Real-time measurement of combustion generated particles with photofragmentation-fluorescence

Excimer laser fragmentation-fluorescence spectroscopy (ELFFS) is a viable t echnique for real-time monitoring of carbonaceous particles in combustion e xhausts. The exhaust from a single-cylinder two-stroke engine is diluted an d diverted into the laser interrogation region, resulting in a particle con centration of approximately I X 107/cm(3). Light from a 193 nm ArF laser ph otofragments the particles and then produces fluorescence from the atomic c arbon fragments at 248 nm, CH fragments at 431 nm, and C-2, fragments at 46 8 nm. The atomic carbon fluorescence signal is proportional to the number c oncentration of particles in the laser interrogation region. The 100-shot ( 1 s) detection limit for particles in the exhaust is 1 mg/m(3), expressed a s a mass concentration of particulate matter. Interferences from carbon mon oxide and carbon dioxide are neg. ligible. The relative fluorescence yield at 248 nm is four times greater from particles than from the gas phase hydr ocarbons present in the exhaust. This high yield suggests that the gas phas e hydrocarbon interference would not be problematic for measurements of die sel exhaust, where the ratio of particulate carbon to gas phase hydrocarbon is high.