Joachim Gronki

In-Cylinder Combustion Visualization in an Auto-Igniting Gasoline Engine using Fuel Tracer- and Formaldehyde-LIF Imaging

In an optical accessible 4-stroke engine laser-induced fluorescence (LIF) imaging measurements of fuel tracer (3-pentanone) and formaldehyde were performed during the compression stroke and combustion. Formaldehyde (HCHO) is intermediately present at high concentrations within the cool flame and is burned later on when the “hot” combustion proceeds. It can be used as an internally generated tracer to observe the boundaries of the hot combustion zones. Despite the fact that a frequencytripled Nd:YAG laser excites only weak transitions in the HCHO molecule, the high concentration (several thousands ppm) provide for sufficient signal intensity when detecting fluorescence above 395 nm. Using formaldehyde LIF, auto-ignition (occurring close to 356°ca) and the further development of combustion were observed. Combustion was completed within the field of view by 360°ca in most observed engine cycles. 3-pentanone which has been used frequently for fuel-concentration imaging in spark ignited engines was of limited use in the CAI engine due to laser and signal attenuation prior to top dead center as a result of tracer destruction during and UV absorption by cool-flame intermediates.

Multi-species laser-based imaging measurements in a diesel spray

Multi-species laser based imaging measurements have been carried out in a reacting Diesel spray in order to provide a detailed data base for model development and validation. In a high-pressure high-temperature spray chamber the measurements addressed the fuel vapor concentration, ignition and flame development and the soot formation. The fuel vapor distribution was measured quantitatively by Rayleigh scattering and compared to measurements by tracer laser-induced fluorescence. Soot volume fractions were observed by laser-induced incandescence. Fuel vapor and soot distributions were measured simultaneously and provide insight in the ignition and pollutant formation process. Specific digital image processing algorithms were developed to correct for beam steering and laser attenuation.

Temperature-dependent absorption by CO2: implications for UV diagnostics in high-temperature flames

Absorption spectra of hot (900 – 3050 K) CO2 have been measured at 190 – 320 nm. A parameter set allows the calculation of absorption cross sections relevant for laser diagnostic in combustion processes.

Investigations on laser-induced incandescence (LII) for soot diagnostics at high pressure

LII has been investigated in sooting ethylene/air flames at 1 – 15 bar with wavelength-, energy-densityand time-resolved detection. LII decay coefficients increase linearly with pressure. Pressure influence on the LII intensity is limited with prompt detection. OCIS codes: (120.1740) combustion diagnostics; (300.6280) fluorescence, luminescence