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Simultaneous crank-angle-resolved measurements of gasoline concentration and gas temperature were made with two-color mid-infrared (mid-IR) laser absorption in a production spark-ignition engine (Nissan MR20DE, 2.0L, 4 cyl, MPI with premium gasoline). The mid-IR light was coupled into and out of the cylinder using fiber optics incorporated into a modified spark plug. The absorption line-of-sight was a 5.3 mm optical path located closely adjacent to the ignition spark providing spatially resolved absorption. Two sensor wavelengths were selected in the strong bands associated with the carbon-hydrogen (C-H) stretching vibration near 3.4 μm, which have an absorption ratio that is strongly temperature dependent. Fuel concentration and temperature were determined simultaneously from the absorption at these two wavelengths.

Negative valve overlap (NVO) is a valve strategy employed to retain and recompress residual burned gases to assist HCCI combustion, particularly in the difficult regime of low-load operation. NVO allows the retention of large quantities of hot residual burned gases as well as the possibility of fuel addition for combustion control purposes. Reaction of fuel injected during NVO increases charge temperature, but in addition could produce reformed fuel species that may affect main combustion phasing. The strategy holds potential for controlling and extending low-load HCCI combustion. The goal of this work is to demonstrate the feasibility of applying two-wavelength PLIF of 3-pentanone to obtain simultaneous, in-cylinder temperature and composition images during different parts of the HCCI/NVO cycle. Measurements are recorded during the intake and main compression strokes, as well as during the more challenging periods of NVO recompression and re-expansion.

Simultaneous crank-angle-resolved measurements of gasoline vapor concentration, gas temperature, and liquid fuel droplet scattering were made with three-color infrared absorption in a direct-injection spark-ignition engine with premium gasoline. The infrared light was coupled into and out of the cylinder using fiber optics incorporated into a modified spark plug, allowing measurement at a location adjacent to the spark plug electrode. Two mid-infrared (mid-IR) laser wavelengths were simultaneously produced by difference-frequency-generation in periodically poled lithium niobate (PPLN) using one signal and two pump lasers operating in the near-infrared (near-IR). A portion of the near-IR signal laser residual provided a simultaneous third, non-resonant, wavelength for liquid droplet detection. This non-resonant signal was used to subtract the influence of droplet scattering from the resonant mid-IR signals to obtain vapor absorption signals in the presence of droplet extinction.