William P. Partridge

SpaciMS: spatial and temporal operando resolution of reactions within catalytic monoliths

Monolithic catalysts are widely used as structured catalysts, especially in the abatement of pollutants. Probing what happens inside these monoliths during operation is, therefore, vital for modelling and prediction of the catalyst behavior. SpaciMS is a spatially resolved capillary-inlet mass spectroscopy system allowing for the generation of spatially resolved maps of the reactions within monoliths. In this study SpaciMS results combined with 3D CFD modelling demonstrate that SpaciMS is a highly sensitive and minimally invasive technique that can provide reaction maps as well as catalytic temporal behavior. Herein we illustrate this by examining kinetic oscillations during a CO oxidation reaction over a Pt/Rh on alumina catalyst supported on a cordierite monolith. These oscillations were only observed within the monolith by SpaciMS between 30 and 90% CO conversion. Equivalent experiments performed in a plug-flow reactor using this catalyst in a crushed form over a similar range of reaction conditions did not display any oscillations demonstrating the importance of intra monolith analysis. This work demonstrates that the SpaciMS offers an accurate and comprehensive picture of structured catalysts under operation.

Assessing Reductant Chemistry During In-Cylinder Regeneration of Diesel Lean NOx Traps

Lean NOx Trap (LNT) catalysts are capable of reducing NOx in lean exhaust from diesel engines. NOx is stored on the catalyst during lean operation; then, under rich exhaust conditions, the NOx is released from and reduced by the catalyst. The process of NOx release and reduction is called regeneration. One method of obtaining the rich conditions for regeneration is to inject additional fuel into the engine cylinders while throttling the engine intake air flow to effectively run the engine at rich air:fuel ratios; this method is called “in-cylinder” regeneration. In-cylinder regeneration of LNT catalysts has been demonstrated and is a candidate emission control technique for commercialization of light-duty diesel vehicles to meet future emission regulations. In the study presented here, a 1.7-liter diesel engine with a LNT catalyst system was used to evaluate in-cylinder regeneration techniques. Characterization of the exhaust reductant chemistry during in-cylinder regeneration was performed. The effects of various injection strategies and fuels and the resulting exhaust chemistry on the performance of the LNT catalyst were analyzed. In addition, exhaust species measurement of NOx and select reductants were performed inside of the catalyst cells with a capillary-based mass spectrometry technique. The effect of various injection parameters on exhaust chemistry species and LNT performance are discussed. Results indicate that fuel chemistry does affect engine-out hydrocarbon (HC) species, but not engine-out carbon monoxide (CO) or hydrogen (H2) generation. Higher engine-out CO and H2 correlate to improved NOx reduction, irrespective of HCs.

Time-Resolved Measurements of Emission Transients By Mass Spectrometry

Transient emissions occur throughout normal engine operation and can significantly contribute to overall system emissions. Such transient emissions may originate from various sources including cold start, varying load and exhaust-gas recirculation (EGR) rates; all of which are dynamic processes in the majority of engine operation applications (1). Alternatively, there are systems which are inherently dynamic even at steady-state engine-operation conditions. Such systems include catalytic exhaust-emissions treatment devices with self-initiated and sustained oscillations (2) and NOX adsorber systems (3,4,5). High-speed diagnostics, capable of temporally resolving such emissions transients, are required to characterize the process, verify calculated system inputs, and optimize the system.

Effective Model for Prediction of N2O and NH3 Formation During the Regeneration of NOx Storage Catalyst

In this paper we propose an effective global kinetic model that allows prediction of N2O and NH3 formation during the reduction of stored NOx in dependence on the composition of the rich mixture (H2/CO/C3H6), actual operating temperature, and length of regeneration period. A bench flow reactor equipped with a high-speed FTIR was used to measure dynamic evolution of gas components during periodic lean/rich operation of a fully formulated NSRC catalyst (PtPdRh/Ba/Ce–Zr/Mg–Al/Al2O3).

Nondestructive X-ray Inspection of Thermal Damage, Soot and Ash Distributions in Diesel Particulate Filters

We describe novel results of ongoing research at 3DX-RAY Ltd and Oak Ridge National Laboratory using new, commercially available, nondestructive x-ray techniques to make engineering measurements of diesel particulate filters (DPF). Nondestructive x-ray imaging and data-analysis techniques were developed to detect and visualize the small density changes corresponding to the addition of substances such as soot and ash to DPF monoliths. The usefulness of this technique was explored through the analysis of field-aged samples, accelerated-aged samples, and the synthetic addition of ash and soot to clean DPF samples. We demonstrate the ability to visualize and measure flaws in substrates and quantify the distribution of ash and soot within the DPF. We also show that the technology is sensitive enough for evaluations of soot and ash distribution and thermal damage without removing the DPF from its metal casing.

Emission control research to enable fuel efficiency: Department of energy heavy vehicle technologies

The Office of Heavy Vehicle Technologies supports research to enable high-efficiency diesel engines to meet future emissions regulations, thus clearing the way for their use in light trucks as well as continuing as the most efficient powerplant for freight-haulers. Compliance with Tier 2 rules and expected heavy duty engine standards will require effective exhaust emission controls (after-treatment) for diesels in these applications. DOE laboratories are working with industry to improve emission control technologies in projects ranging from application of new diagnostics for elucidating key mechanisms, to development and tests of prototype devices. This paper provides an overview of these R and D efforts, with examples of key findings and developments.

Fe-Zeolite Functionality, Durability, and Deactivation Mechanisms in the Selective Catalytic Reduction (SCR) of NOx with Ammonia

Since the introduction of the first emissions control regulations in the 1970s and 1980s [1], catalysis has been implemented extensively to maintain compliance and dramatically reduce the harmful pollutants emitted from combustion engines. For stoichiometric exhaust, primarily from gasoline-powered vehicles, precious metals, or platinum-group metals (PGM), such as Pt, Pd, and Rh, have been the hallmark of three-way catalysis, e.g., [2, 3, 4], as they are highly active in oxidation of carbon monoxide (CO) and hydrocarbons (HCs) as well as the reduction of nitrogen oxides (NOx). The chemistry behind these reactions is equilibrium driven, as the more benign products of CO2, H2O, and N2 are thermodynamically favored. However, these catalysts only function properly if the exhaust is at or near stoichiometric conditions. As a result, gasoline vehicle manufacturers began designing their engine control systems to operate with stoichiometric air/fuel ratios to optimize catalyst performance and minimize emissions. The need for more fuel-efficient vehicles, both with respect to increasing fuel costs and future CO2 emissions regulations, is driving vehicle manufacturers to investigate more efficient combustion strategies, such as lean-burn gasoline, or increase production of more fuel-efficient diesel vehicles.

Mapping of exhaust gas recirculation and combustion-residual backflow in the intake ports of a heavy-duty diesel engine using a multiplexed multi-species absorption spectroscopy sensor

The combustion-residual backflow into the intake ports of a commercial diesel engine (Cummins ISX series) was spatiotemporally mapped using a multiplexed multi-species absorption spectroscopy sensor system; the resulting cycle- and cylinder-resolved measurements are applicable for assessing cylinder charge uniformity, control strategies, and computational fluid dynamics tools. On-engine measurements were made using four compact (3/8 in Outside Diameter) stainless steel probes which enabled simultaneous multi-point measurements, required minimal engine hardware modification, and featured a novel tip design for measurement of gas flows parallel to the probe axis. Three sensor probes were used to perform simultaneous backflow measurements in intake runners corresponding to three of the six engine cylinders, and a fourth probe was installed in the intake manifold plenum for tracking dynamics introduced by an external exhaust gas recirculation mixer. Near-crank-angle resolved measurements (5 kHz, that is, 1.2 crank angle resolution at 1000 RPM) were performed during steady-state engine operation at various levels of external exhaust gas recirculation to measure the gas properties and penetration distance of the backflow into the intake runners on a cylinder- and cycle-basis. Validation of computational fluid dynamics model results is also presented to demonstrate the utility of such measurements in advancing engine research.

A Light-Emitting Diode- (LED-) Based Absorption Sensor for Simultaneous Detection of Carbon Monoxide and Carbon Dioxide

A sensor was developed for simultaneous measurements of carbon monoxide (CO) and carbon dioxide (CO2) fluctuations in internal combustion engine exhaust gases. This sensor utilizes low-cost and compact light-emitting diodes (LEDs) that emit in the 3–5 µm wavelength range. An affordable, fast response sensor that can measure these gases has a broad application that can lead to more efficient, fuel-flexible engines and regulation of harmful emissions. Light emission from LEDs is spectrally broader and more spatially divergent when compared to that of lasers, which presented many design challenges. Optical design studies addressed some of the non-ideal characteristics of the LED emissions. Measurements of CO and CO2 were conducted using their fundamental absorption bands centered at 4.7 µm and 4.3 µm, respectively, while a 3.6 µm reference LED was used to account for scattering losses (due to soot, window deposits, etc.) common to the three measurement LEDs. Instrument validation and calibration was performed using a laboratory flow cell and bottled-gas mixtures. The sensor was able to detect CO2 and CO concentration changes as small as 30 ppm and 400 ppm, respectively. Because of the many control and monitor species with infra-red absorption features, which can be measured using the strategy described, this work demonstrates proof of concept for a wider range of fast (250 Hz) and low-cost sensors for gas measurement and process monitoring.

Chapter 9:Reduction of Stored NOx with CO/H2 and Hydrocarbons: A Spatial Resolution Analysis

Lean NOx traps (LNT) are multi-function multi-component catalysts which operate in an integral and transient reactor mode to reduce NOx in the exhaust from diesel or lean-burn gasoline engines. This chapter addresses the regeneration phase of the LNT operation, discussing various types of reductants and reactions involved. We describe how reductants of different reactivity influence catalyst functions, reactions, and overall regeneration efficiency. The presented examples highlight the importance of understanding the spatial and temporal development of key reactions and their interplay to rationalize the global performance of practical LNTs which are generally honeycomb-shaped ceramic monoliths. The emphasis is on explaining global NOx removal performance (i.e., activity and selectivity) based on the insights gained through spatially resolved techniques, including initial distribution and redistribution of stored NOx; oxygen storage and reduction; transformation of feed reductants; and formation and utilization of reduction intermediates. Pathways leading to N2O and NH3 byproduct formation as well as mitigation strategies are also discussed.