Inter-correlations between smoke opacity, Legal Particulate Sampling (LPS) and TEOM, during transient operation of a diesel engine

The Particulate Matter (PM) emissions from a diesel passenger car were measured using three units concurrently: a commercially-available opacimeter (Celesco), a Tapered Element Oscillating Microbalance (TEOM) and a Legal Particulate Sampling (LPS) unit consisting of dilution tunnel with Constant Volume Sampling (CVS). The opacimeter provides a time resolved measurement for the visible component of the Particulate Matter (PM); the TEOM does the same for particulate mass. The motivation was to determine whether the opacimeter or TEOM could be used to suggest the likely result with CVS during transient engine operation. This would be accomplished more conveniently by empirical correlations, but with the advantage, that temporal variations during transients are then available.

Forty-seven tests were conducted on a 4-cylinder 1.8l Turbo-Diesel Common-Rail Injection (TDCi) engine, operated under transient conditions according to the European Extra-Urban Drive Cycle (0-70kph EUDC). A linear relationship was found to exist between the CVS and the opacimeter, with the latter signal integrated with respect to time throughout the EUDC. The highest transient smoke emissions were consistently associated with the highest scheduled transient Exhaust Gas Recirculation (EGR) demands.

The TEOM was unable to capture the fastest transient features in the emission behaviour; the opacimeter was better able to pin-point the operating conditions responsible for these events. It should, however, be noted that the transient maneuvers in the EUDC are quite gentle: real-world duty cycles contain harsher accelerations for which further correlations may be required.