Development of a High Sensitivity and High Response Portable Smoke Meter

The filtration efficiency of a DPF drops when it suffers a failure such as melting and cracks during regeneration. And then, on-board diagnostics (OBD) device has become needed worldwide to detect a DPF failure. In the development of an OBD soot sensor, evaluation of the sensor demands a portable instrument which can measure the soot concentration for on-board and in-field use. Some of the emission regulations require the in-field emission measurements under normal in-use operation of a vehicle. This study is intended to develop a high sensitivity and high response portable smoke meter for on-board soot measurements and a reference to OBD soot sensors under development. The smoke meter accommodates a 650 nm laser diode, and its principle is based on light extinction in high soot concentration range and backward light scattering for low soot concentration measurement. Raw exhaust sample flows through a thermo-controlled optical tube at a flow rate of 3 liter/min, and the total system unit weighs only 16 kg. Both extinguished and scattered light intensities were calibrated against soot mass concentration of the exhaust of a 3 liter Euro IV turbo-charged diesel engine. The performance, durability and anti-vibration stability were evaluated on bench and road tests, and the instrument was found to have a dynamic range from 0.01 mg/m³ to 1000 mg/m³, and a response time of 0.35 second. On-board test verification ensured the smoke meter vibration- and acceleration-proof operation.