A Study of a Gasoline-Fueled Near-Zero-Emission Vehicle Using an Improved Emission Measurement System

This paper concerns research on an emission control system aimed at reducing emission levels to well below the ULEV standards. As emission levels are further reduced in the coming years, it is projected that measurement error will increase substantially. Therefore, an analysis was made of the conventional measurement system, which revealed the following major problems.

1. 1.
   The conventional analyzer, having a minimum full-scale THC range of 10 ppmC, cannot measure lower concentration emissions with high accuracy.
2. 2.
   Hydrocarbons are produced in various components of the measurement system, increasing measurement error.
3. 3.
   Even if an analyzer with a minimum full-scale THC range of 1 ppmC is used in an effort to measure low concentrations, the 1 ppmC measurement range cannot be applied when the dilution air contains a high THC concentration. This makes it impossible to obtain highly accurate measurements.
4. 4.
   Since the conventional CVS has a constant flow rate, there are some test phases with an excess dilution rate, which lowers the exhaust gas concentrations, resulting in larger measurement error.

Improvements were made to the conventional measurement system with the aim of resolving these problems. As a result, a system has been established that can measure emission levels of around one-tenth of the ULEV standards with much greater accuracy than the previous system.

This improved measurement system is now being used to develop an exhaust gas aftertreatment system that integrates an electrically heated catalyst (EHC), a three-way catalyst (TWC) and an HC adsorber. In addition, the individual performance of the HC adsorber and the TWC has also been improved. Although this aftertreatment system is still at the research stage, preliminary test results indicate that it has the potential to reduce emission levels to one-tenth of the ULEV limits.