High-Speed Imaging for Direct-Injection Gasoline Engine Research and Development

In recent years, new laser and camera technology have enabled the development of high-speed imaging diagnostics for measurements at frame rates commensurate with the time scales of turbulent mixing, combustion, and emission formation in internal combustion engines. The ability to study the evolution of in-cylinder flow, fuel/air mixing, ignition, and combustion within individual cycles and for many consecutive cycles provides new insights into the physics and chemistry of internal combustion engine performance. Data for model development and device development are obtained with unprecedented access to the identification of random events such as cycle to cycle variation and ignition instabilities. This paper summarizes high-speed diagnostics developments with a focus on application to spark-ignition direct-injection gasoline engines. A range of optical techniques is described along with examples of applications in research and near-production engines. Measurements of in-cylinder velocities were conducted with particle image velocimetry. The spray evolution was followed with Mie scattering. Quantitative fuel distributions were recorded with laser-induced fluorescence. Fuel impingement on surfaces was quantified with refractive index matching. Combined velocity and fuel measurements were used to study ignition reliability. Chemiluminescence techniques provided insights into the evolution of the spark plasma as well as the growing flame kernel. Chemiluminescence and black body radiation imaging yielded insights into the formation and oxidation of soot.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86776/1/Sick8.pd

High-Speed Imaging of OH* and Soot Temperature and Concentration in a Stratified-Charge Direct-Injection Gasoline Engine

In-cylinder soot formation and oxidation in a stratified-charge spark-ignited direct-injection (SIDI) engine have been studied with a high-speed (9000 frames/s) camera system with three intensified detectors. Continuous records of soot temperature and relative soot concentration within individual engine cycles are evaluated from images of soot radiation at two wavelengths (650 and 750 nm). Combustion is followed simultaneously by imaging OH* chemiluminescence (306 nm). The spatially and temporally resolved data allow the two most important soot sources to be quantified separately for a typical part-load operating condition. (1) Soot first forms in partially premixed flame propagation through rich zones, but the high soot temperatures (_2000–2400 K) and rapid mixing with surrounding hot lean regions lead to rapid soot oxidation and burnout. (2) Soot formation in pool fires (diffusion flames fed by thin films of liquid fuel on the piston) begins later and continues until late in the cycle, when further significant soot oxidation is unlikely (soot temperatures have dropped to _1500 K, and OH* chemiluminescence is no longer detectable). For this SIDI engine design and operating condition, pool fires are the dominant source of engine-out soot.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86743/1/Sick27.pd

Partially-Premixed Flames in Internal Combustion Engines

This was a joint university-industry research program funded by the Partnerships for the Academic-Industrial Research Program (PAIR). The research examined partially premixed flames in laboratory and internal combustion engine environments at Vanderbilt University, University of Michigan, and General Motors Research and Development. At Vanderbilt University, stretched and curved ''tubular'' premixed flames were measured in a unique optically accessible burner with laser-induced spontaneous Raman scattering. Comparisons of optically measured temperature and species concentration profiles to detailed transport, complex chemistry simulations showed good correspondence at low-stretch conditions in the tubular flame. However, there were significant discrepancies at high-stretch conditions near flame extinction. The tubular flame predictions were found to be very sensitive to the specific hydrogen-air chemical kinetic mechanism and four different mechanisms were compared. In addition, the thermo-diffusive properties of the deficient reactant, H2, strongly affected the tubular flame structure. The poor prediction near extinction is most likely due to deficiencies in the chemical kinetic mechanisms near extinction. At the University of Michigan, an optical direct-injected engine was built up for laser-induced fluorescence imaging experiments on mixing and combustion under stratified charge combustion conditions with the assistance of General Motors. Laser attenuation effects were characterized both experimentally and numerically to improve laser imaging during the initial phase of the gasoline-air mixture development. Toluene was added to the isooctane fuel to image the fuel-air equivalence ratio in an optically accessible direct-injected gasoline engine. Temperature effects on the toluene imaging of fuel-air equivalence ratio were characterized. For the first time, oxygen imaging was accomplished in an internal combustion engine by combination of two fluorescence trackers, toluene and 3-pentanone. With this method, oxygen, fuel and equivalence ratio were measured in the cylinder. At General Motors, graduate students from the University of Michigan and Vanderbilt University worked with GM researchers to develop high-speed imaging methods for optically accessible direct-injection engines. Spark-emission spectroscopy was combined with high-speed spectrally-resolved combustion imaging in a direct-injected engine