Search Results

The technique of using cylinder pressure data for diagnosing the combustion process in a reciprocating internal combustion engine has been used for some time. Much of the early work, however, was qualitative comparisons of the heat release rate diagrams. Only recently have efforts been made to reduce the heat release diagrams to functional or numerical representations which could be used to make fuel-to-fuel and engine-to-engine comparisons. This paper describes work in which cylinder pressure measurements were taken from an operating diesel engine using a high-speed data acquisition system. Combustion chamber pressure measurements were made at approximately 1.0- degree increments over several engine cycles using a real-time data acquisition system. The pressure data were used to calculate apparent heat release and indicated horsepower. Both radiative and convective heat transfer computations were included in the calculational procedures.

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™.

The key feature of diesel fuel ignition quality is ignition delay time. In the American Society for Testing and Materials standard test for cetane number measurement, (ASTM D 613) the ignition delay time is held constant while the compression ratio is varied until ignition occurs at the set time. On the other hand, commercial diesel engines have set compression ratios and therefore, the ignition delay time varies with the cetane number of the fuel. The shorter this delay time, the wider the time window over which the combustion processes are spread. This leads to a more controlled heat release rate and pressure rise, resulting in prevention of diesel knock and in lowering of emissions. High cetane fuels exhibit short ignition delay times. The Constant Volume Combustion Apparatus (CVCA) precisely measures the ignition delay time of fuels. This study investigates the CVCA as a supplementary tool for characterization of diesel fuel ignition quality under a variety of conditions.

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.

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.

Autoignition of coal-water-slurry (CWS) fuel in a two-stroke engine operating at 1900 RPM has been achieved. A Pump-Line-Nozzle (PLN) injection system, delivering 400mm3/injection of CWS, was installed in one modified cylinder of a Detroit Diesel Corporation (DI)C) 8V-149TI engine, while the other seven cylinders remained configured for diesel fuel. Coal Combustion was sustained by maintaining high gas and surface temperatures with a combination of hot residual gases, warm inlet air admission, ceramic insulated components and increased compression ratio. The coal-fueled cylinder generated 85kW indicated power (80 percent of rated power), and lower NOx levels with a combustion efficiency of 99.2 percent.

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.

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.

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.

Four broad boiling range materials, representative of current and future feedstocks for diesel fuel, were processed to two levels of sulfur and aromatic content. These materials were then distilled into six to eight fractions each. The resulting 63 fuels were then characterized physically and chemically, and tested in both a constant volume combustion apparatus and a single cylinder diesel engine. The data obtained from these analyses and tests have been analyzed graphically and statistically. The results of the initial statistical analysis, reported here, indicate that the ignition quality of a fuel is dependent not only on the overall aromatic content, but also on the composition of the material formed during hydroprocessing of the aromatics. The NOx emissions, however, are related mainly to the aromatic content of the fuel, and the structure of the aromatic material.

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.

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.

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.

The work described in this paper includes the preparation and combustion testing of fuels that consist of fractions of several different distillate materials that represent different feed stocks and different processing technology. Each of the fuels have been tested in a constant volume combustion apparatus to determine the relationship between ignition delay time, temperature and cetane number. These relationships are discussed in terms of the composition and properties of each fraction, and the processing that each of the feedstocks were exposed to.

The engine-out emissions and fuel consumption rates for a modern, heavy-duty diesel engine were compared when fueling with a conventional diesel fuel and three water-blend-fuel emulsions. Four different fuels were studied: (1) a conventional diesel fuel, (2) PuriNOx,™ a water-fuel emulsion using the same conventional diesel fuel, but having 20% water by mass, and (3,4) two other formulations of the PuriNOx™ fuel that contained proprietary chemical additives intended to improve combustion efficiency and emissions characteristics. The emissions data were acquired with three different injection-timing strategies using the AVL 8-Mode steady-state test method in a Caterpillar 3176 engine, which had a calibration that met the 1998 nitrogen oxides (NOX) emissions standard.

Significant reductions of particulate matter (PM) and nitrogen oxides (NOx) emissions from diesel engines have been realized through fueling with water-fuel emulsions. However, the physical and chemical in-cylinder mechanisms that affect these pollutant reductions are not well understood. To address this issue, laser-based and chemiluminescence imaging experiments were performed in an optically-accessible, heavy-duty diesel engine using both a standard diesel fuel (D2) and an emulsion of 20% water, by mass (W20). A laser-based Mie-scatter diagnostic was used to measure the liquid-phase fuel penetration and showed 40-70% greater maximum liquid lengths with W20 at the operating conditions tested. At some conditions with low charge temperature or density, the liquid phase fuel may impinge directly on in-cylinder surfaces, leading to increased PM, HC, and CO emissions because of poor mixing.

In-cylinder control of particulate emissions in a diesel engine depends on careful control and understanding of the fuel injection and air/fuel mixing process. It is extremely difficult to measure physical parameters of the injection and mixing process in an operating engine, but it is possible to simulate some diesel combustion chamber conditions in a steady flow configuration whose characteristics can be more easily probed. This program created a steady flow environment in which air-flow and injection sprays were characterized under non-combusting conditions, and emissions measurements were made under combusting conditions. A limited test matrix was completed in which the following observations were made. Grid-generated air turbulence decreased particulates, CO, and unburned hydrocarbons, while CO2 and NOx levels were increased. The turbulence accelerated combustion, resulting in more complete combustion and higher temperatures at the measurement location.

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.

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.