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Spark plugs instrumented with a ring of optical fibers in the threaded-body region have seen considerable use in the past ten years, and it is expected that their application to unmodified production engines will increase in the years to come. Interpretation of the optical signals obtained with the probe is often difficult, particularly under lean operating conditions where the low luminosity of the flame leads to imprecise flame arrival detection. A systematic look at the optical signals, along with direct imaging of the flame, has been undertaken to calibrate and optimize the determination of flame arrival times. In addition, an evaluation of the different models available for the analysis of the flame arrival data is made. Data fits are compared with real flame images, to determine which model best estimates the convective velocity of the flow and the expansion speed of the flame kernel.

A new diagnostic technique is described that has the capability of making real-time, in situ measurements of the volatile fraction of diesel particulate matter (PM). LIDELS uses two laser pulses of comparable energy, separated in time by an interval sufficiently short to freeze the flow field, to measure the change in PM volume caused by laser-induced desorption of the volatile fraction. The first laser pulse produces elastic light scattering (ELS) that gives the volume of the total PM, and also deposits the energy to desorb the volatiles. ELS from the second pulse gives the volume of the remaining solid portion of the PM, and the ratio of these two measurements is the quantitative solid volume fraction. Calibration is required for the individual total PM and solid fraction to be quantitative. Applicability of the technique is demonstrated for load and EGR sweeps for a turbocharged, direct-injection diesel engine.

A comparison of scanning mobility particle sizer (SMPS) and laser-induced incandescence (LII) measurements of diesel particulate matter (PM) was performed. The results reveal the significance of the aggregate nature of diesel PM on interpretation of size and volume fraction measurements obtained with an SMPS, and the accuracy of primary particle size measurements by LII. Volume fraction calculations based on the mobility diameter measured by the SMPS substantially over-predict the space-filling volume fraction of the PM. Correction algorithms for the SMPS measurements, to account for the fractal nature of the aggregate morphology, result in a substantial reduction in the reported volume. The behavior of the particulate volume fraction, mean and standard deviation of the mobility diameter, and primary particle size are studied as a function of the EGR for a range of steady-state engine speeds and loads for a turbocharged direct-injection diesel engine.

Double-pulse laser-induced desorption with elastic laser scattering (LIDELS) is a diagnostic technique capable of making time-resolved, in situ measurements of the volatile fraction of diesel particulate matter (PM). The technique uses two laser pulses of comparable energy, separated in time by an interval sufficiently short to freeze the flow field, to measure the change in PM volume caused by laser-induced desorption of the volatile fraction. The first laser pulse of a pulse-pair produces elastic laser scattering (ELS) that gives the total PM volume, and also deposits the energy to desorb the volatiles. ELS from the second pulse gives the volume of the remaining solid portion of the PM, and the ratio of these two measurements is the quantitative solid volume fraction. In an earlier study, we used a single laser to make real-time LIDELS measurements during steady-state operation of a diesel engine.