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The ignition process of fuel reactivity controlled PCCI combustion was investigated using engine experiments and detailed CFD modeling. The experiments were performed using a modified all metal heavy-duty, compression-ignition engine. The engine was fueled using commercially available gasoline (PON 91.6) and ULSD diesel delivered through separate port and direct injection systems, respectively. Experiments were conducted at a steady state-engine load of 4.5 bar IMEP and speed of 1300 rev/min. In-cylinder optical measurements focused on understanding the fuel decomposition and fuel reactivity stratification provided through the charge preparation. The measurement technique utilized point location optical access through a modified cylinder head with two access points in the firedeck. Optical measurements of natural thermal emission were performed with an FTIR operating in the 2-4.5 μm spectral region.

We discuss combustion gas spectra measured by interference spectrometers and their relevance for engine studies. First, we discuss infrared H2O thermal emission spectra from in-cylinder piston engine gases with a novel operation mode of a standard FTIR. Second, we discuss ultraviolet OH absorption spectra in an atmospheric-pressure flame using a spatial heterodyne spectrometer (SHS) suitable for single-shot measurements of spectra from engines. We emphasize the unique ability of interference spectrometers to gather high-resolution spectra at high throughput and the associated value to the engine researcher.