Design of On-Line Measurement System for Fine Particle Number Concentration of Vehicle Exhaust Based on Diffusion Charge Theory

摘要

The concentration of particulate matter is an important parameter to measure exhaust emissions from motor vehicles. This article discusses the design of an on-line measurement system for fine particle number concentration. Based on charging models in continuum regime, a unipolar charger with free electron capture function was designed. After a high-sensitivity I-V conversion circuit was built in the micro current detection module, we designed a wide-range Faraday cup electrometer. The experimental results show that the charger can efficiently charge 23 nm-2.5 μm particles, achieve a stable discharge with an average discharge current of -5 μA (relative error is less than 1 %). And a wide-range Faraday cup can achieve a ±500 pA range, fA—level electrical signal measurement. Compared with the AVL-APC 489 instrument, the integrated system experimental test is better than 87.2%, which can meet the on-line testing requirements for the concentration of motor vehicle exhaust particulates.