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As countermeasures against global warming caused by carbon dioxide, improvement of automotive fuel economy to lower CO2 emission becomes important. In order to promote less CO2 vehicles, appropriate methods to evaluate vehicle fuel economy performance are needed. However, the existing fuel economy test is limited to passenger cars and light duty trucks. The test is executed on a chassis dynamometer. However, if this test method is applied to heavy-duty vehicles (HDV), a large sized chassis dynamometer is needed. Furthermore, heavy duty vehicles have wide variations in a combination of an equipped engine, body shape, a transmission gear, a permissible limit of pay load, and so on. This leads to the increase in the number of chassis dynamometer tests. Therefore, it is difficult to use chassis dynamometer test to evaluate HDV fuel economy performance.

The authors have developed a new partial flow dilution tunnel (hereafter referred to as PPFT), whose principal device is a flux splitting gas divider, as a new means of measuring particulate emissions which can be applied to transient cycle testing of diesel engines. The advantage of this system is that it can achieve perfect constant velocity splitting by means of its structure, and theoretically can also maintain high splitting performance despite fluctuations in the exhaust flow rate, including those due to engine exhaust pulsation. We compared this system with a full tunnel by analyzing the basic performance of the system and measuring particulate matter (PM) using an actual vehicle engine.

The full-flow dilution tunnel (hereinafter referred to as full tunnel) measurement method has become the de facto standard for the evaluation of particulate matter (hereinafter referred to as PM) emitted from diesel-powered vehicles. However, due to its drawbacks such as bulkiness and expensiveness, a method that uses a very small partial dilution tunnel (hereinafter referred to as micro tunnel) has been developed, mainly in Europe, nearly to the level of practicality. With this method, a higher degree of freedom in controlling sampling flow and temperature can be obtained. Another advantage of the micro tunnel is that the system is compact. However, the micro tunnel's measurement accuracy remains uncertain because the accumulation of measurement data is not yet sufficient. Measuring PM while varying micro tunnel operating parameters permitted a check on the equivalency with a full tunnel system.

In addition to PM total matter, PM size distribution is recently receiving increased attention because of the dependency of PM size on human health effects. Thus, PM size distributions and the emission behavior under various driving patterns are becoming important in diesel particulate emissions. Electrical Low Pressure Impactor (ELPI)_is a candidate to measure continuously, not only PM mass, but also particulate size distribution. Therefore, we investigated using ELPI to measure diesel particulate mass and size distribution, together with time series behaviors under various driving patterns. This study demonstrated the feasibility of continuous measurement of PM size distribution by means of an ELPI. The typical PM size distribution curve on weight base has a peak of 0.18 micrometer. The typical PM size distribution curve on number base has a peak of 0.11 micrometer. Engine load influences these characteristics.

Combined system with EGR and Manifold water injection was developed for trial to control exhaust NOx emissions from heavy-duty diesel powered vehicles and its effects were experimentally studied under not only steady-state but also actual driving conditions including transient. From the experimental analyses under steady-state conditions, it was recognized that higher NOx reduction may be possible with this combined system compared with the use of each method alone under the same level of other pollutants. Then, several control conditions of the system were chosen and their effects to exhaust emissions were investigated under actual driving conditions, and consequently, about 50% of NOx reduction was recognized without significant increase of other pollutants by the combination of EGR at light and medium load regions and limited water injection at heavy load regions where accelerator opening is 70% or over.

Experiments and analyses were carried out to determine the effects of EGR on NOx and other pollutants for heavy-duty direct injection diesel engines under steady state conditions. Then based on them, optimum EGR control method was examined for effective NOx reduction without causing substantial increases of other pollutants under transient conditions. A simple EGR control system was developed for trial to achieve almost the same effects of the said method. Results of experiments with this system indicated that the EGR control method was capable of substantial reduction of NOx mass emission during transient engine operations equivalent to actual driving conditions, with different pay-loads and average vehicle speeds. REDUCTION of the NOx mass emission from heavy-duty diesel powered vehicles during actual driving operations, is one of the most important demands in automobile technologies.

To control the transient automatic operation of engines with two variables (speed and torque), feedback control has been used conventionally. Feedback control, however, does not have sufficient transient characteristics, and it is extremely difficult to perform accurate mode trace operation. To improve the control characteristics in transient operation, we have developed a new-concept automatic engine control system. The new system performs predictive control using an engine performance model that is obtained from learning operation. It is now very easy to perform operations that require accurate traces; operations such as exhaust emission and fuel consumption measurements.