Investigation of Diesel Fuel Properties on Emissions, 03-9173Printer Friendly Version
Inclusive Dates: 01/01/00 - Current
Background - Diesel engines are the most energy-efficient power plant available for use in transportation. These engines emit high levels of oxides of nitrogen (NOx) and particulate matter (PM). Governments around the world have recognized the dangers to public health and have responded with extremely stringent standards on these emissions. The current standards for NOx and PM are 50 percent lower than 10 years ago, and the proposed standards for 2007 are 90 percent lower than today's regulations.
Three elements place SwRI in a leadership role in fuels and emissions research. SwRI's role will be aggressively utilized to promote and attract significant external funding. The first element was created in a previous SwRI-funded project in which a number of fuels were tested in an advanced low-emission diesel engine developed at SwRI. This internally funded project demonstrated the Institute's expertise in this area of engine-fuel interaction and attracted a number of large outside funded projects. These projects resulted in the accumulation of a large matrix of fuels that have complete chemical and physical property characterization. Some questions remain from these studies regarding the role of certain nitrogen-containing additives on the NOx emissions and on the role of the traditional fuel combustion characteristic called cetane number.
The second element resulted from another SwRI-funded project that focused on the development of a novel, low-emission combustion system called Homogeneous Charge Compression Ignition (HCCI). Publication of these results has resulted in significant international interest in the concept, leading to the formation of a large industry project to develop the SwRI HCCI process further. The SwRI work indicates that HCCI has fuel-combustion requirements different from the diesel and spark ignition engines. It is apparent that the success of HCCI is dependent on the development of a new HCCI fuel.
The third element involves a Constant Volume Combustion Apparatus (CVCA) that was developed at SwRI for determination of the pressure- and temperature-dependent autoignition characteristics of fuels. The CVCA can be used to determine the ignition delay times and combustion rates of fuels as functions of the temperature and pressure. SwRI licensed the ignition delay technique to Advanced Engine Technology (AET) for determination of the cetane number. AET, marketing the apparatus under the trade name IQT (Ignition Quality Tester), is currently working with the American Society for Testing and Materials (ASTM) to have the IQT accepted as an ASTM procedure. It is anticipated that royalty fees to SwRI will grow significantly with ASTM approval and with industry acceptance of the apparatus.
Approach - More than fifty different, well-characterized, fully formulated fuels will be tested in the CVCA to determine the ignition delay times and the combustion rates as functions of the initial pressure and temperature. In addition, selected fuels will be tested repeatedly to generate sufficient quantities of combustion products to perform gas chromatography (GC) analysis. The GC analysis will focus on fuels that contain nitrate-based ignition improvers to determine the role of the additive on both the ignition delay time and the NOx formation. The ignition delay data will be used to define the autoignition temperature as functions of fuel composition.
The proposed project will serve several functions. First, the results of the ignition delay time measurements and the GC analysis will be used to explain the engine emission results obtained from the client-funded projects. These results will add credibility to the engine-fuel test procedure and lead to additional client-funded fuel tests and measurements in the SwRI engine. Second, the ignition delay results will support the significance of the CVCA technique and increase the demand for the IQT and the resulting royalties to SwRI. The elevated-pressure autoignition temperature data will be used to attract the interest of SwRI's fuel company clients in the development of a new fuel specifically formulated for HCCI engines. The previously SwRI-funded project indicated that this aspect is an important one for the HCCI fuel. The results of the GC analysis will also be used to determine the role of nitrate-based cetane improvers on emissions formation in modern diesel engines. It is anticipated that the project results will be presented in three peer-reviewed publications.
Accomplishments - This internal research project is approximately 75 percent complete. The logistics of properly operating the IQT were determined, and the system and supporting hardware was installed. A photograph of the combustion chamber and injection system is shown below. An engineer was fully trained in the operation, troubleshooting, and assembly of the unit, and a technician was trained in the day-to-day operation of the unit. A process to filter and blanket the fuels was established.
An array of fuels was tested at standard pressure and temperatures to determine the cetane number, based on ignition delay. The effect of fuel aging was pronounced. The cetane results for some of the aged fuels differed from the cetane number obtain in a cetane engine. SwRI participated in preliminary round-robin testing of the IQT. AET and the IQT users are attempting to have the IQT certified as an alternative to the cetane engine test method (ASTM D 613). The IQT is also more accurate (±1 cetane number) than the cetane engine procedure (±3 cetane number). The IQT has less maintenance and operational costs and is easier to use. The first round-robin evaluation went well and SwRI's unit performed very well as compared to the average of the IQT units. A second and possibly a third round-robin procedure will be required before ASTM accepts the IQT as an alternative procedure.
A process to screen HCCI fuels was established, and eight HCCI fuels have been fully tested with this procedure. The results provide ignition delay versus temperature for different fuels or additive levels. These data provide an excellent screening tool for HCCI use. The hardware has been set up to allow for GC analysis of fuels. At least two fuels will be tested at various levels of ethylhexal nitrate additive in order to study the effects of nitrogen conversion during combustion. In addition, the toxicity of nitrosamines will be examined.