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In this paper, a control strategy to switch NSR (NOx storage and reduction) function from standard DeNOx by rich combustion to DiAir (Diesel NOx After-treatment by Adsorbed Intermediate Reductants) and additional advantages to use HCI (Hydrocarbon Injector) during desulfation were introduced. Investigations under a transient cycle suggest that NOx conversion with DiAir is strongly affected by preliminary NOx storage condition in the NSR catalyst. To avoid NOx breakthrough just after starting HC dosing for DiAir, a rich operation to reduce stored NOx was shown to be important and high NOx conversion could be maintained using this control strategy under a transient cycle. Furthermore, by combining HCI and in-cylinder post injection, usage of rich condition for NSR DeSOx can be expand to wider engine speed and load area.

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.

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.

Diesel particulate and NOx reduction system (DPNR) is an effective technology for the diesel after-treatment system, which can reduce particulate matter (PM) and nitrogen oxides (NOx) simultaneously. The DPNR has been developed under the Toyota D-CAT (Diesel Clean Advanced Technology) concept. Further improvement of the DPNR is hoped for cleaner air in the future. This paper reviews the results of our study to improve the NOx purification performance on the DPNR. The NOx reduction performance of the catalysts deteriorates due to thermal deterioration and sulfur poisoning. In order to improve the thermal resistance of the catalysts, the suppression of precious metal sintering in the catalyst has been studied. As a result, higher catalytic activity after aging especially under lower temperature conditions was obtained. On the other hands, improvement of desulfurization performance is one of the key technologies in order to keep the high NOx reduction capability of the catalyst.

An alternative calibration logic for engine control maps of the modern diesel engine has been developed for efficient engine calibration. This logic consists of both a fuzzy rule-based calibration and numerical optimization with DoE, (design of Experiments). This logic reduced more than 50% of calibration time against DoE. In this paper, we describe the concept and performance of the logic in detail. Especially, the details of the calibration algorithm are described.

The introduction of a large amount of EGR gas into cylinders is effective for reducing exhaust emissions in diesel engines. As combustion characteristics under the condition of higher EGR rate are highly influenced by the amount of intake charge gas and its composition. It requires a precise control method for preventing the increase of NOx and particulate matter (PM) in spite of the transient conditions of supercharging and tolerance of turbocharger. In this study, a new control method was developed based on the observed oxygen concentration of charge gas and excess air ratio (stands for the oxygen concentration of burnt gas) which are the main physical factors governing NOx and PM formation. In a conventional method, the intake airflow rate is controlled to meet a target value determined in advance in the stationary engine operating condition.

A new method that optimizes the control map of hydrocarbon addition to diesel exhaust gas for hydrocarbon selective catalyst reduction (HC-SCR) has been developed. This method is comprised of a numerical HC-SCR model and a new optimization technique using Evolutionary Programming based on the evolution of living things. As a result of this evaluation, the number of calculations to obtain the optimized control map with this method was one third that using the conventional method. By using the obtained optimized control map, the NOx conversion was found to be greater by 18% than that with the constant addition of hydrocarbon.