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In this paper, emissions reduction technologies applied to high-speed direct injection (HSDI) diesel passenger car engines to meet the stricter exhaust emission legislation are described. To reduce smoke, the F.I.E. has been improved by using a radial-piston distributor pump which delivers fuel-injection-pressure up to 120MPa. Cooled exhaust gas re-circulation (EGR) system and increase in volume ratio of the combustion chamber has made it possible to increase EGR ratio and reduced nitrogen oxides (NOx) and smoke simultaneously. Furthermore, improvements in the oxidation catalyst activating temperature reduces PM at lower exhaust gas temperatures. As a result of applying these technologies, a clean and economical HSDI diesel engine for passenger cars, which complies with Japanese '98 exhaust emissions legislation and has better fuel economy than indirect injection (IDI) diesel engines (above 15%), has been developed.

Since a NOx trap catalyst cyclically releases and reduces NOx with rich exhaust gas, generating of a rich spike becomes important for application to diesel engines, which always operate with overall lean combustion. In addition, a NOx trap catalyst is poisoned and degraded in performance by the presence of SO2 in the exhaust gas. When the NOx absorbing efficiency thus decreases, it is necessary to regenerate the catalyst by a sulfur purge (desulfation) process in order to remove SO2. It is apparent that there are many factors and effects to understand before one can apply this catalyst system to a diesel engine, therefore we have carried out an inquiry into a performance of the NOx catalyst used the model gas equipment with known gas mixtures. The rich spike was generated with diesel fuel (light oil), resulting in a transient equivalence ratio spike > 1, to simulate diesel exhaust gas.

An after-treatment system consisting of a lean NOx trap, diesel particulate filter (DPF), and diesel oxidation catalyst (DOC) was applied to a light-duty commercial vehicle engine. Extensive exhaust gas testing under the transient JE05 test cycle was carried out. Lean NOx trap characteristics and issues related to transient operation were clarified and areas for system improvement were suggested. When exhaust gas temperatures were low, the NOx conversion efficiency was low, then stored NOx remained in the catalyst during rich operation, without desorption and reduction. The first half of the JE05 test cycle has relatively low exhaust gas temperatures, while the latter half has more high speed operation with rapidly increasing and higher catalyst temperature. Because of this, NOx trapped in the catalyst during the first half was desorbed and expelled during the high temperature second half, resulting in a lower NOx conversion rate for the entire test cycle.