Full course evolution characteristics of DPF active regeneration under different inlet HC concentrations

Environmental problems have become a major issue for diesel engine development. Although emission aftertreatment systems such as DPFs (diesel particulate filters), LNTs (lean NOx traps) and SCR (selective catalytic reduction) have been used in diesel vehicles, the manufacturing cost increase caused by this equipment can be hard to be control. Thus, it is better for engine emissions to be reduced by improving the combustion system. A dual-fuel combustion concept is a recommended method to improve a combustion system and effectively reduce emissions. Low reactivity fuel including gasoline and natural gas, which was supplied to the intake port by the FPI (port fuel injector), improved the premixed air-fuel mixture conditions before ignition. Additionally, a small amount of high reactivity fuel, in this case diesel, was injected into the cylinder directly as an ignition source. This dual-fuel combustion promises lower levels of NOx (nitrogen oxide) and PM (particulate matter) emissions due to the elimination of local rich regions in the cylinder. However, it is challenging to control the dual-fuel combustion because the combustion stability and efficiency deteriorate due to the lack of ignition source and reactivity. Thus, it is important to establish an appropriate dual-fuel operating strategy to achieve stable, high efficiency and low emission operation. As a result of this research, a detailed operating method of dual-fuel PCI (premixed compression ignition) was introduced in detail at a low speed and low load condition by using a single cylinder diesel engine. Engine operating parameters including the gasoline ratio, a diesel injection strategy consisting of multiple injectors and timing, the EGR (exhaust gas recirculation) rate and the intake pressure were controlled to satisfy the low ISNOx (indicated specific NOx) and PM emissions levels (0.21 g/kWh and 0.1 FSN, 0.040 g/kWh, respectively) as per the EURO-6 regulation without any after-treatment systems. The results emphasized that a well-constructed dual-fuel PCI operating strategy showed low NOx and PM emissions and high GIE (gross indicated fuel conversion efficiency) with excellent combustion stability.

The diesel particulate filters (DPF) used to remove particulate matter (PM) in exhaust gas from diesel engines need to have periodical active regeneration for burning PM accumulated in DPF. Since active regeneration is carried out at high exhaust temperatures of 600 °C or more, it involves issues of fuel economy and emissions. This report describes the effort to resolve these issues by taking steps to promote the oxidation of PM and reduce DPF regeneration time by catalyst coated DPF. Attention was focused on Silver (Ag) catalyst, which possesses a PM oxidation function, as a new catalyst. An analysis of the mechanism on the PM oxidation activity, an evaluation of its properties by various model gas testing, and results from evaluation of performance conducted using an engine bench are reported on. As the result of a search for catalyst material that promotes a PM oxidation reaction, it was found that Ag2O was a highly active catalyst material. Furthermore, as the result of efforts to achieve greater stability in performance, Ag/Ce material was found to be a catalyst possessing both high performance and stability. The mechanism of Ag/Ce catalyst was analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). As a result, it was found that the supply of oxygen from complex oxides of Ce contributed to the formation of active species Ag2O, which played a role in stabilizing performance. In order to presume the performance of Ag/Ce catalyst in practical use, regeneration tests under various different conditions by using a model gas test equipment was conducted. As a result of that, the Ag/Ce catalyst exhibited high PM oxidation performance compared to the conventional Pt catalyst under all the conditions that were conducted. It was also found in regeneration testing by using engine bench that Ag/Ce catalyst showed greater PM oxidation performance, as in model gas testing, by comparison with conventional technology. As the result of DPF regeneration simulation under NEDC mode conditions, a 43 % shortening effect on regeneration time relative to regeneration conditions when using conventional technology was confirmed. Furthermore, the oil–ash, heat and sulfur durability test were conducted by accelerated aging test. It was found that although Ag/Ce catalyst exhibited some reduction of performance due to ash accumulation, no reduction due to heat or sulfur was observed, showing that this catalyst possesses high durability.

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.

<div class="htmlview paragraph">A 2005 prototype diesel aftertreatment system consisting of diesel oxidation catalysts (DOC), Cu/zeolite Selective Catalytic Reduction (SCR) catalyst, and Catalyzed Diesel Particulate Filter (CDPF) was aged to an equivalent of 120k mi on an engine dynamometer using an aging cycle that incorporated both city and highway driving modes. The program demonstrated durable reduction in particulate matter (PM) and nitrogen oxides (NOx) emissions to federal Tier 2 levels on a 6000 lbs light-duty truck application. Very low sulfur diesel fuel (∼15 ppm) enabled lower PM emissions, reduced the fuel penalty associated with the emission control system, and improved long-term system durability. A total of 643 filter regenerations occurred during the aging that raised the entire catalyst system to high temperatures on a regular basis. After testing the aged system on a 6000 lbs light-duty diesel truck, a post mortem analysis was completed on core samples taken from the DOC, SCR catalyst, and filter. It was found that the outlet of the DOC and the inlet of the SCR were deteriorated most significantly. Known catalyst poisons such as P were found in the DOC and SCR washcoats. The filter contained residual ash that was composed mainly of Ca, P and Zn compounds. The inlet of the SCR catalyst contained Pt that degraded the NOx conversion in that portion of the catalyst. Overall, the system was still quite functional and delivered 74% NOx conversion on the U.S. Federal Test Procedure (FTP-75) for light-duty vehicles</div>

<div class="section abstract"><div class="htmlview paragraph">The diesel particulate filter (DPF) is an effective technology for particulate matter (PM) and particle number (PN) reduction. On heavy-duty diesel engines, the passive regeneration by Diesel Oxidation catalysts (DOC) and catalyzed DPFs (CDPF) is widely used for its simplicity and low cost, which is generally combined with the active regeneration of exhaust fuel injection.</div><div class="htmlview paragraph">This study investigated a DOC-CDPF system with exhaust fuel injection upstream of the DOC. The system was integrated with a 7-liter diesel engine whose engine-out PM emission was below the Euro IV level and tested on an engine dynamometer. PM and PN concentrations were measured based on the Particle Measurement Programme (PMP), and the number/size spectrum for particles was obtained by a Differential Mobility Spectrometer (DMS). The filtration efficiency of DPF on PN was higher than 99% in ESC test, while the efficiency on PM was only 58%. During the active regeneration, a certain amount of diesel fuel was injected into the tailpipe and then oxidized in the DOC. The exotherm of the fuel oxidation, the temperature distribution of the DOC, and the concentrations of gaseous emissions were investigated by analyzing the effects of various factors including fuel injection rate, injector location, DOC inlet temperature and exhaust mass flow rate. Increasing fuel injection rate led to hydrocarbons (HC) slip downstream of the DOC at high space velocity (SV). N<sub>2</sub>O was generated as a by-product during diesel fuel oxidation in the DOC, especially at the beginning of fuel injection.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Diesel aftertreatment (AT) systems are critical for controlling emissions of CO, HC, NO<sub>X</sub>, and PM in the on-road transportation sector. Ensuring compliance with regulatory standards throughout the AT system's lifespan requires precise prediction of various degradation mechanisms under real-world operating conditions and mitigating their impact through proper catalyst sizing and advanced controls. In the SwRI A2CAT-II consortium, a medium-duty diesel engine production aftertreatment system was subjected to full useful life aging, involving chemical poisoning with phosphorus (P) and sulfur (S) species, along with hydrothermal aging following the DAAAC protocol. This study was aimed to model and predict the aging trajectory of this production AT system thereby capturing changes in system dynamics under both steady-state and transient conditions. The system, designed to meet the 0.2 g/bhp-hr standard, comprised a Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF), Selective Catalytic Reduction (SCR), and Ammonia Slip Catalyst (ASC). It was aged to 3600 hours equivalent to the DAAAC protocol and tested across a series of steady-state and regulatory cycles (HFTP, RMC, and LLC) at degreened, 33%, 66%, and 100% aging points. A linear decrease in system NOx conversion was observed between 0% to 66% aging, followed by a nonlinear drop from 66% to 100%. The cumulative decline in NOx conversion was 0.8%, which could significantly impact systems designed to meet a 0.05 g/bhp-hr target.</div><div class="htmlview paragraph">IntroductionAftertreatment durability demonstration is a mandatory validation exercise for on-road medium and heavy-duty diesel engine certification. This requirement ensures that the emission compliance can be achieved for the intended full useful life (FUL) of the engine system or multiple vehicle families. Conventional Deterioration Factor (DF) approach considers linear effect of sulfur and phosphorous poisoning on the catalysts over the entire useful life based on performance from 33% of aging the catalysts and extrapolating them to FUL. However, based on various studies, the impact of fuel derived Sulfur on diesel aftertreatment components was found to be exponentially significant particularly on the SCR due to the sulfur poisoning effect which require an active means to liberate sulfur to maintain appropriate SCR NOx conversion performance. Phosphorous from lubricating oil is known to adversely affect the activity of the oxidation catalyst in a catalyzed DPF thereby reducing the passive regenerative performance of DPF. For these reasons, an extensive understanding of chemical poisoning (particularly Sulfur and Phosphoros) and hydrothermal aging are warranted to design, validate and demonstrate the durability of aftertreatment components that are subjected to the prolonged chemical exposure.</div><div class="htmlview paragraph">To address the extensive challenges in durability demonstration, the Diesel Aftertreatment Accelerated Aging Protocol, or DAAAC, was developed by Southwest Research Institute as a part of consortium effort that includes input from diesel engine manufacturers [<span class="xref">1</span>, <span class="xref">2</span>, <span class="xref">3</span>]. DAAAC is an accelerated aging cycle developed for each application based on the available field data. It includes the exposure from hydrothermal aging, sulfur and lubricant derived poison at accelerated rates. The protocol also requires the entire aftertreatment system to be aged as a complete system, since the upstream components, such as DOC, can impact the chemical makeup of sulfur derived constituents.</div><div class="htmlview paragraph">The protocol does not introduce chemical constituents not normally observed in the field. The accelerated chemical exposure rate is limited only to a degree that has previously demonstrated successful correlation to normal, unaccelerated aging. The Protocol also requires that chemical aging mechanisms are to be introduced and / or consumed in a manner representative of the engine’s defined consumption pathways. Examples include sulfur exposure via high sulfur fuel or gaseous SO<sub>2</sub> and oil consumption via pre-combustion / post-combustion pathways. The Protocol also does not introduce chemical components that are not normally present in oil or fuel (other than doping the fuel with higher concentrations of sulfur, but this amount is relatively small). A comprehensive step by step breakdown of DAAAC protocol is presented elsewhere [<span class="xref">2</span>].</div><div class="htmlview paragraph">The primary objective of this paper is to disseminate the observation of long-term impacts of chemical poisoning and hydrothermal aging on a production aftertreatment catalyst subjected to FUL DAAAC protocol. The results of this experimental campaign were used to develop and validate a model capable of predicting hydrothermal and chemical aging mechanisms of conventional diesel aftertreatment to optimize long term emissions reduction performance. The paper is divided into following sections: <ol class="list nostyle"><li class="list-item"><span class="li-label">1</span><div class="htmlview paragraph">Introduction: An overview of the system</div></li><li class="list-item"><span class="li-label">2</span><div class="htmlview paragraph">Background: A review of literature in the field of diesel AT aging</div></li><li class="list-item"><span class="li-label">3</span><div class="htmlview paragraph">Test Campaign: Description of experimental setup used for collection of both steady state and transient data.</div></li><li class="list-item"><span class="li-label">4</span><div class="htmlview paragraph">Experimental setup: Description of burner stand used for data collection.</div></li><li class="list-item"><span class="li-label">5</span><div class="htmlview paragraph">Results and Discussion: Description of experimental results followed by discussion about underlying degradation mechanism identified through simulation work.</div></li><li class="list-item"><span class="li-label">6</span><div class="htmlview paragraph">Summary and conclusion</div></li></ol></div></div>

<div class="section abstract"><div class="htmlview paragraph">Since Non-Road Mobile Machinery (NRMM) China stage IV legislation has been implemented from 2022, some engines within maximum rated power between 37 to 560 kW are required for gaseous emissions, particulate matter (PM) and particulate number (PN) control, evaluated over testing cycle of Non-Road Transient Cycle (NRTC) and Non-Road Steady Cycle (NRSC). The pollutants from diesel engines, widely used in NRMM applications, can be controlled using aftertreatment systems which are comprised of a diesel oxidation catalyst (DOC) and a diesel particulate filter (DPF), or optionally a selective catalytic reduction (SCR). In this paper, a compact D-DPF design is introduced and discussed on application in harvesters, tractors, and forklifts. Because harvesters have higher exhaust gas temperature than other applications, more passive regeneration behaviors were observed. Subsequently, a compact design of DOC catalyst on DPF (D-DPF) was studied, in other words is to coat DOC catalyst on DPF. For a diesel engine with 3.6 litter(L) displacement application, the total length of D-DPF was shortened around 15% compared to the conventional design of a DOC and a downstream DPF. Meantime, D-DPF design also has higher gaseous emission conversion rate for CO and hydrocarbons (HCs) at high temperature range. The soot loadings can be balanced in the D-DPF system for long time during real operating condition for harvesters’ machinery. By fuel injection upstream of D-DPF, the temperature in the middle of D-DPF can reach 600 °C to actively regenerate the DPF. This type of design of D-DPF is proved to be a very cost-effective solution for NRMM China stage IV application with real operation condition and relevant testing data.</div></div>

Experimental study on the particulate matter and nitrogenous compounds from diesel engine retrofitted with DOC+CDPF+SCR

Real-time particulate emissions rates from active and passive heavy-duty diesel particulate filter regeneration

This paper presents a control-oriented model describing the dynamics of oxygen concentration through a Diesel engine aftertreatment system that includes a Diesel oxidation catalyst (DOC) and a Diesel particulate filter (DPF). Exhaust gas oxygen concentration is important for catalysts such as NOx conversion efficiencies of selective catalytic reduction (SCR) systems and lean NOx traps (LNT). In the presence of low-pressure loop exhaust gas recirculation (EGR), the exhaust gas oxygen concentration after-DPF also influences combustion. Due to the chemical reactions occurring inside DOC and DPF, the exhaust gas oxygen concentration considerably varies through the aftertreatment systems. Directly measuring the exhaust gas oxygen concentrations at different locations through the exhaust gas aftertreatment system is costly and unreliable. A dynamic model is thus needed in order to design model-based observers to estimate the exhaust gas oxygen concentrations at various locations. The oxygen-related reactions within a DOC and a DPF are investigated in this study. A lumped-parameter, control-oriented DOC-DPF oxygen concentration dynamic model was developed by a multi-objective optimization method and validated with experimental data obtained on a medium-duty Diesel engine equipped with full aftertreatment systems. Experimental results show that the model can well capture the oxygen dynamics across the Diesel engine aftertreatment systems.

The successful utilization of a diesel particulate filter (DPF) to reduce particulate matter (PM) in a passenger car diesel engine necessitates a periodic regeneration of the DPF catalyst without deterioration of the drivability and emission control performance. For successful active DPF regeneration, the exhaust gas temperature should be over 500 °C to oxidize the soot loaded in the DPF. Previous research increased the exhaust gas temperature by applying early and late post fuel injection with a look-up table (LUT) based feedforward control implemented into the engine management system (EMS). However, this method requires enormous calibration work to find the optimal timing and quantity of the main, early, and late post fuel injection with less certainty of accurate torque control. To address this issue, we propose a cylinder pressure based multiple fuel injection (MFI) control method for active DPF regeneration. The feedback control of the indicated mean effective pressure (IMEP), lambda, and DPF upstream temperature was applied to precisely control the injection quantity of the main, early, and late post fuel injection. To determine their fuel injection timings, a mass fraction burned 60% after location of the rate of heat release maximum (MFB60aLoROHRmax) was proposed based on the cylinder pressure information. The proposed control method was implemented in an in-house EMS and validated at several engine operating conditions. During the regeneration period, the exhaust gas temperature tracked the desired temperature, and the engine torque fluctuation was minimized with minimal PM and NOx emissions.

The objective of this program was to explore a combination of advanced injection control and urea-selective catalytic reduction (SCR) to reduce the emissions of oxides of nitrogen (NOx) and particulate matter (PM) from a Tier 2 off-highway diesel engine to Tier 3 emission targets while maintaining fuel efficiency. The engine used in this investigation was a 2004 4.5L John Deere PowerTechTM; this engine was not equipped with exhaust gas recirculation (EGR). Under the original CRADA, the principal objective was to assess whether Tier 3 PM emission targets could be met solely by increasing the rail pressure. Although high rail pressure will lower the total PM emissions, it has a contrary effect to raise NOx emissions. To address this effect, a urea-SCR system was used to determine whether the enhanced NOx levels, associated with high rail pressure, could be reduced to Tier 3 levels. A key attraction for this approach is that it eliminates the need for a Diesel particulate filter (DPF) to remove PM emissions. The original CRADA effort was also performed using No.2 Diesel fuel having a maximum sulfur level of 500 ppm. After a few years, the CRADA scope was expanded to include exploration of advanced injection strategies to improve catalyst regeneration and to explore the influence of urea-SCR on PM formation. During this period the emission targets also shifted to meeting more stringent Tier 4 emissions for NOx and PM, and the fuel type was changed to ultra-low sulfur Diesel (ULSD) having a maximum sulfur concentration of 15 ppm. New discoveries were made regarding PM formation at high rail pressures and the influences of oxidation catalysts and urea-SCR catalysts. These results are expected to provide a pathway for lower PM and NOx emissions for both off- and on-highway applications. Industrial in-kind support was available throughout the project period. Review of the research results were carried out on a regular basis (annual reports and meetings) followed by suggestions for improvement in ongoing work and direction for future work. A significant portion of the industrial support was in the form of experimentation, data analysis, data exchange, and technical consultation.

Multi-catalytic soot filtration in automotive and marine applications

Diesel Particulate Filters (DPFs) are regarded as the most effective technology to reduce particulate matter (PM) emissions from modern diesel engines. PM mass collected inside the filter needs to be periodically oxidized to clean the porous walls in order to avoid excessive backpressure that could negatively affect engine and turbocharger performances leading to higher fuel consumption. Diesel Oxidation Catalysts (DOCs), on the other hand, represent an effective means to reduce hydrocarbon (HC) emissions and set the proper chemical conditions at the inlet of the DPF to enhance soot oxidation during filter regeneration. Due to the impact that these devices have on tailpipe emissions, monitoring functions aimed at assessing the health of these systems need to be implemented in the engine on-board diagnostics (OBD) system. Further, in-depth understanding of filtration and regeneration mechanisms, together with the ability of predicting actual DPF loading conditions, could play a key role in optimizing regeneration strategies adopted to keep the particulate filter within safe operating conditions. Hence, the use of real-time, yet accurate models is of primary importance to face with advanced control challenges, such as the integration of DOCs and DPFs with the engine or other critical aftertreatment components, or to properly develop model-based OBD monitors.;This study aims at addressing the challenges related with real-time modeling of both DOCs and DPFs with special regard to the calibration of key parameters. At first, the development of a 1-D model for the diesel oxidation catalyst is presented;: two different approaches representing two different trade-offs in terms of model complexity/speed are discussed and analyzed. A 1-D model of a DPF is then presented, addressing the coupling of filtration and regeneration over cake, washcoat and wall thicknesses. Moreover, the approach followed to develop the DPF model is innovative as it is directly integrated via analytical functions, thus improving the discretized approach used in similar models. Finally, an innovative model tuning methodology called "Virtual Conditioning" is presented and applied to generate robust model calibrations.;Numerical results are compared with experimental data gathered at West Virginia University's (WVU) Engine and Emissions Research Laboratory (EERL) using a Mack heavy-duty diesel engine coupled to a Johnson Matthey C-CRT aftertreatment system. The study shows that: a) DOC model is capable of predicting outlet emissions concentrations with an accuracy within 15% and minimal computational requirements over both steady-state and transient operating conditions; b) DPF wall and washcoat layer present different regeneration and collection dynamics, whose

<div class="htmlview paragraph">The tightening legislation in the on-road heavy-duty diesel area means that pollution control systems will soon be widely introduced on such engines. A number of different aftertreatment systems are currently being considered to meet the incoming legislation, including Diesel Particulate Filters (DPF), Diesel Oxidation Catalysts (DOC) and Selective Catalytic Reduction (SCR) systems.</div> <div class="htmlview paragraph">Relatively little is known about the interactions between lubricant-derived species and such aftertreatment systems. This paper describes the results of an experimental program carried out to investigate these interactions within DPF, DOC and SCR systems on a state-of-the-art 9 litre engine.</div> <div class="htmlview paragraph">The influence of lubricant composition and lube oil ash level was investigated on the different catalyst systems. In order to reduce costs and to speed up testing, test oil was dosed into the fuel. Tests without dosing lubricant into the fuel were also run.</div> <div class="htmlview paragraph">Driving distances of up to 115,000 km (based on oil consumption) were simulated in these experiments. Following such treatments, no significant change in the activity of the CR-DPF oxidation catalyst, Diesel Oxidation Catalysts or SCR catalysts were observed. In each case, the distribution of oil-derived species was studied as a function of distance down the catalyst. It was found that the Ca, Zn and P were generally present in higher concentrations at the front of the catalyst, decreasing down the unit. In contrast, sulfur is distributed evenly throughout the length of each catalyst. This is because sulfur can be deposited from the gas phase and is more mobile on the catalyst surface.</div> <div class="htmlview paragraph">Interestingly, when doping high ash oil into the fuel it was found that the back pressure of the DPF system increased rapidly. This is particularly important since it is known that used engine oil is sometimes poured back into the fuel tank for disposal. These results imply that this practice may strongly affect the efficiency of DPF devices.</div> <div class="htmlview paragraph">This rapid increase in back pressure is a consequence of doping the fuel with the high ash oil, since operation of the engine with the high ash oil without doping, or with a low ash oil with doping, resulted in only a gradual increase in back pressure. In addition, the distribution of the ash in the filter was strongly affected when doping the high ash oil into the fuel, in that the ash was uniformly distributed down the length of the filter. In the other experiments carried out here, and in measurements of field-aged filters, the ash thickness increases with distance into the filter. These observations reveal that care needs to be taken when doping oil into the fuel to accelerate the observation of oil-derived effects in DPF systems.</div>