Browse Topic: Diesel particulate filters
This paper presents the collaborative efforts of the USCAR GPF OBD Working Group to evaluate and recommend On-Board Diagnostic (OBD) monitoring requirements for Gasoline Particulate Filters (GPFs). The group, comprising representatives from major OEMs, aims to establish a unified understanding of GPF monitoring capabilities and propose regulatory recommendations to CARB. The paper outlines the physics of soot generation and oxidation, regulatory interpretations, and diagnostic strategies, culminating in a proposed framework for GPF OBD compliance. The material in this paper was previously presented at the 2024 SAE OBD Symposium [1].
The legislation of CEV Stage V emission norms has necessitated advanced Diesel Particulate Filter calibration strategies to ensure optimal performance across diverse construction equipment applications in the Indian market. Considering the various duty cycles of cranes, backhoe loaders, forklifts, compactors, graders, and other equipment, different load conditions and operational environments require a comprehensive strategy to enhance DPF efficiency, minimize regeneration frequency, and maintain compliance with emission standards. The DPF, as an after-treatment system in the exhaust layout, is essential for meeting emission standards, as it effectively traps particulate matter. Regeneration occurs periodically to burn the soot particles trapped inside the DPF through ECU management. Therefore, understanding soot loading and in-brick DPF temperature behavior across various applications is key. This paper explores the challenges in DPF calibration for CEV Stage V and provides a comprehensive approach to address these challenges, including optimizing soot loading and thermal management for different duty cycles across various applications within a unified calibration framework. The frugal Off-Highway Vehicle market expects a leaner Exhaust Gas Treatment approach, which increases the challenges of thermal management and soot loading. Additionally, the market is moving towards extracting maximum BMEP from their engines, which impacts passive regeneration and DPF thermal stability, among other parameters.
The current and upcoming Internal Combustion Engine (ICE) emission norms are very stringent. It is difficult to meet emission standards with just combustion optimization techniques. As a result, post-treatment is required for Engine-out emissions. Otherwise, these hazardous gases impact the ecosystem of living beings. Many technologies are implemented at the exhaust for reducing the emissions. Diesel Particulate Filter (DPF) is one such technique to achieve lower Particulate Matter (PM) and Particulate Number (PN) emission goals. In order to achieve such emission reduction, the DPF undergoes periodic cleaning called regeneration. During regeneration, the exhaust systems including DPF are maintained at elevated temperatures to achieve proper cleaning. When the vehicle is in regeneration, sudden braking or accelerator pedal release leads to engine Drop to Idle speeds (DTI), which sharply increases the temperature gradient inside the DPF which may result in physical damage like cracks, melting and fractures to the DPF substrate. In the occurrence of the above scenario, DPF replacement is the only option which will be an additional expense to the end user. This paper proposes a software solution to address the above issue by detecting the DTI conditions during regeneration and applying corrective actions.
Diesel Particulate Filters (DPFs) have been used extensively worldwide as a Particle Mass (PM) / Particle Number (PN) reduction technology for various diesel applications. Based on CARB’s latest Tier 5 regulation workshop, PM emission targets are expected to become a lot more stringent; from 0.02 g/kWh to 0.005 g/kWh (75% reduction compared to Tier 4 Final (Tier 4f)). Also, CO2 emission targets are expected to be introduced for Tier 5. In parallel, EU Stage VI emission regulation standards and implementation timing could be announced sometime in late 2024. It is expected that PN emission standards will be tightened such as extending measurement range of PN from 23 nm to 10 nm. With Tier 5 and EU Stage VI regulations approaching, several OEMs are considering implementing a common aftertreatment system that can meet emission targets for both regions. High filtration efficiency and low backpressure DPFs will be required to meet PM/PN and CO2 emission standards. NGK has developed several DPF materials with various cell structures within the past couple of years to meet future stringent regulations worldwide. To understand the severity of future regulations, engine testing was conducted to compare PM / PN filtration performance of several different filters. Both Cordierite (Cd) and Silicon Carbide (SiC) materials were evaluated since different materials are being considered depending on soot regeneration strategies. DPF properties ranging from medium to low mean pore size (MPS) were studied and compared with Tier 5 PM / Stage VI PN targets as a reference point. In this paper, the suitable DPF for future regulation based on these results will be shown.
The automobile industry is going through one of the most challenging times, with increased competition in the market which is enforcing competitive prices of the products along with meeting the stringent emission norms. One such requirement for BS6 phase 2 emission norms is monitoring for partial failure of the component if the tailpipe emissions are higher than the OBD limits. Recently PM (soot) sensor is employed for partial failure monitoring of DPF in diesel passenger cars.. PM sensor detects soot leakage in case of DPF substrate failure. There is a cost factor along with extensive calibration efforts which are needed to ensure sensor works flawlessly. This paper deals with the development of an algorithm with which robust detection of DPF substrate failure is achieved without addition of any sensor in the aftertreatment system. In order to achieve this, a thermodynamic model of DPF substate was created using empirical relations between parameters like exhaust flow rate, exhaust gas temperature and soot mass content. The modeling was done in both empty (no soot) and filled (threshold soot content) DPF substrate conditions. There were two methodologies, namely integration method and normalization method. In integration method the pressure drop across DPF substate in actual running condition is cumulatively summed up and compared with the integrated modelled value achieved from the thermodynamic model. If the ratio between modelled and actual crosses the threshold value, a DPF substrate failure flag is raised. In normalization method, actual pressure drop across DPF is corrected using empirical thermodynamic relations for exhaust temperature and soot mass content. The corrected pressure drop is normalized for the exhaust flow rate and then averaged based on release conditions. If the averaged values is lower than the threshold, a DPF substrate failure flag is raised. DPF substrate failure is intimated only when both the methodologies raise the failure flag. The algorithm was tested with actual failed DPF sample and robust detection was observed (more than 90% detection accuracy) and no misdetection.
Recent legislations require very low soot emissions downstream of the particulate filter in diesel vehicles. It will be difficult to meet the new more stringent OBD requirements with standard diagnostic methods based on differential sensors. The use of inexpensive and reliable soot sensors has become the focus of several academic and industrial works over the past decade. In this context, several diagnostic strategies have been developed to detect DPF malfunction based on the soot sensor loading time. This work proposes an advanced online diagnostic method based on soot sensor signal projection. The proposed method is model-free and exclusively uses soot sensor signal without the need for subsystem models or to estimate engine-out soot emissions. It provides a comprehensive and efficient filter monitoring scheme with light calibration efforts. The proposed diagnostic algorithm has been tested on an experimentally validated simulation platform. 2D signatures are generated from soot sensor signal for nominal and faulty configurations. Gaussian dispersions on soot estimator (30%) and sensor model (15%) have been considered. Based on a statistical analysis, a relevant threshold is defined satisfying a compromise between non-detection and false alarm rates. The selected threshold is then used for online DPF diagnostic using NEDC cycle. The obtained results are promising and clearly show the performance of the proposed method in terms of non-detection and false alarm rates. The resulting diagnostic scheme can be easily integrated in the ECU for onboard DPF monitoring.
To meet stringent emission norms and commercial vehicle customer demands, the selection of an after-treatment system (ATS) plays a considerable role. Therefore, the selected ATS should substantially reduce nitrogen oxide emission by proper decomposition of ammonia and particulate matter without significantly increasing the thermal stress on DPF. Though the BS-VI after-treatment architecture is derived from EURO-VI, only a certain level of technology for the vehicle operating conditions in India can be implemented. However, numerous vehicle operating condition challenges in the Indian market must be explicated. Correspondingly, it should be addressed with a robust durability validation methodology to enhance the ATS product performance in challenging environments. This paper discusses SCR catalysts emission performance and ammonia decomposition durability validation methodology for commercial vehicles. In addition, during various vehicle duty cycle conditions, the effectiveness of DPF and DOC is recognized based on minimized soot loadings in the DPF based on soot regeneration strategies. Hence, on the one hand, the design of DOC is optimized to recognize passive soot regeneration effectively by oxidation NO into NO2. On the other hand, for facilitating regeneration temperature (DOC at >500°C) during HC dosing in the exhaust pipe, DOC catalyst effectiveness is also essential. Accordingly, based on the scenario above, the impact of soot loading and back pressure on DPF material durability is also validated for vehicle operating conditions.
Thermal management in off road vehicles is critical because it directly or indirectly affects engine performance, fuel economy, safety, and emission. With the introduction of stringent exhaust emission norms such as the EU stage V and EPA Final Tier 4, modern engines use a Diesel Particulate Filter (DPF) to trap the soot particles present in the exhaust gases. These soot particles are burned using a process called regeneration where skin temperature of DPF increases beyond 400 °C. Situation becomes more worst when the vehicle is shutdown just after the regeneration, where the coolant fan is off and there is no active airflow. Hot air gets trapped and start increasing under hood temperature, affecting the performance of other sub systems like air intake, electrical components, aftertreatment sensors etc. There are several ways to manage this heat load. Normally the heat built up in the under-hood compartment escape to the environment by two paths - convection and radiation. This convective and radiated heat load must be guided smartly to allow it escape and safeguard all the critical components. This paper proposes different techniques to do so and effectively manage thermal load during vehicle hot shutdown condition. The work described in this paper are outcomes and learnings captured during various ongoing live projects. All the necessary testings were conducted in house.
Major share of Small Commercial Vehicles (SCV) applications is operated in city conditions with frequent stops and short driving distance. Drivers will often operate these SCV with loads that exceed their rated specifications. Such driving profiles are particularly observed in food, e-commerce delivery, garbage collection vehicles which are driven inside the city. During Diesel Particulate Filter (DPF) regeneration events in these conditions, it is a challenge to maintain light-off temperature of oxidation catalyst. This may lead to prolonged regeneration durations with multiple regeneration interrupts and poor regeneration efficiency. Frequent engine start operations and lower passive regeneration result in a low regeneration interval. The extended DPF regeneration duration in combination with a low regeneration interval will result in high oil dilution. The study focuses on identifying such driving profiles and defining counter measures to improve the regeneration performance. This involves applying an ECO mode to optimize the soot rate only during challenging driving conditions and escalation-based algorithms that use auxiliary loads to increase exhaust temperatures and thus improve regeneration efficiency. These measures help to improve regeneration performance with lower fuel consumption and reduced oil dilution.
The move away from fossil fuels and the diversification of the primary energy sources used are imperative both in terms of mitigating global warming and ensuring the political independence of the Western world. For the industries of agriculture and forestry, it is possible to secure the basic energy supply through their own yield. The use of vegetable oil is a possibility to satisfy the energy requirements for agricultural machines both autonomously and sustainably. Up to now, rapeseed has been the most important plant for oil production in Western Europe. In the EU, rapeseed oil is currently credited with up to 60% fossil CO2 savings compared to conventional diesel fuel. As a result, since 2018, rapeseed oil is no longer considered as biofuel in the EU. However, if cultivation and processing are completely based on renewable energy sources, up to 90% of fossil CO2 emissions can be saved in the future. This also applies to rapeseed oil, which is a by-product of animal feed production. In addition, pure rapeseed oil is chemically unchanged and thus biodegradable, which makes it particularly attractive for use in environmentally sensitive areas. To increase the attractiveness of rapeseed oil as a fuel for the agricultural industry, a multi-fuel concept for the flexible use of rapeseed oil, diesel fuel and any mixtures of these two fuels would be beneficial, as it minimizes economic risks due to price fluctuations, availability, and taxation. For implementing such a concept, technical adjustments to the propulsion system are necessary. In existing vegetable oil vehicles, cost-intensive additional components are required for diesel particulate filter regeneration. Conventional regeneration via post-injected fuel (which does not participate in combustion) leads to dilution of the engine oil with vegetable oil. This study elaborates the possibilities of DPF regeneration in vegetable oil operation by internal engine measures without the need for post-injection. This includes strategies for generating exhaust gas temperatures in high-idle operation which are suitable for regeneration. For this purpose, strategies combining throttling and retarded combustion are used. The measures were successfully tested with respect to their effectiveness for DPF regeneration. It could also be proved that no increased engine oil dilution occurs as a result of the regeneration procedure. For a prospective series application, however, regeneration should also be possible in transient engine operation. For this purpose, the measures developed for high-idle regeneration have been transferred to partial load points to gain insight into their applicability for transient engine operation. In addition, the effect of external EGR on regeneration has been considered. As the previous investigations of high-idle regeneration showed that regeneration is most critical when pure rapeseed oil is used, the studies of regeneration in part-load operation were limited to pure rapeseed oil. The systematic parameter variations carried out during the studies helped to improve the understanding of the system and the mechanisms of regeneration. The results of the investigation show that the exhaust gas temperature can be increased significantly by the measures studied. However, achieving the exhaust temperature required for DPF regeneration remains a challenge for certain operating points.
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