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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.

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.

Exposure of hydrocarbons (HCs) and particulate matter (PM) under certain real-world operating conditions leads to carbonaceous deposit formation on V-SCR catalysts and causes reversible degradation of its NOx conversion. In addition, uncontrolled oxidation of such carbonaceous deposits can also cause the exotherm that can irreversibly degrade V-SCR catalyst performance. Therefore carbonaceous deposit mitigation strategies, based on their characterization, are needed to minimize their impact on performance. The nature and the amount of the deposits, formed upon exposure to real-world conditions, were primarily carried out by the controlled oxidation of the deposits to classify these carbonaceous deposits into three major classes of species: i) HCs, ii) coke, and iii) soot. The reversible NOx conversion degradation can be largely correlated to coke, a major constituent of the deposit, and to soot which causes face-plugging that leads to decreased catalyst accessibility.

Regeneration of diesel particulate filters poses major challenges in developing the particulate matter emission control technology to meet EPA 2007/2010 emissions regulations. The problem areas are multifold due to the complexity involved in designing the filter system, developing regeneration strategies and controlling the regeneration process. This paper discusses the need for active regeneration systems. It also addresses several key limitations and trade-offs between the regeneration strategy, chemical kinetics, exhaust gas temperature and the regeneration efficiency. Passive regeneration of diesel particulate filter systems is known to be highly dependent on the engine-out [NOx/PM] ratio as well as exhaust temperature over the duty cycle. Using catalytic oxidation of auxiliary fuel injected into the system, the exhaust gas temperature can be successfully enhanced for filter regeneration.

Real-world operation of diesel oxidation catalysts (DOCs), used in a variety of aftertreatment systems, subjects these catalysts to a large number of permanent and temporary deactivation mechanisms. These include thermal damage, induced by generating exotherm on the catalyst; exposure to various inorganic species contained in engine fluids; and the effects of soot and hydrocarbons, which can mask the catalyst in certain operating modes. While some of these deactivation mechanisms can be accurately simulated in the lab, others are specific to particular engine operation regimes. In this work, a set of DOCs, removed from prolonged service in the field, has been subjected to a detailed laboratory study. Samples obtained from various locations in these catalysts were used to characterize the extent and distribution of deactivation.

Changing diesel engine emission requirements for 2002 have led many diesel engine manufacturers to incorporate cooled Exhaust Gas Recirculation, EGR, as a means of reducing NOx. This has resulted in higher levels of soot being present in used oils. This paper builds on earlier work with fresh oils and describes a study of the effect of highly sooted oils on the low temperature pumpability in diesel engines. Four experimental diesel engine oils, of varying MRV TP-1 viscosities, were run in a Mack T-8 engine to obtain a soot level ranging between 6.1 and 6.6%. These sooted oils were then run in a Cummins M11 engine installed in a low temperature cell. Times to lubricate critical engine components were measured at temperatures ranging between -10 °C and -25 °C. A clear correlation was established between the MRV TP-1 viscosity of a sooted oil and the time needed to lubricate critical engine components at a given test temperature.

Advanced flow-reactor capabilities created at Cummins were applied to the study of the diesel particulate matter (soot) oxidation process. This approach complemented the on-engine studies with a number of important features, including accurate control of gas composition and soot layer temperature. Using the developed methodology for quantitative soot oxidation studies in a broad range of temperatures (200-700°C), an initial set of experiments was performed to compare the behavior of the real and model soot samples under the identical conditions (10%vol. of O2, 0-15%vol. of H2O). It was found that presence of H2O vapor synergistically enhances the rate of oxidation by O2 of the diesel soot sample. However, the behavior of the model soot sample (carbon black) was virtually not affected by H2O. Kinetic analysis of the obtained results revealed an unusual type of behavior, with the activation energy of soot oxidation increasing in the course of the experiment.

Cummins Westport Inc. (CWI) released for production the latest version of its C8.3G natural gas engine, the C Gas Plus, in July 2001. This engine has increased ratings for horsepower and torque, a full-authority engine controller, wide tolerance to natural gas fuel (the minimum methane number is 65), and improved diagnostics capability. The C Gas Plus also meets the California Air Resources Board optional low-NOx (2.0 g/bhp-h) emission standard for automotive and urban buses. Two pre-production C Gas Plus engines were operated in a Viking Freight fleet for 12 months as part of the U.S. Department of Energy's Fuels Utilization Program. In-use exhaust emissions, fuel economy, and fuel cost were collected and compared with similar 1997 Cummins C8.3 diesel tractors. CWI and the West Virginia University developed an ad-hoc test cycle to simulate the Viking Freight fleet duty cycle from in-service data collected with data loggers.

Diesel engines are far more efficient than gasoline engines of comparable size, and emit less greenhouse gases that have been implicated in global warming. In 2000, the US EPA proposed very stringent emissions standards to be introduced in 2007 along with low sulfur (< 15 ppm) diesel fuel. The California Air Resource Board (CARB) has also established the principle that future diesel fueled vehicles should meet the same low emissions standards as gasoline fueled vehicles and the EPA followed suit with its Tier II emissions regulation. Achieving such low emissions cannot be done through engine development and fuel reformulation alone, and requires application of NOx and particulate matter (PM) aftertreatment control devices. There is a widespread consensus that NOx adsorbers and particulate filter are required in order for diesel engines to meet the 2007 emissions regulations for NOx and PM. In this paper, the key exhaust characteristics from an advanced diesel engine are reviewed.

Several complementary experimental techniques were applied to investigate kinetics of diesel soot oxidation by O2 in an attempt to provide accurate data for modeling of the Diesel Particulate Filters regeneration process. For two diesel soot samples with measurably different properties, it was shown that the complexity of their overall kinetic behavior was due to an initial period of rapidly changing reactivity. This initial high reactivity was understood not to be related to the SOF, and was quantitatively correlated to the extent of soot pre-oxidation. This initial reactivity can affect the averaged apparent kinetic parameters, for example resulting in the lower apparent activation energy values. After the initial soot pre-oxidation, which consumed ∼10-25% of carbon, the remaining soot was behaving very uniformly, producing linear Arrhenius plots in a remarkably broad range of temperatures (330-610°C) and integral conversions (up to 90%).

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.

Production PM sensors are now available and are likely to be key components of PM aftertreatment systems designed to meet 2013 OBD requirements. In this paper a highly simplified analysis is used to give insight into the sensor response of resistive-based devices, and to motivate possible diagnostic strategies. The method has been applied to successive sets of FTP data recorded with DPF's of different failure levels, and despite the very approximate nature of the underlying model, the method appears to discriminate reliably between them.

The modern diesel engine is used around the world to power applications as diverse as passenger cars, heavy-duty trucks, electrical power generators, ships, locomotives, agricultural and industrial equipment. The success of the diesel engine results from its unique combination of fuel economy, durability, reliability and affordability - which drive the lowest total cost of ownership. The diesel engine has been developed to meet the most demanding on-highway emission standards, through the introduction of advanced technologies such as: electronic controls, high pressure fuel injection, and cooled exhaust gas recirculation. The standards to be introduced in the U.S. in 2007 will see the introduction of the Clean Diesel which will achieve near-zero NOx and particulate emissions, while retaining the customer values outlined above.

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.

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.

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.

Biodiesel is a promising alternative to traditional diesel fuel due to its similar combustion properties to diesel and lower carbon emissions on a well-to-wheel basis. However, combusting biodiesel still generates hydrocarbon (HC), CO, NOx and particulate matter (PM) emissions, similar to those from traditional diesel fuel usage. Therefore, aftertreatment systems will be required to reduce these emissions to meet increasingly stringent emission regulations to minimize the impact to the environment. Diesel oxidation catalysts (DOC) are widely used in modern aftertreatment systems to convert unburned HC and CO, to partially convert NO to NO2 to enhance downstream selective catalytic reaction (SCR) catalyst efficiency via fast SCR and to periodically clean-up DPF via controlled soot oxidation. In this work, we focus on the performance difference between biodiesel and diesel over a commercial DOC catalyst to identify the knowledge gap during the transition from diesel fuel to biodiesel.