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Conventional diesel fuel has been in the market for decades and used successfully to run diesel engines of all sizes in many applications. In order to reduce emissions and to foster energy source diversity, new fuels such as alternative and renewable, as well as new fuel formulations have entered the market. These include biodiesel, gas-to-liquid, and alternative formulations by states such as California. Performance variations in fuel economy, emissions, and compatibility for these fuels have been evaluated and debated. In some cases contradictory views have surfaced. “Sustainable”, “Renewable”, and “Clean” designations have been interchanged. Adding to the confusion, results from one fuel in one type of engine such as an older heavy-duty engine, is at times compared to that of another fuel in another type such as a modern light-duty engine. This study was an attempt to compare the performance of several fuels in identical environments, using the same engine, for direct comparison.

Conventional diesel fuel has been in the market for decades and used successfully to run diesel engines of all sizes in many applications. In order to reduce emissions and to foster energy source diversity, new fuels such as alternative and renewable, as well as new fuel formulations have entered the market. These include biodiesel, gas-to-liquid, and alternative formulations by states such as California. Performance variations in fuel economy, emissions, and compatibility for these fuels have been evaluated and debated. In some cases contradictory views have surfaced. “Sustainable”, “Renewable”, and “Clean” designations have been interchanged. Adding to the confusion, results from one fuel in one type of engine such as an older heavy-duty engine, is at times compared to that of another type such as a modern light-duty. This study was an attempt to compare the performance of several fuels in an identical environment, using the same engine, for direct comparison.

Conventional diesel fuel (1) has been on the market for decades and used successfully to run diesel engines of all sizes in many applications.* In order to reduce emissions and to foster energy source diversity, new fuels such as alternative and renewable, as well as new formulations, have entered the market. These include biodiesel, gas-to-liquid, and alternative formulations by states such as California. Performance variations in fuel economy, emissions, and compatibility for these fuels have been evaluated and debated. In some cases, contradictory views have surfaced. “Renewable” and “clean” designations have been interchanged. Adding to the confusion, results from one fuel in one type of engine, such as an older heavy-duty engine, is at times compared to that of another type, such as a modern light-duty engine.

Researchers and cooperative groups worldwide conducted research and developed several test methods to gauge the lubricity of diesel fuel. This was necessary because the more recent fuel specifications require a higher level of hydrotreating which in turn can result in a reduction of diesel fuel lubricity. An appropriate test method was needed to enable measures to restore fuel lubricity and to enable fuel suppliers to comply with the newly adopted diesel fuel lubricity specification. The current test method that is used by most regions of the world is the High Frequency Reciprocating Rig, HFRR. Although this test method was developed and selected by the ISO group originally, and is fundamentally the same, it has been adopted in slightly different forms by regions of the world. One common element in all forms of the test method is its poor precision when compared to test methods for other fuel properties.

A working group of the International Organization of Standardization (ISO), in cooperation with the Coordinating European Council (CEC), has conducted a round robin test program to compare laboratory bench tests to evaluate the lubricity characteristics of diesel fuels. The goal of the ISO program was to generate sufficient data from these test methods and from fuel injection equipment performance tests to select a test method for determining diesel fuel lubricity. The ISO group also aimed to produce sufficient information to define a minimum lubricity level that would protect fuel delivery system components. Four laboratory test methods were included in the program. These consisted of Falex's Ball on Three Seats (BOTS), Lubrizol's Modified Ball-on-Cylinder Lubricity Evaluator (BOCLE), Paramins' High Frequency Reciprocating Rig (HFRR), and the U.S. Army's Scuffing Load BOCLE.

The trend toward low environmental impact diesel fuel has resulted in new formulations that not only benefit the environment, but that can enhance diesel engine performance as well. The sulfur content of highway diesel fuel has been reduced to a maximum of 0.05 wt % nationwide. California has an additional requirement of a maximum of 10% aromatics content which covers most highway and nonhighway vehicles. However, fuels with higher aromatics levels can be certified if they demonstrate equivalent emissions. The introduction of these new fuels, coupled with the rapid changes in engine design to meet new emission regulations, has created the need to evaluate a number of fuel properties to ensure proper performance while protecting certain engine components (1)*. Diesel fuel lubricity and its effect on some fuel injection system equipment, such as rotary distributor pumps, is one such issue which is being investigated by a number of groups.

The sulfur content of all highway diesel fuel was required to be reduced to a maximum of 0.05 wt % starting October 1993. This federal requirement results in further fuel processing by refineries. The hydrotreating process used to reduce fuel sulfur has the potential to reduce the fuel's lubricating characteristics. Fuel producers and fuel injection equipment suppliers have been concerned about the likelihood of increased component wear upon the introduction of these new fuels. Low sulfur fuels have been produced and marketed in Southern California since 1985 with no apparent evidence of any field problem. Nevertheless, concern outside of this area exists. Therefore, one such fuel with a sulfur content well below 0.05% was used to conduct a vehicle test to evaluate its effect on the fuel injection pump. This fuel and a low aromatics diesel fuel were used to investigate the effect of various levels of two different sulfur compounds on the lubricity characteristics of the fuels.

Federal regulations require all highway diesel fuel to have a maximum sulfur level of 500 ppm, effective October 1993. California regulations require a maximum 10% aromatics content in addition to the low sulfur content. The hydrotreating processes used to reduce fuel sulfur and aromatics contents to meet these new regulations have the potential of reducing fuel lubricity by reducing the amount of polar impurities such as nitrogen compounds which provide lubricity. This is a great concern for many fuel injection equipment suppliers and fuel producers. Several low aromatics diesel fuels were produced in a pilot plant facility and analyzed using a Ball-on-Cylinder Lubricity Evaluator (BOCLE). These fuels were then tested in a pump endurance test facility using two types of fuel-lubricated rotary-distributor fuel injection pumps.