Performance of platinum/alumina catalysts in automobile engine exhaust with oscillatory air/fuel ratio

Cho, Byong K.

doi:10.1021/ie00073a007

Cited by 34 publications

(13 citation statements)

References 10 publications

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“…The frequency and the width of the oscillation are determined by the response characteristics of the fuel management control loop. Several and often contradicting views have been expressed in the past, regarding the e!ect of the oscillation on catalyst e$ciency (Cho, 1988;Muraki et al, 1985;Shinjoh et al, 1989;Cho and West, 1986). In the interesting review of Silveston (1996) it is concluded that the periodic oscillations are bene"cial during the cold start phase, when the catalyst operates at low temperatures, but they can be unfavorable at high-temperature operation.…”

Section: Oscillating A/f Scanmentioning

confidence: 99%

Modeling dynamic phenomena in 3-way catalytic converters

Koltsakis

Stamatelos

1999

Chemical Engineering Science

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Mathematical modeling of 3-way catalytic converter (3WCC) operation is increasingly employed in automotive catalyst and converter systems optimization. The majority of the models employed in this direction employ a &quasi-steady' approach in the reaction kinetics computations. This approach is useful in predicting real-world performance of the catalyst. However, certain improvements, that are produced by the application of specially tuned redox oscillations, can not be predicted. This paper presents an approach embodying certain types of dynamic phenomena into an existing 3-WCC quasi-steady model. The dynamic model developed according to this approach is validated against literature data and results from experimental investigations. It is con"rmed, that the catalyst behavior under dynamic exhaust composition conditions signi"cantly di!ers from what is predicted under the quasi-steady-state assumption. More speci"cally, oxygen storage and the transient character of water gas shift reaction are shown to a!ect dynamic behavior. The results of this investigation encourage further application of mathematical modeling in areas like lambda control strategy optimization, which lied beyond the scope of traditional 3WCC models.

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Section: Oscillating A/f Scanmentioning

confidence: 99%

Modeling dynamic phenomena in 3-way catalytic converters

Koltsakis

Stamatelos

1999

Chemical Engineering Science

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“…At 300 o C, however, the modulation results in a significant drop in the CO conversion and the time-average conversion efficiency drops to 52.6% from its steady state value of 68.6%. While the trend of negative effect of modulation on the catalyst conversion performance at higher temperatures has been reported in literature (Cho 1988), the significant drop in CO conversion at 300 o C requires further investigation. Under these operating conditions and low exhaust temperatures, HC conversion is low.…”

Section: Effect Of Modulation In Air-fuel Ratiomentioning

confidence: 74%

“…Particularly, at temperatures below light-off values, the exhaust gas composition modulation has been found to result in a significant rate enhancement for CO oxidation over catalyst (Cutlip, 1979;AbdulKareem et al, 1980;Schlatter and Mitchell, 1980;Taylor and Sinkevitch, 1983;Cho and West, 1986;Zhou et al, 1986). Cho (1988) found higher conversions for all three pollutants by feed composition modulation around a timeaverage stoichiometric point below the reaction light-off temperature. This trend reverses above the reaction light-off temperatures.…”

Section: Introductionmentioning

confidence: 99%

Effect of engine exhaust gas modulation on the cold start emissions

Shamim

2011

Int.J Automot. Technol.

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This paper presents a computational investigation of the effect of engine exhaust gas modulations on the performance of an automotive catalytic converter during cold starts. The objective is to assess if the modulations can result in faster catalyst light-off conditions and thus reduce cold-start emissions. The study employs a single-channel based, onedimensional, non-adiabatic model. The modulations are generated by forcing the variations in exhaust gases air-fuel ratio and gas compositions. The results show that the imposed modulations cause a significant departure in the catalyst behavior from its steady behavior, and modulations have both favorable and harmful effects on pollutant conversion during the cold-starts. The operating conditions and the modulating parameters have substantial influence on catalyst behavior. KEY WORDS : Engine emissions, Engine exhaust after-treatment, Dynamic behavior, Numerical simulations NOMENCLATURE C g j : gas phase concentration of species j, mol/m 3 C s j : surface concentration of species j, mol/m 3 c pg : specific heat of gas, J/(kg·K) c ps : specific heat of substrate, J/(kg·K) D h : hydraulic diameter, m D j : diffusion coefficient of species j, m 2 /s G a : geometric surface area, m 2 /m 3 DH k : heat of reaction of species k, J/mol h g : heat transfer coefficient between flow and substrate, J/(m 2 ·s·K) h ∞ : heat transfer coefficient between substrate and atmosphere, J/(m 2 ·s·K) km j : mass transfer coefficient for species j, m/s L : catalyst length, m Nu : Nusselt number, dimensionless Pr : Prandtl number, dimensionless R k : reaction rate of k th reaction, mol/(m 2 ·s) Re : Reynolds number, dimensionless Sc : Schmidt number, dimensionless S ext : external surface to volume area ratio, m 2 /m 3 t : time, s T ∞ : ambient temperature, K T g : gas temperature, K T s : substrate temperature, K v g gas flow velocity, m/s X inlet species concentration at the catalyst inlet, mol/m 3 X outlet species concentration at the catalyst outlet, mol/m 3 z : coordinate along catalyst axis, m ε : void volume fraction, dimensionless λ g : thermal conductivity of gas, J/m·s·K λ s : thermal conductivity of substrate, J/(m·s·K) ρ g : gas density, kg/m 3 ρ s : substrate density, kg/m 3

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“…now Cooper Energy Systems. The test engine is a The effect of transient air± fuel ratio control has Superior 6G-825, which is typical of many of the been studied in the automotive field [2,3]. However, medium speed, naturally aspirated engines used for the technology has yet to be applied to industrial gas production.…”

Section: Introductionmentioning

confidence: 99%

The effect of air-fuel ratio control strategies on nitrogen compound formation in three-way catalysts

DeFoort

Olsen

Willson

2004

International Journal of Engine Research

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The ability of three-way catalysts (TWCs) to effectively remove CO and NOx from the exhaust is directly controlled by the air-fuel ratio at which the accompanying engine is operated. In a stoichiometric engine, small variations in the air-fuel ratio have large effects on the catalyst performance. These effects include wide variations in removal efficiencies and catalytic production of ammonia. The effect of the air-fuel ratio on catalysts has been well studied on automotive engines; these studies show the importance of maintaining an air-fuel ratio close to stoichiometric conditions. In automotive systems a ‘dithering’ technique is used in which the air-fuel ratio is modulated to widen the window of control. The effect of dithering on industrial engines has not been studied. A research programme was conducted to evaluate the effects of the air-fuel ratio on the performance of three-way catalysts operating on natural gas-fuelled industrial engines, the test programme aims at optimizing the engine based on the performance of the catalyst. This project has shown that dithering is an effective technique for enhancing the performance of TWCs on industrial engines. These results show that the allowable air-fuel ratio deviations are much larger with dithering and that the production of ammonia is significantly reduced.

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Performance of platinum/alumina catalysts in automobile engine exhaust with oscillatory air/fuel ratio

Cited by 34 publications

References 10 publications

Modeling dynamic phenomena in 3-way catalytic converters

Modeling dynamic phenomena in 3-way catalytic converters

Effect of engine exhaust gas modulation on the cold start emissions

The effect of air-fuel ratio control strategies on nitrogen compound formation in three-way catalysts

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