Aftertreatment System Research Articles

Transferability Assessment of OBD-Related Calibration and Validation Activities from the Vehicle to HiL Applications

With the Euro 7 pollutant emission legislation currently under discussion, advanced and more efficient exhaust aftertreatment systems are being developed. The technologies required for these are leading to an increase in the number of components and control systems requiring diagnoses strategies under the on-board diagnostics (OBD) legislation. With concurrent shorter development times and significant reductions in budgets allocated to conventional powertrain development, challenges in the field of OBD calibration and verification are already rising sharply. In response to these challenges, hardware-in-the-loop (HiL) approaches have been successfully introduced to support and replace conventional development methods. The use of complex simulation models significantly improves the quality of calibrations while minimizing the number of required prototype vehicles and test resources, thus reducing development costs. This paper presents a feasibility study for moving OBD-related calibration and validation tasks from the vehicle to a HiL platform. In this context, the calibration and verification process of an active diagnostic for monitoring the condition of the three-way catalyst (TWC) and the oxygen sensors in the exhaust aftertreatment system is presented. It is shown that all relevant signals are simulated with sufficient accuracy to ensure a robust transfer from the vehicle to a HiL test bench. Special attention is given to the simulation of aged components and their influence on the emission behavior of the system. Furthermore, it is discussed that transferring OBD tasks from the vehicle to the HiL test bench could result in significant savings in development time and a reduction in the number of physical prototype vehicles and test resources required.

Component Level Failure Analysis of Mounting Strap Joint Fitted on Vehicle Engine Exhaust After-Treatment System

Exhaust Gas Processors (EGP) or Exhaust After Treatment Systems (EATS) are usually mounted on vehicle chassis or engine body with the help of mounting straps due to its ease of installation. It is prescribed for any industry to manufacture an optimized design of strap joint and duly test it before making an entry to the market. There is no standard method available to be followed by the industry for strap validation at an earlier stage. Most of the strap joint designed and tested based either on MAST test (done in the later stages) or on the experience. So, to test the strap joint at an earlier stage there is a need to design a component level strap joint validation method with a goal to assess the durability of strap joint vulnerable to fatigue failures due to vibration over-amplification in a bracketed after-treatment assembly while able of detecting any design flaws and eliminating or reducing numbers of potential test induced failures. The objective of this work is to define and document a systematic approach for component level strap joint validation method used to mount after treatment system components. Due to geometrical complexity and nature of material, geometrical nonlinearity and material nonlinearity were considered in the analysis. Also, for getting the most realistic results contact nonlinearity was also considered. And finally, out of various approaches investigated, an approach which was able to replicate failures in a more exact manner comparable to assembly level test was recommended as the component level strap validation method.

A Review of Thermal Energy Management of Diesel Exhaust after-Treatment Systems Technology and Efficiency Enhancement Approaches

The DOC (diesel oxidation catalyst), DPF (diesel particulate filter), SCR (selective catalytic reduction), and ASC (ammonia slip catalyst) are widely used in diesel exhaust after-treatment systems. The thermal management of after-treatment systems using DOC, DPF, SCR, and ASC were investigated to improve the efficiency of these devices. This paper aims to identify the challenges of this topic and seek novel methods to control the temperature. Insulation methods and catalysts decrease the energy required for thermal management, which improves the efficiency of thermal management. Thermal insulation decreases the heat loss of the exhaust gas, which can reduce the after-treatment light-off time. The DOC light-off time was reduced by 75% under adiabatic conditions. A 400 W microwave can heat the DPF to the soot oxidation temperature of 873 K at a regeneration time of 150 s. An SCR burner can decrease NOx emissions by 93.5%. Electrically heated catalysts can decrease CO, HC, and NOx emissions by 80%, 80%, and 66%, respectively. Phase-change materials can control the SCR temperature with a two-thirds reduction in NOx emissions. Pt-Pd application in the catalyst can decrease the CO light-off temperature to 113 °C. Approaches of catalysts can enhance the efficiency of the after-treatment systems and reduce the energy consumption of thermal management.

Study on the Emission Characteristics of Typical City Buses under Actual Road Conditions

Five typical in-use city buses in Tangshan with different emission standards, fuel power types, and emission control technology routes were selected as the research objects. PEMSs (Portable Emissions Measurement Systems) and OBD (On-Board Diagnostic) remote monitoring technologies were used to conduct research on actual road conditions and emission characteristics. The research aimed to analyze the driving characteristics of different power types of bus engines and after-treatment systems, as well as their impact on emissions. The results indicated that the actual road driving is mainly in the urban and suburban areas of the local region. Additionally, the VSP (Vehicle Specific Power) was found to be distributed in the low- and medium-speed range of mode Bin0~Bin24. The emission rates of each pollutant showed an increasing trend with the increase in VSP. THC and NOx emissions of CNG and LNG buses are significantly higher than those of gas–electric hybrid buses. However, the PM emissions are lower. Therefore, it is necessary to strengthen the NOx emission control of CNG and LNG buses. With the improvement in emission standards and the use of hybrid technology, CO2 and NOx emissions of China IV buses can be reduced by 13% and 53.5% compared with China III buses of the same tonnage. The CO2 and NOx emissions of China V buses using natural gas combustion and an electric mixture are 20% and 18.8% lower than those of China V buses of the same tonnage using only natural gas. In the actual operation of the diesel–electric hybrid bus equipped with the SCR (Selective Catalytic Reduction) system, the working time of the engine is about 35.5 ± 5%, and the working time of the SCR system only accounts for 65.5 ± 12%. The low working conditions of the SCR system and the low temperature of SCR system are the reasons for the high NOx concentration at the rear end of the SCR system when the hybrid electric bus is running at low speeds.

Study on Urea Crystallization Risk Assessment and Influencing Factors in After-Treatment System of Diesel Engines

In order to meet the increasing pollutants discharge standard, the selective catalytic reduction (SCR) module in the diesel engine after-treatment system is an important means to reduce nitrogen oxide (NOx) emissions. SCR systems are prone to urea crystallization at lower temperatures, especially during the cold-start conditions of diesel engines. In this study, we use the diesel engine after-treatment system test bench to obtain the boundary parameter of the simulation modules, and the urea crystallization risk assessment model of the diesel SCR system is established. Comparing the computational fluid dynamics (CFD) results with the test bench results, it is shown that the predicted urea film distribution of the assessment model is in good agreement with the experimental results. In order to clarify the various factors that affect the urea crystallization risk, this paper conducts a simulation analysis on a nozzle and mixer structure and operating parameters. The CFD results indicate that the increase in urea spray time will increase the maximum urea film thickness on the SCR system mixer surface. Exhaust temperature is the most important influencing factor. When the diesel engine exhaust temperature increases from 190 °C to 300 °C, the maximum urea film thickness decreases by 32 and the urea film mass accumulation decreases by 5%. Exhaust flow has a small impact on urea crystallization risk. When the exhaust flow increases from 300 kg/h to 600 kg/h, the maximum urea film thickness decreases by 39% and the urea film mass accumulation decreases by about 1%. In addition, urea spray rate, nozzle numbers, spray angle, and spray cone angle are also factors that affect urea crystallization risk.

Effects of fuel composition and vehicle operating temperature on in vitro toxicity of exhaust emissions

The study evaluates the impact of after-treatment systems, aromatic fuel content, and cold operating temperature on exhaust emission toxicity from vehicles complying with the Euro 6d emission regulation.

Preliminary Results from Life Cycle Assessment of a Product-Service System for Tailpipe Particle Measuring

Road vehicle fuel combustion emits large quantities of air pollutants such as respirable suspended particles. They are deemed to have severe impacts on human health. Therefore, concentration measurements to identify vehicles with malfunctioning after-treatment systems are crucial. This study assesses the environmental impacts of the production and use phase of a device detecting and quantifying those particle emissions caused by automobiles, also considering associated services such as regular calibration. The focus is on the comparison of environmental impacts of this product-service system and its possible emission avoidance by ensuring stipulated limits. For this purpose, the environmental performance is assessed by means of an adjusted break-even point method. Our work shows that the identification and replacement of 21 improperly working exhaust filters already offset the environmental burden of one device in at least one impact category.

Numerical Study on NO Conversion Characteristics of Ceramic and Metallic Monoliths Under Steady-State External Heat Loss in Marine After-Treatment System

Numerical Study on NO Conversion Characteristics of Ceramic and Metallic Monoliths Under Steady-State External Heat Loss in Marine After-Treatment System

Emissions from Light-Duty Vehicles—From Statistics to Emission Regulations and Vehicle Testing in the European Union

The article offers a comprehensive examination of vehicle emissions, with a specific focus on the European Union’s automotive industry. Its main goal is to provide an in-depth analysis of the factors influencing the emission of microcontaminants from light-duty vehicles and the challenges associated with their removal via exhaust aftertreatment systems. It presents statistical insights into the automotive sector and explores the relationships between vehicle categories, fuel types, and the emission of regulated and nonregulated pollutants, as well as relevant legal regulations such as the European Emission Standard. The article delves into the characteristics of vehicle exhaust, compares exhaust-gas aftertreatment systems, and introduces factors affecting emissions from gasoline engines, including downsizing, fuel composition, and engine operating parameters. It also considers the impact of driving style, start–stop systems, and related factors. Concluding, the article offers an overview of vehicle-testing procedures, including emission tests on dynamometer chassis and real driving emissions. With the growing global vehicle population and international environmental regulations, a focus on solid particles containing microcontaminants is paramount, as they pose significant risks to health and the environment. In summary, this article provides valuable insights into vehicle emissions, significantly contributing to our understanding of this crucial environmental issue.

Data-driven machine learning model of a Selective Catalytic Reduction on Filter (SCRF) in a heavy-duty diesel engine: A comparison of Artificial Neural Network with Tree-based algorithms

The Selective Catalytic Reduction on Filter (SCRF) system is yet to be deployed in current heavy-duty diesel engine aftertreatment system. Due to the thermal, space and cost benefits of the SCRF, it could become a useful component of the after-treatment system of a heavy-duty diesel engine, as regulators continue to demand an even cleaner environment. Ammonia cross-sensitivity of NOx sensors at the post-SCRF location poses challenges in measuring NOx emission accurately at this location and in turn affects the NOx conversion efficiency calculations. Developing a model that could replace the NOx sensor helps to mitigate the ammonia cross-sensitivity challenge as well as provides a medium to measure post-SCRF NOx concentration and NOx conversion efficiency while saving the cost on NOx sensors. This work focuses on a data-driven approach to developing a model for predicting NOx conversion efficiency across the SCRF using Artificial Neural Network, Bootstrap Forest, and Boosted Tree methods. Further, the three modeling techniques were also compared for accuracy and computation cost.

Thermal Management of Diesel Engine Aftertreatment System Based on Ultra-Low Nitrogen Oxides Emission

To achieve diesel engine ultra-low nitrogen oxide emission, light-off selective catalyst reduction (LO-SCR) has been suggested for better performance with lower exhaust temperature. An electric heater upstream of the exhaust aftertreatment system was applied to significantly decrease the NOx emission at a low exhaust temperature. With a 7.2 kW electric heater coupled with LO-SCR, the NOx emission during 200~500 s of the world harmonized transient cycle (WHTC) decreased from 282.6 ppm to 61.5 ppm, which is a decrease of 45%. Application of an upstream diesel oxidation catalyst (DOC) decreased the NOx emission by 63% at the same interval at the cost of worse cold-start performance. The urea input was also adjusted to avoid NOx emission during the latter part of the WHTC.

Experimental investigation of the effect of ammonia substitution ratio on an ammonia-diesel dual-fuel engine performance

This research experimentally examines an ammonia-diesel dual fuel system, not widely covered in existing literature but acknowledged as an effective approach to reduce engine carbon footprints in alignment with global decarbonization trends, focusing on enhancing understanding of performance, combustion, and emission characteristics vital for designing and optimizing these engines for commercialization. The results indicate that in an ammonia-air mixture atmosphere, diesel undergoes a prolonged ignition process, enhancing the role of premixed combustion. Increasing ammonia substitution at constant speed and load reduces the weight of mixing-controlled combustion, leading to larger areas in the chamber where diesel flames cannot reach. Ammonia oxidation mainly occurs near the diesel flame, as overly lean ammonia-air mixtures fail to sustain stable flame propagation. This results in considerable unburned ammonia emissions, particularly in regions beyond diesel flame reach and engine crevices, adversely affecting combustion efficiency and diminishing the thermal efficiency advantages of such operation. Furthermore, while ammonia combustion contributes to fuel-borne nitrogen oxides (NOx) formation, the overall NOx emissions from ammonia-diesel engines are reduced due to lower combustion temperatures and the deNOx properties of amino groups. However, the partial oxidation of ammonia during the late expansion stroke generates significant levels of nitrous oxide (N2O), a greenhouse gas, in the emissions, counteracting the intended reduction of carbon dioxide. These experimental findings highlight the necessity of focusing on both improving in-cylinder combustion quality and developing effective aftertreatment systems for NH3 and N2O capture, as crucial steps towards enhancing the environmental performance and market viability of ammonia-diesel dual fuel engines.

A New Generation of Hydrogen-Fueled Hybrid Propulsion Systems for the Urban Mobility of the Future

The H2-ICE project aims at developing, through numerical simulation, a new generation of hybrid powertrains featuring a hydrogen-fueled Internal Combustion Engine (ICE) suitable for 12 m urban buses in order to provide a reliable and cost-effective solution for the abatement of both CO2 and criteria pollutant emissions. The full exploitation of the potential of such a traction system requires a substantial enhancement of the state of the art since several issues have to be addressed. In particular, the choice of a more suitable fuel injection system and the control of the combustion process are extremely challenging. Firstly, a high-fidelity 3D-CFD model will be exploited to analyze the in-cylinder H2 fuel injection through supersonic flows. Then, after the optimization of the injection and combustion process, a 1D model of the whole engine system will be built and calibrated, allowing the identification of a “sweet spot” in the ultra-lean combustion region, characterized by extremely low NOx emissions and, at the same time, high combustion efficiencies. Moreover, to further enhance the engine efficiency well above 40%, different Waste Heat Recovery (WHR) systems will be carefully scrutinized, including both Organic Rankine Cycle (ORC)-based recovery units as well as electric turbo-compounding. A Selective Catalytic Reduction (SCR) aftertreatment system will be developed to further reduce NOx emissions to near-zero levels. Finally, a dedicated torque-based control strategy for the ICE coupled with the Energy Management Systems (EMSs) of the hybrid powertrain, both optimized by exploiting Vehicle-To-Everything (V2X) connection, allows targeting H2 consumption of 0.1 kg/km. Technologies developed in the H2-ICE project will enhance the know-how necessary to design and build engines and aftertreatment systems for the efficient exploitation of H2 as a fuel, as well as for their integration into hybrid powertrains.

Model-Based Calibration and Control of Tailpipe Nitrogen Oxide Emissions in a Light-Duty Diesel Engine and Its Assessment through Model-In-The-Loop

The present paper investigates two different strategies for model-based calibration and control of tailpipe nitrogen oxide emissions in a light-duty 3.0 L diesel engine equipped with an aftertreatment system (ATS). The latter includes a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and an underfloor selective catalytic reduction (SCR) device, in which the injection of diesel exhaust fluid (DEF), marketed as ‘AdBlue’, is also taken into account. The engine was modeled in the GT-SUITE environment, and a previously developed model-based combustion controller was integrated in the model, which is capable of adjusting the start of injection of the main pulse and the total injected fuel mass, in order to achieve desired targets of engine-out nitrogen oxide emissions (NOx) and brake mean effective pressure (BMEP). First, a model-based calibration strategy consisting of the minimization of an objective function that takes into account fuel consumption and AdBlue injection was developed and assessed by exploring different weight factors. Then, a direct model-based controller of tailpipe nitrogen oxide emissions was designed, which exploits the real-time value of the SCR efficiency to define engine-out NOx emission targets for the combustion controller. Both strategies exploit the model-based combustion controller and were tested through a Model-in-the-Loop (MiL) under steady-state and transient conditions. The advantages in terms of tailpipe NOx emissions, fuel consumption, and AdBlue injection were finally discussed.

A simulation and experiment study on the emission reduction potential of light-duty diesel engine retrofitted with an after-treatment system: a case study

ABSTRACT In this study, a simulation and experiment on laboratory conditions were conducted to investigate the effects of a retrofitted DOC-DPF-SCR system on the performance and pollutants of an in-service old-generation light-duty diesel engine. Simulations demonstrate that DOC and SCR have little effect on engine performance, but the particle filter does. With 220 mm, 240 mm, and 260 mm DPF cores, brake power was reduced by 1.9%, 4.5%, and 12.0% at rate condition and 1.2%, 3.6%, and 10.8% at maximum brake torque condition. The after-treatment system can reduce soot by 64.8% to 81.9% at full load conditions and 55.6% to 83.3% as the load varies at a constant speed. NOx emissions were reduced significantly by an average value of 81.9% at full load and 21.7% to 78.1% at a constant speed, depending on load. The DOC combined with DPF also influenced incomplete combustion products as the concentration of CO and HC decreased by 73.6% and 76.5% on average at full load conditions. Following emission standards, HC and CO emissions were reduced by 63.8% and 68.7%, respectively; NOx and PM were decreased by 71.1% and 76.6% when the engine was retrofitted with the after-treatment system. After retrofitting, the old-generation diesel engine can pass the Euro II standard.

Preliminary assessment of the potential for rapid combustion of pure ammonia in engine cylinders using the multiple spark ignition strategy

In pursuit of carbon neutrality, the adoption of zero-carbon fuels in internal combustion engines offers a path to zero carbon emissions. Among such fuels, ammonia (NH3) stands out as an effective hydrogen energy carrier with a higher energy density and a more advanced production-storage-transportation lifecycle than hydrogen (H2) fuel, making it a superior alternative. Nevertheless, achieving high combustion efficiencies in engine cylinders requires the use of fuels with fast flame speeds, since the time scales of the combustion event are practically milliseconds. The inherent flame speed of NH3 falls short, typically necessitating augmentation with H2. Yet, the in-situ generation of H2 from NH3 remains constrained, rendering the flame speed of NH3 less competitive against traditional fuels like gasoline and natural gas. To address the dual challenges of slow flame speed of NH3 and the difficulty of generating large amounts of H2 from NH3 onboard, this study evaluates an alternative method of accelerating the ammonia combustion in the engine combustion chamber through the use of multiple spark plugs, which is limited discussed in existing research. Numerical simulations performed in this study show that the application of the multi-spark strategy increases the mass burn rate, advances the combustion phasing, shortens the combustion duration, increases the engine power output, improves the fuel economy, and reduces the unburned ammonia emissions, all of which indicate that rapid combustion of pure ammonia is achieved in the combustion chamber. Moreover, the use of multiple spark points does not lead to a marked increase in nitrogen oxides emissions, thereby ensuring no added stress on exhaust aftertreatment systems. In addition, pure ammonia combustion appears to be very well adapted to this strategy, as evidenced by the avoidance of excessive cylinder pressures and pressure rise rates—a challenge faced by conventional spark ignition engines, given ammonia notably slower flame speed relative to conventional petroleum-based fuels. Overall, all these findings strongly support that the multi-spark ignition system presents a compelling direction for future zero-carbon ammonia engines. However, it is crucial to address design challenges to ensure that the engine head layout provides sufficient cooling, structural robustness, optimal breathing efficiency, and reliable multi-ignition events within the confined space.

The impact on passenger car emissions associated with the promotion and demise of diesel fuel

The promotion and growth in the use of diesel fuel in passenger cars in the UK and Europe over the past two decades led to considerable adverse air quality impacts in urban areas and more widely. In this work, we construct a multi-decade analysis of passenger car emissions in the UK based on real driving emissions data. An important part of the study is the use of extensive vehicle emission remote sensing data covering multiple measurement locations, time periods, environmental conditions and consisting of over 600,000 measurements. These data are used to consider two scenarios: first, that diesel fuel use was not promoted in the early 2000s for climate mitigation reasons, and second, that there was not a dramatic decline in diesel fuel use following the Dieselgate scandal. The strong growth of diesel fuel use coincided with a time when diesel NOx emissions were high and, conversely, the strong decrease of diesel fuel use coincided with a time when diesel vehicle after-treatment systems for NOx control were effective. We estimate that the growth in diesel car use in the UK results in excess NOx emissions of 721 kt over a three decade period; equivalent to over 7 times total annual passenger car NOx emissions and greater than total UK NOx emissions of 681.8 kt in 2021 and with an associated damage cost of £5.875 billion. However, the sharp move away from diesel fuel post-Dieselgate only reduced NOx emissions by 41 kt owing to the effectiveness of modern diesel aftertreatment systems.

A method to quantify the advantages of a variable valve train for CI engines

Today’s CI engines are subject to strict regulations of pollutant emissions and ambitious fuel consumption targets. Therefore, the interaction between the engine and the exhaust aftertreatment system (ATS) has become increasingly important. Numerous studies have shown that a variable valve train (VVT) improves the interaction between engine and ATS. However, most of these studies either quantify the advantage on a specific engine or only present complex CFD models, such that the results are not easily transferable to different engines. Thus, engine manufacturers cannot directly use these results to assess the advantage of various VVT strategies for their engines. In this paper, we propose a cycle-discrete cylinder model based on first principles which allows to simulate various VVT strategies. In contrast to present methods based on CFD, the proposed cylinder model can be realized with the equations presented. Furthermore, the model is identified with measurement data of an engine without a VVT. A separate engine, which is retrofitted with a fully VVT, is used to validate the proposed modeling approach. Using the identified model in combination with a mean-value model of the air path, we are able to simulate the effects of early intake valve closing, early exhaust valve opening, and cylinder deactivation for a complete CI engine that has no VVT installed. The model is then used to highlight the advantage of a VVT for two scenarios at part-load operation. At cold start, where the temperature of the ATS must be increased quickly, variable valve timing achieves higher enthalpy flows to the ATS while also lowering engine-out NOx emissions when compared to a standard engine strategy. If the ATS is at the operating temperature, cylinder deactivation achieves significantly higher enthalpy flows which prevents the ATS from cooling down. In addition, cylinder deactivation also lowers fuel consumption and engine-out NOx emissions.

The impact of environmental conditions on the heat and emissions produced by large diesel engines in underground mines

Diesel-powered equipment generates significant heat and emissions in an underground mine. Studies in literature demonstrate that changes in ambient temperature and relative humidity affect engine performance and its emissions, which may in turn affect worker exposure. This study builds and simulates models of six Tier 2 turbocharged diesel engines, including aftertreatment systems, with displacement between 12.8 and 18.9 liters, to determine what, if any, feedback mechanism exists between local changes in temperature, pressure, and relative humidity, and the output of heat, nitrogen oxides, and soot from the engines. This study analyzes the simulation results under conditions representative of an actual mine, where measurements of 29°C, 80% relative humidity, and 103 kPa ambient pressure represent baseline conditions. After engines had operated for two hours, these same measurements were 37°C, 60% relative humidity, and 103 kPa ambient pressure. In the period between baseline and peak-temperature conditions, heat output increases up to 1.9% across all models, soot increases up to 5.2%, and nitrogen oxides decrease up to 16%. Results from this study can be used in a production scheduling optimization model to improve thermal management of the mine and to minimize heat-related disruptions in operations.

Study on Rates of NH3 Adsorption and Desorption in SCR on Various Engine Operation Conditions

Aging diesel engines on the road require the development of an after-treatment system to meet current emission regulations, and a reduction in NOx (Nitrogen Oxide) is significant. The SCR (Selective Catalytic Reduction) system is the after-treatment system for removing NOx from exhaust gas in diesel engines using NH3 (Ammonia) gas. However, the mixing and conversion process between NH3 and NOx in SCR has not been entirely clarified. That process produces NH3 slip in the catalyst surface; the NH3 slip will make the after-treatment performance worse. This study informs how the UWS (Urea Water Solution) injection controlling method can minimize the NH3 slip in the after-treatment system. For this, the NH3 adsorption and desorption rates are important factors for determining the quantity of UWS injection in the system. The NH3 adsorption rate and desorption rate in the SCR are not significantly affected by engine speed, i.e., the exhaust gas flow rate. However, as the exhaust gas temperature increased, the adsorption rate and desorption rate of NH3 in the SCR increased. Through this, the exhaust gas temperature dramatically affects the NH3 adsorption rate and desorption rate in the SCR. Therefore, if the urea water is injected based on this knowledge that the NH3 adsorption amount in the SCR decreases as the exhaust gas flow rate increases, NH3 slip can be suppressed and a high NOx reduction rate can be achieved. Therefore, if the SCR adsorption and desorption mechanisms are analyzed according to the exhaust temperature and the exhaust flow rate in this paper, it can be used as a reference for selecting an appropriate SCR when retrofitting an old diesel engine car.