Close-coupled Catalyst Research Articles

Influence of Pre-Turbine Small-Sized Oxidation Catalyst on Engine Performance and Emissions under Driving Conditions

The earlier activation of the catalytic converters in internal combustion engines is becoming highly challenging due to the reduction in exhaust gas temperature caused by the application of CO2 reduction technologies. In this context, the use of pre-turbine catalysts arises as a potential way to increase the conversion efficiency of the exhaust aftertreatment system. In this work, a small-sized oxidation catalyst consisting of a honeycomb thin-wall metallic substrate was placed upstream of the turbine to benefit from the higher temperature and pressure prior to the turbine expansion. The change in engine performance and emissions in comparison to the baseline configuration are analyzed under driving conditions. As an individual element, the pre-turbine catalyst contributed positively with a relevant increase in the overall CO and HC conversion efficiency. However, its placement produced secondary effects on the engine and baseline aftertreatment response. Although small-sized monoliths are advantageous to minimize the thermal inertia impact on the turbocharger lag, the catalyst cross-section is in trade-off with the additional pressure drop that the monolith causes. As a result, the higher exhaust manifold pressure in pre-turbine pre-catalyst configuration caused a fuel consumption increase higher than 3% while the engine-out CO and HC emissions did around 50%. These increments were not completely offset despite the high pre-turbine pre-catalyst conversion efficiency (>40%) because the partial abatement of the emissions in this device conditioned the performance of the close-coupled oxidation catalyst.

Effect of high temperature pretreatment on the thermal resistance properties of Pd/CeO2/Al2O3 close-coupled catalysts

Fresh Pd/CeO2/Al2O3 close coupled catalyst was prepared by the stepwise impregnation method and calcined at 550 °C for 3 h, which was then pretreated at 700, 800, and 900 °C for 3 h, respectively. Finally, these pretreated catalysts were aged at 1000 °C for 3 h to study their anti-aging properties. The catalytic activities of the catalysts were investigated detailedly, and the results showed that the catalyst pretreated at 800 °C before aging treatment possessed the best anti-aging performance for C3H8 oxidation. XRD and XPS results indicated that well-crystallized CeO2 particles were formed during calcinations at 800 °C, which made CeO2 an effective promoter. HRTEM revealed that Pd particles found on the edge of CeO2 over the aged catalyst pretreated at 800 °C were relatively smaller than those over the catalysts without pretreatment. H2-TPR and XPS results also implied that the interaction between well-crystallized CeO2 and Pd suppressed the deactivation of PdO sites and further enhanced the catalytic performance.

Promotion of a Pd/Al2O3 close-coupled catalyst by Ni

The influence of a nickel promoter on the catalytic behavior of a modified alumina supported Pd close-coupled catalyst was investigated. Doping with nickel improved the catalytic activity for the reactions of C3H8, especially over the aged catalyst. T50 and T90 of the aged Pd catalyst were decreased by 31 and 30 °C, respectively. The single reaction results revealed that doping with Ni promoted the catalytic activity for the C3H8 + NO reaction. The fresh and aged catalysts were characterized by H2-temperature-programmed reduction, CO chemisorption, high resolution transmission electron microscopy, and X-ray photoelectron spectroscopy, which revealed that the doping with Ni inhibited the sintering of active PdOx species and the formation of undesired metallic Pd0, and led to improved reducibility of active PdOx and increased the surface area of PdOx species.

A highly efficient Rh-modified Pd/Al2O3 close-coupled catalyst

The close-coupled catalysts Pd/Al2O3 and Rh-Pd/Al2O3 were prepared by the impregnation method and characterized by H2 temperature-programmed reduction, CO chemisorption, and X-ray photoelectron spectroscopy. Both overall catalytic activity and specific reactions associated with C3H8 elimination were assessed. The light-off temperature and complete conversion temperature decreased by 23 and 18 °C, respectively, upon addition of Rh to the Pd/Al2O3 catalyst. The addition of Rh promotes the catalytic activity during C3H8 reactions, particularly in the presence of NO. The introduction of Rh not only inhibits sintering of PdOx and increases the dispersion of these same species, but also changes the electronic state of the PdOx in the catalyst.

Modelling of passive ammonia selective catalytic reduction system for lean-burn spark ignition direct injection engines

Lean-burn spark ignition direct injection (SIDI) engines offer potential fuel economy savings; however, the lack of simple and cost-effective lean nitrogen oxide (NO x) aftertreatment systems hinder their broad application. Lean NO x traps (LNT) and urea selective catalytic reduction (SCR) catalysts have been widely investigated as possible lean gasoline aftertreatment technologies, but with limited acceptance. Passive ammonia SCR operation is a promising low-cost alternative for lean NO x aftertreatment with SIDI engines. The aftertreatment system includes close-coupled three-way catalyst (TWC) converters and one or more under-floor SCR catalysts. Ammonia (NH3) is formed on the TWC with short pulses of rich engine operations and the generated NH3 is then stored on the under-floor SCR catalysts. During subsequent lean operations, the NO x that breaks through the TWC converters is reduced to nitrogen by NH3 stored on the SCR catalysts. This paper provides an overview of system level analysis as a complement to experimental testing in the development of a passive NH3 SCR-based aftertreatment system. Various aftertreatment architectures (SCR type, the order, and location of the catalysts) were efficiently evaluated and screened, to achieve the best trade-off between engine back-pressure, catalyst warm-up, emission constraints, and acceptable thermal ageing under high-speed/load conditions.

Recent Solutions for the Abatement of Hydrocarbon Emissions During the Cold Start of Light Vehicles

During the last twenty years the number of patent publications in the field of the control of hydrocarbon compounds during the cold start period of a gasoline engine has strongly increased and seems now that the number of patents tends to increase during the following years. This fact has been related with increasingly stringent legislations all over the world which highlights the importance of developing efficient systems for the control of cold start hydrocarbon emissions. The technologies that show a higher number of patents are the hydrocarbon trap, the close-coupled catalyst and the electrically heated catalyst.

Durability of three-way and close-coupled catalysts for Euro IV regulation

The durability of three-way catalyst (TWC) and corresponding close-coupled catalyst (CCC) for Euro IV stage regulation was investigated through Vehicle Road Running Mode tests, whereas emissions of regulated pollutants of three car fleet were investigated at every 100,000 km miles. The results showed that HC, NO x , and CO emission values could meet Euro IV regulation limits at every point. The redox properties of TWC and CCC were measured by CO reduction during each isothermal. It was obvious that both aged TWC and aged CCC behaved a good redox property at 673 and 773 K. Based on XRD and BET measurement results, TWC and CCC washcoat were characterized with good thermal stability.

The application of an exhaust heat exchanger to protect the catalyst and improve the fuel economy in a spark-ignition engine

A close-coupled catalyst (CCC) can reduce engine cold-start emissions by utilizing the energy in the exhaust gas. However, in case the engine is operated at high engine speed and load condition, the catalytic converter may be damaged and eventually deactivated by thermal ageing. Excess fuel is sometimes supplied intentionally to lower the exhaust gas temperature, avoiding thermal ageing. This sacrifices fuel economy and exhaust emissions. This paper describes the results of an exhaust heat exchanger to lower the exhaust gas temperature, mainly under high load conditions. The heat exchanger was installed between the exhaust manifold and the inlet of the CCC to avoid thermal ageing. The exhaust heat exchanger successfully decreased the exhaust gas temperature, which eliminated the requirement of fuel enrichment under high-load conditions. A reduction of fuel consumption by approximately 7.7 per cent at high vehicle speed was achieved due to no fuel enrichment. Although the amount of hydrocarbon during the cold start increases due to the increment of the catalyst light-off time, it still meets the EURO-IV regulations. This problem could be resolved by adopting the solenoid valve to cut off the coolant at the inlet of the coolant passage of the heat exchanger.

Experimental study of flow dynamics in close-coupled catalyst manifolds

Time-resolved flow dynamics in an automotive exhaust manifold with a close-coupled catalyst is investigated experimentally on a charged motored engine (CME) flow rig. Flow similarity between CME and fired engine conditions is discussed analytically. Oscillating hot-wire anemometry (OHW) is used to measure the bidirectional phase-locked velocity. Strong time-resolved mean catalyst velocity fluctuations are observed. These are analysed as Helmholtz resonances, using a one-dimensional gas dynamic model of the manifold. The spatial and temporal occurrence of instantaneous reverse flow in the catalyst are investigated, for varying engine load conditions. Periodic backflow occurs throughout large portions of the catalyst cross-section, and proves to be linked strongly to the observed Helmholtz resonances.

Experimental Validation of the Addition Principle for Pulsating Flow in Close-Coupled Catalyst Manifolds

Designing an exhaust manifold with close-coupled catalyst (CCC) relies heavily on time-consuming transient computional fluid dynamics. The current paper provides experimental validation of the addition principle for pulsating flow in CCC manifolds. The addition principle states that the time-averaged catalyst velocity distribution in pulsating flow equals a linear combination of velocity distributions obtained for steady flow through each of the exhaust runners. A charged motored engine flow rig provides cold pulsating flow in the exhaust manifold featuring blow down and displacement phases, typical of fired engine conditions. Oscillating hot-wire anemometry is used to measure the bidirectional velocity, with a maximum measurable negative velocity of −1m∕s. In part load and zero load conditions, instantaneous reverse flow occurs following the blow-down phase. The two-stage nature of the exhaust stroke combined with strong Helmholtz resonances results in strong fluctuations of the time-resolved mean catalyst velocity. The validity of the addition principle is quantified based on the shape and magnitude similarity between steady and pulsating flow distributions. Appropriate nondimensional groups are used to characterize the flow and quantify the similarity. Statistical significances are provided for the addition principle’s validity. The addition principle is valid when the nondimensional scavenging number S exceeds a critical value Scrit, corresponding to cases of low engine speed and/or high flow rate. This study suggests that the CCC manifold efficiency with respect to catalyst flow uniformity could be quantified using a single scalar parameter, i.e., Scrit. The results from the current study are discussed with respect to previously reported results. The combined results are in good agreement and provide a thorough statistically founded experimental validation of the addition principle, based on a broad applicability range.

Influence of Pulsating Flow on Close-Coupled Catalyst Performance

Close coupling of automotive three-way catalytic converters is becoming a common practice in order to reduce pollutant emissions during cold start. In such applications, the exhaust gas mass flow may fluctuate, as a function of crankshaft angle. A simplified one-dimensional channel model is developed, assuming that pollutant conversion in the catalyst is mass transfer limited. This model is applied to evaluate the effect of pulsations in catalyst performance, and assess the accuracy of the “quasi-steady state” approach usually involved in three-way catalytic converter models, when applied to simulate converters under pulsating flow.

Study of pulsating flow in close-coupled catalyst manifolds using phase-locked hot-wire anemometry

Phase-locked sampling has been applied to hot-wire anemometry in order to investigate the pulsating flow inside two types of automotive exhaust manifolds fitted with a close-coupled catalyst. An isothermal dynamic flow bench has been used to compare the catalyst velocity distribution in steady operation to crank-angle resolved velocity distributions measured in pulsating flow. The latter were obtained using phase-locked averaging. A rotating valve and a cylinder head were used to generate the pulsating flow. Experimental results proved the addition principle, i.e. the time-averaged velocity distribution in pulsating flow is proportional to a specific linear combination of velocity distributions, resulting from steady flow through each runner.

배기매니폴드 직접부착 촉매장치의 배기 유동특성

The exhaust gas flow in the inlet collector of close coupled catalyst(CCC) adapted to the exhaust manifold is very complex flow because the exhaust gas is a pulsation flow with several port flow. The distribution of gas flow and temperature in inlet collector effect to the efficiency of catalytic converter. In this study, it measures temperatures on several point in inlet collector with two kind of inlet collector volume. And it analyzes with CFD to exhaust manifold and close coupled catalyst for temperature and flow. Comparing to measured and analyzed result, it find increasing of collector volume effects to catalyst temperature distribution and uniformity of catalytic converter<br/>

Predicting the flow field inside a close-coupled catalyst—the effect of entrance losses

A methodology is described for improving the prediction of the flow distribution in automotive close-coupled catalysts using computational fluid dynamics (CFD). Steady and pulsating flow simulations have been performed and compared with measurements obtained on an isothermal flow rig. By incorporating an extra pressure loss due to oblique entry at the monolith improved flow predictions are obtained. This work extends the methodology that has previously been developed for axisymmetric systems.

A combined experimental and computational approach to improve catalyst flow uniformity and light-off behaviour

This study is concerned with the systematic approach to improve catalyst flow uniformity and light-off behaviour through the basic understanding of exhaust flow characteristics. An experimental and computational approach to the unsteady compressible flow for exhaust manifold and close-coupled catalyst (CCC) system attached to a four-cylinder double overhead camshaft gasoline engine was performed to investigate the flow distribution of exhaust gases and finally to increase the conversion efficiency of catalyst. An experimental study was conducted to measure the velocity distributions inside the exhaust manifold and CCC under practical engine conditions by using laser Doppler velocimetry. In this study, through experiment and calculation, the effects of the geometric configuration of exhaust manifold on flow structure and its maldistribution in the monolith were mainly investigated to understand the exhaust flow patterns in terms of flow uniformity and to obtain the better light-off for further emission reduction. On the basis of the design guidance resulting from this fundamental study, an improved exhaust manifold (type II) was designed and manufactured. The effects of improved exhaust flow characteristics on vehicle emission were demonstrated through the vehicle emission tests.

Recent advances in automobile exhaust catalyst

Catalysts that were recently developed by Toyota for the control of automobile exhaust are reviewed. (1) A system combining a close-coupled catalyst with high heat resistance and an under-floor catalyst with high oxygen storage capacity were developed for low emission vehicles. (2) Based on a new concept, a three-way catalyst having the ability to store NOx at oxidizing atmosphere and to reduce stored NOx at stoichiometric or reducing atmosphere was developed for automotive lean burn engines. (3) A thin wall ceramic substrate was developed for better catalyst performance.

Emission results from a 48-car test evaluation of MMT performance additive

Ethyl Corporation (‘Ethyl’) has conducted extensive fleet testing to investigate the effect of a manganese-based antiknock additive (MMT) on exhaust emissions from production cars. The fleet consisted of 48 cars — six cars each of eight models representing more than 50% of 1988 US sales. Three of each model were tested for 75 000 miles using the base fuel and the other three used the base fuel plus 0.03125 g Mn/gallon as MMT. Results of this testing show that use of the additive will not cause or contribute to the failure of emission control systems. Exhaust back pressure data for the 48-car fleet as well as a test of a close-coupled catalyst at 80 miles/h showed no indication of catalyst distress or plugging. Catalyst conversion efficiency was generally higher for units aged on the MMT fuel. Particulate emission data showed that approximately 12% of the input manganese was exhausted as airborne manganese for the FTP cycle. The significant increase in particulate emissions from addition of MMT reported by the EPA was shown to have resulted from contamination of the fuel with chlorofluorocarbons.