Jeffrey Naber

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.

Modeling engine spray/wall impingement

A computer model was used to study the impingement of sprays on walls. The spray model accounts for the effects of drop breakup, drop collision and coalescence, and the effect of drops on the gas turbulence. A new submodel was developed to describe the spray/wall interaction process. Predictions of the effect of engine swirl, ambient gas pressure (density), wall inclination angle and the distance from the nozzle to the wall, were in good qualitative agreement with the experiments

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.

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.

Analysis of Combustion Knock Metrics in Spark-Ignition Engines

Combustion knock detection and control in internal combustion engines continues to be an important feature in engine management systems. In spark-ignition engine applications, the frequency of occurrence of combustion knock and its intensity are controlled through a closedlooped feedback system to maintain knock at levels that do not cause engine damage or objectionable audible noise. Many methods for determination of the feedback signal for combustion knock in spark-ignition internal combustion engines have been employed with the most common technique being measurement of engine vibration using an accelerometer. With this technique single or multiple piezoelectric accelerometers are mounted on the engine and vibrations resulting from combustion knock and other sources are converted to electrical signals. These signals are input to the engine control unit and are processed to determine the signal strength during a period of crank angle when combustion knock is expected. As the accelerometer detects a number of sources of vibrations in addition to the desired vibration from knock, the signal quality varies significantly from engine to engine, cylinder to cylinder, and over the operating conditions of the engine. To evaluate the effectiveness and accuracy of knock detection via accelerometers, a reference system is commonly employed. One of the most common reference metrics is the signal strength of the combustion pressure over the appropriate frequency range as measured with in-cylinder pressure transducers. This analysis examines both cylinder pressure and accelerometer-based knock intensity metrics, where the pressure-based knock intensity metric is used as the reference measure. Distributions of the knock metrics over a number of engine cycles for various engine speeds, loads, cam timings, and knock levels are measured and fit to a log-normal model distribution. The lognormal model is shown to provide a good fit to the measured distribution and also captures the characteristics of the distribution to include skewness and peakness. In addition the accelerometer intensity metric is correlated to the reference pressure intensity metric. The result of this correlation provides the coefficient of determination, which is used as a measure of the accelerometer intensity metrics ability to indicate knock. The effects of the distribution of the pressure intensity metric on the coefficient of determination are examined by analyzing subsets of the distribution

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.

An Experimental Study of Active Regeneration of an Advanced Catalyzed Particulate Filter by Diesel Fuel Injection Upstream of an Oxidation Catalyst

Passive regeneration (oxidation of particulate matter without using an external energy source) of particulate filters in combination with active regeneration is necessary for low-load engine operating conditions. For low-load conditions, the exhaust gas temperatures are less than 250\mDC and the PM oxidation rate due to passive regeneration is less than the PM accumulation rate. The objective of this research was to experimentally investigate active regeneration of a catalyzed particulate filter (CPF) using diesel fuel injection in the exhaust gas after the turbocharger and before a diesel oxidation catalyst (DOC) and to collect data for extending the MTU 1-D, 2-layer model to include the simulation of active regeneration. The engine used in this study was a 2002 Cummins ISM turbocharged 10.8 L heavy-duty diesel engine with cooled EGR. The exhaust after-treatment system consisted of a Johnson Matthey DOC and CPF (a CCRT\sR). Steady-state loading experiments at 20% load at rated speed were performed for different times in order to achieve three particulate matter loadings of 1.1, 2.2 and 4.1 grams of particulate/liter of filter. Active regeneration was carried out at three CPF-inlet temperatures of 500, 550 and 600\mDC to cover a range of temperatures and filter loadings for thermal regeneration. The dependent data of fuel usage, time of regeneration, mass of PM oxidized and maximum substrate temperature are presented as a function of mass loading and inlet CPF temperature. The results show that higher CPF-inlet temperature and particulate matter mass loading are more effective for regeneration of the CPF and lower fuel usage in grams of PM oxidized per gallon of fuel used whereas low temperatures and lower mass loadings were not as effective due to lower reaction rates. 90% of the HC from the diesel fuel injection were oxidized across the DOC while the other 10% were oxidized across the CPF under the test conditions.

Accelerometer Based Sensing of Combustion in a High Speed HPCR Diesel Engine

The capability to detect combustion in a diesel engine has the potential of being an important control feature to meet increasingly stringent emission regulations and for the development of alternative combustion strategies such as HCCI and PCCI. In this work, block-mounted accelerometers are investigated as potential feedback sensors for detecting combustion characteristics in a high-speed, high-pressure common rail (HPCR), 1.9L diesel engine. Accelerometers are positioned in multiple placements and orientations on the engine, and engine testing is conducted under motored, single and pilot-main injection conditions. Engine tests are then conducted at varying injection timings to observe the resulting time and frequency domain changes of both the pressure and acceleration signals. The higher-frequency (3 kHz \mL f\ mL 25 kHz) components of the in-cylinder pressure are found to correlate to the peak rate of incylinder heat release and indicated a potential application to the detection of combustion. The accelerometer and pressure signals are analyzed through the use of various functions including angle-dependant fast Fourier transforms (FFT) and coherence to isolate frequency components that are well correlated between the cylinder pressure and accelerometer signals. In addition, these analysis techniques are used to compare the three accelerometer orientations and the individual accelerometer placements.

Fuel impingement in a direct injection diesel engine

Abstract : High injection pressure impinging spray experiments and modeling were performed under simulated diesel engine conditions (pressure and density) at ambient temperature. A spray impinged normal to a small crown in the bowl of a simulated piston. High speed photography was used in the constant volume bomb to examine the effect of impingement on fuel mixing. The spray model which includes drop breakup, coalescence, impingement, and vaporization effects was used to predict fuel mixing in the bomb. The spray distributions predicted by the model are compared to the photographs obtained in the bomb. Reprints.

Effects of Blending Gasoline With Ethanol and Butanol on Engine Efficiency and Emissions Using a Direct-Injection, Spark-Ignition Engine

The new U.S. Renewable Fuel Standard requires an increase of ethanol and advanced biofuels to 36 billion gallons by 2022. Due to its high octane number, renewable character and minimal toxicity, ethanol was believed to be one of the most favorable alternative fuels to displace gasoline in spark-ignited engines. However, ethanol fuel results in a substantial reduction in vehicle range when compared to gasoline. In addition, ethanol is fully miscible in water which requires blending at distribution sites instead of the refinery. Butanol, on the other hand, has an energy density comparable to gasoline and lower affinity for water than ethanol. Butanol has recently received increased attention due to its favorable fuel properties as well as new developments in production processes. The advantageous properties of butanol warrant a more in-depth study on the potential for butanol to become a significant component of the advanced biofuels mandate. This study evaluates the combustion behavior, performance, as well as the regulated engine-out emissions of ethanol and butanol blends with gasoline. Two of the butanol isomers; 1-butanol as well as iso-butanol, were tested as part of this study. The evaluation includes gasoline as a baseline, as well as various ethanol/gasoline and butanol/gasoline blends up to a volume blend ratio of 85% of the oxygenated fuel. The test engine is a spark ignition, direct-injection, (SIDI), four-cylinder test engine equipped with pressure transducers in each cylinder. These tests were designed to evaluate a scenario in terms of using these alcohol blends in an engine calibrated for pump gasoline operation. Therefore no modifications to the engine calibration were performed. Following this analysis of combustion behavior and emissions with the base engine calibration, future studies will include detailed heat release analysis of engine operation without exhaust gas recirculation. Also, knock behavior of the different fuel blends will be studied along with unregulated engine out emissions.Copyright