Assessment of Tribological Characteristics of Low-Sulfur and Ultralow-Sulfur Diesel under Practical Load and Temperature Scenarios

The lubricating properties of diesel are an imperative aspect for the optimal functioning of fuel injection components. Regulatory standards followed by refineries utilize accelerated wear testing methodologies. These tests provide indicative results for judging the lubricity but are not conclusive for determining wear in functional applications attributed to higher loads and other environmental factors. In the course of this article, a tribological evaluation was carried out on Low-Sulfur Diesel (LSD) and Ultralow Sulfur Diesel (ULSD) by utilizing modified test parameters incorporating higher loads and a more extensive gradient of temperature on High-Frequency Reciprocating Rig (HFRR) tribotester. The variance in the resultant coefficient of friction (COF) and wear scar concerning the change in parameters was observed as well as a comparative analysis was drawn between both test fuels. Further to analyze the impact of temperature on the tribological behavior of diesel, a ramp test was carried out with static load and a temperature range from 40°C to 80°C ramp up and down. The results obtained through the experimentation specific to boundary lubrication indicated a difference of 175 μm in wear-scar size between both the fuels when tested at a load of 180 N. This figure signified the importance of a higher testing load as both fuels qualified the manufacturer’s set lubricity requirement of 460 μm wear-scar diameter tested under the International Organization for Standardization (ISO)-12156/1 standard, which dictates a testing load of 2 N. In the ramp testing procedure, it was observed that at a temperature of 60°C, the ULSD obtained a peak COF of 0.889; whereas at temperatures of 40°C and 80°C, a lower COF of 0.8287 ± 0.0050 was obtained, highlighting the significance of temperature on the tribological properties of diesel.