Repeatable steady-state measurement of particulate number emissions in engine experiments

Abstract

Particulate number count is an important consideration for engine developers due to changes in emissions legislation. Changes are driven by an increasing body of evidence that particulate number, particularly smaller particles, have a deleterious effect on human health. This article presents the results of an investigation into the key factors influencing particulate number emissions measurement repeatability during dynamometer-based testing of a gasoline direct-injection engine. At the outset of this work, a review of literature summarises some of the current discussion concerning particulate formation, evolution and measurement to identify the key factors that influence these three things. Having established what these factors are a number of engine experiments are undertaken to determine how sensitive particulate number measurements are to change in these factors and therefore how great an influence they are on measurement repeatability in engine experiments of a similar type. The investigation highlights a number of important results, showing that particular regard ought to be given to the pre-conditioning of engine internal surfaces which begins when the engine is started. In addition, the effect of coolant temperature (including the dynamics of the control system) is observed and highlighted as another key source of variation as is intake air temperature.

Investigating the impact of gasoline composition on PN in GDI engines using an improved measurement method

“…Engine History). 28 To this end, the effect of engine pre-conditioning (i.e. running the engine for a specified duration in a specified operating point) on the subsequent PN measurement was investigated.…”

“…Sampling location was also investigated given the potential effects of mechanisms such as deposition. 28 Sampling was carried out at the tailpipe downstream of the after-treatment system (tailpipe sampling), as well as immediately after the exhaust valve (engine-out sampling), using a probe fitted on a spacer between the exhaust manifold and the engine block. The probe was curved and extended towards the cylinder, so that the tip was positioned as close as possible to the exhaust valve (at a distance of approximately 60-70 mm).…”

A Combined Experimental and Computational Fluid Dynamics Investigation of Particulate Matter Emissions from a Wall-Guided Gasoline Direct Injection Engine

“…Data was acquired with a sample rate of 10 Hz. Due to the typical erratic behaviour of PM measurements, and measurement variability in the nucleation mode range, where high number-low diameter samples are acquired, every operating condition was repeated three times, in different days and under nominally identical conditions to reduce random errors and increase repeatability [12,14,42]. The data was collected and processed via the manufacturer software to obtain average values of number density, mass concentration and particle diameter.…”

“…In spite of the limitations of the statistical analysis, which is due to a reduced CFD-generated sample, the results indicate the two-equation functional model gives a meaningful account of the prevailing phenomena and can be used as a benchmark for further development. If the typical lack of repeatability and the inherent erratic behaviour of PM emissions in GDI engines [12,42] are taken into account, one might conclude that the model returns acceptable qualitative predictions of particle number density. Due to the expected propagation of model errors, considering a further combustion temperature factor within an expression of the form PN Den ∼ f(U I ϕ )•f(T), does not improve at this stage the predictive power of the model.…”

On the Validity of Steady-State Gasoline Engine Characterization Methodology for Generation of Optimal Calibrations Used in Real World Driving

“…The results presented in literature give an indication of typical levels of uncertainty of measured tailpipe emissions made over various drive cycles, these are summarized in Table 1. To the authors' knowledge there is only one source [18] that discusses repeatability of raw sample (feed gas) emissions for engine-based calibration related characterization activities.…”