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To meet increasingly stringent diesel exhaust emissions requirements, original equipment manufacturers (OEMs) have introduced common rail fuel injection systems that develop pressures of up to 2000 bar (30,000 psi). In addition, fuel delivery schemes have become more complicated, often involving multiple injections per cycle. Containing higher pressures and allowing for precise metering of fuel requires very tight tolerances within the injector. These changes have made injectors more sensitive to fuel particulate contamination. Recently, problems caused by internal diesel injector deposits have been widely reported. In this paper, the results of an investigation into the chemical nature and probable sources of these deposits are discussed. Using an array of techniques, internal deposits were analyzed from on a number of sticking injectors from the field and from OEM test stands in North America.

A 1000-hour test was conducted to determine the durability effects of 2-ethylhexyl nitrate (2-EHN) cetane improver on heavy duty diesel engines. Two identical 1993 DDC Series 60 engines were run side-by-side on a severe duty cycle. Both were fueled with a commercial low sulfur fuel. The fuel in one engine was treated with 7500 ppm of 2-EHN cetane improver. At the end of the test, engine wear and deposit comparisons were made to determine the effect of high cetane improver treat rates on engine durability. After 1000 hours of operation, the engine running on fuel treated with 2-EHN cetane improver exhibited lower engine wear and deposits than the engine run without cetane improver. Analysis of oil samples drawn every 100 hours indicated no difference in wear metals or other physical properties when cetane improver was used. Fuel analyses demonstrated that 2-EHN did not degrade under the high operating temperatures of this modern heavy-duty diesel engine.

A 100-hour engine dynamometer test for intake valve deposits (IVD) which uses a Ford 2.3L engine was developed by the Coordinating Research Council (CRC). Recently, this test has been approved by the American Society for Testing and Materials (ASTM) as Test Method D 6201-97. Since this test offers improvements in test variability, duration, and cost, it is expected to replace ASTM D 5500-94, a 16,000-km vehicle test run using a BMW 318i, as the key performance test for the Certification of Gasoline Deposit Control Additives by the EPA Final Rule. As a step in the replacement process, a correlation between valve deposit levels for the CRC 2.3L Ford IVD test and ASTM D 5500 BMW IVD test must be determined. This paper provides a statistical review of available data in an attempt to provide such a correlation.

A number of factors have contributed to a growing awareness of diesel fuel quality. Recent regulations promulgated by the California Air Resources Board and the U.S. Environmental Protection Agency have emphasized the importance of diesel fuel properties on vehicle performance and emissions. This has created an interest in premium diesel fuel in the United States. Premium diesel has long been used in Europe to address the performance needs of the passenger car diesel market. Studies show that additives can improve the quality of diesel fuel. A new application of cetane improvers is to reduce emissions from diesel engines. Other combustion improvers may also be employed. Diesel detergents are used to insure that these low emission levels can be maintained over extended periods. Engine tests recently developed by OEMs are being used to quantify the performance benefits of these additives.

Four commercially available low-sulfur diesel fuels were additized with two chemically different cetane improvers. Both neat and additized fuels were evaluated in a 1991 prototype heavy-duty diesel (HDD) engine using the EPA Hot Start Transient Cycle. Hydrocarbon (HC), carbon monoxide (CO), nitrogen oxide (NOx), and particulate emissions were determined for each of the 18 fuel formulations tested. Results show that cetane improvers lower HC and CO emissions and, in some cases, NOx and particulate emissions. CO and HC emissions decreased as cetane number increased. The use of cetane improvers should help refiners design diesel fuel formulations which meet California requirements and assist original equipment manufacturers (OEM's) in meeting their emission targets.