Andrew Peter Walker

Mechanism of the lean NOx reaction over Cu/ZSM-5

Abstract Transient techniques (including TAP, temporal analysis of products) have been used to probe the mechanism of the lean NO x reaction over Cu/ZSM-5. The activation of propene and nitric oxide by Cu/ZSM-5, in the presence and absence of oxygen, have been investigated by TAP to elucidate the nature of the reducing species involved in the formation of nitrogen. Propene is converted to long-lived (carbon-rich)_ species on the zeolite whether oxygen is present or not, and it is these deposited coke species which act as the reductant in this catalyst system. The ability of the coke to reduce nitric oxide is significantly enhanced by the presence of oxygen. The crucial role of the oxygen appears to be to induce the generation of an adsorbed state of NO x on the exchanged-Cu sites; these NO 2 -type species exist at temperatures characteristic of high lean NO x activity. During temperature-programmed reaction under a fuel-lean (oxidising) exhaust-gas, both nitric oxide and propene are retained at lower temperatures; as the temperature rises, so propene retention (as coke) and total oxidation begin to compete. However, there are sufficient reducing species still present on the surface to allow substantial reduction of the -NO 2 species, as the latter approach their limit of thermal stability.

Optimising the Low Temperature Performance and Regeneration Efficiency of the Continuously Regenerating Diesel Particulate Filter (CR-DPF) System

An electrooptical scanning device which can detect the relative position of register mark applied to a moving web, either serially on a single track or in two parallel, side-by-side tracks which extend in the direction of movement of the web. Light from a light source positioned some distance above the web is split into three light beams and the light beams are reflected downwardly towards the web. Lenses are positioned to receive and direct the light beam at an oblique angle onto the marks on the track or tracks. The lenses are aligned with the tracks and the light beam passing through a given lens is directed to the opposite track to illuminate three positions, two on the first track and one position on the second track. Light impinging on the web at these positions is scattered. Vertically upwardly scattered light is captured by the lens overlying the particular illuminated position and hence directed via suitable optics to photo-detectors which generate output signals that can be used to determine the relative locations of the marks to thereby detect any misalignments of the web.

The Use of NO x Adsorber Catalysts on Diesel Engines

NOx adsorber catalysts (NACs) can be applied in lean-burn gasoline and diesel engines to reduce NOx emissions. Typically NACs are formulated using platinum as an oxidation catalyst, barium as a storage component and rhodium for NOx reduction. There has been intense research to optimise these catalysts for use on diesel engines aimed at increasing their efficiency, durability, sulfur tolerance and operating temperature window. This paper describes these developments and outlines the current level of knowledge of NOx adsorber catalyst systems using results from small-scale laboratory tests as well as engine-bench work.

The development of a model capable of predicting diesel lean NOx catalyst performance under transient conditions

Abstract Steady state kinetics data from a commercial Pt-based lean NOx catalyst have been used to formulate a kinetic model to describe the performance of the catalyst. It is clear from this analysis that steady state kinetics in isolation are not sufficient to provide a full picture of the operational performance of such a catalyst. However, when this kinetic analysis is combined with mechanistic information obtained over the catalyst, the resulting model is extremely powerful. Within this paper, the development of the kinetic model is described, and the requirement for both accurate mechanistic information and detailed kinetic measurements is clearly demonstrated. The use of the model to predict the performance of a light-duty diesel vehicle under light-off conditions is described, and the power and flexibility of the model within the lean NOx area are emphasised.

Investigations of the Interactions between Lubricant-derived Species and Aftertreatment Systems on a State-of-the-Art Heavy Duty Diesel Engine

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. 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. 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. 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. 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. 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.

Driving down on-highway particulate emissions

It has been reported that particulate emissions from diesel vehicles could be associated with damaging human health, global warming and a reduction in air quality. These particles cover a very large size range, typically 3 to 10 000 nm. Filters in the vehicle exhaust systems can substantially reduce particulate emissions but until very recently it was not possible to directly characterise actual on-road emissions from a vehicle. This paper presents the first study of the effect of filter systems on the particulate emissions of a heavy-duty diesel vehicle during real-world driving. The presence of sulfur in the fuel and in the engine lubricant can lead to significant emissions of sulfate particles < 30 nm in size (nanoparticles). We have demonstrated that when using low sulfur fuel in combination with a uniquely formulated low sulfur lubricant and a suitable filter system that the particulate emissions of a heavy-duty vehicle were reduced to the levels already present in the ambient environment. PM EMISSIONS AND DIESEL PARTICULATE FILTER (DPF) TECHNOLOGY Diesel Particulate Matter (PM) consists primarily of carbonaceous soot and a Volatile Organic Fraction (VOF) composed mainly of hydrocarbons with lesser amounts of nitrate and sulfate species. It is becoming increasingly recognised that PM emissions from dieselpowered vehicles may have adverse environmental effects. For example, it was proposed that the elemental carbon fraction can increase global warming effects. In addition, the medical community is closely examining the effects of PM on human health as a function of particle size. Reports in scientific literature suggest that there is a link between environmental exposure to fine particles less than 2.5 m in size to adverse health effects. These studies elucidated a range of causal mechanisms but have not developed a quantitative understanding of their relative importance. Studies that are more recent investigated the hypothesis that ultrafine particles <100 nm in size are detrimental to human health. It has also been reported that the relationship between ultrafine particles and health may be at least partially due to the high efficiency of particle deposition in the respiratory tract for the very small particles (Alveolar deposition is highest for particles approximately 20 nm in size). Regulatory agencies such as the U.S. Environmental Protection Agency (EPA) have adopted mass-based air pollution regulations for particulate matter. Other metrics, such as particle number or surface area, may be more important in characterising the physical properties of aerosol related to health effects. Figure 1 illustrates relationships between combustion aerosol number, surface area and mass weighted size distributions. In this case the distribution typifies a diesel aerosol distribution. The shape of the aerosol size distribution from a spark ignition engine would be similar but with relatively less material in the accumulation mode region. 2006-01-0916 Driving Down On-Highway Particulate Emissions D. B. Kittelson, W. F. Watts and J. P. Johnson University of Minnesota, Department of Mechanical Engineering

The Development and Performance of the Compact SCR-Trap System: A 4-Way Diesel Emission Control System

The tightening of Heavy Duty Diesel (HDD) emissions legislation throughout the world is leading to the development of emission control devices to enable HDD engines to meet the new standards. NOx and Particulate Matter (PM) are the key pollutants which these emission control systems need to address. Diesel Particulate Filters (DPFs) are already in use in significant numbers to control PM emissions from HDD vehicles, and Selective Catalytic Reduction (SCR) is a very promising technology to control NOx emissions. This paper describes the development and performance of the Compact SCR-Trap system - a pollution control device comprising a DPF-based system (the Continuously Regenerating Trap system) upstream of an SCR system. The system has been designed to be as easy to package as possible, by minimising the total volume of the system and by incorporating the SCR catalysts on annular substrates placed around the outside of the DPF-based system. This novel design gives rise to an easy-to-package emission control device capable of providing very high conversions of all four major pollutants, NOx, PM, CO and HC. The design details are discussed, and the performance of the system over both steady state and transient cycles is presented. NOx conversions of up to 92% have been demonstrated, and the systems emissions of all four pollutants are well inside the Euro V, and probably also the US 2007 limits (subject to verification of PM).

The mechanism of the lean Nox reaction over Pt-based catalysts

Abstract It is now well established that Cu/ZSM-5, the first generation lean NO x catalyst, is not suitable for widespread application on vehicles because it can undergo rapid and irreversible deactivation under real operating conditions. Pt-based catalysts offer an, active and stable alternative to Cu/ZSM-5. Steady state reactor experiments have demonstrated that Pt/Al 2 O 3 catalysts are active for the lean NO x reaction at temperatures as low as 200°C. Both N 2 and N 2 O are generated by such catalysts While there is no simple correlation between NO reduction activity and Pt surface area, there is certainly a very good inverse correlation between the maximum NO reduction activity and the temperature. The most effective catalysts for NO reduction are those which are active at the lowest temperatures. Temporal Analysis of Products (TAP) has been used to obtain an in-depth mechanistic understanding of the lean NO x reaction over a Pt/Al 2 O 3 catalyst. the predominant mechanism for selective NO reduction involves the reduction of oxidised Pt sites by the hydrocarbon, followed by the decomposition of NO on these reduced Pt sites. A detailed model of the lean NO x reaction over Pt/Al 2 O 3 is presented which is capable of explaining all the results obtained in this work, as well as those reported in the literature.

Development of Partial Filter Technology for HDD Retrofit

Diesel oxidation catalyst and particulate filter technologies are well established and their applications are well known. However, there are certain limitations with both technologies due to their inherent technical characteristics. Both technologies get 75-90% reduction of HC and CO. A typical oxidation catalyst can be applied to almost any heavy duty diesel application and achieve 20 to 30% reduction in PM mass but no significant reduction in the number of PM particles. On the other hand, diesel particulate filters are very effective at removing >90% of the particles by mass and >99% by number. Unfortunately, passive DPF technology cannot be applied to all applications since the filter regeneration is limited by engine out NOx to PM ratio as well as exhaust temperature. For this reason, particulate filters can not universally be applied to older “dirtier” engines with high PM emissions. This creates a technology gap for a passive device that can be successfully applied to old, high PM emission engines to achieve significant reduction in both PM mass and PM number. This paper will discuss the development of a passive PM control device referred to as a partial filter technology or PFT. This device combines an oxidation catalyst with a unique filter technology that can reduce PM by up to 77%. The new filter material combines the attributes of a flow through substrate with those of a wall flow filter to collect some but not necessarily all the engine out soot and thus provide PM reduction without leading to filter plugging. Due to the flow through characteristics, excess soot beyond filter capacity is not collected in the PFT and thus the exhaust is able to continue to flow without a significant increase in back pressure. The PFT system also utilizes the NO2:C reaction used by passive diesel particulate filter systems to oxidize a portion of the soot and passively regenerate the filter. In addition, the filter does not accumulate significant amounts of lube oil ash and this may minimize the need for a periodic ash cleaning maintenance. Engine bench emission testing with this system has shown PM reductions ranging from 77% for fresh (degreened) system to 63% for an aged system along with >90% HC and CO reductions. On-road operational data collected on various model year applications over a two year period has shown stable back pressure since installation. In addition, no adverse operational or maintenance issues were noted which can be attributed to the installation of the PFT system. This paper describes the development and testing of this passively regenerating partial filter technology.

Combined SCR and DPF Technology for Heavy Duty Diesel Retrofit

The retrofitting of diesel engines with oxidation catalyst and particulate filter technology for the reduction of particulate matter (PM), hydrocarbons (HC) and carbon monoxide (CO) emissions has become an established practice. The design and performance of such systems have been commercially proven to the point that the application of these technologies is a cost effective means for states to effectively meet pollution reduction goals. One of the reasons that these technologies are so widely applied is because they can be sized and fitted based on easily measurable vehicle parameters and published engine emission information. These devices generally work passively with basic temperature and back pressure monitoring devices being used to alert the operator to upset conditions. The application of an effective NOx reduction technology in similar retrofit installation, is more complicated. There are no passive NOx reduction technologies that can be retrofit onto HDD vehicles. Because of the long useful life of existing HDD vehicles, a retrofit SCR technology that could provide 80% NOx reduction will be very beneficial. Previously, a retrofit CRDPF plus SCR technology was demonstrated for NOx reductions of 80% [1]. However, this system was primarily designed for development and demonstration purposes and there is a need for a truly commercialized retrofit product. In order to be widely acceptable, a retrofit SCR technology needs to be flexible in its control and installation, allowing it to fit on to a large cross section of vehicles. It must also be durable and cost effective. This paper will discuss the development of a commercially available four-way (NOx, PM, CO and HC) emission reduction product for retrofit on HDD vehicles. The system combines the Johnson Matthey CRT ® filter with a urea SCR system and is known commercially as SCRT® system. This paper will discuss the development of such a system through integration of the injection system hardware, control algorithm and catalysts. The SCRT® system utilizes a urea injection system that is deployed on the vehicle as components giving the product more flexibility and lower cost. The urea injection components are: urea pump, air regulator, dosing unit and nozzle. The system utilizes a control system that allows the application engineer to customize it to the engine and catalyst size. It can also use either an engine map or NOx sensor for urea injection control. Transient and steady state test cell data demonstrating > 80% NOx reduction with this system are presented. In addition, chassis dyno emissions results and field data from Europe are reported, demonstrating successful on-road performance of the system.