Time-Resolved Laser-Induced Incandescence Measurements for the EPA Heavy-Duty Federal Test Procedure

Abstract

Laser-induced incandescence (LII) is a promising new diagnostic for measuring the volume fraction of elemental carbon in engine exhaust. The technique is considerably more precise and sensitive than conventional measurement procedures, and can be applied either with or without dilution. However, LII has been slow to gain acceptance because of presumed complexity of use and high initial cost. In this paper we demonstrate a prototype LII system that offers turn-key operation and long-term cost that is highly competitive with other techniques because of very low labor costs. The LII system ran unattended for 7.5 weeks, logging 1078 heavy-duty diesel engine tests during 24/7 operation of a dilution tunnel facility. Among the tests logged were 363 FTP steady-state mode tests and 250 FTP transient tests for which gravimetric measurements of total particulate matter (PM) were obtained. Of these tests, removal of the filter-based volatile matter using supercritical fluid extraction was performed on 142 and 147 of the tests, respectively. The correlation between the time-integrated LII signals and the dry gravimetric measurements for the steady-state mode tests is used to calibrate the LII measurements in mass units. This calibration is then used to evaluate the correlation between the LII and dry gravimetric measurements for the transient tests. Finally, time-resolved LII measurements for the steady-state mode tests are presented to illustrate three forms of unsteadiness that would seem undesirable.