Richard R. Steeper

Piston Wetting in an Optical DISI Engine: Fuel Films, Pool Fires, and Soot Generation

Piston-wetting effects are investigated in an optical direct-injection spark-ignition (DISI) engine. Fuel spray impingement on the piston leads to the formation of fuel films, which are visualized with a laser-induced fluorescence (LIF) imaging technique. Oxygen quenching is found to reduce the fluorescence yield from liquid gasoline. Fuel films that exist during combustion of the premixed charge ignite to create piston-top pool fires. These fires are characterized using direct flame imaging. Soot produced by the pool fires is imaged using laser elastic scattering and is found to persist throughout the exhaust stroke, implying that piston-top pool fires are a likely source of engine-out particulate emissions for DISI engines.

Oxidation rates of common organic compounds in supercritical water

Abstract Supercritical water oxidation is a rapidly emerging thermal waste-processing technology with potential as a hazardous-waste-treatment method for a variety of industrial chemicals ranging from common organic solvents to complex industrial formulations. An important design consideration in the development of supercritical water oxidation is the optimization of reactor operating temperature and feed preheat temperatures. In this paper, the temperature dependence of the oxidation in supercritical water of seven common organic compounds is examined over a temperature range of 430–585°C and reaction times ranging from 7 to 30 s at 27.6 MPa (4000 psi). The reactants are examined at approximate concentrations of 0.4 wt.% at conversion efficiencies from 50% to >99.9%. The materials examined were methanol, phenol, methyl ethyl ketone, ethylene glycol, acetic acid, methylene chloride, and 1,1,1-trichloroethane. The conversion of these compounds was monitored using total organic carbon and gas chromatography on liquid effluent samples. The results indicate that for most compounds, temperatures over 550°C and residence times near 20 s afford conversion efficiencies of greater than 99.95% based on total organic carbon.

Methane and methanol diffusion flames in supercritical water

Abstract Our interest in understanding supercritical-water oxidation as a process for the destruction of hazardous wastes has led us to examine hydrothermal diffusion flames that can ignite in supercritical waterfuel-oxygen mixtures. We injected pure oxygen into water-methane and water-methanol mixtures at 275 bar, varying fuel concentrations from 1 to 50 mol % and temperatures from 380 to 510 °C. Measurements of minimum fuel concentrations required for the spontaneous ignition of diffusion flames in supercritical water are reported. The flames ignite at methane or methanol concentrations as low as 6 mol % at temperatures near 500 °C. The ignition-threshold concentrations rise as temperature is decreased to 400 °C. Visual and shadowgraph video records reveal an insensitivity of flame height to diminishing fuel concentration. In contrast, both luminosity and average flame temperature vary strongly with fuel concentration. Flame structures are detectable long after flame luminosity is no longer visible, with measured average flame temperatures within a few hundred degrees of ambient.

An LIF equivalence ratio imaging technique for multicomponent fuels in an IC engine

A method for identifying fuel/tracer mixtures suitable for laser-induced fluorescence (LIF) measurements of in-cylinder equivalence ratios is presented. The concentrations of multiple LIF tracers are adjusted so that the total vapor-phase fluorescence is proportional to the instantaneous mass evaporation rate. In this way, LIF image intensities are proportional to local fuel mass, which in turn can be converted into local fuel equivalence ratios. Uncertainty generated by pressure and temperature dependencies of ketone tracers is assessed. A two-fuel-component mixture developed with the method is used to measure two-dimensional fuel equivalence ratios in an optically accessible direct-injection spark-ignition engine. Results are compared with the equivalence ratio distribution of a mixture with a single fuel component. It is found that the effect of fuel volatility on the equivalence ratio distribution at the time of spark becomes more distinct as the start-of-injection timing is retarded.

An experimental investigation of the incineration and incinerability of chlorinated alkane droplets

An experimental investigation has been conducted on the vaporization, combustion, and extinction of droplets of pure chlorinated alkanes and their mixtures with n-alkanes in “inert” and oxidizing environments. From results on the droplet vaporization/combustion rates, the state of extinction, and temporal changes in the droplet composition, it is shown that droplets of lightly chlorinated alkanes as represented by monochloroalkanes burn almost as vigorously as normal alkanes, that heavily chlorinated alkanes as represented by 1, 1, 2, 2-tetrachloroethane (TECA) burn weakly if at all, that TECA can be rendered to burn vigorously with the addition of only 25 volume percent of an equal-volatility alkane, and that this enhancement can be further improved by decreasing the volatility of the additive. Implications on hazardous waste incineration are discussed.

CO2-Based Thermometry of Supercritical Water Oxidation

We have demonstrated the suitability of CO2 Raman spectra as a thermometry probe of the fluid mixtures encountered in supercritical water oxidation. Measured temperature accuracies of ±6% are presented. Measurements were made of the v1 2v2 Fermi resonance features of CO2 in a supercritical water environment. Over the temperature range of interest to researchers of supercritical water oxidation, ∼400–650°C, hot bands appear in the Raman spectrum of CO2 with sufficient spectral intensity to serve as a convenient measure of the fluid temperature. We have analyzed these hot bands by taking the ratio of their integrated intensity with the integrated intensity of the fundamental. Over the temperature range of 390 to 540°C, the intensity ratio of the first pure hot band feature to the fundamental of v1 shows a very nearly linear dependence on temperature. The experimental ratio measurements are well explained by standard Raman theory if the Fermi resonance is accounted for. As discussed, the CO2 spectral line shape is affected by the high pressure (P > 22.1 MPa) used in supercritical work, but these changes do not affect the extraction of a fluid temperature from the spectra.

Application of a Tunable-Diode-Laser Absorption Diagnostic for CO Measurements in an Automotive HCCI Engine

An infrared laser absorption technique has been developed to measure in-cylinder concentrations of CO in an optical, automotive HCCI engine. The diagnostic employs a distributed-feedback, tunable diode laser selected to emit light at the R15 line of the first overtone of CO near 2.3 {micro}m. The collimated laser beam makes multiple passes through the cylinder to increase its path length and its sampling volume. High-frequency modulation of the laser output (wavelength modulation spectroscopy) further enhances the signal-to-noise ratio and detection limits of CO. The diagnostic has been tested in the motored and fired engine, exhibiting better than 200-ppm sensitivity for 50-cycle ensemble-average values of CO concentration with 1-ms time resolution. Fired results demonstrate the ability of the diagnostic to quantify CO production during negative valve overlap (NVO) for a range of fueling conditions.