Search Results

Simultaneous laser-induced incandescence and light scattering measurements were used to obtain images of the evolving soot field within an optically-accessible DI diesel engine. Optimum signal collection parameters were established based on preliminary measurements in an ethylene diffusion flame. The effects of intake air temperature on soot formation during diesel combustion were investigated. Although increased soot production was evident for the higher intake air temperature cases, local particle diameters and number densities of the soot were unaffected for each of the cases tested.

The application of planar laser-induced Rayleigh scattering for quantitative 2-D measurements of vapor-phase fuel concentration in the main combustion zone of a direct-injection Diesel engine has been explored, developed and demonstrated. All studies were conducted in an optically accessible direct-injection Diesel engine of the “heavy-duty” size class at 1200 rpm and motored TDC conditions which were typical of the production version of this engine. First, this study verifies that beyond 27 mm from the injector all the fuel is vapor phase. This was done by investigating the Diesel jet under high magnification using 2-D elastic scatter imaging and subsequently evaluating the signal intensities from the droplets and other interfering particles (Mie scattering) and the vapor (Rayleigh scattering).

An experiment was performed using an optically accessible direct injection (DI) diesel engine to investigate the effects of exhaust gas recirculation (EGR) on diesel combustion. EGR was simulated using nitrogen and carbon dioxide as intake air diluents. Timing was adjusted to maintain constant start of combustion for all cases. Both diluents were found to be effective in reducing emissions of oxides of nitrogen. Soot emission was not changed by the addition of nitrogen; however, carbon dioxide substantially reduced soot emission while simultaneously reducing NOx emissions. NOx is reduced by intake air dilution is a change in flame temperature.

A flamelet model is used to calculate combustion in a diesel engine, and the results are compared to experimental data available from an optically accessible, direct-injection diesel research engine. The 3∼D time-dependent Kiva-II code is used for the calculations, the standard Arrhenius combustion model being replaced by an ignition model and the coherent flame model for turbulent combustion. The ignition model is a four-step mechanism developed for heavy hydrocarbons which has been previously used for diesel combustion. The turbulent combustion model is a flamelet model developed from the basic ideas of Marble and Broadwell. This model considers local regions of the turbulent flame front as interfaces called flamelets which separate fuel and oxidizer in the case of a diffusion flame. These flamelets are accounted for by solving a transport equation for the flame surface density, i.e., the flame area per unit volume.

Two-dimensional laser-sheet imaging and high-speed cinematography have been used to examine the combustion process in a newly constructed, optically accessible, direct-injection Diesel engine of the “heavy-duty” size class. The design of this engine preserves the intake port geometry and basic dimensions of a Cummins N-series production engine. It also includes several unique features to provide considerable optical access. An extended piston with piston-crown window and a window in the cylinder head allow the processes in the combustion bowl and squish region to be observed simultaneously. Windows at the top of the cylinder wall provide orthogonal-optical access with the capability of allowing the laser sheet to enter the cylinder along the axis of the spray. Finally, this new engine incorporates a unique separating cylinder liner that permits rapid cleaning of the windows. Studies were performed at a medium speed (1200 rpm) using a Cummins closed-nozzle fuel injector.

An experimental study has been conducted to characterize NO and soot evolution in an optically-accessible D.I. diesel engine with a square combustion chamber. Two-dimensional laser-induced fluorescence was used to characterize NO evolution. Soot evolution was characterized by two-dimensional laser-induced incandescence (LII) and Mie scattering techniques as well as direct photography of the flame luminosity. The engine operating parameters were set to provide optimum conditions for NO imaging. Attenuation of the UV beam proved to be the major obstacle in obtaining NO images. Therefore, oxygen was added to the intake air charge in order to reduce the optical density of the combustion medium. The NO images showed that the NO formation started almost immediately after ignition and ceased no later than 40 degrees ATDC. No soot images could be obtained by the laser-induced incandescence or Mie scattering methods before 20 degrees ATDC since the soot concentration was very low.

Soot and fuel distributions have been studied in an optically accessible direct-injection diesel engine of the “heavy-duty” size class. Laser-induced incandescence (LII) was used to study the effects of changes in the engine speed on the in-cylinder soot distribution, and elastic (Mie) scattering and laser-induced fluorescence (LIF) were used to examine the fuel distribution. The investigation showed that, in this engine, soot is distributed throughout the cross section of the combusting region of the fuel jet for engine speeds ranging from 600 to 1800 rpm. No indication was found that soot occurs preferentially around the periphery of the plume. The LII images showed that the soot concentration decreases with increasing engine speed and injection pressure, and that the soot distribution extends much further upstream (toward the injector) at the lower engine speeds than at higher speeds.

The effects of platinum and palladium catalysts on the enhancement of methanol combustion were investigated in a high pressure flow reactor and in a single-cylinder, D.I. Diesel engine. Initial studies were carried out in the flow reactor to determine the effect of catalyst temperature and equivalence ratio on the products of methanol combustion. Afterwards, Diesel engine studies were performed with in-cylinder catalysts applied to the exhaust valves in order to maintain high catalyst temperature required for high reactivity. Comparisons were based on performance, combustion characteristics, and emissions. Results of the flow reactor studies show that the catalytic ignition temperature, found to be 570 K, did not vary significantly with equivalence ratio. The Diesel engine experiments revealed that a decrease in glow plug temperature of 400 K was achievable while providing better performance and reduced emissions, including aldehydes, compared to the non-catalytic case.

A combusting plume in an optically accessible direct-injection diesel engine was studied using simultaneous 2-D imaging of laser-induced incandescence (LII) and natural flame luminosity, as well as simultaneous 2-D imaging of LII and elastic scattering. Obtaining images simultaneously via two different techniques makes the effects of cycle-to-cycle variation identical for both images, permitting the details of the simultaneous images to be compared. Since each technique provides unique information about the combusting diesel plume, more can be learned from comparison of the simultaneous images than by any of the techniques alone. Among the insights gained from these measurements are that the combusting plume in this engine has a general pattern of high soot concentration towards the leading edge with a lower soot concentration extending upstream towards the injector. Also, the soot particles are found to be larger towards the leading edge of the plume than in the upstream region.

The oxidation of 1-butene and n-butane in air at elevated pressure was investigated in a high pressure chemical flow reactor. Results are presented for pressures of 3, 6, and 10 atm, temperatures near 900K, and lean equivalence ratio. Gas samples were analyzed using gas chromatography with aldehydes sampled using a dinitrophenylhydrazine/acetonitrile procedure employing gas chromatography/mass spectrometry analysis. Major common products observed include CO, CH2O, C2H4, C3H6, and CO2. Additional major products included 1,3-C4H6 for 1-butene and 1-C4H8 for n-butane. Fuel conversion was increased with increased pressure, temperature, and equivalence ratio with 1-butene more reactive than n-butane. Large levels of lower molecular weight carbonyls resulted from 1-butene whereas significant amounts of conjugate and lower molecular weight alkenes resulted from n-butane. Trends in product distributions with increasing pressure were successfully accounted for by current autoignition theories.

Enhancement of methanol combustion in a direct injected Diesel engine using catalytically coated glow plugs was examined for platinum and palladium catalysts and compared to a non-catalytic baseline case. Experiments were performed for 6 and 10 brake Kilowatts (bKW) at 2500 rpm. Comparisons were made based on combustion, performance, and emissions including carbon monoxide (CO), oxides of nitrogen (NOx), unburned hydrocarbons (UHC), unburned methanol (UBM), and aldehydes. Results show a decrease in glow plug temperature of 100 K is achievable using platinum catalysts, and 150 K for palladium. Furthermore, the palladium catalyst was found to provide better combustion characteristics than the platinum catalyst. Also, the use of both catalysts produced lower aldehyde emissions, and the palladium reduced NOx emissions as well. However, unburned methanol increased for both catalytic glow plugs with respect to the non-catalytic case.

Laser-induced incandescence (LII) has been explored as a diagnostic for qualitative two-dimensional imaging of the in-cylinder soot distribution in a diesel engine. Advantages of LII over elastic-scatter soot imaging techniques include no interfering signals from liquid fuel droplets, easy rejection of laser light scattered by in-cylinder surfaces, and the signal intensity being proportional to the soot volume fraction. LII images were obtained in a 2.3-liter, single cylinder, direct-injection diesel engine, modified for optical access. To minimize laser sheet and signal attenuation (which can affect almost any planar imaging technique applied to diesel engine combustion), a low-sooting fuel was used whose vaporization and combustion characteristics are typical of standard diesel fuels. Temporal and spatial sequences of LII images were made which show the extent of the soot distribution within the optically accessible portion the combusting spray plume.

An optically accessible D] Diesel engine has been constructed tostudy combustion, emission, spray, and flow field phenomena. The goal of the present investigation is tostudy the effect that intake charge temperature variation at constant density has on combustion, emissions, and spray vaporization in both quiescent and swirling environments. The results indicate that raising intake temperatures decreased the ignition delay, peak rate of premixed burning, and premixed fraction. Increasing intake temperature increased the peak rate of diffusion burning in the quiescent environment, but mixing effects balanced temperature effects in the swirl environment and peak diffusion burning remained constant. In general, NOx increased with increasing temperature and amount of diffusion burning, but lower temperature data suggests that premixed and diffusion burning are both contributing to NO production.

A study has been experimentally conducted in an optically-accessible DI Diesel engine operating on 50/50 mixture of iso-octane and tetradecane to evaluate a planar laser light scattering technique for the in-cylinder study of soot. Two simultaneous images, taken with vertically and horizontally polarized scattered light, were used to determine the polarization ratio, CHH/CW. This magnitude of the polarization ratio was employed to distinguish soot particles from fuel droplets. The spatial and temporal variations of soot during the combustion cycle were investigated with images taken at various crank angles and swirl levels at three different planes in the combustion bowl. For the high swirl case, soot was uniformly distributed in the combustion bowl. For the non-swirl case, however, soot was mainly observed near the wall and at the top plane, and was observed to exist later into the expansion stroke.

The performance, combustion, and emissions of three coal-derived, test fuels were compared to a Phillips D-2 control fuel in a single cylinder, direct-injected, Diesel engine. The three synthetic test fuels were formed by varying the degree of hydrotreatment of a coal-liquid produced from the Exxon Donor Solvent (EDS) process; the three fuels have Cetane numbers of 29, 34.2, and 38.2. The objective of this research was to examine the effect of the degree of hydrotreatment on combustion, performance, and emission characteristics. The emissions measurements included both gas-phase emissions (CO, NOx, unburned hydrocarbons, and aldehydes), and particulate emissions. In addition, the Ames test was used to analyze the mutagenic activity of the soluble organic compounds found in the exhaust particulate.

The effects of the chemical composition of Diesel fuels on emissions is a critical issue for future Diesel fuels and synthetic fuels. In order to understand these effects, a series of fuels prepared from blends of pure hydrocarbons were studied in a single cylinder, DI Diesel engine. The base fuel was a 2:1 mixture by volume of iso-octane and tetradecane with a Cetane number of 40.5. The additive compounds chosen for this study were 1-methylnaphthalene, tetralin, and decalin; each additive was blended into the base fuel at several concentrations so that the effect of the chemical compound on emission trends could be determined. To minimize changes in the combustion process, as fuel composition changed, the injection timing was varied in order to adjust for Cetane number differences between fuels. Comparisons were made on the basis of performance, regulated exhaust emissions, including CO, NOx UHC, and particulates, aldehyde emissions, and soluble organic fraction.

The potential for catalytically enhanced ignition in low-heat rejection Diesel engines has been experimentally studied under engine simulated conditions in a high pressure chemical flow reactor. Results are presented for propane oxidation on platinum at 6 and 10 atmospheres, at temperatures from 800K to 1050K, and at equivalence ratios from 0.5 to 4.0. For turbulent transport rates which are typical of those in an engine, as much as 20% of the fuel was found to react on the catalyst before the onset of the gas-phase ignition reactions. Depending on the adiabaticity of the combustion chamber walls, this could lead to significant thermal enhancement of the gas-phase ignition process. Evidence of chemical enhancement was also observed, at 10 atm under very fuel rich conditions, in terms of a change in the concentration and distribution of the hydrocarbon intermediate species. Possible mechanisms for the observed chemical enhancement due to surface generated species are discussed.

Three synthetic fuels, derived from coal, were compared to a Phillips DF-2 control fuel. These fuels were tested in a single-cylinder, direct-injected, Diesel engine. Comparisons were made on the basis of performance, combustion characteristics, gas-phase emissions including aldehydes, and particulate emissions. In addition, the mutagenic activity of the soluble organic compounds from the particulates were analyzed using the Ames test. The objective of these experiments was to determine how well the synthetic fuels would perform as direct replacements for DF-2. All three synthetic fuels were manufactured from an initial batch of middle distillates produced by the Exxon Donor Solvent (EDS) process. The first fuel was a blend of the EDS middle distillate and the baseline DF-2 with a cetane number of 35.

Diesel engines are a source of suspended ambient particulate matter, and some concerns have been raised about the health effects from the inhalation of these particles. Nitrated polycyclic aromatics adsorbed on these particles have been shown to have the potential to cause mutations in living cells. Particulate matter collected on teflon-coated glass fiber filters produces results that may be open to question because of the possible generation of artifactual nitrated aromatics during the filtration process. An experiment using a constant-volume combustion bomb was used with four oxidants (air, nitrogen-free oxidant (29% O2 21% Ar 50% CO2), 50% O2/50% N2, and O2 (99.95% pure)), to address the concern over artifactual generation of nitrated-PAH on the filtration medium. Soot samples were collected both in situ on a cooled plug and on teflon-coated glass fiber filters in the exhaust line. Chemical comparisons of the collected samples were accomplished using chromatographic procedures.