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The objective of the work reported in this paper was to develop and demonstrate an injection nozzle which can be used to inject both diesel fuel and methanol in to a direct injection diesel engine. The constraints on the nozzle were that it must provide acceptable fuel metering and atomization for the diesel fuel so that the engine can be operated at rated load on diesel fuel alone, or operate at full load with the diesel fuel as a pilot for the methanol. An additional constraint was that the nozzle design was to be easily adaptable to the existing injection nozzle so that engine head modifications are not required. The initial design was evaluated in a constant volume test chamber in which the pressure was varied from atmospheric to engine compression pressures.

During the 1980's, vegetable oils, microemulsions containing fatty alcohols as surfactants, and fatty esters have been extensively investigaed as alternative fuels to #2 diesel fuel (DF-2) used in farm tractors. Despite the importance of vegetable oils (mainly triglycerides) and fatty derivatives to the alternative fuel program, cetane numbers for pure triglycerides and many fatty derivatives were not reported. In the current study, estimated cetane numbers of these materials have been determined by use of a constant volume combustion bomb. Prior research has shown that this equipment can produce cetane numbers that correlate satisfactorily with engine cetane numbers as determied by ASTM D 613. The influence of chemical structure on ignition delay and cetane number was investigated. Evidence is presented that shows the current cetane number scale is not always suitable for these fatty materials. Suggestions are made as to what might be done to remedy this problem.

A new combustion concept has been developed and tested for improving the low to moderate load efficiency and NOx emissions of natural gas engines. This concept involves operation of a dual-fuel natural gas engine on Homogeneous Charge Compression Ignition (HCCI) in the load regime of idle up to 35 % of the peak torque. A dual-fuel approach is used to control the combustion phasing of the engine during HCCI operation, and conventional spark-ignited natural gas combustion is used for the high-load regime. This concept has resulted in an engine with power output and high-load fuel efficiency that are unchanged from the base engine, but with a 10 - 15 % improvement to the low to moderate load fuel efficiency. In addition, the engine-out NOx emissions during HCCI operation are over 90% lower than on spark-ignited natural gas operation over the equivalent load range.

This paper reports on the fourth part of a continued study on further research and development with the automated Ignition Quality Tester (IQT™). Research over the past six years (reported in SAE papers #961182, 971636 and 1999-01-3591) has demonstrated the capabilities of this automated apparatus to measure the ignition quality and accurately determine a derived cetane number (DCN) for a wide range of middle distillate and non-conventional diesel fuels. The present paper reports on a number of separate investigations supporting these continued studies.

Twelve different hole shapes for diesel injector tips were characterized with DF-2 diesel fuel for spray cone angle over a range of injection pressures from 21 MPa (3 kpsi) to 69 MPa (10 kpsi). A baseline and two of the most radical designs were also tested for drop-size distribution and liquid volume fraction (liquid fuel-air ratio) over a range of pressures from 41 MPa (6 kpsi) to 103 MPa (15 kpsi). All hole shapes were circular in cross-section with minimum diameters of 0.4 mm (0.016 in.), and included converging and diverging hole shapes. Overall hole lengths were constant at 2.5 mm (0.098 in.), for an L/d of 6.2. However, the effective L/d may have been less for some of the convergent and divergent shapes.

Vegetable oils are candidates for alternative fuels in diesel engines. These oils, such as soybean, sunflower, rapeseed, cottonseed, and peanut, consist of various triglycerides. The chemistry of the degradation of vegetable oils when used as alternate diesel fuels thus corresponds to that of triglycerides. To study the chemistry occurring during the precombustion phase of a vegetable oil injected into a diesel engine, a reactor simulating a diesel engine was constructed. Pure triglycerides were injected into the reactor in order to determine differences in the precombustion behavior of the various triglycerides. The reactor allowed motion pictures to be prepared of the injection event as the important reaction parameters, such as pressure, temperature, and atmosphere were varied. Furthermore, samples of the degradation products of precombusted triglycerides were collected and analyzed (gas chromatography / mass spectrometry).

This paper explores the possibility of on-board fuel classification for fuel property adaptive compression-ignition engine control system. The fuel classifier is designed to on-board classify the fuel that a diesel engine is running, including alternative and renewable fuels such as bio-diesel. Based on this classification, the key fuel properties are provided to the engine control system for optimal control of in-cylinder combustion and exhaust treatment system management with respect to the fuel. The fuel classifier employs engine input-output response characteristics measured from standard engine sensors to classify the fuel. For proof-of-concept purposes, engine input-output responses were measured for three different fuels at three different engine operating conditions. Two neural-network-based fuel classifiers were developed for different classification scenarios. Of the three engine operating conditions tested, two conditions were selected for the fuel classifier to be active.

Four different vegetable oils, degummed soybean, once refined cottonseed, peanut and sunflower oils, were injected into a high-pressure, high-temperature environment of nitrogen. The environment was controlled to resemble, thermodynamically, conditions present in a diesel engine at the time of fuel injection. Samples were removed from the sprays of these oils while they were being injected. A sonic, water-cooled probe and a cold trap were used to collect the samples. Chemical analyses of the samples indicated that significant chemical changes occur in the oils during the injection process. The major change is the formation of low-molecular weight compounds from the C18:2 and C18:3 fatty acids.

Mixtures of methanol, water and heavier alcohols, simulating “raw’ methanol at various levels of processing, were tested in a constant volume combustion apparatus (CVCA) and in a single-cylinder, direct-injection diesel engine. The ignition characteristics determined in the CVCA indicated that the heavier alcohols have beneficial effects on the auto-ignition quality of the fuels, as compared to pure methanol. Water, at up up to 10 percent by volume, has little effect on the ignition quality. In all cases, however, the cetane numbers of the alcohol mixtures were very low. The same fuels were tested in a single cylinder engine, set-up in a configuration similar to current two-valve DI engines, except that the compression ratio was increased to 19:1. Pure methanol and five different blends of alcohols and water were tested in the engine at five different speed-load conditions.

High-speed movie films, and laser-diffraction drop sizing were used to evaluate the structure, penetration rate, cone angle, and drop size distribution of diesel sprays in a constant volume pressure vessel. As further means of evaluating the data, comparisons are made between the film measurements, and calculations from a dense gas jet model. In addition to the high-speed film data that describes the overall structure of the spray as a function of time, a laser diffraction instrument was used to measure drop size distribution through a cross-section of the spray. In terms of the growth of the total spray volume (a rough measure of the amount of air entrained in the spray), spray impingement causes an initial delay, but generally the same overall growth rate as an equivalent unimpeded spray. Agreement between measurements and calculations is excellent for a diesel spray with a 0.15 mm D orifice and relatively high injection pressures.

Because of its dominant role in diesel engine performance and emissions, the fuel injection process has become an area of very active research and development. It is now clear that location, shape, rate of development, and mass flow distribution within each fuel jet are all important in controlling fuel air mixing, wall interactions, combustion rate, and the resulting levels of emissions. The objective of this project was to develop an instrument for measurement of the instantaneous fuel mass and momentum distribution in the jets issuing from diesel injection nozzles. The goal was to develop an instrument concept that can be used in the laboratory for fundamental measurements, as well as a quality control system for use in manufacture of the injection nozzles. The concept of the instrument is based on the measurement of the instantaneous momentum of the fuel jet as it impacts on a surface equipped with pressure sensitive elements.

A combustion-based analytical method, initially developed by the Southwest Research Institute (SwRI) referred to as the Constant Volume Combustion Apparatus (CVCA), has been further researched/developed by an SwRI licensee (Advanced Engine Technology Ltd.) as an Ignition Quality Tester (IQT) for laboratories and refineries. The IQT software/hardware system permits rapid and precise determination of ignition quality for middle distillate fuels. Its features, such as low fuel volume requirement, complete test automation, and self-diagnosis, make it highly suitable for commercial oil industry and research applications. Operating and test conditions were examined in the context of providing a high correlation with cetane number (CN), as determined by the ASTM D-613 method. Preliminary investigation indicates that the IQT results are highly repeatable (± 0.30 CN), providing a high sensitivity to CN variation over the 33 to 58 CN range.

Biodiesel is a mixture of esters (usually methyl esters) of fatty acids found in the triglycerides of vegetable oils. The different fatty compounds comprising biodiesel possess different ignition properties. To investigate and potentially improve these properties, the cetane numbers of various fatty acids and esters were determined in a Constant Volume Combustion Apparatus. The cetane numbers range from 20.4 for linolenic acid to 80.1 for butyl stearate. The cetane numbers depend on the number of CH2 groups as well as the number of double bonds and other factors. Various oxygenated compounds were studied for their potential of improving the cetane numbers of fatty compounds. Several potential cetane improvers with ignition delay properties giving calculated cetane numbers over 100 were identified. The effect of these cetane improvers depended on their concentration and also on the fatty material investigated.

A combustion-based analytical method, initially developed by the Southwest Research Institute (SwRI) and referred to as the Constant Volume Combustion Apparatus (CVCA), has been further researched/developed by an SwRI licensee (Advanced Engine Technology Ltd.). This R&D has resulted in a diesel fuel Ignition Quality Tester (IQT) that permits rapid and precise determination of the ignition quality of middle distillate and alternative fuels. Its features, such as low fuel volume requirement, complete test automation, and self-diagnosis, make it highly suitable for commercial oil industry and research applications. A preliminary investigation, reported in SAE paper 961182, has shown that the IQT results are highly correlated to the ASTM D-613 cetane number (CN). The objective of this paper is to report on efforts to further refine the original CN model and report on improvements to the IQT fuel injection system.

A 2003 heavy-duty diesel engine (2002 emissions level) was used to test a representative biodiesel fuel as well as the methyl esters of several different fatty acids. The fuel variables included degree of saturation, the oxygen content, and carbon chain length. In addition, two pure normal paraffins with the corresponding chain lengths of two of the methyl esters were also tested to determine the impact of chain length. The dependent variables were the NOx and the particulate emissions (PM). The results indicated that the primary fuel variable affecting the emissions is the oxygen content. The emissions results showed that the highest oxygen content test fuel had the lowest emissions of both NOx and PM. As compared to the baseline diesel fuel the NOx emissions were reduced by 5 percent and the PM emissions were reduced by 83 percent.

Due to the cost and mobility advantages of diesel-powered mine vehicles over electric vehicles, it is anticipated that the diesel engine will become more widely used in underground mines in this country. Concern has arisen, however, over the impact of diesel exhaust emissions on the air quality in the underground mine environment. A literature search has been conducted to identify known effects of fuel properties on the reduction of diesel exhaust emissions. Reductions can be obtained by optimizing fuel properties and by considering alternative fuels to standard diesel fuel. However, the data base is relatively small and the results highly dependent on engine type and operating conditions. Engine studies on a typical mine diesel are necessary to draw quantitative conclusions regarding the reduction of emissions, especially particulates and NO2 which have not been generally addressed in previous studies.

It is now a fairly well established fact that excessive ring and cylinder bore wear can result from the operation of an S. I. engine on neat methanol. The mechanism leading to the excessive wear were investigated using both engine and bench tests. Engine tests using prevaporized superheated methanol indicated that the wear results from reactions between the combustion products and the cast iron cylinder liner, where the presence of liquid methanol in the combustion chamber appears to be an important part of the mechanism. These reactions were investigated using a spinning disc combustor. The spinning disc combustor was used to provide a source of burning methanol droplets which were subsequently quenched on a water-cooled cast iron surface. The condensate formed on the cast iron surface was collected and analyzed for chemical composition. Infrared analysis indicated the presence of large quantities of iron formate, a reaction product of iron and formic acid.

Hybrids are fuels derived from combinations of different energy sources and which are generally formulated as solutions, emulsions, or slurries. The underlying objective of this program is to reduce the use of petroleum-derived fuels and/or to minimize the processing requirements of the finished hybrid fuels. Several hybrid fuel formulations have been developed and tested in a direct injection single-cylinder diesel engine. The formulations included solutions of ethanol and vegetable oils in diesel fuel, emulsions of methanol and of ethanol in diesel fuel; and slurries of starch, cellulose, and “carbon” in diesel fuel. Based on the progress to date, the solutions and emulsions appear to be viable diesel engine fuels if the economic factors are favorable and the storage and handling problems are not too severe. The slurries, on the other hand, are not to the same point of development as the solutions and emulsions.

A constant volume bomb was used to determine basic combustion characteristics of isooctane, n-heptane, methanol, propane and methane. Results show that the laminar flame velocity of a quiescent homogeneous air/fuel mixture can be derived from pressure-time data in the bomb. The effects of pressure, temperature, and charge dilution on flame velocity and ignition are presented. A thermo-chemical kinetic model accurately predicted concentrations of nitric oxide during combustion and in the burned gas.

Combustion studies on various potential alternative fuels were performed for the U.S. Array Belvoir Research and Development Center in a two-stroke heavy duty diesel engine. One cylinder of the engine was instrumented with a pressure transducer. A high-speed data acquisition system was used to acquire cylinder pressure histories synchronously with crankangle. The heat release diagrams, along with the calculated combustion efficiencies of the fuels were compared to a referee grade diesel fuel. The calculated and measured combustion parameters include heat release centroids, cumulative heat release, peak pressure, indicated horsepower, peak rate of pressure rise, indicated thermal efficiency, energy input, and ignition delay. Regression analyses were performed between various fuel properties and the calculated and measured combustion performance parameters. The fuel properties included specific gravity, cetane number, viscosity, boiling point distribution.