Dennis L. Siebers

EFFECTS OF GAS DENSITY AND VAPORIZATION ON PENETRATION AND DISPERSION OF DIESEL SPRAYS

Ambient gas density and fuel vaporization effects on the penetration and dispersion of diesel sprays were examined over a gas density range spanning nearly two order of magnitude. This range included gas densities more than a factor of two higher than top-dead-center conditions in current technology heavy-duty diesel engines. The results show that ambient gas density has a significantly larger effect on spray penetration and a smaller effect on spray dispersion than has been previously reported. The increased dependence of penetration on gas density is shown to be the result of gas density effects on dispersion. In addition, the results show that vaporization decreases penetration and dispersion by as much as 20% relative to non-vaporizing sprays; however, the effects of vaporization decrease with increasing gas density. Characteristic penetration time and length scales are presented that include a dispersion term that accounts for the increased dependence of penetration on ambient density. These penetration time and length scales collapse the penetration data obtained over the entire range of conditions examined in the experiment into two distinct non-dimensional penetration curves: one for the non-vaporizing conditions and one for the vaporizing conditions. Comparison of the two nondimensional penetration curves to a theoretical penetration correlation for non-vaporizing sprays helped isolate and explain the effects of droplets and vaporization on penetration. The theoretical penetration correlation was derived using the penetration time and length scales and simple model for a non-vaporizing spray that has been previously presented in the literature. The correlation is in good agreement with the non-vaporizing data from this experiment and other commonly quoted penetration data sets. It also provides a potential explanation for much of scatter in the penetration predicted by various correlations in the literature.

Soot Formation in Diesel Fuel Jets Near the Lift-Off Length

Abstract Soot formation in the region downstream of the lift-off length of diesel fuel jets was investigated in an optically accessible constant-volume combustion vessel under quiescent-type diesel engine conditions. Planar laser-induced incandescence and line-of-sight laser extinction were used to determine the location of the first soot formation during mixing-controlled combustion. OH chemiluminescence imaging was used to determine the location of high-heat-release reactions relative to the soot-forming region. The primary parameters varied in the experiments were the sooting propensity of the fuel and the amount of fuel-air premixing that occurs upstream of the lift-off length. The fuels considered in order of increasing sooting propensity were: an oxygenated fuel blend (T70), a blend of diesel cetane-number reference fuels (CN80), and a #2 diesel fuel (D2). Fuel-air mixing upstream of the lift-off length was varied by changing ambient gas and injector conditions, which varied either the lift-off length or the air entrainment rate into the fuel jet relative to the fuel injection rate. Results show that soot formation starts at a finite distance downstream of the lift-off length and that the spatial location of soot formation depends on the fuel type and operating conditions. The distance from the lift-off length to the location of the first soot formation increases as the fuel sooting propensity decreases (i.e. in the order D2 < CN80 < T70). At the baseline operating conditions, the most upstream soot formation occurs at the edges of the jet for D2 and CN80, while for T70 the soot formation is confined to the jet central region. When conditions are varied to produce enhanced fuel-air mixing upstream of the lift-off length in D2 fuel jets, the initial soot formation shifts towards the fuel jet centre and eventually no soot is formed. For all experimental conditions, the observed location of soot formation relative to the heat-release location (lift-off) suggests that soot formation occurs in a mixture of combustion products originating from partially premixed reactions and a diffusion flame. The results also imply that soot precursor formation rates depend strongly on fuel type in the region between the lift-off length and the first soot formation.

Hydrogen combustion under diesel engine conditions

Abstract The autoignition and combustion of hydrogen were investigated in a constant-volume combustion vessel under simulated direct-injection (DI) diesel engine conditions. The parameters varied in the investigation included: the injection pressure and temperature, the orifice diameter, and the ambient gas pressure, temperature and composition. The results show that the ignition delay of hydrogen under DI diesel conditions has a strong, Arrhenius dependence on temperature; however, the dependence on the other parameters examined is small. For gas densities typical of top-dead-center (TDC) in diesel engines, ignition delays of less than 1.0 ms were obtained for gas temperatures greater than 1120 K with oxygen concentrations as low as 5% (by volume). These data confirm that compression ignition of hydrogen is possible in a diesel engine at reasonable TDC conditions. In addition, the results show that DI hydrogen combustion rates are insensitive to reduced oxygen concentrations. The insensitivity of ignition delay and combustion rate to reduced oxygen concentration is significant because it offers the potential for a dramatic reduction in the emission of nitric oxides from a compression-ignited DI hydrogen engine through use of exhaust-gas-recirculation.

Comparison of Nitric Oxide Removal by Cyanuric Acid and by Ammonia

Abstract Selective, non-catalytic techniques for removing nitric oxide (NO) from the exhaust gases of combustion processes include the addition of cyanuric acid, ammonia, or urea to the hot exhaust. This paper compares the effects of temperature and exhaust gas composition on the cyanuric acid (CA) and the ammonia (NH3) nitric oxide reduction processes and examines the decomposition of dry urea. The experiments were conducted in an electrically heated quartz flow reactor using mixtures of N2, 02, H2, H2, O, CO, and NO that simulated exhaust gases from overall lean hydrocarbon combustion processes Comparison of the CA and the NH3 nitric oxide reduction processes shows that the effects of the exhaust O2, H2, O, and CO concentrations on the NO reduction level and the temperature range over which the NO reduction occurs are different for each process. The comparison also shows that the by-products of each process are different for some conditions. These differences indicate that the detailed chemical mechanis...

Effects of natural gas composition on ignition delay under diesel conditions

Effects of variations in natural gas composition on the autoignition of natural gas under direct-injection (DI) diesel engine conditions were studied experimentally in a constant-volume combustion vessel and computationally using a chemical kinetic model. Four fuel blends were investigated: pure methane, a capacity-weighted mean natural gas, a high-ethane-content natural gas, and a natural gas with added propane typical of peak shaving conditions. Experimentally measured ignition delays were longest for pure methane and became progressively shorter as ethane and propane concentrations increased. At conditions characteristic of a DI compression ignition natural gas engine at Top Dead Center (CR = 23 : 1, p = 6.8 MPa, T = 1150 K), measured ignition delays for the four fuels varied from 1.8 ms for the peak shaving and high ethane gases to 2.7 ms for pure methane. A computational model, incorporating detailed chemical kinetics of oxidation of methane, ethane, propane and other small hydrocarbons was used to predict the influences of fuel composition on ignition, focusing on the four fuel types considered in the experimental study. Numerically predicted variations in ignition delay as a function of natural gas composition agreed with these measurements. The model results are used to interpret the kinetic factors responsible for the observations.

Orifice Diameter Effects on Diesel Fuel Jet Flame Structure

The effects of orifice diameter on several aspects ofdiesel fuel jet flame structure were investigated in a constant-volume combustion vessel under heavy-duty direct-injection (DI) diesel engine conditions using Phillips research grade #2 diesel fuel and orifice diameters ranging from 45 μm to 180 μm. The overall flame structure was visualized with time-averaged OH chemiluminescence and soot luminosity images acquired during the quasi-steady portion of the diesel combustion event that occurs after the transient premixed burn is completed and the flame length is established. The lift-off length, defined as the farthest upstream location of high-temperature combustion, and the flame length were determined from the OH chemiluminescence images. In addition, relative changes in the amount of soot formed for various conditions were determined from the soot incandescence images. Combined with previous investigations of liquid-phase fuel penetration and spray development, the results show that air entrainment upstream of the lift-off length (relative to the amount of fuel injected) is very sensitive to orifice diameter As orifice diameter decreases, the relative air entrainment upstream of the lift-off length increases significantly. The increased relative air entrainment results in a reduced overall average equivalence ratio in the fuel jet at the lift-off length and reduced soot luminosity downstream of the lift-off length. The reduced soot luminosity indicates that the amount of soot formed relative to the amount of fuel injected decreases with orifice diameter. The flame lengths determined from the images agree well with gas jet theory for momentum-driven nonpremixed turbulent flames.

An investigation of diesel soot formation processes using micro-orifices

Soot formation processes of diesel fuel jets were investigated in a constant-volume combustion vessel under heavy-duty, direct-injection (DI) diesel engine conditions using orifice diameters as small as 50 μ m. Soot was measured with line-of-sight laser extinction and planar laser-induced incandescence techniques, and flame liftoff lengths were determined with time-averaged OH chemiluminescence imaging. Results show that as fuel-air mixing upstream of the liftoff length increases, the amount of soot measured within a fuel jet decreases. When the cross-sectional average equivalence ratio at the liftoff length decreases to a value less than approximately 2, soot is no longer formed within the fuel jet. The soot measurements provide direct proof of the link between soot formation and mixing of fuel and air upstream of the liftoff length previously observed using total soot luminosity measurements. The non-sooting conditions were achieved with the 50 μ m micro-orifice at an ambient gas temperature and density of 1000 K and 14,8 kg/m 3 and ambient oxygen concentrations between 21% and 10%. The temperature and density are typical of DI diesel in-cylinder conditions. The lack of soot for the lower oxygen concentration conditions, which have substantially lower flame temperatures, suggests that NO x and soot can potentially be simultaneously reduced with small orifices and exhaust-gas recirculation.

Natural Gas Autoignition Under Diesel Conditions: Experiments and Chemical Kinetic Modeling

The effects of ambient gas thermodynamic state and fuel composition on the autoignition of natural gas under direct-injection diesel conditions were studied experimentally in a constant-volume combustion vessel and computationally using a detailed chemical kinetic model. Natural gas compositions representative of variations observed across the U.S. were considered. These results extend previous observations to more realistic natural gas compositions and a wider range of thermodynamic states that include the top-dead-center conditions in the natural gas version of the 6V-92 engine being developed by Detroit Diesel Corporation. At temperatures less than 1200 K, the experiments demonstrated that the ignition delay of natural gas under diesel conditions has a dependence on temperature that is Arrhenius in character and a dependence on pressure that is close to first order. The Arrhenius temperature dependence agrees with observations previously reported for natural gas and well-established trends for conventional diesel fuels. Natural gas composition did not change the nature of the above dependencies but did affect the magnitude of the ignition delay. The measured ignition delays were longest for pure methane and became progressively shorter as ethane and propane concentrations increased. 37 refs., 17 refs., 7 tabs.

Removal of nitric oxide from exhaust gas with cyanuric acid

Abstract Addition of gaseous isocyanic acid (HNCO) to the exhaust of combustion systems or chemical process has been proposed as a method for reducing nitric oxide (NO) emissions. The HNCO selectively reduces NO in the exhaust through a multistep chemical reaction mechanism. This article presents an experimental investigation of the proposed NO reduction process using cyanuric acid as the source of HNCO. At elevated temperature cyanuric acid decomposes and forms HNCO. The effects of temperature, exhaust gas composition, cyanuric acid concentration (i.e., HNCO concentration), and surfaces were examined. The experiments were conducted in an electrically heated quartz flow reactor using either exhaust from a diesel engine or simulated exhaust gas. The results demonstrate that gas phase NO reduction approaching 100% can be obtained. The lowest temperature for which gas phase NO reduction is observed is 950 K. The exhaust gas composition is the primary factor in determining the specific temperature range over which the NO reduction occurs, as well as the magnitude of the NO reduction, for a fixed cyanuric acid input. Three species in the exhaust gas that have a strong influence on the NO reduction process are O 2 , H 2 O, and CO. The results also demonstrate the cyanuric acid, HNCO, and N 2 O can be emitted when the NO reduction occurs in the gas phase. Finally, the results show that surfaces can have a major effect, either shifting the NO reduction to lower temperatures or causing a net production of NO.

Fuel Effects on Soot Processes of Fuel Jets at DI Diesel Conditions

The effects of fuel composition on soot processes in diesel fuel jets were studied in an optically-accessible constant-volume combustion vessel at experimental conditions typical of a Dl diesel. Four fuel blends used in recent engine studies were investigated, including three oxygenates and one diesel reference fuel: (1) T70, a fuel blend containing the oxygenate tetraethoxy-propane; (2) BM88, a fuel blend containing the oxygenate dibutyl-maleate; (3) GE80, a fuel blend containing the oxygenate tri-propylene-glycol-methyl-ether and (4) CN80, a diesel reference fuel composed of an n-hexadecane and heptamethyl-nonane mixture. Measurements of the soot distribution along the axis of quasi-steady fuel jets were performed using laser extinction and planar laser-induced incandescence (PLII) and were compared to previous results using a #2 diesel fuel (D2). In addition to the soot measurements, lift-off length and ignition delay measurements were performed for an extensive range of ambient gas temperatures and densities. Flame lift-off lengths were used in the interpretation and analysis of the soot measurements. Lift-off lengths, ignition delays and soot levels for these fuel blends follow similar trends with respect to ambient temperature or density established using D2 fuel. With increasing ambient temperature or density, lift-off length and ignition delay decrease and peak soot levels in a fuel jet increase. The increase in peak soot level is linear with respect to temperature and non-linear with respect to ambient density. Although following established trends with temperature or density, at a given experimental condition there is significant variation in lift-off length, ignition delay, and soot level for each fuel blend. The soot level in decreasing order with respect to fuel composition is: D2 > CN80 > BM88 > T70 > GE80. The distance from the injector to the region of first soot formation has an inverse relationship to the sooting propensity given above. That is, the first-soot distance is longest for GE80 and shortest for D2. The order in sooting tendency is found at either fixed ambient and injector operating conditions or at equivalent fuel-oxygen mixtures at the jet lift-off length, confirming that fuel molecular structure effects are important to the soot processes at diesel conditions. Differences in soot level with respect to fuel composition are quantified at many experimental conditions and axial positions of the fuel jet.