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Four fuels in the gasoline boiling range where tested in a constant volume combustion bomb and a variable compression ratio HCCI engine. The fuels were tested using a port fuel injection system. The results of the experiments defined the range of HCCI operation in terms of the Coefficient of Variation (COV) of IMEP and the maximum rate of pressure rise. The results for the test fuels are compared to each other and to a baseline gasoline. The results are discussed in terms of the effects of the fuel properties (basically, various measure of ignition quality) on the engine heat release rates and efficiencies.

Southwest Research Institute (SwRI) is exploring the feasibility of extending the performance and fuel efficiency of the spark ignition (SI) engine to match that of the emission constrained compression (CI) engine, whilst retaining the cost effective 3-way stoichiometric aftertreatment systems associated with traditional SI light duty engines. The engine concept, which has a relatively high compression ratio and uses heavy EGR, is called “HEDGE”, i.e. High Efficiency Durable Gasoline Engine. Whereas previous SwRI papers have been medium and heavy duty development focused, this paper uses results from simulations, with some test bed correlations, to predict multicylinder torque curves, brake thermal efficiency and NOx emissions as well as knock limit for light and medium duty applications.

SwRI has developed a new technology concept involving the use of high EGR rates coupled with a high-energy ignition system in a gasoline engine to improve fuel economy and emissions. Based on a single-cylinder study [1], this study extends the concept of a high compression ratio gasoline engine with EGR rates > 30% and a high-energy ignition system to a multi-cylinder engine. A 2000 MY Isuzu Duramax 6.6 L 8-cylinder engine was converted to run on gasoline with a diesel pilot ignition system. The engine was run at two compression ratios, 17.5:1 and 12.5:1 and with two different EGR systems - a low-pressure loop and a high pressure loop. A high cetane number (CN) diesel fuel (CN=76) was used as the ignition source and two different octane number (ON) gasolines were investigated - a pump grade 91 ON ((R+M)/2) and a 103 ON ((R+M)/2) racing fuel.

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.

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.

Three different carbon blacks were used to formulate nine different slurries in DF-2. The rheological properties of each formulation were examined to determine deviations from Newtonian behavior. The spray characteristics of selected formulations were then examined in a high-pressure, high-temperature injection bomb. The cone angle decreased and the penetration rates increased for all of the slurries tested as compared to straight DF-2. These changes were more pronounced as the concentration of carbon black increased. Six formulations of three types of carbon black were tested in a single-cylinder, direct-injection CLR engine. Apparent heat release rates were computed as a function of crankangle from the cylinder pressure data. Based on the engine performance tests and some limited durability testing it appears that well-formulated carbon black slurries have only minor effects on engine performance and durability.

Slurry fuels of various forms of solids in diesel fuel were developed and evaluated for their relative potential as fuel for diesel engines. Thirteen test fuels with different solids concentrations were formulated using eight different materials. The injection and atomization characteristics (transient diesel sprays) of the test fuels were examined in a spray bomb in which a nitrogen atmosphere was maintained at high pressure and temperature, 4.2 MPa and 480°C, respectively. The diagnostics of the sprays included high-speed movies and high-resolution still photographs. The slurries were also tested in a single-cylinder CLR engine in both direct-injection and prechamber configurations. The data included the normal performance parameters as well as heat release rates and emissions. In most cases, the slurries performed very much like the baseline fuel. The combustion data indicated that a large fraction (90 percent or more) of the solids were burning in the engine.

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.

As a part of an overall project to improve the techniques for rating the ignition quality of diesel engine fuels, the experiments described in this paper involve examination of the relationship between cetane number and both the physical and chemical ignition delay times. The ignition delay times have been determined from accurate pressure histories obtained during the injection and ignition of a variety of test fuels in a constant volume combustion bomb using a quiescent, high-temperature, high-pressure air environment. The test fuels have included blends of the primary reference fuels as well as other fuels selected because of specific physical properties or chemical composition. The correlation between the cetane numbers of the fuels and various ignition delay times are examined.

Changing fuel quality, increasingly stringent exhaust emission standards, demands for higher efficiency, and the trend towards higher specific output, all contribute to the need for a better understanding of the ignition process in diesel engines. In addition to the impact on the combustion process and the resulting performance and emissions, the ignition process controls the startability of the engine, which, in turn, governs the required compressions ratio and several of the other engine design parameters. The importance of the ignition process is reflected in the fact that the only combustion property that is specified for diesel fuel is the ignition delay time as indicated by the cetane number. The objective of the work described in this paper was to determine the relationship between the ignition process as it occurs in an actual engine, to ignition in a constant volume combustion bomb.

One of the major problems created by the use of methanol fuels in SI engines is the high cylinder bore and ring wear rates observed during operation at low engine temperatures. The objective of the work reported in this paper was to identify the processes controlling the corrosion/wear mechanism in methanol-fueled, spark-ignition engines. Basically, three different types of experiments were performed during this project. The experiments consisted of: 1. Combustion experiments designed to identify the combustion products of methanol at various locations within a confined methanol flame; 2. Exposure studies designed to define the specific role of each of the combustion products on the corrosion mechanism; 3. Lubricant screening experiments designed to identify the mode of penetration of the oil film, and the location, in the microscale, of the surface attack. Performic acid was identified as the corrosive agent.

A variable-compression ratio, direct-injection diesel engine (VCR) has been designed and assembled at Southwest Research Institute with the intention of examining the current procedures for rating the ignition quality of diesel fuels and the meaning of ignition delay as an indicator of ignition and combustion quality. Using a slightly modified ASTM D 613 procedure, the engine has been used to rate the ignition quality of 43 different test fuels. The ratings obtained in the VCR engine are compared to the corresponding rating obtained using the standard cetane rating procedure. Some of the problems associated with the standard procedure became apparent during these experiments. The experimental results are discussed in terms of the problems and the advantages of a proposed VCR-based rating procedure.

The ignition delay times of forty-two different fuels were measured in a constant volume combustion bomb. The measurements were performed at three different initial air temperatures using fuels ranging from the primary reference fuels for cetane rating to complex mixtures of coal-derived liquids. The ignition delay times were examined in terms of the classical definitions of the physical and chemical delay times. The previously used definitions were found to be inadequate, and new definitions have been proposed. The total ignition delay times were studied in the context of providing a means for rating the ignition quality of the fuels. Fuel ignition quality rating schemes are discussed, including one based on the current cetane number scale as well as one based on a new scale which includes a measure of the sensitivity of the various fuels to the air temperature.

A single-cylinder, variable-compression ratio, direct-injection diesel engine was designed and constructed to study the ignition quality of seventeen different test fuels, ranging from the primary reference fuels to a vegetable oil. The objective of the work was to compare the ignition quality rating of the fuels using the standard cetane rating technique to ratings obtained in the test engine. The ignition delay times have been measured as functions of the engine speed, load, and compression ratio. As in the standard cetane rating technique, injection timing was adjusted so that combustion started at top dead center. This was accomplished by adjusting the injection timing as the speed, load, and compression ratio were varied. The resulting data is plotted as the ignition delay times versus compression ratio at the various speed-load conditions.

This paper reports on the third part of a continued study (SAE Papers 961182, 971636) to develop the Ignition Quality Tester (IQT™). Past research has shown that this automated laboratory/refinery apparatus can be used to accurately predict the cetane number of middle distillates and alternative fuels using small sample volumes (< 50 mL). The paper reports on the main objective of a study performed by Advanced Engine Technology Ltd. (AET), in co-operation with its research partners. The primary research objective of this work is to further the understanding of fuel preparation (fuel air mixing) and start of combustion processes in the IQT™. Key to this understanding is the manner in which single molecule compounds and full boiling-range diesel fuels behave during these processes. Insights are provided into the manner in which the American Society for Testing and Materials (ASTM) D-613 primary reference fuels (PRFs) undergo fuel preparation and start of combustion in the IQT™.