Investigation of Diesel Fuel Properties on Emissions, 03-9173

Principal Investigators
Andrew C. Matheaus
Thomas W. Ryan, III

Inclusive Dates: 01/01/00 - 10/31/01

Background - SwRI engineers developed a constant volume combustion apparatus (CVCA) to determine 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 a function of the temperature and pressure. SwRI licensed the ignition delay technique to Advanced Engine Technology Ltd. (AET) for determination of the cetane number (CN) of test fuels. CN is normally measured in a special test engine, following a well-specified test procedure (ASTM D 613). The current engine-based technique has been criticized as being expensive and failing to represent ignition and combustion performance in modern diesel engines.

AET is marketing the CVCA under the trade name IQT™ (Ignition Quality Tester). AET is currently working with the American Society for Testing and Materials (ASTM) to have the IQT accepted as an ASTM procedure. The IQT requires much less fuel, is faster and less expensive, requires less operator training, is more accurate, and more flexible than the current technique. So far, AET has paid SwRI approximately $10,000 in royalty fees. It is anticipated that this income will grow significantly with ASTM approval and with industry acceptance of the apparatus. The IQT also received an R&D 100 Award for the year 2001.

Approach - The research team believes that the utility of the IQT can be expanded dramatically with further development. Two areas of expanded use were examined in this project. The first area involved development of the relationships between the ignition, combustion, and emissions formation in the IQT to the corresponding processes in modern diesel engines. Development of these correlations would provide opportunities to use the IQT as a screening device for new fuel formulations. The second area involved the development of an IQT-based technique for screening and rating fuels for use in advanced engines, such as the SwRI homogeneous charge compression ignition (HCCI) engine. HCCI is a new mode of SwRI-developed engine combustion that produces very low levels of emissions and is very efficient.

Accomplishments - More than fifty different fuels were tested in the IQT to determine the ignition delay times and the combustion rates under different initial pressures and temperatures. In addition, selected fuels were tested repeatedly to generate sufficient quantities of combustion products to perform analysis of the combustion products. The analysis focused on fuels that contain nitrate-based ignition improvers to determine the role of the additive on both the ignition delay time and the NO_x formation. The ignition delay data were also used to define the autoignition temperature as a function of fuel composition.

Development of the correlation between the processes in the IQT and a modern engine were hampered by aging of the test fuels available from a previous engine program. In the process of completing these experiments, it was discovered, however, that the IQT provides a good prediction of the octane number as well as the cetane number, which opens up the opportunity to develop a single universal fuel rating methodology.

SwRI also participated in two round-robin tests of the IQT. AET and the IQT users are attempting to have the IQT certified as an alternative test to the cetane engine (ASTM D 613). The IQT is also more accurate (less than one cetane number) than the cetane engines (less than three cetane number). The IQT has less maintenance and operational costs and is easier to use. The round robins went well, and SwRI's unit performed very well as compared to the average of the IQT units. 

A process to screen HCCI fuels was established. Several different potential HCCI fuel formulations have been fully tested with this procedure. The results provide ignition delay versus temperature for different fuels or additive levels. These data represent an excellent screening tool for HCCI use. 

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