Laser Diagnostics of Particulate Concentration in Diesel Exhaust

Abstract

Particulate emissions from diesel vehicles are attracting special attention because of their bad effects on human respiratory organs. Because the mass emissions of diesel particulates, mostly soot particles, from a vehicle are evaluated under a transient mode test, the time resolved measurements of soot particles in diesel exhaust are essential. This article describes the principles and performances of three laser diagnostics, Extinction technique, Laser Induced Incandescence (LII) technique and Photo-acoustic Sensor (PASS) developed currently to meet this requirement. An instrument that the author developed based on the extinction has a simple structure, high responsiveness and relatively low sensitivity. The LII technique features high sensitivity, but requires a high power laser to heat soot particles to a high temperature. The PASS detects photoacoustic pressure emitted from laser heated soot particles and has high sensitivity, but its responsiveness is relatively low for the transient mode engine tests.