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Similar to single-brick SCR architectures, the multi-brick SCR systems described in this paper require urea injection control software that meets the NOx conversion performance target while maintaining the tailpipe NH3 slip below a given threshold, under all driving conditions. The SCR architectures containing a close-coupled SCRoF and underfloor SCR are temperature-wise more favorable than the under-floor location and lead to significant improvement of the global NOx conversion, compared to a single-brick system. But in order to maximize the benefit of close-coupling, the urea injection control must maximize the NH3 stored in the SCRoF. The under-floor SCR catalyst can be used as an NH3 slip buffer, lowering the risk of NH3 slip at the tailpipe with some benefit on the global NOx conversion of the system. With this approach, the urea injection strategy has a limited control on the NH3 coverage of the under-floor SCR catalyst.

The progressive trend towards the GDi engine downsizing, the focus on better fuel efficiency and performance, and the regulatory requirements with respect to the combustion emissions have brought the focus of attention on strategies for improvement of in-cylinder mixture preparation and identification and elimination of the sources of combustion emissions, in particular the in-cylinder particulate formation. This paper discusses the fuel system components, injector dynamics, spray characteristics and the single cylinder engine combustion investigation of a 40 [MPa] capable conventional GDi inwardly-opening multi-hole fuel injection system. It provides results of a study of the influence of fuel system pressure increase between 5 [MPa] to 40 [MPa], in conjunction with the injector static flow and spray pattern, on the combustion characteristics, specifically the particulate and gaseous emissions and the fuel economy.

In previous work, Gasoline Direct Injection Compression Ignition (GDCI) has demonstrated good potential for high fuel efficiency, low NOx, and low PM over the speed-load range using RON91 gasoline. In the current work, a four-cylinder, 1.8L engine was designed and built based on extensive simulations and single-cylinder engine tests. The engine features a pent roof combustion chamber, central-mounted injector, 15:1 compression ratio, and zero swirl and squish. A new piston was developed and matched with the injection system. The fuel injection, valvetrain, and boost systems were key technology enablers. Engine dynamometer tests were conducted at idle, part-load, and full-load operating conditions. For all operating conditions, the engine was operated with partially premixed compression ignition without mode switching or diffusion controlled combustion.

The focus of this study is investigation of the influence of fuel system pressure, intake tumble charge motion and injector seat specification - namely the static flow and the plume pattern - on the GDi engine particulate emissions under the homogenous combustion operation. The paper presents the spray characteristics and the single cylinder engine combustion data for the Delphi Multec® 14 GDi multi-hole fuel injector, capable of 40 [MPa] fuel system pressure. It provides results of a study of the influence of fuel pressure increase between 5 [MPa] to 40 [MPa], for three alternative seat designs, on the combustion characteristics, specifically the particulate and gaseous emissions and the fuel consumption. In conjunction with the fuel system pressure, the effect of enhanced charge motion on the combustion characteristics is investigated.

The successful commercialization of lean burn gasoline engines is dependent upon development of an effective emission aftertreatment system which can provide HC, CO, and NOx control not only under lean operating conditions, but also when the engine operates at the stoichiometric point under conditions of high engine speed and/or load. NOx adsorber catalysts (NOx traps) are capable of storing NOx under lean condition, and subsequently releasing and catalyzing its reduction under conditions rich of the stoichiometric point. Aftertreatment systems based on these types of catalysts show great potential for reaching current and future emission standards. Key to the successful application of NOx adsorber catalysts is the development of engine control strategies which maximize NOx conversion while minimizing the fuel economy penalty associated with adsorber regeneration. In this paper limitations associated with NOx trap adsorption and regeneration strategies are discussed.

A new adsorber system for reducing cold start HC emissions has been developed that offers a passive and simplified alternative to previous HC adsorber technologies. The series flow in-line adsorber concept combines existing catalyst technology with a zeolite based HC adsorber by simply incorporating one additional adsorber catalyst substrate into conventional catalytic converters without any valving, purging lines or special substrates. The HC adsorber catalyst consist of a durable zeolite, a washcoat binder, precious group metals and rare earth promoters on standard monolithic substrates. For selected vehicle applications, a single converter containing a light off catalyst, a catalyzed HC adsorber and a standard three-way catalyst can be used in the underfloor position. Even after severe engine aging, the vehicle FTP results show that this new technology remains effective in reducing the cold start HC emissions while providing good CO and NOx conversions.

An adsorber system for reducing cold start hydrocarbon (HC) emissions has been developed combining existing catalyst technologies with a zeolite-based HC adsorber. The series flow in-line concept offers a passive and simplified alternative to other technologies by incorporating one additional adsorber substrate into existing converters without any additional valving, purging lines, or special substrates. This contribution describes the current development status of hydrocarbon adsorber aftertreatment technologies. We report results obtained with a variety of adsorber, start-up, and underfloor catalyst system combinations. In each case, it was possible to achieve HC emission levels in compliance with the ULEV standards, and in the best cases, demonstrating HC emissions substantially below the legislated standard.

High cell density (HCD) (≥ 600 cpsi) and /or ultra thin wall (UTW) (≤ 4 mil) extruded ceramic monolith substrates are being used in many new automotive catalyst applications because they offer (1) increased geometric surface area, (2) lower thermal mass, (3) increased open frontal area and (4) higher heat and mass transfer rates. Delphi has shown in previous papers how to use the effectiveness, NTU theory, to optimize the various benefits of these HCD / UTW catalysts. A primary disadvantage of these low solid fraction substrates is their reduced structural strength, as measured by a 3-D hydrostatic (isostatic) test. The weakest of these new substrates is only 10 to 20% as strong as standard 400 × 6.5 substrates. Improved converter assembly methods with lower, more uniform forces will likely be required to successfully assemble converters with such weak substrates in production.

Palladium-rhodium catalyst technologies have been investigated to establish the relationship between emission performance and their oxygen storage capacity (OSC) or other physical properties. Catalyst performance was evaluated using stand dynamometer and FTP testing after both oven air aging and engine aging. Monolith catalysts were characterized for aged surface area and precious metal dispersion. Various components of the washcoat supports were characterized by surface area and X-ray diffraction (XRD) analysis for phase composition and CeO2-ZrO2 solid solution crystallite size. The correlation between OSC delay times and tailpipe emissions for NMHC, CO and NOx was highly nonlinear in these studies. Addition of CeO2-ZrO2 solid solution components to the washcoat significantly improved steady state activity after aging, but did not significantly affect the correlation between emissions and OSC.

The use of catalytic aftertreatment to reduce residual hydrocarbons and carbon monoxide from the exhaust stream of 2-stroke 2-wheel vehicles is reported. The impact of applying three different catalyst technologies to the exhaust streams of two motorcycles was examined. Mass emission and modal results generated from 50cc and 110cc motorcycles during the India Driving Cycle (IDC) were used to characterize catalyst performance. The results indicate that the effective implementation of catalytic aftertreatment to 2-stroke 2-wheel vehicles depends strongly on both catalyst formulation and the specific application. Catalysts can be formulated to possess desired selectivity allowing flexibility in meeting emissions standards.

The beneficial effects of CeO2/ZrO2 solid solutions on the performance of fully formulated Pt, Rh TWC (three-way-conversion) catalysts were measured using both stand dynamometer and FTP testing after severe engine aging. The performance advantages were consistent with an enhancement of the chemical promotional effects of CeO2. These included increased effectiveness for CO and NOx conversion and to a lesser extent for HC compared to catalysts prepared with the same loading of Ce and Zr but no solid solution formation. Higher performance could be achieved with the CeO2/ZrO2 solid solution catalysts having half the Ce loading of conventional catalysts prepared with pure CeO2. The physico-chemical properties of the catalysts were characterized using both XRD and TPR. XRD was used to determine the degree of solid solution formation between CeO2 and ZrO2 and TPR was used to characterize the redox properties/oxygen storage of the catalysts before and after aging.

Regulations are being considered or have already been enacted to limit the exhaust emissions of hydrocarbons, CO and NOx from small engines, such as those used in the lawn and garden industry. One of the most promising ways for engine manufacturers to comply with current and future emission standards is through the use of catalysts. However, these small engines provide an environment with a number of challenges for emission catalyst activity and durability which are not found with automotive exhaust, which is traditionally where catalysts of this type have been used. Problems unique to the small engine can include extremely short catalyst residence times, high hydrocarbon and carbon monoxide to oxygen ratios, overall high levels of emissions leading to high reaction exotherms, and pertubated flow due to single cylinder operation. A number of catalyst variables were tested using 4-stroke engines.

The effectiveness of using catalytic aftertreatment to control excessive hydrocarbon and carbon monoxide emissions is well known. However, a thorough understanding of how the catalyst and vehicle work together as an integrated system is still in developmental stages. A major goal of the investigation was to examine catalyst performance under the dynamic conditions existing during normal vehicle operation. The impact of applying catalytic aftertreatment, with and without the addition of secondary air, to three small 2-stroke motorcycles is examined. It is found that catalysts respond well to the varied conditions encountered with 2-stroke engine powered vehicles. While the addition of secondary air is beneficial to increased hydrocarbon reductions, its impact on carbon monoxide can be variable and a function of vehicle operation.

Fuel systems associated with Gasoline Direct Injection (GDi) engines operate at pressures significantly higher than Port Fuel Injection (PFI) engine fuel systems. Because of these higher pressures, GDi fuel systems require a high pressure fuel pump in addition to the conventional fuel tank lift pump. Such pumps deliver fuel at high pressure to the injectors multiple times per engine cycle. With this extra hardware and repetitive pressurization events, vehicles equipped with GDi fuel systems typically emit higher levels of audible noise than those equipped with PFI fuel systems. A common technique employed to cope with pump noise is to cover or encase the pump in an acoustic insulator, however this method does not address the root causes of the noise. To contend with the consumer complaint of GDi system noise, Delphi and Magneti Marelli have jointly developed a high pressure fuel pump with reduced audible output by concentrating on sources of noise generation within the pump itself.

Dual-brick catalyst systems containing Pd-only catalysts followed by Pt/Rh three-way catalysts (TWCs) are effective emission solutions for both close-coupled and underfloor LEV/ULEV applications due to optimal hydrocarbon light-off, NOx control, and balance of precious metal (PGM) usage. Dual-brick [Pd +Pt/Rh] systems on 3.8L V-6 LEV-calibrated vehicles were characterized as a function of PGM loading, catalyst technology, converter volumes, and substrate cell density. While hydrocarbon emissions improve with increasing Pd loading, decreasing the front catalyst volume at constant Pd content (resulting in higher Pd density) improved light-off emissions. Use of 600cpsi substrates improved underfloor NMHC emissions on a 3.8L vehicle by ∼ 6-10mg/mi compared to 400cpsi catalysts, and thus allowing reduction of catalyst volume while achieving ULEV emission levels without air addition.

Although improvements in NOx adsorber formulations are increasing the sulfur resistance of these materials, and legislation continues to further restrict sulfur levels in fuels, sulfur poisoning remains as one of the key issues associated with successful commercialization of NOx adsorber technology throughout the world. Because of the stability of the sulfate poisons, high temperatures which stress the thermal stability of some of the most efficient NOx adsorbents are required for desulfation. Additionally, the rich condition which favors sulfur release simultaneously increases the H2S content of the emission. Sulfur traps offer the potential for reducing the formation of poisoning sulfates on downstream NOx adsorbents. Results characterizing the sulfur scavenging efficiency of these materials, as well as the conditions required for their regeneration will be presented. Strategies for their successful application on motor vehicles will be discussed.

Thinwall substrates used in modern catalytic converters are more sensitive to assembly and operating forces. Various converter assembly processes are characterized using real time force transducer technology. The force distribution data from these assembly methods are presented. The analysis of this data leads to recommendations for packaging of converters depending on catalyst strength.

This paper presents the results of an exploratory study examining the production of particulate matter (PM) by 2-wheel vehicles and the impact of catalytic aftertreatment on these emissions. Information is presented demonstrating the efficacy of catalytic aftertreatment for significantly reducing not only hydrocarbons (HC) and carbon monoxide (CO), but also PM emissions from motorcycles equipped with small 2-stroke engines. The generation of PM by 5 test vehicles during realistic driving conditions is discussed and the impact of catalyst performance characteristics on the reduction of these releases is examined. Vehicle based test data, obtained with a mini-dilution tunnel, clearly demonstrates the benefits to the environment achievable through the use of catalytic aftertreatment.

Close coupled catalysts and new ceramic catalyst substrates have significantly improved the light-off performance of automotive converters required to meet stringent emission requirements. The hotter environment of these catalytic converters and the lower structural strength of the ceramic substrates require the rethinking of converter designs. The development of new package requirements to accommodate the change in environment and new substrates are discussed. A historical perspective on converter durability is presented as reference. Development of durability test protocols is essential to verifying product durability performance to these new environments. Data collection and documentation of testing templates are shown to demonstrate the effectiveness of tests that represent real world environments. Design improvements to address failure modes are discussed along with durability improvement results.

Advances in extrusion die technology allow ceramic substrate suppliers to provide new monolithic automotive substrates with considerably higher cell densities and thinner wall thicknesses. These new substrates offer both faster light off and better steady state efficiencies providing new flexibility in the design of automotive catalytic converters. The effectiveness-NTU methodology is used to evaluate various design parameters of the HCD substrates. Various theoretical derivations are supported with experimental results on substrates with cell densities ranging from 400 to 1200 cells per square inch with varying wall thicknesses. Performance effects such as steady state conversion, transient response both thermal and emission, flow restriction and FTP emissions results are evaluated. Poison deposition is studied and the effects on emissions performance evaluated.