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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.

Our two types of NOx storage-reduction (NSR) catalyst have been tested under various conditions of thermal endurance; the performance of these catalysts have been regressed to give the formulas that enable to estimate the performance after thermal endurance; and we have found the method to simplify (shorten the duration of) the thermal endurance tests and that the thermal deterioration of NSR catalysts is controlled by the worst condition of endurance (at least approximately). The regression formula for the amount of potassium that contributes to the catalyst performance (active K) after the endurance has also been obtained. These formulas predict that the amount of active K is the least for the worst condition of endurance and suggest a difference in deterioration mechanism that reflects the performance between low and high temperatures and the portion of worse deterioration (front or rear).

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.

A methanol fueled, lean burn system has been developed to improve both specific fuel consumption and NOx emissions. A 1.6L four-cylinder engine with increased compression ratio has been used to develop this system. Three major components of the Toyota Lean Combustion System (T-LCS) have been applied: (1) A helical port with a swirl control valve (2) A lean mixture sensor (3) Timed, multi-point fuel injection. A 2250 lb. Inertia Weight test vehicle has been fitted with this engine, and fuel system materials have been modified. This methanol, lean burn system has improved the fuel economy by about 12% still satisfying the 1986 emission standards of the U.S.A. and Japan. Aldehyde emissions have also been evaluated.