Three-way Catalyst Converter Research Articles

On-road tailpipe characterization of exhaust ammonia emissions from in-use light-duty gasoline motor vehicles

A Portable Emissions Monitoring System (PEMS) has been used to estimate ammonia emission rates from a representative fleet of 47 in-use light-duty gasoline motor vehicles over 145 on-road Real Driving Emissions (RDE) tests. The PEMS modules were carried onboard the tested vehicles and were wired such that their ceramic exhaust emission sensors were mounted directly in the tailpipe. The on-road RDE tests were conducted over an urban testing route that included residential and highway roads, uphill and downhill road segments, stop signs, traffic lights, and a school zone with a reduced speed limit. The entire vehicle test sample had an average ammonia emission rate of 114.7 mg/mile ±135.3 (StD). This would yield an estimated 2909 metric tons per year of NH3 emissions from the Wasatch fleet on-road gasoline motor vehicles. Old vehicles with aged Three-Way Catalyst (TWC) converters had higher NH3 emissions rates than newer vehicles with newer TWC converters. For instance, Tier 0, Tier I, NLEV, Tier II and Tier III vehicles had average emission rates of 563.1, 177.8, 213.6, 94.4 and 18.9 mg/mile, respectively. Carbon monoxide, and nitrogen oxides had a strong correlation with ammonia emission rates, with r ≥ 0.70. A Moderate correlation was found with vehicles’ mileage (r = 0.6), model year (r = −0.5), engine displacement (r = 0.4), and number of cylinders (r = 0.4). The outcomes highlight vehicle contributions to the atmospheric NH3 inventory and the impact of vehicle characteristics and ammonia precursor concentrations on ammonia emission rates from gasoline vehicles.

Water evaporation model of a catalyst converter in the context of hybrid electric vehicles energy and pollutants management

The energy and pollutants management of Hybrid Electric Vehicles (HEV) consists in determining at each instant the optimal torque split between the Internal Combustion Engine (ICE) and the Electric Motor (EM). This torque choice aims to minimize both fuel consumption and pollutants emissions. A critical piece of information in this context is the value of the Three-Way Catalyst Converter (3WCC) conversion efficiency. This value is highly dependent on the 3WCC temperature; it is hence of major importance to have an accurate estimation of it. Although the literature is abundant about simple 0D thermal models of 3WCC, it is tempting to implement a more accurate and consequently complex model. In particular, both moisture from the exhaust gases during engine start and from ambient air during cooling phases lead to the formation of a liquid water film on the monolith’s exchange surface, causing a strong temperature plateau during the warm-up phase. The water evaporation causing a delay in the 3WCC temperature increase, it could lead to a serious degradation of the pollutants emissions if not taken into account. This paper proposes hence a 1D thermal model including water phase changing that allows a 72% decrease in the 3WCC temperature estimation error during the warm up phase. This accuracy gain, occurring in a phase where the converter temperature has not reached its full efficiency, provides a 1-2% reduction in CO, HC and NO x emissions.

Making precious metals cheap: A sonoelectrochemical – Hydrodynamic cavitation method to recycle platinum group metals from spent automotive catalysts

Platinum group metals, such as Pd and Pt, found in three-way catalyst converters were recycled in a two-step method: hydrodynamic cavitation followed by sonoelectrochemical dissolution. High shear forces were obtained by using a convergent nozzle with a throat diameter of 0.2 mm, feeded by a plunger pump at a pressure of 60 MPa. Cavitating submerged jets acted locally on the water dispersed waste catalyst. As-obtained samples were analyzed by scanning electron microscopy and transmission electron microscopy. Electron microscopy on the initial sample showed that round shaped Pd and Pt nanoparticles were randomly distributed on the Al2O3 matrix. Cavitated samples show two zones in which Pt and Pd were partially and completely separated from the cordierite. The hydrodynamic cavitation separates the Pd and Pt from the cordierite leading to an apparent increase in Pd and Pt concentrations of 9% and 34% respectively. Conventional electrochemistry showed a dissolution of 20% in 1 h. To further accelerate the dissolution, a sonotrode operating at 20 kHz and 75 W was placed inside an electrochemical cell in order to increase the mass transport and obtain high dissolution rates. Indeed, the results showed that 40% of the available Pd and Pt can be recycled in just 1 h. In the absence of hydrodynamic cavitation and using conventional electrochemistry less than 10% of the available Pt and Pd is recovered in 1 h. The cost analysis showed that Pd and Pt can be recovered at less than 10 EUR per g which is 5 times smaller than their current market price.

Nucleation mode particle evolution in a gasoline direct injection engine with/without a three-way catalyst converter

For gasoline direct injection (GDI) engines, as the exhaust gas temperature decreases, the hydrocarbon-to-particle conversion may occur, generating nucleation mode particles. A three-way catalyst converter (TWC) may have effects on the particle evolution as exhaust temperature decreases. In the present study, the effects of TWCs on particulate matter emissions and hydrocarbon-to-particle conversion process under different exhaust gas temperatures are researched.The particle size distributions are compared between the pre-TWC (upstream of the TWC) and post-TWC (downstream of the TWC) positions. Results show that the reduction of total particle number concentrations is 40–80% after exhaust gas passes the TWC, which is higher at higher load. The TWC has higher reduction efficiencies for particles in smaller size ranges. In the size range of 4–8 nm, the reduction efficiencies for particles are more than 96%. For particles larger than 50 nm, the TWC doesn’t show remarkable effects on particle number (PN) concentrations.The particle evolution and the hydrocarbon-to-particle conversion with regard to the exhaust gas temperatures are also investigated. At the post-TWC position, the PN concentrations of nucleation mode are much lower compared with those of accumulation mode, and not sensitive to exhaust temperature variations. The PN concentrations of nucleation mode at the pre-TWC position with the sampling temperature of 170 °C are slightly higher than those at the post-TWC position. PN concentrations of nucleation mode at the pre-TWC position increase sharply when the sampling temperature decreases from 110 °C to 50 °C. It is suggested that TWCs don’t convert the nucleation mode particles directly, but remove those semi-volatile hydrocarbon components as precursors of nucleation mode particles forming in low exhaust temperatures.

Influence of composite after-treatment catalyst on particle-bound polycyclic aromatic hydrocarbons–vapor-phase emitted from modern advanced GDI engines

With mutagenic and cacogenic potential polycyclic aromatic hydrocarbons (PAHs) generated from engine source which have contributed to a substantial share of air toxic, so in order to characterize and eliminate the PAHs emissions of commercial engine fuelled, an experimental study has been carried out on a V6 gasoline engine working in spark-ignition (SI) and homogeneous charge compression ignition (HCCI) equipped with smart three-way catalyst converter (TWC). The particle phase and gas phase of PAHS in engine exhaust, downstream and upstream the catalyst were collected by stainless-steel cartridges containing XAD-2 resin to capture PAHs species. The vapour phase and particulate bound PAHs compounds observed with two and three rings to exist almost entirely in the gas phase, on the other hands, five or more fused rings are predominantly adsorbed on soot particles, the intermediate – 4 ring PAHS exist in the two PAHS phases, naphthalene is the most abundant polycyclic aromatic hydrocarbon that was detected in the exhaust vapour-phase on both engine modes. The prototype catalytic converter eliminates most of the polycyclic aromatic hydrocarbons species in both PAHS phases, particle phase and gas phase, except for NAP species. A prototype catalyst showed higher efficient conversion on PAHS particulate-bound phase than vapor phase for both engine modes. However, when hydrogen was added upstream of the catalyst, the catalyst conversion efficiency in reducing naphthalene was increased by approximately 20%.

Evaluating real-world emissions of light-duty gasoline vehicles with deactivated three-way catalyst converters

Three-way catalyst (TWC) converter is one of the most important after-treatment device for modern light-duty gasoline vehicles (LDGVs), which can efficiently control exhaust emissions of carbon monoxide (CO), total hydrocarbons (THC) and nitrogen oxides (NOX). Nevertheless, a considerable part of in-use taxis in Beijing would operate with TWC purposely removed, which have been indicated by vehicular on-board diagnostic (OBD) systems. In light of high vehicle-use intensity for taxis, we recruited three China 4 non-TWC taxis and three China 4 normal taxis in a comparative experimental test by using a portable emissions measurement system (PEMS). The results indicated that non-TWC taxis emitted significantly higher emissions of air pollutants than normal taxis with TWC functioning. For example, average emission factors of non-TWC vehicles were comparable to emission levels of China 1 LDGVs measured in previous studies. By contrast, emissions from normal China 4 taxis were all below China 4 emission limits. Furthermore, an operating mode binning method and a micro-trip approach have been employed to link vehicle emissions with driving conditions. For non-TWC taxis, we identified strong correlations of all pollutant categories between emission factors and average speed. However, such correlations for normal taxis were less strong, in particular for CO and THC emissions that were hardly sensitive to speed changes. This phenomenon indicates that the role of traffic conditions in affecting real-world emissions would become weaker when TWC can effectively mitigate emissions. This paper highlights the importance of in-use emission inspection to avoid any “high emitters” that have violated regulation enforcement.

The Measurement Situation of Concentrations of Gaseous Hydrocarbons

Nowadays, there is an increasing number of vehicles on the road, and because of that, the air pollution is more serious than before. Although there is a three-way Catalyst Converter in every car, which can transform the CO, HC and NOX to the harmless ingredients like H2O from the exhausted fumes. It is not sure that all the gas, such as: HC can be transform entirely. Thus, many vehicle manufactures intend to find some equipment to control and measure the concentration of hydrocarbons from exhausted fumes to meet the requirement of vehicle emission of world standard. This report may help the vehicle companies to solve this problem. This report first mainly describes the specific chemical types of the gaseous hydrocarbon in exhausted fume which are Alkanes, Alkenes, Alcohols, and Ether. And it also posts the disadvantages of these toxic chemicals in exhausted fumes, for instance, it is harmful to human and it pollutes the environment. Secondly, the report introduces some approaches to measure the concentration of hydrocarbon in exhausted fume from vehicles, for examples, Mass Spectrometry and Gas Chromatography, The flame ionization detector, Infrared spectroscopy, and Raman Spectrum. Furthermore, these approaches are used as a medium to find the companies who can provide such equipment to test the concentration of hydrocarbon: Horiba, AVL, and Ocean Optics. The third, the product data from these three companies is listed and compared with each other. Finally, the evaluation result of instruments to measure the concentration of gaseous hydrocarbons is shown as an input to vehicle manufactures.

A novel volumetric efficiency model for spark ignition engines equipped with variable valve timing and variable valve lift Part 1: model development

Estimation of the air charge and the volumetric efficiency is one of the most challenging tasks in the control of internal-combustion engines owing to the intrinsic complexity and the non-linearity of the gas flow phenomena. In particular, with emerging new technologies such as systems with variable valve timing and variable valve lift, the number of effective parameters increases greatly, making the estimation task more complicated. On the other hand, using a three-way catalyst converter needs strict control of the air-to-fuel ratio to around the stoichiometric ratio, and hence more accurate models are required for estimation of the air charge. Therefore, various models have been proposed in the literature for estimation of the volumetric efficiency and the air charge. However, they are either strictly based on physical first principles, making them impractical for conventional applications, or nearly fully empirical and need many experimental data for calibration. In this paper, using a novel approach, a new semiempirical model is proposed for estimation of the volumetric efficiency, which is calibrated with very few experimental data and can be used easily for real-time applications. In addition to the valve timings, the engine speed and the intake manifold pressure, the inlet valve lift is also considered as the model input. The generalizability of the model is proved by applying it to estimate the volumetric efficiency of six different engines. Furthermore, a systematic approach is taken to simplify the proposed model and to strengthen its prediction capability. The result is a simple, practical and generalizable model which can be used for various spark ignition engines, can be trained with very few data and can be utilized for estimating accurately the volumetric efficiency in real-time applications.

Activity and thermal stability of Rh-based catalytic system for an advanced modern TWC

The catalytic activity and thermal durability of Rh supported on a variety of metal oxides for removing NOx in the three-way catalyst (TWC) converter have been investigated under realistic gasoline engine exhaust conditions. Among the Rh/metal oxide catalysts examined, the Rh/ZrO2 catalyst has the best thermal durability. The catalytic activity and thermal stability of the Rh/ZrO2 catalysts have shown strong dependence on the ZrO2 support employed, with the ZrO2 prepared by the sol–gel (SG) and precipitation (P) methods exhibiting the most favorable catalytic performance. The improved TWC performance and thermal stability of the Rh/ZrO2 (SG and P) catalysts compared to other Rh/ZrO2 catalysts are mainly due to the structural difference in the underlying ZrO2 supports. Both ZrO2 (P) and ZrO2 (SG) contain the tetragonal as well as the monoclinic phase of ZrO2, whereas the others are primarily in the monoclinic phase. Deactivation of the Rh/ZrO2 upon thermal aging is mainly caused by the loss of the active metal surface area of Rh due to sintering and/or burial of Rh into the sublattice of ZrO2. The strong interaction of Rh with the tetragonal phase of ZrO2 appears to prevent the burial of Rh into ZrO2 lattice during the thermal aging. A series of comparative kinetic experiments revealed that the Rh/ZrO2 (SG and P) catalysts among other Rh/metal oxide catalysts produce the least amount of harmful NH3, which can be subsequently oxidized to hazardous NOx over the Pd-based oxidation catalyst co-existing in the TWC converter. A dual-brick monolith system washcoated with Rh/ZrO2 (P) and Pd/Al2O3 in the front and the rear bricks, respectively, has shown superior thermal durability over monolith configurations investigated in the present study.

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.

승용차용 세라믹 촉매 담체의 열적 내구성의 실험적 평가

Ceramic honeycomb structures have performed successfully as catalyst supports for meeting hydrocarbon, carbon monoxide and nitrous emissions standards for gasoline-powered vehicles. Three-way catalyst converter has to withstand high temperature and thermal stress due to pressure fluctuations and vibrations. Thermal stress constitutes a major portion of the total stress which the ceramic catalyst support experiences in service. In this study, temperature distribution was measured at ceramic catalyst supports. Thermal durability was evaluated by power series dynamic fatigue damage model. Radial temperature gradient was higher than axial temperature gradient. Thermal stresses depended on direction of elastic modulus. Axial stresses are higher than tangential stresses. Tangential and axial stresses remained below thermal fatigue threshold in all engine operation ranges.

In situ deposition of silver and palladium nanoparticles prepared by the polyol process, and their performance as catalytic converters of automobile exhaust gases

In situ deposition of silver particles onto alumina and palladium particles onto mixed CeZr oxides has been achieved upon chemical reduction of the corresponding metal species (AgNO3 and PdCl2) by ethylene glycol in the presence of polyvinylpyrrolidone. The support oxide powders were found to keep their crystalline structure and morphology after treatment with hot ethylene glycol while the BET surface area decreased after metal deposition. Microprobe maps obtained from energy dispersive X-ray analysis revealed a homogeneous distribution of metal nanoparticles on the surfaces of alumina and of the mixed CeZr oxides. Supported silver and palladium were tested as catalytic converters of simulated exhaust automobile gases. The catalytic activity of silver-loaded alumina powder catalyst for CO and hydrocarbon oxidation as well as NO and NOx reduction, was found to be higher than that of a reference silver catalyst. Palladium-loaded mixed CeZr oxides powder catalyst showed a similar performance to that of a reference palladium catalyst as a three-way catalyst converter.