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This paper describes the development of an integrated simulation model for evaluating the effects of electrically heating the three-way catalyst (TWC) in a series hybrid electric vehicle (s-HEV) on fuel economy and exhaust gas purification performance. Engine and TWC models were developed in GT-Power to predict exhaust emissions during transient operation. These models were validated against data from vehicle tests using a chassis dynamometer and integrated into an s-HEV model built in MATLAB/Simulink. The s-HEV model accurately reproduced the performance characteristics of the vehicle’s engine, motor, generator, and battery during WLTC mode operation. It can thus be used to predict the fuel consumption, emissions, and performance of individual powertrain components. The engine combustion characteristics were reproduced with reasonable accuracy for the first 50 combustion cycles, representing the cold-start condition of the driving mode.

Battery models are being developed as a component of the powertrain systems of hybrid electric vehicles (HEVs) to predict the state of charge (SOC) accurately. Electrically heated catalysts (EHCs) can be employed in the powertrains of HEVs to reach the catalyst light off temperature in advance. However, EHCs draw power from the battery pack and hence sufficient energy needs to be stored to power auxiliary components. In series HEVs, the engine is primarily used to charge the battery pack. Therefore, it is important to develop a control strategy that triggers engine start/stop conditions and reduces the frequency of engine operation to minimize the equivalent fuel consumption. In this study, a battery pack model was constructed in MATLAB-Simulink to investigate the SOC variation of a high-power lithium ion battery during extreme engine cold start conditions (-7°C) with/without application of an EHC.

Diesel oxidation catalysts (DOCs) combining the functions of Pd and Pt-Pd alloys have been used in practice to satisfy the strict exhaust emission regulations that have been specified for passenger cars in recent years. Pd is an indispensable component in DOCs because it exhibits superior oxidation activity for CO and HC. To reduce the amount of precious metal used and to improve robustness, it is important to control the electronic state and gas adsorption characteristics of Pd and PdOx during catalytic reactions.In this study, by investigating the CO adsorption behavior of Pd, it was observed that Pd supported on a CeO2/ZrO2 mixed-oxide material (CZ) showed a preferable CO adsorption state and better CO light-off performance. Pd in Pd/CZ became metallic with increasing reaction time, and the CO oxidation performance of Pd/CZ decreased. This change in activity was correlated with CO adsorption on Pd changing from linear-type to bridge-type adsorption.

Modern diesel emission control systems often use Urea Selective Catalytic Reduction (Urea-SCR) for NOx control. One of the most active SCR catalysts is based on Cu-zeolite, specifically Cu-Chabazite (Cu-CHA), also known as Cu-SSZ-13. The Cu-SCR catalyst exhibits high NOx control performance and has a high thermal durability. However, its catalytic performance deteriorates upon long-term exposure to sulfur. This work describes our efforts to investigate the detailed mechanism of poisoning of the catalyst by sulfur, the optimum conditions required for de-sulfation, and the recovery of catalytic activity. Density functional theory (DFT) calculations were performed to locate the sulfur adsorption site within the Cu-zeolite structure. Analytical characterization of the sulfur-poisoned catalyst was performed using Extreme Ultraviolet Photoelectron Spectroscopy (EUPS) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS).

Diesel exhaust emission control systems often contain DOC (Diesel Oxidation Catalyst) + CSF (Catalyzed Soot Filter) components. In this system PM (particulate matter) is filtered and accumulated in the CSF and such filtered PM is periodically combusted by supplying heat to the CSF. The heat to CSF is generated within the DOC by an exothermic reaction with extra fuel supplied to the DOC. Here the exothermic performance of DOC depends on not only the active catalytic site (such as Pt and/or Pd) but also on the characteristics of the porous material supporting the precious metals. Various properties of Al2O3, i.e. pore diameter, pore volume, BET surface area, acidity, basicity and the Ea (activation energy) of fuel combustion, used in DOCs and PGM particle size of each DOC were measured. The fuel combustion performance of each DOC was evaluated by diesel engine bench.

The reduction of NOx in exhaust gas has been a major challenge in diesel engine development. For the NOx reduction issues, a new Lean NOx Catalyst (LNC) aftertreatment system has been developed by Honda. A feature of the LNC system is the method that is used to reduce NOx through an NH₃-Selective Catalytic Reduction (NH₃-SCR). In an LNC system NOx is adsorbed at lean conditions, then converted to NH₃ at rich conditions and subsequently reduced in the next lean phase. In recent years, as the efficiency of the diesel engine has improved, the exhaust gas temperatures have been reduced gradually. Therefore, the aftertreatment system needs to be able to purify NOx at lower temperatures. The development of a new LNC which has a high activity at low temperature has been carried out. For the improvement of the LNC three material improvements were developed. The first of these was the development of a NOx adsorbent which is matching the targeted exhaust gas temperatures.

Difference of engine combustion characteristics, species and amount of exhaust gas and PM (particulate matter consisted of SOF and Soot and Ash), and especially PM oxidation characteristics were studied when diesel fuel or bio-fuel, here PME (palm oil methyl ester) as an example, was used as a fuel. The fueling rate was adjusted to obtain the same torque for both fuels and engine was operated under several range of EGR (Exhaust Gas Recirculation) ratio. Under such conditions, PME showed shorter ignition delay time and lower R.H.R (rate of heat release) under 0-40% EGR ratio. With respect to engine exhaust gas species, CO, NO, THC and HCHO, CH3CHO concentration was almost the same when the EGR ratio is higher than 35% (Intake-Air/Fuel: A/F=20). However, PME also showed lower exhaust gas emission when the EGR ratio is higher than 30%.

In a Diesel Oxidation Catalyst (DOC) and Catalyzed Soot Filter (CSF) system, the DOC is used to oxidize additional fuel injected into the cylinder and/or exhaust pipe in order to increase the CSF's inlet temperature during soot regeneration. The catalyst's hydrocarbon (HC) oxidation performance is known to be strongly affected by the HC species present and the catalyst design. However, the engine operating conditions and additive fuel supply parameters also affect the oxidation performance of DOCs, but the effects of these variables have been insufficiently examined. Therefore, in this study, the oxidation performance of a DOC was examined in experiments in which both exhaust gas recirculation (EGR) levels and exhaust pipe injection parameters were varied. The results were then analyzed and optimal conditions were identified using modeFRONTIER.

Palladium catalysts are known to show higher methane oxidation performance than platinum and/or rhodium catalysts. In this paper, the higher oxidative dehydrogenation activity on palladium is proposed as a reason for the superior methane oxidation. When other oxidation reactions are considered, higher affinity of palladium to oxygen has also been suggested[1]. In this study, oxygen chemical potential on platinum and palladium catalyst surfaces under oxidation conditions was measured using a specially designed electrochemical sensor. The oxygen chemical potential was calculated from the sensor potential by the Nernst equation. As a result, oxygen potential on palladium during the methane oxidation reaction was found to be much higher than that of platinum, correlating with affinity to oxygen and higher methane oxidation performance. The rate of oxygen adsorption and desorption on platinum and palladium was evaluated in an engine experiment using a dual lambda-sensor procedure.

For diesel emission control systems containing a Diesel Oxidation Catalyst (DOC) and a Catalyzed Soot Filter (CSF) the DOC is used to oxidize the additional fuel injected into the cylinder and/or the exhaust pipe for the purpose of increasing the CSF inlet temperature during the soot regeneration. Hydrocarbon (HC) oxidation performance of the DOC is affected by HC species as well as a catalyst design, i.e., precious metal species, support materials and additives. How engine-out HC species vary as a function of fuel supply conditions is not well understood. In addition, the relationship between catalyst design and oxidation activity of different hydrocarbon species requires further study. In this study, diesel fuel was supplied by in-cylinder, post injection and exhaust HC species were measured by a gas chromatograph-mass spectrometry (GC-MS) and a gas analyzer. The post injection timing was set to either 73°, 88° or 98° ATDC(after top dead center).

To meet the severe PM (Particulate Matter) emission regulation for diesel vehicles, use of a DOC (Diesel Oxidation Catalyst) + CSF (Catalyzed Soot Filter) emission control system has recently been started in Japan. The CSF is used for diesel exhaust soot filtering, and the accumulated soot is periodically combusted to regenerate the CSF. The heat required for the soot regeneration is supplied from the DOC pre-cat under a specific regeneration mode. Additional fuel is supplied to the DOC by post injection and/or fuel dosing into the exhaust pipe upstream of DOC. The resulting exotherm provides the heat for soot combustion on the CSF. Uniform and controlled soot combustion in the CSF is necessary to maintain system durability during the vehicle's life. There are concerns that non-uniform fuel supply to the DOC front face may lead to non-uniform soot combustion in the CSF.

The transient HC performance of diesel oxidation catalysts is known to be greatly improved by addition of Zeolite material. The authors already reported how to estimate the effective washcoat thickness in our previous study [1]. To understand in more detail the effective catalyst layer thickness, a precise gas diffusion model and parameters of HC adsorption and desorption rate were determined in this study. The random pore model was used for a gas diffusion calculation to simulate the macro porosity of the catalyst layer and micro porosity of the Zeolite material. HC adsorption capacity as a function of temperature and HC concentration was measured by Temperature Programmed Desorption (TPD). HC desorption rate was evaluated by changing the TPD ramping rate. HC reaction rate was evaluated by using a model gas reactor. Calculated catalyst performance correlated to the experimental results, thus validating the model.

Palladium is well known to catalyze methane (CH4) oxidation more efficiently than platinum (Pt) and/or rhodium (Rh) catalysts. The mechanism for methane oxidation on palladium is hypothesized to proceed via a radical intermediate. Direct identification of a radical species was not detected by Electron Spin Resonance Spectroscopy (ESR). However, indirect evidence for a radical intermediate was found by identification of ethane (C2H6), the methyl radical(CH3 ˙ ) coupling product, by Mass spectroscopy analysis under CH4/O2 conditions.

Combustion behavior of the SOF (Soluble organic fraction) fraction of diesel particulate by flow-thru type diesel oxidation catalysts (DOC) was studied. A two brick DOC system with an air gap showed higher SOF performance than a single brick DOC of the same total volume. Collision frequency of the TPM (total particulate matter) to the catalyst layer was studied by calculation of the turbulence energy in the gas flow channel. No large difference in collision frequency was observed between one brick and two bricks. The front face effect was calculated from the geometric surface and it was confirmed that such an effect was small in the two brick DOC case. The SOF performance advantage for the two brick DOC system separated by an air gap was due to a thermo-mass effect created by reducing the DOC volume.

Pre-filter diesel oxidation catalyst (DOC) development for a DOC-CSF system has been conducted. The pre-filter DOC is required to efficiently oxidize fuel and generate heat to regenerate accumulated soot within the catalyzed soot filter (CSF). Therefore, high thermal durability is required. In addition, good transient hydrocarbon (HC) activity is required for the DOC to reduce tailpipe HC emissions. The required performance is dependent on the OEM's system control strategy. A DOC catalyst designed to have well dispersed Pt showed high fuel combustion performance. Such high Pt dispersion was obtained by using high specific surface area Al2O3. Zeolite included into the catalyst formulation showed higher transient HC performance compared to a catalyst without zeolite. The effective catalyst layer depth with respect to transient HC activity was studied by computer simulation.

Sulfate generation by diesel oxidation catalysts (DOC) is still a problem although sulfur concentration in the diesel fuel will be reduced in future. Two approaches were attempted to reduce the sulfate generation without inhibiting the HC and CO oxidation performance. One was to use an optimized support material that adsorbs less SO2 and has sufficient specific surface area for HC/CO oxidation. Another approach was to apply a layer on the catalyst, which prevents SO2 adsorption. Sulfate generation was successfully reduced while maintaining high HC/CO oxidation performance.

Ag/Al2O3 was studied as a HC-SCR (Hydrocarbon - Selective Catalytic Reduction) catalyst for diesel application[1, 2 and 3]. Performance required of (or from) this catalyst is high NOx conversion with high thermal durability and sulfur resistance. Also low HC slip is desired. The Ag/Al2O3 system was improved by addition of additives. In the diesel 13-mode (Japan) evaluation, improved Ag/Al2O3 catalyst showed higher de-NOx activity (>50%) compared to the original when fresh. Improved Al2O3 catalyst showed smaller hysteresis of de-NOx activity between ramping up and down the temperature and smaller amount of HC slip. To study the improvement effect, interactions between the HC and catalyst were investigated by TG/DTA-MS (define) and FT-IR (define). TG/DTA measurement results showed that HC/O2 reaction was restrained in the improved catalyst. These results suggest that there was sufficient of HC for NOx reduction on the improved catalyst.

Soot (here, total particulate matter; TPM) accumulation in a diesel particulate filter (DPF) was characterized for two different engine conditions (high speed / high load and low speed / low load). Soot weight distribution within the filter was different in two engine conditions the accumulated PM layer was thicker when the engine conditions were low speed / low load even though the accumulated soot amounts were almost equivalent. Flow field conditions in a DPF were calculated and soot accumulation conditions were assumed from the solution. In the axial direction (with gas flow) uniform soot accumulation was suggested. However, in the radial direction (from center to side), non-uniform accumulation was suggested from the flow field solution and this result was experimentally confirmed. Temperature distribution in the DPF during uncontrolled soot regeneration was also calculated. The simulation suggested that the highest temperature would be observed in the back middle area of DPF.