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Technical Paper

Phenomenological Investigations of Mid-Channel Ash Deposit Formation and Characteristics in Diesel Particulate Filters

Accumulation of lubricant and fuel derived ash in the diesel particulate filter (DPF) during vehicle operation results in a significant increase of pressure drop across the after-treatment system leading to loss of fuel economy and reduced soot storage capacity over time. Under certain operating conditions, the accumulated ash and/or soot cake layer can collapse resulting in ash deposits upstream from the typical ash plug section, henceforth termed mid-channel ash deposits. In addition, ash particles can bond (either physically or chemically) with neighboring particles resulting in formation of bridges across the channels that effectively block access to the remainder of the channel for the incoming exhaust gas stream. This phenomenon creates serious long-term durability issues for the DPF, which often must be replaced. Mid-channel deposits and ash bridges are extremely difficult to remove from the channels as they often sinter to the substrate.
Technical Paper

Polycyclic Aromatic Hydrocarbons in Diesel Engine Exhaust Both with and without Aftertreatment

Since the conception of the internal combustion engine, smoky and ill-smelling exhaust was prevalent. Over the last century, significant improvements have been made in improving combustion and in treating the exhaust to reduce these effects. One group of compounds typically found in exhaust, polycyclic aromatic hydrocarbons (PAH), usually occurs at very low concentrations in diesel engine exhaust. Some of these compounds are considered carcinogenic, and most are considered hazardous air pollutants (HAP). Many methods have been developed for sampling, handling, and analyzing PAH. For this study, an improved method for dilute exhaust sampling was selected for sampling the PAH in diesel engine exhaust. This sampling method was used during transient engine operation both with and without aftertreatment to show the effect of aftertreatment.
Technical Paper

Comparison of Accelerated Ash Loading Methods for Gasoline Particulate Filters

Recent legislation enacted for the European Union (EU) and the United States calls for a substantial reduction in particulate mass (and number in the EU) emissions from gasoline spark-ignited vehicles. The most prominent technology being evaluated to reduce particulate emissions from a gasoline vehicle is a wall flow filter known as a gasoline particulate filter (GPF). Similar in nature to a diesel particulate filter (DPF), the GPF will trap and store particulate emissions from the engine, and oxidize said particulate with frequent regeneration events. The GPF will also collect ash particles in the wall flow substrate, which are metallic components that cannot be oxidized into gaseous components. Due to high temperature operation and frequent regeneration of the GPF, the impact of ash on the GPF has the potential to be substantially different from the impact of ash on the DPF.
Technical Paper

Cylinder Deactivation for Increased Engine Efficiency and Aftertreatment Thermal Management in Diesel Engines

Diesel engine cylinder deactivation (CDA) can be used to reduce petroleum consumption and greenhouse gas (GHG) emissions of the global freight transportation system. Heavy duty trucks require complex exhaust aftertreatment (A/T) in order to meet stringent emission regulations. Efficient reduction of engine-out emissions require a certain A/T system temperature range, which is achieved by thermal management via control of engine exhaust flow and temperature. Fuel efficient thermal management is a significant challenge, particularly during cold start, extended idle, urban driving, and vehicle operation in cold ambient conditions. CDA results in airflow reductions at low loads. Airflow reductions generally result in higher exhaust gas temperatures and lower exhaust flow rates, which are beneficial for maintaining already elevated component temperatures. Airflow reductions also reduce pumping work, which improves fuel efficiency.
Technical Paper

Dilute Measurement of Semi-Volatile Organic Compounds (SVOC) from a Heavy-Duty Diesel Engine

Semi-volatile organic compounds (SVOC) are a group of compounds in engine exhaust that either form during combustion or are part of the fuel and lubricating oil. Since these compounds occur at very low concentrations in diesel engine exhaust, the methods for sampling, handling, and analyzing these compounds are critical to obtaining good results. An improved dilute exhaust sampling method was used for sampling and analyzing SVOC in engine exhaust, and this method was performed during transient engine operation. A total of 22 different SVOC were measured using a 2012 medium-duty diesel engine. This engine was equipped with a stock diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and a selective catalytic reduction (SCR) catalyst in series. Exhaust concentrations for SVOC were compared both with and without exhaust aftertreatment. Concentrations for the engine-out SVOC were significantly higher than with the aftertreatment present.
Technical Paper

Axial NO2 Utilization Measurements within a Partial Flow Filter during Passive Regeneration

Measuring axial exhaust species concentration distributions within a wall-flow aftertreatment device provides unique and significant insights regarding the performance of complex devices like the SCR-on-filter. In this particular study, a less complex aftertreatment configuration which includes a DOC followed by two uncoated partial flow filters (PFF) was used to demonstrate the potential and challenges. The PFF design in this study was a particulate filter with alternating open and plugged channels. A SpaciMS [1] instrument was used to measure the axial NO2 profiles within adjacent open and plugged channels of each filter element during an extended passive regeneration event using a full-scale engine and catalyst system. By estimating the mass flow through the open and plugged channels, the axial soot load profile history could be assessed.
Journal Article

Extension of Analytical Methods for Detailed Characterization of Advanced Combustion Engine Emissions

Advanced combustion strategies used to improve efficiency, emissions, and performance in internal combustion engines (IC) alter the chemical composition of engine-out emissions. The characterization of exhaust chemistry from advanced IC engines requires an analytical system capable of measuring a wide range of compounds. For many years, the widely accepted Coordinating Research Council (CRC) Auto/Oil procedure[1,2] has been used to quantify hydrocarbon compounds between C1 and C12 from dilute engine exhaust in Tedlar polyvinyl fluoride (PVF) bags. Hydrocarbons greater than C12+ present the greatest challenge for identification in diesel exhaust. Above C12, PVF bags risk losing the higher molecular weight compounds due to adsorption to the walls of the bag or by condensation of the heavier compounds. This paper describes two specialized exhaust gas sampling and analytical systems capable of analyzing the mid-range (C10 - C24) and the high range (C24+) hydrocarbon in exhaust.
Technical Paper

Demonstration of a Novel, Off Road, Diesel Combustion Concept

There are numerous off-road diesel engine applications. In some applications there is more focus on metrics such as initial cost, packaging and transient response and less emphasis on fuel economy. In this paper a combustion concept is presented that may be well suited to these applications. The novel combustion concept operates in two distinct operation modes: lean operation at light engine loads and stoichiometric operation at intermediate and high engine loads. One advantage to the two mode approach is the ability to simplify the aftertreatment and reduce cost. The simplified aftertreatment system utilizes a non-catalyzed diesel particulate filter (DPF) and a relatively small lean NOx trap (LNT). Under stoichiometric operation the LNT has the ability to act as a three way catalyst (TWC) for excellent control of hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx).
Journal Article

Solid Particle Emissions from Vehicle Exhaust during Engine Start-Up

Human exposure to vehicle exhaust during engine start-up can be encountered on a daily basis in parking lots, home garages, and vehicle stop/star traffic environment. This work is the first pilot study to characterize solid particle number and size distribution during engine start-up using various light-duty vehicles with different technology engines. A total of 84 vehicles were tested in this pilot study, consisting of post-2007 diesel engines equipped with high efficiency diesel particulate filters (DPFs) as well as modern gasoline port fuel injected (PFI) and gasoline direct injected (GDI) engines equipped with three-way-catalysts (TWCs). Particle concentration from DPF equipped diesel engines were found to be the lowest, while GDI and 8-cylinder PFI engines had the highest particle emissions.
Journal Article

Analytic Solution for the Flow Distribution and Pressure Drop of Ceramic Partially-Plugged Wall Flow Diesel Particulate Filters

A 1-dimensional analytic solution has been developed to evaluate the pressure drop and filtration performance of ceramic wall-flow partial diesel particulate filters (PFs). An axially resolved mathematical model for the static pressure and velocity profiles prevailing inside wall-flow filters, with such unique plugging configurations, is being proposed for the first time. So far, the PF models that have been developed are either iterative/numerical in nature [1], or based on commercial CFD packages [7]. In comparison, an analytic solution approach is a transparent and computationally inexpensive tool that is capable of accurately predicting trends as well as, offering explanations to fundamental performance behavior. The simple mathematical expressions that have been obtained facilitate rational decision-making when designing partial filters, and could also reduce the complexity of OBD logic necessary to control onboard filter performance.
Technical Paper

Development of the Methodology for Quantifying the 3D PM Distribution in a Catalyzed Particulate Filter with a Terahertz Wave Scanner

Optimizing the performance of the aftertreatment system used on heavy duty diesel engines requires a thorough understanding of the operational characteristics of the individual components. Within this, understanding the performance of the catalyzed particulate filter (CPF), and the development of an accurate CPF model, requires knowledge of the particulate matter (PM) distribution throughout the substrate. Experimental measurements of the PM distribution provide the detailed interactions of PM loading, passive oxidation, and active regeneration. Recently, a terahertz wave scanner has been developed that can non-destructively measure the three dimensional (3D) PM distribution. To enable quantitative comparisons of the PM distributions collected under different operational conditions, it is beneficial if the results can be discussed in terms of the axial, radial, and angular directions.
Technical Paper

Development and Demonstration of a Soot Generator Integrated Bench Reactor

Experimental evaluation of soot trapping and oxidation behaviors of various diesel particulate filters (DPF) has been traditionally hampered by several experimental difficulties, such as the deposition of soot particles with well-characterized and consistent properties, and the tracking of the soot oxidation rate in real time. In the present study, an integrated bench flow-reactor system with a soot generator has been developed and its capabilities were demonstrated with regards to: Consistently and controllably loading soot on DPF samples; Monitoring the exhaust gas composition by FTIR, including quantification of the soot oxidation rate using CO and CO2; Measuring soot oxidation characteristics of various DPF samples. Soot particles were produced from a laminar propane co-flow diffusion flame.
Journal Article

Compression Brake Noise with DPF and SCR

Compression brake noise (also known as “Jake Brake” noise) has been a significant issue for heavy duty trucks for several decades. As a result of compression brake noise, there are many local ordinances in North America banning the use of engine brakes, and some countries such as Australia and South Africa have in the past considered total bans on compression brakes. Previous research showed that the primary problem is caused by operators who remove the OEM muffler system and replace it with a “straight stack” exhaust pipe with no sound reducing properties. On the other hand, even with the OEM exhaust system in place, compression brake noise is sometimes significant. The introduction of exhaust aftertreatment to meet stringent 2010 EPA emissions requirements (diesel particulate filters and selective catalytic reduction systems, DPF + SCR) provides two potential benefits for compression brake noise.
Journal Article

Diesel Cold-Start Emission Control Research for 2015-2025 LEV III Emissions

The diesel engine can be an effective solution to meet future greenhouse gas and fuel economy standards, especially for larger segment vehicles. However, a key challenge facing the diesel is the upcoming LEV III emissions standard which will require significant reductions of hydrocarbon (HC) and oxides of nitrogen (NOx) from current levels. The challenge stems from the fact that diesel exhaust temperatures are much lower than gasoline engines so the time required to achieve effective emissions control with current aftertreatment devices is considerably longer. The objective of this study was to determine the potential of a novel diesel cold-start emissions control strategy for achieving LEV III emissions. The strategy combines several technologies to reduce HC and NOx emissions before the start of the second hill of the FTP75.
Journal Article

Measurement of Dioxin and Furan Emissions during Transient and Multi-Mode Engine Operation

This study analyzed the impact of transient and multi-mode engine conditions on emissions of dioxins and furans from a variety of diesel aftertreatment configurations. Exhaust aftertreatment systems included combinations of diesel oxidation catalyst, diesel particulate filter, and either Cu/zeolite or Fe/zeolite selective catalytic reduction catalyst. EPA method TO-9A was modified for proportional exhaust gas sampling, whereas EPA method 0023A was modified for raw exhaust gas sampling. Dioxin and furan emissions were first measured with modified method TO-9A during Federal Test Procedure transient cycles, but no toxic dioxins or furans were detected. Measurements were then taken with modified method 0023A during Ramped Mode Cycles-Supplemental Emissions Test experiments. Because more rigorous pre-cleaning and sample extraction procedures were used with this method and lower detection limits were achieved by the analytical laboratory, some dioxin and furan congeners were detected.
Technical Paper

Decoupling the Interactions of Hydrocarbons and Oxides of Nitrogen Over Diesel Oxidation Catalysts

Oxidation of NO to NO₂ over a Diesel Oxidation Catalyst (DOC) plays an important role in different types of aftertreatment systems, by enhancing NOx storage on adsorber catalysts, improving the NOx reduction efficiency of SCR catalysts, and enabling the passive regeneration of Diesel Particulate Filters (DPF). The presence of hydrocarbon (HC) species in the exhaust is known to affect the NO oxidation performance over a DOC; however, specific details of this effect, including its underlying mechanism, remain poorly understood. Two major pathways are commonly considered to be responsible for the overall effect: NO oxidation inhibition, due to the presence of HC, and the consumption of the NO₂ produced by reaction with hydrocarbons. In this work we have attempted to decouple these two pathways, by adjusting the catalyst inlet concentrations of NO and NO₂ to the thermodynamic equilibrium levels and measuring the composition changes over the catalyst in the presence of HC species.
Technical Paper

A Test Method for Evaluating Feasibility of Lean Nitrous Oxide Traps

The Lean NOx Trap (LNT) is a technology that could be used to reduce oxides of nitrogen from heavy-duty diesel engines to meet emissions standards (US 2010 and EURO 4/5/6). This paper describes a case-study for evaluating the feasibility of an LNT. LNTs suffer from sulfur poisoning and thermal aging limitations. Catalyst formulations allow reversal of sulfur poisoning through desulfation procedures. A case study was performed using a 7-liter diesel engine equipped with VGT, common rail fuel injection system, cooled EGR, oxidation catalyst and DPF. The LNT was positioned after the particulate filter. Gaseous raw emissions were measured from engine and various stages of aftertreatment. A Fourier Transform Infrared (FTIR) analyzer was used to characterize Ammonia and SO₂. Temperatures were measured in the substrate. Fast response NOx sensor allowed for continuous monitoring of the NOx in the LNT. A wide-range O₂ sensor was also utilized to measure equivalence ratio.
Journal Article

Meeting the US Heavy-Duty EPA 2010 Standards and Providing Increased Value for the Customer

The paper will discuss the design and development of heavy-duty diesel engines to meet the US EPA 2010 on-highway standards - 0.2 g/HP-hr NOx and 0.01 g/HP-hr particulate matter (PM). In meeting these standards a combination of in-cylinder control and aftertreatment control for both NOx and particulate has been used. For NOx control, a combination of cooled exhaust gas recirculation (EGR) and selective catalytic reduction (SCR) is used. The SCR catalyst uses copper zeolite to achieve high levels of NOx conversion efficiency with minimal ammonia slip and unparalleled thermal durability. For particulate control, a diesel particulate filter (DPF) with upstream oxidation catalyst (DOC) is used. While the DPF may be actively regenerated when required, it operates predominantly with passive regeneration - enabled by the high NOx levels between the engine and the DPF, associated with high efficiency SCR systems and NO₂ production across the DOC.
Technical Paper

Dependence of Fuel Consumption on Engine Backpressure Generated by a DPF

In recent years, Diesel Particulate Filter (DPF) systems have become the state-of-the-art technology to realize low particulate emission for light, medium or heavy-duty diesel vehicles. In addition to good filtration efficiency and thermo-mechanical robustness, the engine backpressure resulted from the DPF installation is an important parameter which directly impacts the fuel economy of the engine. The goal of this experimental test series was to determine the dependence of fuel consumption on engine backpressure resulted from a DPF installed on a heavy-duty application. The testing was executed on a MY2003 Volvo D12 heavy-duty diesel engine in an engine test cell at Southwest Research Institute (SwRI). Empty DPF cans were used with an exhaust valve to mimic the post turbo pressure levels for two different types of DPF materials at nine selected engine operating points of the European Stationary Cycle (ESC).
Technical Paper

Portable Emissions Measurement for Retrofit Applications – The Beijing Bus Retrofit Experience

In 2005, the United States Environmental Protection Agency (EPA) and Southwest Research Institute (SwRI) embarked on a mission to help the city of Beijing, China, clean its air. Working with the Beijing Environmental Protection Bureau (BEPB), the effort was a pilot diesel retrofit demonstration program involving three basic retrofit technologies to reduce particulate matter (PM). The three basic technologies were the diesel oxidation catalyst (DOC), the flowthrough diesel particulate filter (FT-DPF), and the wallflow diesel particulate filter (WF-DPF). The specific retrofit systems selected for the project were verified through the California Air Resources Board (CARB) or the EPA verification protocol [1]. These technologies are generally verified for PM reductions of 20-40 percent for DOCs, 40-50 percent for the FT-DPF, and 85 percent or more for the high efficiency WF-DPF.