Search Results

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.

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.

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.

The engine selected for this work was a Caterpillar 3176 engine. Engine exhaust emissions, performance, and heat release rates were measured as functions of engine configuration, engine speed and load. Two engine configurations were used, a standard 1994 design and a 1994 configuration with EGR designed to achieve a NOx emissions level of 2.5 gm/hp-hr. Measurements were performed at 7 different steady-state, speed-load conditions on thirteen different test fuels. The fuel matrix was statistically designed to independently examine the effects of the targeted fuel properties. Cetane number was varied from 40 to 55, using both natural cetane number and cetane percent improver additives. Aromatic content ranged from 10 to 30 percent in two different forms, one in which the aromatics were predominantly mono-aromatic species and the other, where a significant fraction of the aromatics were either di- or tri-aromatics.

Five different diesel fuel feedstocks were processed to two levels of aromatic (0.05 sulfur, and then 10 percent) content. These materials were distilled into 6 to 8 narrow boiling range fractions that were each characterized in terms of the properties and composition. The fractions were also tested at five different speed load conditions in a single cylinder engine where high speed combustion data and emissions measurements were obtained. Linear regression analysis was used to develop relationships between the properties and composition, and the combustion and emissions characteristics as determined in the engine. The results are presented in the form of the regression equations and discussed in terms of the relative importance of the various properties in controlling the combustion and emissions characteristics. The results of these analysis confirm the importance of aromatic content on the cetane number, the smoke and the NOx emissions.

Methods to reduce direct injected diesel engine emissions in the combustion chamber will be discussed in this paper. The following NOx emission reduction technologies will be reviewed: charge air chilling, water injection, and exhaust gas recirculation (EGR). Emphasis will be placed on the development of an EGR system and the effect of EGR on NOx and particulates. The lower limit of NOx that can be obtained using conventional diesel engine combustion will be discussed. Further reductions in NOx may require changing the combustion process from a diffusion flame to a homogeneous charge combustion system.

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.

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.

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.

Diesel engine optimization for low emissions and high efficiency involves the use of very high injection pressures. It was generally thought that increased injection pressures lead to improved fuel air mixing due to increased atomization in the fuel jet. Injection experiments in a high-pressure, high-temperature flow reactor indicated, however, that high injection pressures, in excess of 150 MPa, leads to greatly increased penetration rates and significant wall impingement. An endoscope system was used to obtain movies of combustion in a modern, 4-valve, heavy-duty diesel engine. Movies were obtained at different speeds, loads, injection pressures, and intake air pressures. The movies indicated that high injection pressure, coupled with high intake air density leads to very short ignition delay times, ignition close to the nozzle, and burning of the plumes as they traverse the combustion chamber.

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.

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.

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.

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.

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.

In 1997 the US EPA formed a Heavy-Duty Engine Working Group (HDEWG) in the Mobile Sources Technical Advisory Subcommittee to address the questions related to fuel property effects on heavy-duty diesel engine emissions. The Working Group consisted of members from EPA and the oil refining and engine manufacturing industries. The goal of the Working Group was to help define the role of the fuel in meeting the future emissions standards in advanced technology engines (beyond 2004 regulated emissions levels). To meet this objective a three-phase program was developed. Phase I was designed to demonstrate that a prototype engine, located at Southwest Research Institute, represented similar emissions characteristics to that of certain manufacturers prototype engines. Phase II was designed to document the effects of selected fuel properties using a statistically designed fuel matrix in which cetane number, density, and aromatic content and type were the independent variables.

In 1995, US Environmental Protection Agency (EPA) formed the Heavy-Duty Engine Working Group (HDEWG). The objective of the group was to assess the role diesel fuel could play in meeting exhaust emission standards proposed for model year 2004+ heavy-duty diesel engines. The group developed a three-phase program to achieve this objective. This paper describes the development of test fuels used in Phase 2 of the EPA HDEWG Program to investigate the effect of fuel properties on heavy-duty diesel engine emissions. It discusses the design of the fuel matrix, reviews the process of test fuel preparation and presents the results of a multi-laboratory fuel analysis program. Fuel properties selected for investigation included density, cetane number, mono- and polyaromatic hydrocarbon content.

The U.S. Environmental Protection Agency (EPA) formed a Heavy-Duty Engine Working Group (HDEWG) in the Mobile Sources Technical Advisory Subcommittee in 1995. The goal of the HDEWG was to help define the role of the fuel in meeting the future emissions standards in advanced technology engines (beyond 2004 regulated emissions levels). A three-phase program was developed. This paper presents the results of the statistical analysis of the data collected in the Phase II program. Included is a description of the design of the fuel test matrix, and a listing of the regression equations developed to predict emissions as a function of fuel density, cetane number, monoaromatics, and polyaromatics. Also included is a description of selected analyses of the emissions from a smaller set of fuel data that allowed direct comparison of the effects of natural and boosted cetane number.

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.

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.