Application of a Tapered Element Oscillating Microbalance to Continuous Diesel Particulate Measurement 850405

A Tapered Element Oscillating Microbalance (TEOM) was used to measure transient diesel particulate emissions. Light duty IDI and DI engined vehicles were tested over the LA4 Drive Cycle. One vehicle, a 1.6 litre IDI diesel engined VW Golf (Rabbit), was also tested over the Japanese 10-mode and European ECE-15 Cycles. Transient particulate emissions were also measured from a heavy duty DI diesel engine tested according to the US Federal Heavy Duty Transient Test Procedure. The TEOM proved to be very flexible, permitting continuous particulate measurements to be made at each of the conditions studied. Particulate mass determined by the TEOM over a complete cycle was generally lower, typically by between 13 and 28%, than that measured using conventional gravimetric filtration procedures. A new calibration technique was devised which improved the correlation between TEOM and gravimetric results.

PARTICULATE EMISSION RATES from light duty vehicles powered by diesel engines are currently subject to legislative limits in the United States. The prescribed method for the measurement of particulates involves driving a vehicle over a specific cycle which includes a wide range of engine operating conditions.

During a test the total exhaust from the engine is continuously mixed in a dilution tunnel with ambient air. A portion of the mixture is passed through a filter. Upon completion of a test the filter is weighed and the particulate mass calculated and converted into a mass emission rate. Currently vehicles powered by heavy duty diesel engines are not subject to particulate legislation. However, from 1987 regulations are proposed which will necessitate the collection of particulate emissions from these engines over a transient cycle.

The measurement of particulate in the manner described precludes the identification of the engine conditions which contribute most to the emission during a transient test.

Clearly, in order to achieve a minimum particulate emission rate from an engine in the most economical fashion, it is necessary to identify engine operating conditions which produce high rates of particulate emissions. To accomplish this over a transient cycle requires that the particulate emission rate be continuously measured.

Transient particulate emissions have previously been determined using opacity meters (1,2 and 3)*, photoacoustic spectrometers (1,2,4,5 and 6) a pressure drop monitor (7) and a tapered element oscillating microbalance, TEOM, (8,9). The relative merits of these instruments have been examined by the Smoke and Particulate Panel of the Diesel Exhaust Composition Program Group of the Co-ordinating Research Council (10). This paper describes further work on the application of a TEOM to the continuous measurement of diesel particulate emissions. The objectives of the study were twofold.

1. 1.
   To assess the suitability of the TEOM to the quantitative and continuous measurement of particulate from a variety of diesel engines over important test cycles.
2. 2.
   To investigate the accuracy of the TEOM by comparing particulate mass determined by the TEOM with that obtained using conventional gravimetric procedures.