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Diesel engines with relatively good fuel economy are known as an effective means of reducing CO₂ emissions. It is expected that diesel engines will continue to expand as efforts to slow global warming are intensified. Diesel particulate and NOx reduction system (DPNR), which was first developed in 2003 for introduction in the Japanese and European markets, shows high purification performance which can meet more stringent regulations in the future. However, it is poisoned by sulfur components in exhaust gas derived from fuel and lubricant. We then developed the sulfur trap DPNR with a sulfur trap catalyst that traps sulfur components in the exhaust gas. High purification performance could be achieved with a small amount of platinum group metal (PGM) due to prevention of sulfur poisoning and thermal deterioration.

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.

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.

An unprecedented phenomenon that achieves high NOx conversion was found over an NSR catalyst. This phenomenon occurs when continuous short cycle injections of hydrocarbons (HCs) are supplied at a predetermined concentration in lean conditions. Furthermore, this phenomenon has a wider range of applicability for different catalyst temperatures (up to 800 degrees Celsius) and SVs, and for extending thermal and sulfur durability than a conventional NOx storage and reduction system. This paper analyzes the reaction mechanism and concludes it to be highly active HC-deNOx by intermediates generated from adsorbed NOx over the base catalysts and HCs partially oxidized by oscillated HC injection. Subsequently, a high performance deNOx system named Di-Air (diesel NOx aftertreatment by adsorbed intermediate reductants) was demonstrated that applies this concept to high speed driving cycles.

The poisoning of three way catalysts (TWC) by the phosphorus contained in oil formulations containing zinc dialkyldithiophosphate (ZDDP) is examined. Catalysts were exposed to various types of ZDDP and detergents under conditions that were known to reduce performance through phosphorus poisoning without the blocking of sites by formation of glazing. The presence of phosphorus was detected with energy dispersive x-ray spectroscopy (EDX). In addition to analyzing the surface concentration of the phosphorus on the washcoat, the catalyst was cross cut so phosphorus that diffused into the washcoat could be mapped. The total phosphorus in the catalyst could then be calculated. The amount of total phosphorus detected correlated well with the reduced activity of the catalyst as measured by the temperature of 50% conversion.

Premixed diesel combustion modes including low temperature combustion and MK combustion are expected to realize smokeless and low NOx emissions. As ignition must be delayed until after the end of fuel injection to establish these combustion modes, methods for active ignition control are being actively pursued. It is reported that alcohols including methanol and ethanol strongly inhibit low temperature oxidation in HCCI combustion offering the possibility to control ignition with alcohol induction. In this research improvement of diesel combustion and emissions by ethanol intake port injection for the promotion of premixing of the in-cylinder injected diesel fuel, and by increased EGR for the reduction of combustion temperature.

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.

In order to further improve the performance of NOx storage-reduction catalysts (NSR catalysts), focus was placed on their high temperature performance deterioration via sulfur poisoning and heat deterioration. The reactions between the basicity or acidity of supports and the storage element, potassium, were analyzed. It was determined that the high temperature performance of NSR catalysts is enhanced by the interaction between potassium and zirconia, which is a basic metal oxide. Also, a new zirconia-titania complex metal oxides was developed to improve high temperature performance and to promote the desorption of sulfur from the supports after aging.

To realize the high performance of the three-way catalyst, this development focused on the heat resistance of the CeO2-ZrO2 solid solution (CZ) that possesses the oxygen storage capacity (OSC). A new concept of the OSC compound with high durability is proposed. We devised a new method of inhibiting the coagulation of the primary CZ particles by placing diffusion barrier layers made of alumina among the primary CZ particles. This material is called “ACZ”. The specific surface area of ACZ was larger than that of the conventional CZ after durability test. The sintering of Pt on the ACZ-added catalyst is inhibited and the crystal size of CZ in the ACZ-added catalyst is smaller than that in the CZ-added catalyst. The OSC and the light off temperature of the ACZ-added catalyst are improved.

The effects of the phosphorus and sulfated ash contents of engine oils on the deactivation of monolithic three-way catalysts and oxygen sensors were studied. The effect of temperature was evaluated as well. The catalysts and oxygen sensors were poisoned in a 100-hour engine bench test. As a result, it was learned that engine oils with higher phosphorus contents showed a higher concentration of phosphorus on the catalyst surfaces, and the ability of the catalysts to convert carbon monoxide and oxides of nitrogen decreased. However, the phosphorus content was not observed to have any effect on hydrocarbons. The sulfated ash reduced the phosphorus concentration on the catalyst surface, but it also had a negative effect on the catalytic activity. The deactivation of the catalysts was much more noticeable at 800°C than at 720°C. In the tests at 720°C and 800°C, no deactivation of the oxygen sensors was observed, regardless of the composition of the engine oil.

New 2A/F systems different from usual A/F-O2 systems are being developed to cope with strict regulation of exhaust gas. In the 2A/F systems, 2A/F sensors are equipped in front and rear of a three-way catalyst. The A/F-O2 systems are ideas which use a rear O2 to detect exhaust gas leaked from three-way catalyst early and feed back. On the other hand, the 2A/F systems are ideas which use a rear A/F sensor to detect nearly stoichiometric gas discharged from the three-way catalyst accurately, and to prevent leakage of exhaust gas from the three-way catalyst. Therefore, accurate detection of nearly stoichiometric gas by the rear A/F sensor is the most importrant for the 2A/F systems. In general, the A/F sensors can be classified into two types, so called, one-cell type and two-cell type. Because the one-cell type A/F sensors don’t have hysteresis, they have potential for higher accuracy.

In conventional gasoline engine vehicles, three-way catalysts are used to simultaneously remove HC, CO and NOx from the exhaust gas. The effectiveness of the catalyst to remove these harmful species depends strongly on the oxygen concentration in the exhaust gas. Deterioration of three-way catalyst results in a reduction in its purification activity and OSC (oxygen storage capacity). In this investigation, additive elements were used to enhance the durability and OSC of the catalyst support material. An optimized formulation of a CeO2-ZrO2 and a ZrO2 material was developed to have excellent durability, improved OSC, enhanced interaction between precious metals and support materials, and increase thermal stability. Using these newly developed support materials, catalysts with increased performance was designed.

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.

In response to various reformulated gasoline regulations, several studies have been conducted to evaluate the relationship between fuel properties and vehicle exhaust emissions. These studies, however, have focused on the fuel effect and have not examined the most promising advanced technology emission control systems on low emission vehicles. Toyota's reformulated gasoline research first set out to study the effect fuel compositions has on 2 different emission control systems. On both systems, non-methane hydrocarbon (NMHC) emissions were significantly affected by the 50% and 90% distillation temperature (T50 and T90). A correlation was also found exhaust olefine content and the amount of MTBE contained in the fuel. Research was also conducted on the specific ozone reactivity (SOR) of exhaust hydrocarbons. Various fuels with similar specifications but blended from different feedstocks were evaluated.

In developing an oxidation catalyst for reducing diesel particulates, it is necessary to balance two conflicting characteristics. One is high oxidizing activity so that the catalyst can reduce the Soluble Organic Fraction (SOF) efficiency even at low exhaust temperatures. The other is the suppression of sulphate formation at high exhaust temperatures. First it was studied that active metals and coating materials are given effects on the reduction of SOF, the formulation of sulphate and durability, by using catalysts equivalent in composition to the oxidation catalyst for gasoline-engines. Based on these findings, a two-stage catalyst wasdeveloped. It satisfies the two characteristics at a comparatively high levelby slecting materials and optimizing the catalyst composition.

It is widely known that pellet-typed catalysts are deactivated by phosphorus (ZnDTP) that comes from engine oils. In this paper, the poisoning of monolithic three-way catalysts and oxygen sensors by engine oils is studied. First, catalysts and oxygen sensors were poisoned on the engine bench by test oils in which the quantity of phosphorus and ash was varied. Next, performance of the catalysts and sensors alone was examined and the vehicle exhaust emission at FTP mode was measured on a chassis dynamometer. The results indicate that phosphorus in engine oils poisons the monolithic catalyst and the oxygen sensor resulting in deterioration of the vehicle NOx exhaust emission. However, Ca sulfonate and Mg sulfonate detergents act by restraining phosphorus poisoning of the catalyst and the oxygen sensor. Through analysis of the catalyst and sensor surfaces, it is concluded that phosphorus poisons the catalyst and sensor forming a dense coating.

The Pd only three-way catalyst with Rh as an activator completely removed has been developed. The catalyst has been improved with regards to its thermal stability and its NOx reduction capability in the fuel rich region. These two factors have been known as the weak points of Pd catalyst. The thermal stability of the Pd catalyst was improved by modifying the washcoat alumina to yield a higher thermal stability. On the other hand, the NOx reduction capability was controlled by adding a combination of La and Ba. The developed Pd only three-way catalyst demonstrated the equivalent performance to a current production Pt/Rh catalyst after engine dynamometer aging up to 800°C.

A new 3-way catalyst with NOx conversion performance for lean-burn engines has been developed. The catalyst oxidizes NOx and stores the resulting nitrate, which is then reduced by HC and CO during engine operation around the stoichiometric air/fuel ratio. Both the composition of the storage component and the particle sizes of the noble metal were optimized. In addition, a special air fuel mixture control has been developed to make the best of the NOx storage-reduction function. The present catalyst showed 90% conversion efficiency and improved fuel economy by 4% in the Japanese 10-15 mode test cycle. The efficiency remained at 60% or more after durability test.

The 50% and 90% distillation temperature (T50 & T90), aromatics, olefins and sulfur content are regulated in California Phase2 Reformulated Gasoline. The effects of these properties on the exhaust emissions were investigated. Twelve test fuels with little interaction between T50, T90, aromatics and olefins were prepared. Exhaust emissions were measured using a TLEV according to 1975 Federal Test Procedure (75 FTP). T50 had a large effect on exhaust HC emissions. T90 also affected HC emissions. Both increasing and decreasing T50, T90 showed increasing exhaust HC emissions. These results suggest that an optimum range of T50 and T90 exist for lowering exhaust HC emissions. The effects of sulfur on exhaust emissions were also investigated. A Pt/Rh type catalyst (production type) and a Pd type catalyst (prototype) were prepared. These catalysts were put on a 94MY TLEV. Increase of sulfur lead to increase of the exhaust emissions with both catalysts.

A multi-dimensional numerical method for predicting the warm-up characteristic of automobile catalytic converter systems was developed to effectively design catalytic converter systems which achieve low tail pipe emissions with satisfactory packagebility. The features of the method are; (1) consideration of the governing phenomena such as gas flow, heat transfer, and chemical reactions (2) capability of predicting warm-up characteristic for not only the catalytic converters but also the system as a whole during emission test modes such as the USA LA-4 mode. The description of the method is presented. The experimental verifications of the method were conducted to assure the accuracy of it. The effect of design parameters such as electrically heated catalyst (EHC), high loading of noble metal and thin honeycomb wall on warm-up characteristic of the catalyst are analyzed in the paper.