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The temporary deactivation of the selective catalytic reduction (SCR) device due to malfunction requires the engine control to engage multiple engine-out calibrations. Further, it is expected that emitted particles will be different in composition, size and morphology when an engine, which meets the 2010 particulate matter (PM) gravimetric limits, is programmed with multiple maps. This study investigated the correlation between SCR-out/engine-out PM emissions from an 11-liter Volvo engine. Measurement of PM concentrations and size distributions were conducted under steady state and transient cycles. Ion Chromatograph analysis on gravimetric filters at the SCR-out has revealed the presence of sulfates. Two different PM size-distributions were generated over a single engine test mode in the accumulation mode region with the aid of a design of experiment (DOE) tool. The SCR-out PM size distributions were found to correlate with the two engine-out distributions.

For engine operations involving low load conditions for an extended amount of time, the exhaust temperature may be lower than that necessary to initiate the urea hydrolyzation. This would necessitate that the controller interrupt the urea supply to prevent catalyst fouling by products of ammonia decomposition. Therefore, it is necessary for the engine controller to have multiple calibrations available in regions of engine operation where the aftertreatment does not perform well, so that optimal exhaust conditions are guaranteed during the wide variety of engine operations. In this study the test engine was equipped with a catalyzed diesel particulate filter (DPF) and a selective catalytic reduction system (SCR), and programmed with two different engine calibrations, namely the low-NOx and the low fuel consumption (low-FC).

Particulate emission control from diesel engines is one of the major concerns in the urban areas in California. Recently, regulations have been proposed for stringent PM emission requirements from both existing and new diesel engines. As a result, particulate emission control from urban diesel engines using advanced particulate filter technology is being evaluated at several locations in California. Although ceramic based particle filters are well known for high PM reductions, the lack of effective and durable regeneration system has limited their applications. The continuously regenerated diesel particulate filter (CRDPF) technology discussed in this presentation, solves this problem by catalytically oxidizing NO present in the diesel exhaust to NO2 which is utilized to continuously combust the engine soot under the typical diesel engine operating condition.

A program has been completed to evaluate ultra-low sulfur diesel fuels and passive diesel particulate filters (DPFs) in truck and bus fleets operating in southern California. The fuels, ECD and ECD-1, are produced by ARCO (a BP Company) and have less than 15 ppm sulfur content. Vehicles were retrofitted with two types of catalyzed DPFs, and operated on ultra-low sulfur diesel fuel for over one year. Exhaust emissions, fuel economy and operating cost data were collected for the test vehicles, and compared with baseline control vehicles. Regulated emissions are presented from two rounds of tests. The first round emissions tests were conducted shortly after the vehicles were retrofitted with the DPFs. The second round emissions tests were conducted following approximately one year of operation. Several of the vehicles retrofitted with DPFs accumulated well over 100,000 miles of operation between test rounds.

Diesel Particulate Filters (DPFs) are well assessed exhaust aftertreatment devices currently equipping almost every modern diesel engine to comply with the most stringent emission standards. However, an accurate estimation of soot content (loading) is critical to managing the regeneration of DPFs in order to attain optimal behavior of the whole engine-after-treatment assembly, and minimize fuel consumption. Real-time models can be used to address challenges posed by advanced control systems, such as the integration of the DPF with the engine or other critical aftertreatment components or to develop model-based OBD sensors. One of the major hurdles in such applications is the accurate estimation of engine Particulate Matter (PM) emissions as a function of time. Such data would be required as input data for any kind of accurate models. The most accurate way consists of employing soot sensors to gather the real transient soot emissions signal, which will serve as an input to the model.

In order to comply with stringent 2010 US-Environmental Protection Agency (EPA) on-road, Heavy-Duty Diesel (HDD) emissions regulations, the Selective Catalytic Reduction (SCR) aftertreatment system has been judged by a multitude of engine manufacturers as the primary technology for mitigating emissions of oxides of nitrogen (NOx). As virtually stand-alone aftertreatment systems, SCR technology further represents a very flexible and efficient solution for retrofitting legacy diesel engines as the most straightforward means of cost-effective compliance attainment. However, the addition of a reducing agent injection system as well as the inherent operation limitations of the SCR system due to required catalyst bed temperatures introduce new, unique problems, most notably that of ammonia (NH₃) slip.

Diesel particulate filters (DPFs) are recognized as the most efficient technology for particulate matter (PM) reduction, with filtration efficiencies in excess of 90%. Design guidelines for DPFs typically are: high removal efficiency, low pressure drop, high durability and capacity to resist high temperature excursions during regeneration events. The collected mass inside the trap needs to be periodically oxidized to regenerate the DPF. Thus, an in-depth understanding of filtration and regeneration mechanisms, together with the ability of predicting actual DPF conditions, could play a key role in optimizing the duration and number of regeneration events in case of active DPFs. Thus, the correct estimation of soot loading during operation is imperative for effectively controlling the whole engine-DPF assembly and simultaneously avoidingany system failure due to a malfunctioning DPF. A viable way to solve this problem is to use DPF models.

Stringent emission regulations have forced drastic technological improvements in diesel after treatment systems, particularly in reducing Particulate Matter (PM) emissions. Those improvements generally regard the use of Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF) and lately also the use of Selective Catalyst Reduction (SCR) systems along with improved engine control strategies for reduction of NOx emissions from these engines. Studies that have led to these technological advancements were made in controlled laboratory environment and are not representative of real world emissions from these engines or vehicles. In addition, formation and evolution of PM from these engines are extremely sensitive to overall changes in the dilution process.

Both field research and certification data show that the lean burn natural gas powered spark ignition engines offer particulate matter (PM) reduction with respect to equivalent diesel power plants. Concerns over PM inventory make these engines attractive despite the loss of fuel economy associated with throttled operation. Early versions of the Cummins L-10 natural gas engines employed a mixer to establish air/fuel ratio. Emissions measurements by the West Virginia University Transportable Heavy Duty Emissions Testing Laboratories on Cummins L-10 powered transit buses revealed the potential to offer low emissions of PM and oxides of nitrogen, (NOx) but variations in the mixture could cause emissions of NOx, carbon monoxide and hydrocarbons to rise. This was readily corrected through mixer repair or readjustment. Newer versions of the L-10 engine employ a more sophisticated fueling scheme with feedback control from a wide range oxygen sensor.

Emissions from light duty vehicles have traditionally been measured using a chassis dynamometer, while heavy duty testing has been based on engine dynamometers. However, the need for in-use vehicle emissions data has led to the development of two transportable heavy duty chassis dynamometers capable of testing buses and heavy trucks. A test cycle has been developed for Class 8 trucks, which typically have unsyncronized transmissions. This test cycle has five peaks, each consisting of an acceleration, cruise period, and deceleration, with speeds and acceleration requirements that can be met by virtually all vehicles in common service. Termed the “WVU 5 peak truck test”, this 8 km (5 mile) cycle has been used to evaluate the emissions from diesel and ethanol powered over-the-road tractors and from diesel and ethanol powered snow plows, all with Detroit Diesel 6V92 engines.

The Tapered Element Oscillating Microbalance (TEOM) measures captured particle mass continuously on a small filter held on an oscillating element. In addition to traditional filter-based particulate matter (PM) measurement, a TEOM was used to characterize PM from the dilute exhaust of trucks examined in two phases (Phase 1.5 and Phase 2) of the Coordinating Research Council (CRC) Heavy-Duty Vehicle Emissions Inventory Project E-55/E-59. Test schedules employed were the Heavy Heavy-Duty Diesel Truck (HHDDT) test schedule that consists of four modes (Idle, Creep, Transient and Cruise), the HHDDT Short (HHDDT_S) which represents high-speed freeway operation, and the Heavy-Duty Urban Dynamometer Driving Schedule (UDDS). TEOM results were on average 6% lower than those from traditional particulate filter weighing. Data (in units of g/cycle) were examined by plotting cycle-averaged TEOM mass against filter mass. Regression (R2) values for these plots were from 0.88 to 0.99.

Hybrid diesel electric buses offer the advantage of superior fuel economy through use of regenerative braking and lowered transient emissions by reducing the need of the engine to follow load as closely as in a conventional bus. With the support of the Department of Energy (DOE), five Lockheed Martin-Orion hybrid diesel-electric buses were operated on the West Virginia University Transportable Laboratory in Brooklyn, New York. The buses were exercised through a new cycle, termed the Manhattan cycle, that was representative of today's bus use as well as the accepted Central Business District Cycle and New York Bus Cycle. Emissions data were corrected for the state of charge of the batteries. The emissions can be expressed in units of grams/mile, grams/axle hp-hr and grams/gallon fuel. The role of improved fuel economy in reducing oxides of nitrogen relative to conventional automatic buses is evident in the data.

Specific aspects of a study aimed at developing a microwave assisted regeneration system for diesel particulate traps are discussed. Results from thermal and microwave characteristic studies carried out in the initial phase of the study are reported. The critical parameters that need to be optimized, for achieving controlled regeneration, are microwave preheating time period, regenerative air supply, regenerative air temperature, and soot deposition. Using a 1000 W magnetron, power measurements were made to select the best waveguide configuration for optimized transmission. A six cylinder naturally aspirated, indirect injection diesel engine was retrofitted with a customized exhaust system that included a Corning EX80 (5.66″ × 6.00″) type ceramic particulate trap. An automated exhaust bypass system enabled trap loading and subsequent regeneration with a customized microwave regeneration system. The paper discusses the salient details of both on-line and off-line regeneration setups.

Alternative compression ignition engine fuels are of interest both to reduce emissions and to reduce U.S. petroleum fuel demand. A Malaysian Fischer-Tropsch gas-to-liquid fuel was compared with California #2 diesel by characterizing emissions from over the road Class 8 tractors with Caterpillar 3176 engines, using a chassis dynamometer and full scale dilution tunnel. The 5-Mile route was employed as the test schedule, with a test weight of 42,000 lb. Levels of oxides of nitrogen (NOx) were reduced by an average of 12% and particulate matter (PM) by 25% for the Fischer-Tropsch fuel over the California diesel fuel. Another distillate fuel produced catalytically from Fischer-Tropsch products originally derived from natural gas by Mossgas was also compared with 49-state #2 diesel by characterizing emissions from Detroit Diesel 6V-92 powered transit buses, three of them equipped with catalytic converters and rebuilt engines, and three without.

Emissions from heavy-duty vehicles may be reduced through the introduction of clean diesel formulations, and through the use of catalyzed particulate matter filters that can enjoy increased longevity and performance if ultra-low sulfur diesel is used. Twenty over-the-road tractors with Detroit Diesel Series 60 engines were selected for this study. Five trucks were operated on California (CA) specification diesel (CARB), five were operated on ARCO (now BP Amoco) EC diesel (ECD), five were operated on ARCO ECD with a Johnson-Matthey Continuously Regenerating Technology (CRT) filter and five were operated on ARCO ECD with an Engelhard Diesel Particulate Filter (DPX). The truck emissions were characterized using a transportable chassis dynamometer, full-scale dilution tunnel, research grade gas analyzers and filters for particulate matter (PM) mass collection. Two test schedules, the 5 mile route and the city-suburban (heavy vehicle) route (CSR), were employed.

Fuel economy and regulated emissions were measured from eight forty-foot transit buses operated on petroleum diesel and a “B20” blend of 80% diesel fuel and 20% biodiesel by volume. Use of biodiesel is attractive to displace petroleum fuel and reduce an operation's carbon footprint. Usually it is assumed that biodiesel will also reduce particulate matter (PM) emissions relative to those of petroleum diesel. Model years of the vehicles evaluated were newer 2007-08 Gillig low-floor buses, 2005 Gillig Phantom buses, and a 2002 Gillig Phantom bus. Engine technology represented three different emissions standards, and included buses with OEM diesel particulate filters. Each bus was evaluated using two transient speed-time schedules, the Orange County Transit Authority (OCTA) driving schedule which represents moderate speed urban/suburban operation and the Urban Dynamometer Driving Schedule (UDDS) which represents a mix of suburban and higher speed on-highway operation.

Biodiesel may be derived from either plant or animal sources, and is usually employed as a compression ignition fuel in a blend with petroleum diesel (PD). Emissions differences between vehicles operated on biodiesel blends and on diesel have been published previously, but data do not cover the latest engine technologies. Prior studies have shown that biodiesel offers advantages in reducing particulate matter, with either no advantage or a slight disadvantage for oxides of nitrogen emissions. This paper describes a recent study on the emissions impact of two biodiesel blends B20A, made from 20% animal fat (tallow) biodiesel and 80% PD, and B20B, obtained from 20% soybean biodiesel and 80% PD. These blends used the same PD fuel for blending and were contrasted with the same PD fuel as a reference. The research was conducted on a 2007 medium heavy-duty diesel truck (MHDDT), with an engine equipped with Exhaust Gas Recirculation (EGR) and a Diesel Particulate Filter (DPF).

Although diesel engines still power most of the heavy-duty transit buses in the United States, many major cities are also operating fleets where a significant percentage of buses is powered by lean-burn natural gas engines. Emissions from these buses are often expressed in distance-specific units of grams per mile (g/mile) or grams per kilometer (g/km), but the driving cycle or route employed during emissions measurement has a strong influence on the reported results. A driving cycle that demands less energy per unit distance than others results in higher fuel economy and lower distance-specific oxides of nitrogen emissions. In addition to energy per unit distance, the degree to which the driving cycle is transient in nature can also affect emissions.