Measuring Diesel Exhaust Particulates by Using Laser-Induced Incandescence

Traditional techniques for particulate measurement in diesel exhausts are limited by either long response times or the need for appreciable operator skill and time. Most of these techniques cannot be used for real-time measurements. With the possibility of future regulations to be based on number density in addition to the traditional mass concentration, there is an impending need for advanced diagnostics for measuring particulates. Argonne is working to adapt recently developed laser-based diagnostics, which overcome such limitations for particulate measurement in diesel exhausts.

Experimental Setup for Implementing LII

Laser-induced incandescence (LII) allows highly time-resolved (~0.05 second resolution) planar imaging of soot concentrations in combustion exhausts. The technique can also be combined with other laser-based techniques to obtain information such as particle number concentration and size, in addition to the soluble organic fraction (SOF). We will optimize LII and associated techniques so that a low-cost portable instrument based on these techniques is possible

Results

The apparatus and infrastructure needed for LII are available in Argonne's laboratories. Instrumentation for validation has also been purchased and commissioned.

Correlation between LII Signals and Mass Concentrations Determined with a TEOM

A computer code was developed to model LII signal dependence on various factors. Such simulations showed key influences that were not apparent through previous studies.

Optimal values for parameters that could not be determined through the computer model were determined through experiments on laboratory-flame exhausts. Subsequently, LII measurements were performed on simulated diesel exhausts. They correlated extremely well (correlation coefficient 94.7%) with measurements performed using a standard technique.

Future Plans

Using LII, we will measure particulate mass concentrations in the exhaust of a diesel engine operated under various steady-state conditions. These measurements will be checked for correlation with measurements performed using standard techniques.

Laser light scattering (LLS) measurements will be performed at various steady-state conditions and will be used along with LII measurements to obtain particle size and number concentrations. Subsequently, laser-induced fluorescence (LIF) will be used to obtain polyaromatic hydrocarbons fluorescence signatures. This information will be used along with the SOF determined through Soxhlet extraction to obtain quantitative correlations.

We will also develop a low-cost LII-based portable instrument to measure diesel exhaust particulates in real time. The initial prototype is designed to measure mass concentrations only. Features that can also measure particle number and size will be incorporated in the future.

Sierra Instruments, Inc., TSI, Inc., and Caterpillar Technical Center have expressed interest in future collaborations, including commercialization of this innovative technology.