Hierarchical multi-time-scale predictive thermal management and fuel optimization for heavy-duty compression ignition engines

<div class="section abstract"><div class="htmlview paragraph">Increasing concerns due to global warming have led to stringent regulation of greenhouse gas (GHG) emissions from diesel engines. Specifically, for GHG phase-2 regulation (2027), more than 4% improvement is needed when compared to phase-1 regulation (2017) in the light heavy-duty (LHD) diesel engine category. At the same time, California Air Resources Board (CARB) and Environmental Protection Agency (EPA) have proposed the new Low NOx standards that require up to 90% reduction in tailpipe (TP) NOx emissions in comparison to the current TP NOx standards that were implemented in 2010. In addition, CARB and EPA have proposed new certification requirements – Low Load Cycle (LLC) and revised heavy-duty in-use testing (HDIUT) based on the moving average window (MAW) method that would require rigorous thermal management. Hence, strategies for simultaneous reduction in GHG and TP NOx emissions are required to meet future regulations.</div><div class="htmlview paragraph">This paper presents potential pathways to achieve the GHG phase-2 and the ultra-low NOx (ULN) regulations with minimum changes in engine design, while meeting the constraints that need to be considered for engine performance stability, component durability, and vehicle drivability. Experimental evaluations were performed focusing on transient cycles such as heavy-duty Federal Test Procedure (hereafter referred as FTP), LLC, and custom transient cycles for HDIUT assessment. We used a model-year (MY) 2021 production Isuzu diesel engine and an advanced dual-dosing aftertreatment system comprising of a close-coupled SCR (ccSCR), diesel oxidation catalyst (DOC), diesel particulate filter (DPF), selective catalytic reduction (SCR), and Ammonia Slip Catalyst (ASC). Conventional thermal management techniques such as multi-injection, intake, and exhaust throttling were implemented to achieve the emissions targets. In addition to the proposed system design, this paper presents following test results from a full-scale system evaluation: <ol class="list nostyle"><li class="list-item"><span class="li-label">1</span><div class="htmlview paragraph">Achieve rapid and sustained turbine-out exhaust temperatures (>200°C) while meeting the engine-out emissions constraints for soot and total hydrocarbon (THC) emissions.</div></li><li class="list-item"><span class="li-label">2</span><div class="htmlview paragraph">A summary of TP NOx, TP N2O and GHG emissions over a composite FTP and LLC.</div></li><li class="list-item"><span class="li-label">3</span><div class="htmlview paragraph">HDIUT assessment results and observations for LLC and custom transient cycles.</div></li><li class="list-item"><span class="li-label">4</span><div class="htmlview paragraph">Robustness evaluation of TP NOx emissions for composite HDT, LLC and custom transient cycles by imposing component variations.</div></li></ol></div></div>

Hydrogen serves as an optimal fuel for engines. Pure hydrogen engines do not generate carbon monoxide and hydrocarbon emissions; instead, they encounter significant nitrogen oxide emissions. Inner-engine control and outer-engine control are two methods to reduce NOx emissions. Outer-engine control primarily mitigates NOx emissions by selective catalytic reduction (SCR), a process that has been extensively researched. Nevertheless, there is a paucity of research about NOx emission regulation in pure hydrogen engines via internal engine management. This work utilised the closed homogeneous reactor (CHR) in Chemkin Pro to model the primary NOx emission control within pure hydrogen engines. The findings indicate that single exhaust gas recirculation (EGR) reduces NOx emissions by 45.3% at an EGR ratio of 20%, suggesting that the reduction in NOx emissions is not substantial. Nonetheless, EGR combined with lean burn reduces NOx emissions by 96.31% at a λ of 1.4 and an EGR ratio of 20%, resulting in ultra-low NOx emissions from pure hydrogen engines. In comparison to single EGR and EGR combined with lean-burn, SNCR is more effective for NOx emission control. An NH3 ratio of merely 10% can reduce NOx emissions by 96.32% in pure hydrogen engines, whilst a 15% NH3 ratio can attain zero NOx emissions in pure hydrogen engines without necessitating a high λ value or EGR ratio. It is essential to precisely regulate the NH3 ratio in the cylinder; otherwise, residual NH3 may be generated, leading to environmental pollution.

The computational fluid dynamical software AVL-FIRE code was used for investigating the impact of multiply injection strategies and spray included angles on combustion and emissions in a marine diesel engine. The fuel injection parameters of spray included angle and pilot injection timing with pilot-main injection, as well as post injection ratio and post injection duration angle with pilot-main-post injection, were all investigated and optimized. The results indicate that retarding pilot injection timing with pilot-main injection declines high temperature region, resulting in a notable reduction in NOx emissions. Since fuel evaporation and burn are hampered by long spray penetration due to low temperature and pressure with pilot injection, a suitable spray included angle are used to offer more efficient air-fuel mixing process. A wider spray included angle simultaneously reduces soot emission and indicated specific fuel consumption (ISFC). Post injection fuel exerts impact on combustion process by causing a great disturbance to flow field during post combustion. Increasing post injection ratio from 4% to 10% at a small post injection duration angle great emission performance is achieved by simultaneous reduction in NOx and soot emissions while only using a slight consumption of ISFC. To summarize, the defeat of traditional NOx-soot trade-off occurs as both NOx and soot emissions are decreased with optimized multiple injection strategy and spray included angle. Particularly, there are respectively four cases with pilot-main injection and two cases with pilot-main-post injection, that achieve simultaneous reduction in NOx emissions, soot emission, and ISFC, compared to the prototype.

The low-temperature operations of diesel engines and aftertreatment systems have attracted increasing attention over the past decade due to the stringent diesel emission regulations and excessive tailpipe emissions at low temperatures. The removal of NOx emissions using selective catalytic reduction (SCR) systems during low-temperature operations remains a significant challenge. One of the popular techniques for alleviating this issue is to employ active thermal management via in-cylinder postinjection to promote aftertreatment system temperatures. Meanwhile, numerous studies have focused on ammonia coverage ratio controls with the aim to maintain high NOx conversion efficiency and low tailpipe ammonia slip. However, most of the active thermal management and SCR controls in the existing literatures were separately and conservatively designed, which can lead to higher cost of SCR operation than needed including diesel fuel consumption through active thermal management and urea solution consumption. The main purpose of this study is to design and coordinate active thermal management and SCR control using nonlinear model predictive control (NMPC) approach to minimize the total cost of SCR operation while obtaining high NOx conversion efficiency and low tailpipe ammonia slip. Simulation results demonstrate that, compared to the baseline control which consists of separated active thermal management and SCR control, the coordinated control is capable of reducing the total cost of SCR operation by 25.6% while maintaining the tailpipe NOx emissions and ammonia slip at comparable levels. Such an innovative coordinated control design concept shows its promise in achieving low tailpipe emissions during low-temperature operations in a cost-effective fashion.

The initial problem on building a mobile robot using embedded system is the hardware flexibility. Currently most of mobile robots use microcontroller. The weakness of building mobile robot using microcontroller is the form and the specification which is inflexible to be added or changed. For that reason this research use FPGA soft processor to design a hardware architecture in the form of system on chip (SoC) as the motor velocity control and robot heading. We divide the mobile robot control into 2 levels which are high level and low level control. High level control is including the positioning and path tracking, while low level control is including kinematic, speed control, heading lock and communication. This research focused on low level control design. The achieved result with the use of FPGA soft processor, is that the programmer can flexibly add and change the hardware architecture and faster program execution resulted from parallel process. On the motor velocity testing, the time to get back into the steady state after receiving disturbance was about 0.6 seconds. On the heading lock testing, the time of the robot to get back into the set point is around 1 second. Resources required to implement soft processor system are 3883 slices register, 1130 slices flip-flop, 3825 slices LUTs and 191 RAM Blocks.

In this paper a hierarchical model predictive control framework for the energy management of a hybrid electric vehicle is extended by replacing the supervisory linear model predictive controller with a nonlinear model predictive controller. The nonlinear system dynamics of a parallel hybrid electric vehicle are incorporated into a nonlinear optimal control problem which is solved at each time instance. The discretization of the continuous time system dynamics is realized via direct multiple shooting. The low-level linear model predictive controller considers the actuator dynamics for optimal tracking of the driver's torque demand while the high-level controller considers the slow dynamics of the vehicle and the battery. The proposed strategy is validated in simulation with the worldwide harmonized light vehicles test cycle and compared to a hierarchical model predictive control framework with linearized system dynamics.

Simultaneous reduction of NOx emission and SOx emission aided by improved efficiency of a Once-Through Benson Type Coal Boiler

<div class="section abstract"><div class="htmlview paragraph">Increasingly stringent emission regulations continue to be legislated around the world to significantly minimize pollutants released to the air by internal combustion engines. After Treatment Systems (ATS) meant for reducing oxides of nitrogen (NOx) in the exhaust into non-harmful species have evolved at a rapid pace over the past two decades. Stringent emissions requirements have driven complex ATS architecture through sensors to measure delta-pressure, NOx, and temperatures. Accurate and precise performance of individual components as well as the integrated ATS is required to ensure regulatory compliance and efficient performance. Both of which require substantial amounts of performance and validation testing. Manufacturers have been developing the ability to accurately and efficiently test the ATS components. To meet the norms for tail pipe or stack emissions of NOx in ‘as new’ condition and during the entire ‘emissions useful life (EUL)’ of the ATS, all components of an ATS must perform with high accuracy, every single time. A well designed ‘automated testbench’ ensures better accuracy in testing the functionality of many parts of the ATS, as rapidly as possible.</div><div class="htmlview paragraph">Dosing Unit (DU), also known as the Urea Dosing Unit, in the ATS is responsible for delivering urea as needed into the exhaust airstream thereby helping in the reduction of NOx from the tail pipe or exhaust stack in the SCR (Selective Catalytic Reduction). This paper describes the development of an automated testbench to validate the performance of the dosing unit. The test bench is designed such that both new and used (returned from field) ATS can be tested or evaluated for performance. The automated testbench for urea dosing has been developed at the Cummins Technical Center in India (CTCI) keeping in mind the needs for similar testbenches for Cummins use in other parts of the world. The test bench design, build, and test process and protocol have been formulated such that the same test bench can be used to test urea dosing units to meet emission standards defined by EPA, CARB, EURO, NS, and other international standards.</div></div>

Recent increases in petroleum fuel costs, CAFE standards, and environmental concerns about CO2 emissions from petroleum based fuels have created an increased opportunity for diesel engines and renewable alternative fuels such as biodiesel. Additionally, the Environmental Protection Agencies Tier II heavy duty and light duty emissions regulations require significant reductions in NOx and diesel particulate matter emissions for diesel engines. As a result, the diesel engine and aftertreatment system is a highly calibrated system that is sensitive to changing fuel characteristics. This study focuses on the impact of soy methyl ester biodiesel blends on combustion performance, carbonaceous soot matter and NOX emissions. Tests were completed with an I4 1.9L, turbocharged, high speed, direct injection diesel engine using commercially available 15 ppm ultra low sulfur diesel, a soy methyl ester B20 (20% biodiesel and 80% ultra low sulfur diesel) biodiesel blend and a pure soy methyl ester biodiesel. Results show a reduction in NOx and carbonaceous soot matter emissions and an increase in brake specific fuel consumption with the use of biodiesel. Further, traditional methodology assumes that diesel fuels with a high cetane number have a reduced ignition delay. However, results from this study show the cetane number is not the only parameter effecting ignition delay.

Engine efficiency improvement is very critical for medium to heavy-duty vehicles to reduce Diesel fuel consumption and enhance U.S. energy security. The tradeoff between engine efficiency and NOx emissions is an intrinsic property that prevents modern Diesel engines, which are generally equipped with exhaust gas recirculation (EGR) and variable geometry turbocharger (VGT), from achieving the optimal engine efficiency while meeting the stringent NOx emission standards. The addition of urea-based selective catalytic reduction (SCR) systems to modern Diesel engine aftertreatment systems alleviate the burden of NOx emission control on Diesel engines, which in return creates extra freedom for optimizing Diesel engine efficiency. This paper proposes two model-based approaches to locate the optimal operating point of EGR and VGT in the air-path loop to maximize the indicated efficiency of turbocharged diesel engine. Simulation results demonstrated that the engine brake specific fuel consumption (BSFC) can be reduced by up to 1.6% through optimization of EGR and VGT, compared to a baseline EGR-VGT control which considers both NOx emissions and engine efficiency on engine side. The overall equivalent BSFCs are 1.8% higher with optimized EGR and VGT control than with the baseline control. In addition, the influence of reducing EGR valve opening on the non-minimum phase behavior of the air path loop is also analyzed. Simulation results showed slightly stronger non-minimum phase behaviors when EGR is fully closed.

In this study, the effect of hydrothermal aging over a commercial diesel oxidation catalyst (DOC) on deterioration in nitrogen dioxide (NO2) production activity has been experimentally investigated based on a micro-reactor DOC experiment. Through this experimental result, the NO2 to nitrogen oxides (NOx) ratio at DOC outlet has been mathematically expressed as a function of DOC temperature according to various aging conditions. The current study reveals that the catalyst aging temperature is a more dominant factor than the aging duration in terms of the decrease in NO2 production performance through DOC. The DOC sample hydrothermally aged for 25 h at 750 °C has displayed the lowest NO2 to NOx ratio compared to the samples aged for 25 ~ 100 h at 650 °C. Also, in this study, the impact of hydrothermal aging of a DOC on the selective catalytic reduction (SCR) efficiency in a ‘DOC + SCR’ aftertreatment system was predicted by using transient SCR simulations. To validate the SCR simulation, this study has conducted a dynamometer test of a non-road heavy-duty diesel engine with employing a commercial ‘DOC + SCR’ system on the exhaust line. The current study has quantitatively estimated the effect of the variation in NO2 to NOx ratio due to the hydrothermal aging of DOC on the NOx removal efficiency of SCR.

Large two-stroke marine diesel engines are used as the prime mover in the majority of ocean going commercial vessels and are currently facing new stringent NOx emission reductions. Selective catalytic reduction is an aftertreatment technology which is able to reduce emitted NOx at allowable levels. In most marine applications, the selective catalytic reduction system is placed on the high pressure side of the turbine, due to limitations at the exhaust gas temperature at the inlet of selective catalytic reduction system. In this article, the operation of a large two-stroke marine diesel with a selective catalytic reduction aftertreatment system, is investigated in heavy weather conditions. Operation of a vessel in heavy weather results in increased ship resistance, wave-induced ship motions, and a highly varying flow field in the propeller due to ship motions. This results in a fluctuation of propeller demanded torque and hence a fluctuation in engine load and exhaust gas temperature which may affect engine and selective catalytic reduction performance significantly. To investigate this phenomenon and taking into account the engine–propeller interaction, the entire propulsion system was modeled, namely the propulsion engine, the high pressure selective catalytic reduction system, the directly driven propeller, and the ship’s hull. A propeller model was employed to simulate the transient propeller torque demand and torque fluctuations due to ship motions. A three-dimensional six degrees of freedom panel code was used to calculate ship motions and wave added resistance in regular waves. The coupled model of the marine propulsion plant was validated against available measured data from a ship-board propulsion system on good weather conditions. The model was then used to simulate the behavior of the system during transient loading conditions in the presence of regular waves.

A hierarchical MPC and sliding mode based two-level control for freeway traffic systems with partial demand information

Selective catalytic reduction (SCR) systems have been widely used in heavy-duty (HD) diesel engines to meet the stringent emission standards for nitrogen oxides. The mobile SCR system has improved the considerable reduction of NOx emission from HD diesel engines. Many investigations have been performed to enhance the catalytic performance and optimize the SCR system within the diesel engines. The purpose of the present study was to investigate the types of nitrogen components (NO, NO2, N2O, and NH3) in the NOx exhaust emissions prior to and after passing through an SCR device. A EURO VI type commercial heavy-duty diesel engine was equipped to an AC dynamometer. World harmonized stationary cycle and transient cycle were introduced to operate the test engine under road conditions. A new quantum-cascade laser analyzer was employed to measure the nitrogen emission species in real time. The engine-out NOx emissions were strongly affected by the load conditions of the engine, which also determined the efficienc...

<div class="section abstract"><div class="htmlview paragraph">Reducing the greenhouse emissions from on-road freight vehicles to meet the climate change mitigation objectives, has become a prime focus of regulatory authorities all over the world. Besides India, the United States, the European Union, Canada, Japan, and China have already established or planned heavy-duty vehicle efficiency regulations addressing CO<sub>2</sub> and NO<sub>X</sub> emissions. In addition, Argentina, Brazil, Mexico, and South Korea are all in various stages of developing policies to improve the efficiency of their commercial vehicle fleets. For CO<sub>2</sub> emissions reduction standards, the U.S. mandates 27% reduction by 2027, EU is calling for 15% reduction by 2025, China for 27% by 2019 over 2012 levels, and India is mandating 10%-15% reduction by 2021 for phase 2 of the new standard. There has also been considerable focus on further reduction in NO<sub>X</sub> emissions from current levels (0.2 g/hp-hr), to the proposed ultra-low NOx standards (0.02 g/hp-hr) in the U.S. for heavy duty engines by 2024.</div><div class="htmlview paragraph">Given these planned and proposed regulatory standards being implemented around the globe, there have been substantial studies and publications focusing on exploring and evaluating technologies that can help deliver the lower tailpipe NOx targets and understand the CO<sub>2</sub> impact associated with it. Majority of the NO<sub>X</sub> emissions from engine, occur during the cold-start portion of the transient regulatory cycles, like HD FTP and WHTC. This is because, a typical heavy-duty diesel aftertreatment system does not achieve substantial NO<sub>X</sub> reduction until approximately 400-500 seconds into the cold-start cycle due to lack of heat from the engine. The result is untreated NOx escaping through to tailpipe. To achieve low NOx emission levels over the composite transient cycles, the engine must provide rapid exhaust heat energy, during the cold-start portion, to reduce the time required by the SCR catalyst to reach catalyst light-off temperature, while controlling the NO<sub>X</sub> emissions. Moreover, high NO<sub>X</sub> conversion efficiency must be maintained during the hot-start portion of cycle. For a conventional heavy-duty engine, providing rapid exhaust heat while controlling NOx emissions has been a challenge, because these are competing demands. Implementing secondary or auxiliary heat sources downstream in the exhaust after treatment system (ATS) comes at CO<sub>2</sub> penalty and adds significant cost and complexity. This has been established in recent publications by organization like SwRI [<span class="xref">1</span>], CARB and Bosch [<span class="xref">2</span>].</div><div class="htmlview paragraph">Achates Power Opposed Piston (OP) engine technology provides ideal solution to this challenge. The opposed-piston engine has several inherent advantages over conventional four-stroke engines, like higher BTE (15-30% higher), higher power density, an air-system that results in reduced pumping work, the ability to control residual combustion gases, two fuel injectors per cylinder providing greater timing flexibility, and the ability to provide rapid engine out heat and temperature rise for the exhaust emission system while maintaining low engine out NO<sub>X.</sub></div><div class="htmlview paragraph">This paper demonstrates results from cold and hot start transient WHTC testing and WHSC testing, conducted at Achates Power, on a three-cylinder opposed-piston engine. Results show that the Achates Power OP Engine can deliver engine out heat and temperature rise that exceeded and sustained catalyst light-off temperature thresholds (250°C) within the first 60-100 seconds in the cold start cycle, while controlling engine out NOx to lower levels when compared to a conventional four-stroke heavy-duty diesel engine. As a result, the OP Engine not only meets current BS-VI and future regulatory emissions requirements but is also able to do so with a significant CO<sub>2</sub> emissions advantage. Furthermore, the inherent advantages of the OP Engine offer unique aftertreatment optimization and downsizing opportunities thereby enabling cost reduction.</div></div>