Matthew J. Hall

The combustion of liquid fuels within a porous media radiant burner

The combustion of liquid fuels within the porous inert media (PIM) of a radiant burner was examined. Existing designs of porous radiant burners have typically relied on premixed mixtures of gaseous fuels and air. A radiant burner was built, and various design configurations were tested using the following types of porous ceramics: magnesia-stabilized zirconia, silicon carbide, and yttrium-stabilized zirconia. The fuel heptane was impinged on the combustion section using an oil spray nozzle with a fixed flow rate of approximately 0.025 lpm. The burner had an insulated combustion section that was 10.0 cm in diameter and consisted of several 2.5-cm-thick ceramics. Stable complete combustion was achieved for heptane at equivalence ratios of 0.57–0.67. Temperature measurements taken across the exit plane of the combustion section were typically within 50°C of each other, indicating radially uniform combustion. For an equivalence ratio of 0.64, axial temperature measurements taken down the side of the combustion section showed relatively low temperatures, 1170–1370°C. Very low emissions of both CO and NOx were measured for the range of stable equivalence ratios. Corrected for 3% oxygen, CO varied from 3 to 7 ppm and NOx varied from 15 to 20 ppm. Several variations of the burner were tested, including higher fuel flow rates, prevaporized fuel, and a quartz-enclosed ceramic section.

A fiber-optic probe to measure precombustion in-cylinder fuel-air ratio fluctuations in production engines

An infrared fiber-optic spark plug probe has been developed that will measure the instantaneous fuel-air ratio of the unburned fuel-air mixture near the spark plug in the cylinder of a production automobile engine. The heart of the device is a probe that is placed into the spark plug hole of an engine. It can house both a spark electrode and a pair of optical fibers. Radiation form an infrared source is supplied to one fiber, while the other fiber carries the absorption signal from the probe to a detector and data acquistion equipment. The probe measures variations in the light transmitted through a region surrounding the spark gap due to fluctuations in the fuel concentration in this region. It can record variations in the air-fuel ratio in an engine cylinder at high enough rates to show how engine operating conditions affect the mixing inside the engine cylinder. The probe was tested in a CFR engine motored at 600 rpm using propane as the fuel. The probe measured the fuel/air ratio spatially averaged over a distance of 8 mm from the tip of the spark plug. The temporal resolution of the measurements was 2.6° crank angle. Four air/fuel equivalence ratios were examined for each of two conditions: one in which the fuel was introduced far upstream of the intake, allowing homogeneous mixing and one in which the fuel was introduced at the intake port. In the cases where the fuel was introduced at the port, strong inhomogeneities were measured during the intake stroke. The mixture in the vicinity of the spark plug became relatively homogeneous by the middle of the compression stroke.

Diluents and Lean Mixture Combustion Modeling for SI Engines with a Quasi-Dimensional Model

Lean mixture combustion might be an important feature in the next generation of SI engines, while diluents have already played a key role in the reductions of emissions and fuel consumption. Lean burning modeling is even more important for engine modeling tools which are sometimes used for new engine development. The effect of flame strain on flame speed is believed to be significant, especially under lean mixture conditions. Current quasi-dimensional engine models usually do not include flame strain effects and tend to predict burn rate which is too high under lean burn conditions. An attempt was made to model flame strain effects in quasi-dimensional SI engine models. The Ford model GESIM was used as the platform. A new strain rate model was developed with the Lewis number effect included. A 2.5L V6 4-valve engine and 4.6L V8 2-valve modular engine were used to validate the modified turbulent entrainment combustion model in GESIM. Results showed that the current GESIM can differ by as much as 10 crank angle degrees compared with test data. The modified GESIM can predict burn duration to within 1--2 CA of experimental data, which is considered very good for engine models.

Measurements of pore scale flows within and exiting ceramic foams

LDA was used to measure the mean velocities and pore scale turbulence intensity of air flowing through ceramic foams having pore sizes between 0.8 and 2.5 mm in diameter. The stream-wise and transverse velocity components were measured near the exit plane, in a region between two foams separated by 5 mm, and within a section of ceramic foam. Mean velocities ranged from 0.25 m/s to 1.5 m/s, corresponding to pore Reynolds numbers between 20 and 200. A transition to a fully developed pore turbulence was achieved at pore Reynolds numbers above approximately 150.

Thermal and Flow Fields Modeling of Fast Spark Discharges in Air

In this study, a two-dimensional axisymmetric computational model of spark discharge in air is presented to provide a better understanding of the dynamics of the process. Better understanding of the modeling issues in spark discharge processes is an important issue for the automotive spark plug community. In this work we investigate the evolution of the shock front, temperature, pressure, density, geometry, and flow history of a plasma kernel using various assumptions that are typically used in spark discharge simulations. A continuum, inviscid, heat conducting, single fluid description of the flow is considered with radiative losses. Assuming local thermal equilibrium, the energy input due to resistive heating is determined using a specified current profile and temperature-dependent gas electrical conductivity in the gap. The spark discharge model focuses on the early time flow physics, the relative importance of conduction and radiation losses, the influence of thermodynamic model choice and ambient pressure effects.

Liquid Fuel Impingement on In-Cylinder Surfaces as a Source of Hydrocarbon Emissions From Direct Injection Gasoline Engines

Hydrocarbon (HC) emissions from direct injection gasoline (DIG) engines are significantly higher than those from comparable port fuel injected engines, especially when late direct injection (injection during the compression stroke) is used to produce a fuel economy benefit via unthrottled lean operation. The sources of engine-out hydrocarbon emissions for late direct injection are bulk flame quench, low temperatures for postcombustion oxidation, and fuel impingement on in-cylinder walls. An experimental technique has been developed that isolates the wall impingement source from the other sources of HC emissions from DIG engines. A series of steady-state and transient experiments is reported for which the HC emissions due to operation with a premixed charge using a gaseous fuel are compared to those when a small amount of liquid fuel is injected onto an in-cylinder surface and the gaseous fuel flow rate is decreased correspondingly. The steady-state experiments show that wetting any in-cylinder surface dramatically increases HC emissions compared to homogeneous charge operation with a gaseous fuel. The results of the transient fuel injection interrupt tests indicate that liquid-phase gasoline can survive within the cylinder of a fully warmed-up firing engine and that liquid fuel vaporization is slower than current computational models predict. This work supports the argument that HC emissions from DIG engines can be decreased by reducing the amount of liquid fuel that impinges on the cylinder liner and piston, and by improving the vaporization rate of the fuel that is deposited on these surfaces.

Transverse dispersion at high Peclet numbers in short porous media

Transverse dispersion is examined in short ceramic foams for a variety of pore sizes and flow rates. Experiments were performed with a localized smoke source as a tracer and a coflow of air. Digital images were taken of the resulting dispersion patterns, and an approximate transverse dispersion coefficient was determined. A precise dispersion coefficient cannot be defined at these high Peclet numbers (106–108) because the dispersion becomes non-Fickian. Nevertheless, the approximate coefficients are shown to be consistent with the values obtained by other researchers for lower Peclet numbers and longer porous media.

Performance Characteristics of a New On-Board Engine Exhaust Particulate Matter Sensor

A new electronic sensor has been developed to measure the time-resolved concentration of carbonaceous particulate matter (PM) emitted in engine exhaust. The sensor is approximately the size of a standard automotive spark-plug or lambda sensor and can be mounted directly in the engine exhaust. It consists of a pair of closely spaced electrically isolated electrodes that protrude into the exhaust flow. One electrode is given a voltage bias of 1000 V while the other is the signal electrode. The sensor is capable of providing cycle-resolved feedback on the carbonaceous PM concentration in the exhaust to the engine control unit (ECU), thereby enabling real-time control of engine operating parameters to lower PM emissions. This paper reports the results of an experimental study of various parameters that affect the performance of the electronic sensor. Parameters considered included sensor electrode length, diameter, electrode spacing, applied bias voltage, bulk flow velocity across the sensor electrodes, and the concentration of carbonaceous particulate matter in engine exhaust. The sensor was tested in the exhaust of a single cylinder diesel engine. The sensor signal varied linearly with the carbon mass concentration in the exhaust, the applied bias voltage and electrode length; it also showed some sensitivity to the bulk flow velocity, and an inverse power dependence on the spacing between the electrodes. Electrode diameter did not have a significant effect on the sensor signal. A correlation was developed to predict the sensor signal under any engine operating condition and values of these parameters. This correlation could be used to develop control strategies for the sensor for on-board operation in a production vehicle. The experiments also provided insight into the physical mechanism governing sensor behavior, regarding the charge transport between the two electrodes of the sensor.

Band-integrated infrared absorptance of low-molecular-weight paraffin hydrocarbons at high temperatures

The spectral absorptance of the 3.4-microm band of methane, ethane, propane, and butane has been measured with a Fourier transform infrared spectrometer over a range of temperatures from 296 to 900 K. The measurements were made at a 4-cm(-1) resolution and integrated over the entire band to give the total absorptance. The total absorptance is found to behave in such a way that it can be correlated by a combination of algebraic expressions that depend on the gas temperature and concentration. Average discrepancies between the correlations and the measurements are less than 4%, with maximum differences of no greater than 17%. In addition, the correlations presented here for methane are shown to be in good agreement with established models. Expressions given for the integrated intensity of each gas show an inverse dependence on temperature, reflecting the associated change in density.

The Texas Diesel Fuels Project, Part 2: Comparisons of Fuel Consumption and Emissions for a Fuel/Water Emulsion and Conventional Diesel Fuels

The Texas Department of Transportation began using an emulsified diesel fuel in 2002. They initiated a simultaneous study of the effectiveness of this fuel in comparison to 2D on-road diesel fuel and 2D off-road diesel. The study included comparisons of fuel economy and emissions for the emulsion, Lubrizol PuriNOx®, relative to conventional diesel fuels. Two engines and eight trucks, four single-axle dump trucks, and four tandem-axle dump trucks were tested. The equipment tested included both older mechanically-controlled diesels and newer electronically-controlled diesels. The two engines were tested over two different cycles that were developed specifically for this project. The dump trucks were tested using the route technique over one or the other of two chassis dynamometer cycles that were developed for this project In addition to fuel efficiency, emissions of NOx, PM, CO, and HCs were measured. Additionally, second-by-second results were obtained for NOx and HCs. Speciation of the HC emissions was performed for one of the off-road engines operating over two different cycles. On average, over all engines and cycles, PuriNOx provided a NOx benefit of about 16%, a fuel efficiency penalty of about 17%, and a PM benefit of about 20%. In general, the NOx benefit and the fuel efficiency penalty were less pronounced for the electronically-controlled diesels. One truck engine/cycle combination was found for which the effect on NOx was not statistically significant at the 95% confidence level. Similarly, two engine/cycle combinations were found for which the effect on PM was not statistically significant, and there was a statistically significant increase in PM for one dump truck. PuriNOx produced significant increases in the emissions of roughly half of the Toxic Air Contaminants evaluated: formaldehyde, acetaldehyde, acrolien, and MEK. PuriNOx did not yield decreased emissions of any TACs.