Test methodology characterizes even very low diesel emissions

January 07, 2014 // By Christoph Hammerschmidt
Germany's national metrology institute PTB has developed a test methodology to measure and characterize density and size of soot particles emitted by diesel engines. The test bench developed by the Braunschweig based scientists has become necessary because the measurement equipment currently used in car repair shops is unable to acquire the low particle emission of future vehicle generations.

Because of more stringent legislation and standards throughout Europe over the past 20 years, emission of soot particles from diesel engines has been reduced from 180 milligrams per kilometre (mg / km) to 5 mg / km. Filters and exhaust gas treatment helped to reduce both the amount of particles as well as their size. Measurement equipment typically used by garages to measure engine emissions therefore hits its limits. The PTB researchers utilized new ways to measure diesel soot detection such as the so-called scattered-light method in combination with a highly stable and exact particle generator. The new test bench is also used to clarify some remaining scientific aspects that ensure the calibration ability of new sensors.

The new particle measurement equipment acquires turbidity and particle mass concentration of soot and measures diesel exhaust gases at a an exactness up to 100 times better than the 'Opazimetre' measurement generation typically used in garages and workshops, introduced around 1993. A joint research program of PTB and the German industry association of car service equipment manufacturers ASA acknowledged that the new method detects even smallest amounts of soot in the air. Since emission limits are regulated by legislation, the equipment used to measure the soot needs to be certified - in this case according to EO 18.9.

The scientific groundwork for the exact acquisition of emission particles have been carried out by PTB and ASA in a joint research project launched in 2010, with the goal to determine the relation between emission gas turbidity and particle mass concentration. This is necessary to enable the comparability of different measurement principles such as the Opazimetre hitherto in use and the new laser-based scattered-light method. For this purpose, the PTB developed a unique test bench that allows users to compare the measurement approaches under extremely stabile and precisely adjustable conditions. The core of the test bench is a soot generator which burns propane gas and