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Engine manufacturers have raised concerns at recent industry meetings regarding the effect that 2 mm porosity filters will have on low temperature operability. An All Weather Chassis Dynamometer (AWCD) program was carried out to address this concern and to extend our general knowledge of low temperature additive performance in 1998/9 model year Heavy Duty Trucks. Known laboratory tests were also evaluated as to their ability to predict vehicle performance. Four trucks equipped with Cummins M11, Detroit Diesel Series 60, Caterpillar C12 (Southern), and Caterpillar C12 (Northern) engines were leased and fitted appropriately to measure their performance under low temperature conditions using Imperial Oil's AWCD in Sarnia, Ontario, Canada. Commercial Low Sulfur No. 2 and Low Sulfur No. 1 diesel fuels were purchased, and a series of blends were prepared representing fuels that would typically be sold during the winter.

Over the past several years, a number of publications have looked at the correlation of laboratory test methods with the low temperature operability limits for the fuel delivery system used with heavy duty Cummins engines. Cummins, which predominates the North American Heavy Duty market, have what is considered the most severe type of fuel delivery system. The Low Temperature Flow Test (LTFT) has been the test which best correlates with this type of vehicle. In this study, the Cummins M11, Cummins NTC, Detroit Diesel 60S, and Caterpillar 3406C Heavy Duty trucks were evaluated in an All Weather Chassis Dynamometer and the results compared to the LTFT and other laboratory tests to see which test best protects all the vehicles. Historical overnight cooling data was examined to compare with the All Weather Chassis Dynamometer cool down cycle to validate the test protocol.

Low sulfur specifications for on-road diesel fuel effective October 1, 1993, and the low aromatics/low sulfur limits issued by CARB (California Air Resources Board) in California have increased the potential for the use of Cold Flow Additives. The additives can be used in winterizing diesel fuel to minimize the need for low sulfur kerosene. However, the only widely accepted laboratory test method which satisfactorily protects actual heavy duty truck operability in North America is ASTM D4539, the Low Temperature Flow Test (LTFT). LTFT is a slow cool test often requiring 16-20 hours to obtain a result. As such it is considered to be of little utility as a product release specification for refineries and terminals. Studies intended to identify faster test methods which would closely relate to LTFT have been undertaken.

Over recent years there has been much interest by end users to secure improved winter diesel fuel quality without sacrificing low temperature operability performance. The industry standard has been to ensure low temperature vehicle operability by lowering the cloud point (believed to be the low temperature vehicle operability limit) with kerosene dilutions. Cold Flow Additives have been used in diesel fuel appliations for over thirty years. In the past ten years, there has been a dramatic increase in the number and types of additives, as well as claims for low temperature operability performance. The purpose of this paper is to clarify the types of Cold Flow Additives (pour point depressants, cloud point depressants and operability additives) available for use in diesel fuel and to differentiate the individual performance benefits and various test methods and their applicability.