermal management in diesel engines

Experimental study of thermal loading management strategy for the transient process of a rotating turbine disk

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. 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.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. 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. 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. 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.

Improving the thermal efficiency of truck diesel engines requires comprehensive optimization of the engine, exhaust aftertreatment (EAT), and possible waste heat recovery (WHR). Lower exhaust temperature at mid and low working points has caused difficulty in both emission clarification and heat recovery, which requires thermal management. Based on the diesel engine bench test and separate bench tests, this paper focuses on the thermal management strategy optimization, to increase the exhaust temperature at lower working points and optimize the thermal efficiency of the whole system. The test and numerical analysis showed that as exhaust temperature increased from 200~250 °C to 300~350 °C, soot passive regeneration reactions were enhanced, nitrogen oxide emission decreased, and energy recovery was improved. Moderate throttle valve adjustment coupled with early post injection could effectively achieve the required temperature increase. The optimized thermal management strategy increased the fuel consumption rate by no more than 1%. Meanwhile, the WHR system output increased significantly, by 62.55% at a certain mid–low working point. System CO2 emission decreased by an average of 5.4% at selected working points.

Long-haul heavy-duty vehicles, including trucks and coaches, contribute to a substantial portion of the modern-day European carbon footprint and pose a major challenge in emissions reduction due to their energy-intensive usage. Depending on the hydrogen fuel source, the use of fuel cell electric vehicles (FCEV) for long-haul applications has shown significant potential in reducing road freight CO2 emissions until the possible maturity of future long-distance battery-electric mobility. Fuel cell heavy-duty (HD) propulsion presents some specific characteristics, advantages and operating constraints, along with the notable possibility of gains in powertrain efficiency and usability through improved system design and intelligent onboard energy and thermal management. This paper provides an overview of the FCEV powertrain topology suited for long-haul HD applications, their operating limitations, cooling requirements, waste heat recovery techniques, state-of-the-art in powertrain control, energy and thermal management strategies and over-the-air route data based predictive powertrain management including V2X connectivity. A case study simulation analysis of an HD 40-tonne FCEV truck is also presented, focusing on the comparison of powertrain losses and energy expenditures in different subsystems while running on VECTO Regional delivery and Longhaul cycles. The importance of hydrogen fuel production pathways, onboard storage approaches, refuelling and safety standards, and fleet management is also discussed. Through a comprehensive review of the H2 fuel cell powertrain technology, intelligent energy management, thermal management requirements and strategies, and challenges in hydrogen production, storage and refuelling, this article aims at helping stakeholders in the promotion and integration of H2 FCEV technology towards road freight decarbonisation.

Energy efficient thermal management at low Reynolds number with air-ferrofluid Taylor bubble flows

Experimental study on the thermal management performance of a power battery module with a pulsating heat pipe under different thermal management strategies

In this paper, we propose an MPC-based precision cooling strategy (PCS) for energy efficient thermal management of an automotive air conditioning (A/C) system. The proposed PCS is able to provide precise tracking of the time-varying cooling power trajectory, which is assumed to meet the passenger comfort requirements. In addition, by leveraging the emerging connected and automated vehicles (CAVs) technology, vehicle speed preview can be incorporated in our A/C thermal management strategy for further energy efficiency improvement. This proposed A/C thermal management strategy is developed and evaluated based on a physics-based A/C system model (ACSim) from Ford Motor Company for the vehicles with electrified powertrains. Over SC03 cycle, for tracking the same cooling power trajectory, the proposed PCS provides 4.9% energy saving at the cost of slight increase in the cabin temperature (less than 1°C), compared with Ford benchmark case. It is also demonstrated that by coordinating with future vehicle speed and shifting the A/C power load, the A/C energy consumption can be further reduced.

Waste heat recovery from diesel engines based on Organic Rankine Cycle

Cylinder deactivation (CDA) has been used in gasoline engines, for decades, as a strategy for fuel consumption reduction. The idea of CDA in the heavy-duty diesel (HDD) engine sector has gained traction as a pathway to fuel efficient thermal management strategy. Oxides of nitrogen (NOx) control has been a major focus over the last decade and maintaining conducive aftertreatment temperatures is a major design aspect. HDD original equipment manufacturers (OEM) have developed a variety of thermal management strategies which almost all revolve around large fuel penalties. The goal of all of these strategies is for thermal management of the diesel particulate filter (DPF) and the selective catalytic reduction (SCR) systems. Low-load duty cycles are a target area of thermal management due to insufficient SCR temperatures for NOx conversion after extended time in these operating regions. Operation inside of this low temperature window include: stop and go, creep mode, downhill coasting and extended idle. In these load scenarios, typical operation is below 30% rated torque of the engines. Studies have shown that reduction in brake-specific fuel consumption (BSFC) results in small exhaust temperature increase. Significant turbine outlet temperature (TOT) increases have been demonstrated with little to no BSFC penalty. Implementation of a cost-effective CDA system, developed by Jacobs Vehicle Systems, has been implemented onto a 6-cylinder 15 L HDD engine platform. Each cylinder has individual control capabilities. The project is focused on reducing fuel penalties associated with thermal management strategies while improving SCR activity. Low-load operation, below 30% power curve, was targeted due to significant SCR substrate cooling when exhaust gases are below the SCR temperature. By increasing the TOT temperature with CDA, the cooling rate of the SCR will reduce, and in some operating conditions, will add heat to the SCR. Steady-state testing observed an increase for all turbine outlet and SCR inlet temperatures using CDA. Each 10% load point resulted in a 1%-14% increase in brake thermal efficiency. Additionally, the fuel benefit varied from a reduction of 8.5% to an increase of 0.9% for operating points tested in the CDA window. While cooling effects of motoring were analyzed, total time to cool the SCR increased by 99% with three cylinders deactivated while motoring the engine.

Effective thermal management strategy for the polymer electrolyte membrane fuel cell (PEMFC) stack is critical in maintaining the overall stack efficiency and durability. The present assessment critically explores the recent developments (predominantly last decade) in thermal management strategies of PEMFCs, which encompasses an in-depth analysis of the thermodynamics, corresponding effects on components of PEMFC and the waste heat recovery system. In general, the operating temperature range of a PEMFC is 60–80°C. Entropy consequence and irreversible transport mechanisms of the reactants are the major contributions to heat generation. Air cooling is employed for compact stacks of less than 5 kW and water cooling is favored for stacks greater than 5 kW. Cooling using nanofluids enables better cooling efficiency than water while downsizing the size and weight of the system. Phase change cooling strategy to attain greater heat removal capacity is broadly employed for stacks greater than 10 kW, which is beneficial in a compact size of the cooling system contrasted to the water cooling system. Passive cooling methods employing vapor chamber, heat pipes and heat spreaders used were another cooling system for stack power ranges between 5 and 10 kW which have the benefit of reduced parasitic losses. In addition to thermal management strategies, integral challenges associated with each thermal management strategy is identified. Discussion on cold start thermal management of fuel cell electric vehicles was provided. Finally, the waste heat recovery system of energy efficiency and overall future prospectus for the betterment of thermal management of PEMFC is emphasized.

A comprehensive system-level modelling methodology for vehicle exhaust and after-treatment system development is presented. Within the constraints required for a development vehicle equipped with a lean-burn direct-injection gasoline engine, system-level analysis was extensively applied to guide the design of the after-treatment system. The size and location of the lean nitrogen oxide (NO x) after-treatment device was determined to achieve the best trade-off between engine back pressure, catalyst light-off, and acceptable thermal ageing under high-speed and high-load conditions. In addition, various after-treatment architecture and layout concepts were efficiently evaluated and screened, requirements for after-treatment components and exhaust thermal management devices were defined, and promising technologies were recommended for further development and testing. Beyond immediate implementation in the development vehicle, several exhaust thermal management strategies (electrically heated converter, lambda split control, engine stop—start, and multiple warm-up) were explored. These technologies have been assessed individually and in combination to formulate effective thermal management strategies under fuel penalty constraints. While the specific applications described in this paper are for a lean-burn gasoline direct-injection development vehicle, the methodology is equally applicable to advanced powertrains with one or more after-treatment devices (diesel engines, alternative fuels, hybrid vehicles, etc.)

Evaluation of thermal management strategy based on zoning of stress states of a gas turbine disk

Numerical investigations on the absorption of a metal hydride hydrogen storage tank based on various thermal management strategies

<div class="section abstract"><div class="htmlview paragraph">An experimental study was carried out in order to determine the effect on performance and pollutant emissions of converting an existing heavy-duty diesel engine for alternative fuel use. More specifically, a HD diesel engine used in commercial vehicle applications with Euro II baseline emission level was studied in two ways: on the one hand the diesel engine was converted to a dedicated lean-burn CNG engine and on the other hand the baseline diesel engine was converted to a dual-fuel engine (diesel + LPG) with multi-point LPG injection in the intake cylinder ports. The CNG engine conversion was achieved by means of some important modifications, such as the reduction of the compression ratio by increasing the volume of the combustion chamber in the piston, the design of a spark plug adapter for the installation of the spark plugs in the cylinder head, the design of a gas injection system to attain efficient multi-point gas flow and injection, and the implementation of a complete electronic management system by means of an engineered gas ECU. Concerning the LPG dual-fuel conversion, some minor modifications were made to the diesel engine such as the installation of the gas train components and the implementation of a gas ECU for the management of the gas and diesel injection using some CAN bus J1939 signals. The emission tests carried out were mainly based on R49-02 ECE and R96 UNECE. The results show the feasibility of this kind of engine conversion in terms of its effect on performance and pollutant emissions compared to the baseline diesel engine certification limits, especially reduced PM reaching Euro V level in this kind of contaminant. The maximum LPG substitution ratio reached in this work was around 30%. The results for maximum speed and 1000-metre acceleration driveability tests performed on an international proving ground with the diesel and CNG engine installed in a truck are also given.</div></div>

Physics-based models in PV-battery hybrid power systems: Thermal management and degradation analysis