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One of the main causes of the inadequate transient response of a 4-valve engine was established as being partition wall-wetting. The possibility of resolving this problem by improving fuel atomization was investigated. An air-mix type injector, although producing finer droplets with more uniform distribution, was not found effective in improving transient response. The development of a two-hole injector is described. This new injector produces twin sprays which are directed into the siamese intake ports without wetting the partition wall. As a consequence, the lean A/F ratio excursion is reduced, torque stumble is eliminated and the conversion efficiency of a three-way catalyst is increased.

To prevent global warming, further reductions in carbon dioxide are required. It is therefore important to promote the spread of electric vehicles powered by internal combustion engines and electric vehicles without internal combustion engines. As a result, emissions from hybrid electric vehicles equipped with internal combustion engines should be further reduced. Interest in catalytic reactions in an electric field with a higher catalytic activity compared to conventional catalysts has increased because this technology consumes less energy than other electrical heating devices. This study was therefore undertaken to apply a catalytic reaction in an electric field to an exhaust emission control. First, the original experimental equipment was built with a high voltage system used to conduct catalytic activity tests.

At the engine restart, when the temperature of the catalytic converter is low, additional fuel consumption would be required to warm up the catalyst for controlling exhaust emission.The aim of this study is to find a thermally optimal way to reduce fuel consumption for the catalyst warm up at the engine restart, by improving the thermal retention of the catalytic converter in the cool down process after the previous trip. To make analysis of the thermal flow around the catalytic converter, a 2-D thermal flow model was constructed using the thermal network method. This model simulates the following processes: 1) heat conduction between the substrate and the stainless steel case, 2) heat convection between the stainless steel case and the ambient air, 3) heat convection between the substrate and the gas inside the substrate, 4) heat generation due to chemical reactions.

Polymer electrolyte membrane fuel cell (PEFC) systems for fuel cell vehicles (FCVs) require both performance and durability. Carbon is the typical support material used for PEFC catalysts. However, hydrogen starvation at the anode causes high electrode potential states (e.g., 1.3 V with respect to the reversible hydrogen electrode) that result in severe carbon support corrosion. Serious damage to the carbon support due to hydrogen starvation can lead to irreversible performance loss in PEFC systems. To avoid such high electrode potentials, FCV PEFC systems often utilize cell voltage monitor systems (CVMs) that are expensive to use and install. Simplifying PEFC systems by removing these CVMs would help reduce costs, which is a vital part of popularizing FCVs. However, one precondition for removing CVMs is the adoption of a durable support material to replace carbon.

Three-way catalyst shows high performance under stoichiometric atmosphere. The CeO2-ZrO2 based materials (CZ) are added as a buffer of O2 concentration. To improve the catalyst performance the larger O2 storage capacity (OSC) are needed. Theoretically, the sulfur oxidation-reduction reaction moves oxygen 8 times larger than cerium. We focused on this phenomenon and synthesized Ln2O2SO4 as a new OSC material. The experimental result under model gas shows that the OSC of Ln2O2SO4 is 5 times lager than CZ.

Performance improvements were studied for the diesel particulate and NOx reduction system (DPNR), a system that simultaneously reduces NOx and Particulate Matter (PM) from diesel engine exhaust gas. The experimental system (hereinafter called the “dual DPNR”) consists of two DPNR catalysts arranged in parallel, each provided with an exhaust throttle valve downstream to control the exhaust gas flow to the catalyst, plus a fuel injector that precisely controls the air-fuel ratio and the catalyst bed temperature. The fuel injector is used to supply a rich mixture to the DPNR catalyst, and the flow of exhaust gas is switched between the two catalysts by operating the exhaust throttle valves alternately. Tests were conducted with the engine running at steady state. The results indicated that the NOx reduction performance dramatically improved and the loss of fuel economy from the NOx reduction reduced.

Catalyst specifications and converter layouts were studied to identify the high conversion performance under various in-use driving conditions, high mileage intervals and extended life cycle. The effects of volumes, configuration, selection and loading distribution of precious metals, additive components and substrate type for catalyst were studied on engine dynamometers and vehicle tests to optimize a catalyst converter system. Moreover, model gas experiments were conducted to analyze deterioration mechanisms and conversion characteristics of catalysts. As a result, the concept of a divided catalyst converter system, which provides separate functions for a close-coupled and an under-floor catalyst, was found to be effective for the future exhaust system. For reducing HC emissions, the close-coupled catalyst should warm up quickly and resist a high temperature. The under-floor catalyst, located at a rather low temperature position, is durable and maintains high NOx conversion.

The development of an alternative oxygen reduction electrocatalyst to platinum based electrocatalysts is critical for practical use of the polymer electrolyte membrane fuel cell (PEMFC). Transition metal sulfide chalcogenides have recently been reported as a possible candidate for Pt replacement. Our work focused on chalcogenides composed of ruthenium, molybdenum, and sulfur (RuMoS). We elucidate the factors affecting electrocatalytic activity of carbon supported RuXMoY SZ catalyst. This was demonstrated through a correlation of oxygen reduction reaction (ORR) activity of the catalysts with structural changes resulting from designed changes in sulfur composition in the catalysts.

The emission characteristics of hydrocarbons during the cold start and the warm-up have been investigated. Timed sampling of hydrocarbon emissions upstream and downstream of a close-coupled catalytic converter have been carried out. The experimental results show that the emission characteristics of hydrocarbons are influenced by both the engine operating conditions and the heating characteristics of the catalytic converter. In the case of engine-out hydrocarbons, the total amount of hydrocarbons drastically decreases but the percentage contribution of the C2-C4 olefins to the engine-out hydrocarbons increases as the warm-up proceeds. Since these olefins have relatively high maximum incremental reactivity (MIR) factors, the specific reactivity (SR) of the engine-out hydrocarbons gradually increases during the warm-up. The adsorption and desorption processes of the engine-out hydrocarbons on the catalyst occur before the catalyst light-off.

A new after-treatment system called DPNR (Diesel Particulate-NOx Reduction System) has been developed for simultaneous and continuous reduction of particulate matter (PM) and nitrogen oxides (NOx) in diesel exhaust gas. This system consists of both a new catalytic technology and a new diesel combustion technology which enables rich operating conditions in diesel engines. The catalytic converter for the DPNR has a newly developed porous ceramic structure coated with a NOx storage reduction catalyst. A fresh DPNR catalyst reduced more than 80 % of both PM and NOx. This paper describes the concept and performance of the system in detail. Especially, the details of the PM oxidation mechanism in DPNR are described.

In this study, reaction path analysis and modeling of NOx reduction phenomena by selective catalytic reduction (SCR) with NH3 over a Cu-chabazite catalyst were conducted considering changes in the valence state of Cu sites and local structure due to differences in ligands to the Cu sites. The analysis showed that in the Cu-chabazite catalyst, NOx was mainly reduced by adsorbed NH3 on divalent Cu sites accompanied by a change in valence state of Cu from divalent to monovalent. It is known that the activation energy of NOx reduction on a Cu-chabazite catalyst changes between low temperatures ≤ 200 °C and mid to high temperatures ≥ 300 °C. To express this phenomenon, a reversible hydrolysis reaction based on the difference in coordination state of hydroxyl groups (OH−) to Cu sites at low and high temperatures was introduced into the model.

The details of Di-Air, a new NOx reduction system using continuous short pulse injections of hydrocarbons (HC) in front of a NOx storage and reduction (NSR) catalyst, have already been reported. This paper describes further studies into the deNOx mechanism, mainly from the standpoint of the contribution of HC and intermediates. In the process of a preliminary survey regarding HC oxidation behavior at the moment of injection, it was found that HC have unique advantages as a reductant. The addition of HC lead to the reduction or metallization of platinum group metals (PGM) while keeping the overall gas atmosphere in a lean state due to adsorbed HC. This causes local O₂ inhibition and generates reductive intermediate species such as R-NCO. Therefore, the specific benefits of HC were analyzed from the viewpoints of 1) the impact on the PGM state, 2) the characterization of intermediate species, and 3) Di-Air performance compared to other reductants.

In this study, reaction path analysis and modeling of NOx reduction phenomena by fast SCR reaction on a Cu-chabazite catalyst were conducted, considering the formation and decomposition of ammonium nitrate (NH4NO3). White crystals of NH4NO3 decompose at temperatures < 200 °C. Thus, the reaction behavior changes at 200 °C under fast SCR reaction conditions. NH4NO3 formation can occur on both Cu sites and Brønsted acid sites, which are active sites for NOx reduction in the Cu-chabazite catalyst, but it is unclear where NH4NO3 accumulates on the catalyst. Analyses using catalyst test pieces with different active sites were performed to estimate this accumulation. The results suggested that NH4NO3 accumulation does not depend on the presence of either Cu sites or Brønsted acid sites. Therefore, it is assumed that NH4NO3 can be accumulated everywhere on the catalyst, including on the zeolite framework. This phenomenon was included in the model as formation/accumulation sites S'.

The deactivation process of automotive catalysts by lead and phosphoruos were studied. The accelerated poisoning test were performed. The activity evaluation and characterisation of poisoned pellet oxidation catalysts showed the following origin of poisoning deactivations. Lead interacts with active materials and phosphorus covers over catalysts to reduce these catalytic performance. In the case of phosphorus and lead co-existence, the activity decreases rapidly because leadphosphate plugges pores of the support. In monolithic catalysts, highly axial distributions of poisons was obserbed. This characteristic distribution is advantageous for the durability of the catalyst.

The knock-suppression effectiveness of exhaust-gas recirculation (EGR) can vary between implementations that take EGR gases after the three-way catalyst and those that use pre-catalyst EGR gases. A main difference between pre-and post-catalyst EGR gases is the level of trace species like NO, UHC, CO and H2. To quantify the role of NO, this experiment-based study employs NO-seeding in the intake tract for select combinations of fuel types and compression ratios, using simulated post-catalyst EGR gases as the diluent. The four investigated gasoline fuels share a common RON of 98, but vary in octane sensitivity and composition. To enable probing effects of near-zero NO levels, a skip-firing operating strategy is developed whereby the residual gases, which contain trace species like NO, are purged from the combustion chamber. Overall, the effects of NO-seeding on knock are consistent with the differences in knock limits for preand post-catalyst EGR gases.

This paper presents the numerical simulation method to predict the deactivation process of three-way catalytic converters. Three-way catalytic converter's deactivation typically results from thermal and chemical mechanisms. The major factor of thermal deactivation is the sintering of noble metal particles, which is known to depend on the ageing temperature and the oxygen concentration in the exhaust gas. The chemical deactivation is mainly caused by the poisoning, which has two effects on the catalyst deactivation. One effect is the loss of the catalyst activity, which is expressed by reduced frequency factors of reaction rates. Another effect is the suppression of the noble metal sintering. Poison deposits prevent the noble metal particles from moving in the washcoat, assisted by the reduced thermal loading of reaction heats, which is caused by the loss of the catalyst activity. Modeling these deactivation factors, we propose the rate expression of noble metal sintering.

A new heating strategy for electrically heated catalysts has been developed which reduces power consumption while achieving the desired hydrocarbon conversion. The relationship between catalyst volume and power consumption is presented. Observations of catalytic reactions by a thermoviewer camera and mathematical simulations are used to optimize the heating pattern. Significant reductions in power consumption, while maintaining conversion efficiency, are reported by heating only the front face of the catalyst. However, prior to mass production additional work is required to improve durability, and reliability and to resolve manufacturing issues.

HEV and PHEV require an improved aftertreatment system to clean the exhaust gas in various driving situations. The efficiency of aftertreatment system is significantly influenced by the residence time of the gas in a catalyst which gas flow has generally strong pulsation. Simulation showed up to 70% reduction of exhaust gas emission if the pulsation could be completely attenuated. A new concept exhaust manifold was designed to minimize pulsation flow by wall impingement, with slight increase of pressure loss. Experimental results with new concept exhaust manifold showed exhaust gas emission were reduced 16% at cold condition and 40% at high-load condition.

The advantages of gasoline direct-injection are intake air cooling due to fuel vaporization which reduces knocking, additional degrees of freedom in designing a stratified injection mixture, and capability for retarded ignition timing which shortens catalyst light-off time. Stratified mixture combustion designs often require complicated piston shapes which disturb the fluid flow in the cylinder, leading to power reduction, especially in turbocharged gasoline direct-injection engines. Our research replaced the conventional shell-type shallow cavity piston with a dog dish-type curved piston that includes a small lip to facilitate stratification and minimize flow disturbance. As a result, stable stratified combustion and increased power were both achieved.

Two effects of rich-spike duration on NOx-storing have been analyzed. The first one, that NOx-storing speed decreases as rich-spike duration increases, is explained as the influence of NOx diffusion in wash-coat layer, which is quantified by a simple mathematical expression for NOx-storing rate. The second one, a peculiar behavior of NOx-storing in appearance of the outlet NOx concentration, is clarified: Heat produced directly or indirectly (via oxygen storage in ceria) by rich-spike warms up the downstream part, which releases excess NOx at the raised temperature. Contributions of the oxygen storage and the carbonate of NOx-storage material are also discussed.