How sulfur content in diesel fuel impacts engine oil formulation

How sulfur content in diesel fuel impacts engine oil formulation

Diesel fuel contains sulfur, which derives from the original crude oil source and can still be present after refining.

Fuel of the future fuel pump

Diesel fuel contains sulfur, which derives from the original crude oil source and can still be present after refining. After combustion in the engine, this sulfur forms particulates that are a primary contributor to air pollution and the cause of harmful corrosion in the engine.

Before global efforts to improve air quality and remove sulfur from fuel came about, high levels of detergent additives were a necessary component of engine oil to protect engine parts from the damage caused by sulfur. Detergency was so important that a common way to interpret engine oil performance or oil life was by measuring the level of detergents in an oil by the total base number (TBN).

Regulations to reduce vehicle emissions over the past several decades have dramatically reduced the allowable sulfur content in diesel fuel. Today, sulfur content in diesel fuel in both the United States and Mexico is 97% lower than what was seen throughout most of the 20th century. This type of fuel is commonly referred to as ultra-low sulfur diesel (ULSD)

The impact of sulfur on engine hardware

After combustion, sulfur from diesel fuel creates sulfuric acid that causes caused corrosive wear on the metal surfaces of an engine. Corrosion of a surface within in a dynamic system such as the cylinder wall/liner can lead to corrosive wear; surface corrosion layers are removed through sliding or abrasion. 

All acids formed within the engine have the potential to cause corrosion, but the risk of corrosion depends on their acidity. The acidity of a fluid is measured according to the mixture’s pH. Both the concentration of acid present, and the strength of the acids in the mixture, will increase the risk of corrosion. 

There are three main types of acids that form in an engine:

  • Sulfur acids are strong acids that form from combustion of fuel containing sulfur. When high sulfur fuel is used, sulfuric acids are the most significant corrosive acids.
  • Nitrogen acids are strong acids that form from nitrogen oxides that result during lean combustion (a process known as nitration).
  • Organic acids are weaker acids that form from partial combustion of the hydrocarbon fuel, or decomposition of the engine oil (processes known as oxidation).

Engine oil protects against corrosion

Historically, the high levels of sulfur common in all fuels required engine oils that prevented the build-up of sulfuric acid and coated engine parts with a protective layer to reduce the level of corrosive wear. Engine oils formulated with basic (alkaline) additives react with sulfur acids, preventing the acids from reaching and attacking the metal surfaces.

There are three main categories of engine oil additives that protect against corrosion.

  • Detergents provide a source of alkaline base, that can neutralize the corrosive acids to form non-corrosive by-products. Many factors control the detergents’ efficacy at neutralizing acids, and modern engine oil formulations will contain many different types of detergents to optimize performance.
  • Antioxidants prevent the formation of organic acids by blocking the process of oxidation. By preventing the degradation of the engine oil, antioxidants extend the life of an engine oil by increasing the oil drain interval (ODI).
  • Corrosion inhibitors protect surfaces against corrosion. The corrosion inhibitors will form a protective layer, acting as a barrier between the metal surface and the corrosive acids.
oilsplash

New types of oil formulation for ULSD fuels

Fuel quality, including fuel sulfur levels, plays a big role in the requirement of the engine oil. Fuel quality can impact engine hardware, so the oil must be formulated to protect against these impacts. Using the correct measure for the way the oil performs is therefore crucial.

The level of sulfur acids created by today’s ULSD fuel are so low that the need for elevated levels of detergents that produce high TBN no longer exist. Instead, protection against organic acid corrosion has become a more necessary requirement of modern engine oil.

Preventing organic acid corrosion with today’s ULSD fuel requires engine oil formulations with a complex mix of detergent, antioxidant and corrosion inhibitor additives to achieve optimum performance. Using an appropriate measurement for the way modern oils perform is important for oil condition monitoring.

This article was contributed by Greg Matheson, engine oil product manager for North America at the Lubrizol Corp.

You May Also Like

Hendrickson partners with Tadano to produce Airtek NXT, Roadmaax products

The Airtek NXT front air suspension and dual steer axle system, along with the Roadmaax high capacity rear air suspension systems, are included as part of the chassis enhancements.

Hendrickson-AIRTEK-NXT-ROADMAXX-1400

Hendrickson Truck Commercial Vehicle Systems announced that it has partnered with Tadano Global to offer the Airtek NXT front air suspension and dual steer axle system and the Roadmaax high capacity rear air suspension systems as a part of the chassis enhancements for the all-terrain cranes for GT-800XL-2 and GT-1200XL-2. 

Aftermarket Auto Parts Alliance announces new IT Security Manager

In this new role, Scarver will play a major role in training, communication and preparedness for IT Security.

PRT Heavy Duty to present portfolio of HD Shocks at MATS

The brand will be exhibiting a complete line of shock absorbers for heavy-duty applications.

JohnDow Dynamic introduces new line of TPMS products

The TPMS retro kit sensors work with virtually any air-filled tire.

JohnDowDynamicTPMS-1400
Navistar launches International S13 Integrated Powertrain for vocational market

The S13 Integrated Powertrain, launched back in August of 2022, is now available for the vocational market.

S13-Vocational-Powetrain-1400

Other Posts

Apollo Tyres names new head of commercial sales for US, Canada

Persons will oversee Apollo’s sales initiatives within the U.S. and Canada for commercial tires.

Apollo-Image-1400
Phillips unveils new manufacturing facilities in Mexico to meet N.A. product demand

The manufacturer plans to relocate its manufacturing in China to Mexico.

Phillips-Mexico-Ribbon-Cutting-1400
Yokohama Tire introduces new commercial truck tire lineup at TMC

The tire lineup included over a dozen offerings, with three new products and the company’s last-mile delivery and ultra wide-base tire options.

Yokohama-Tire-114R-1400
Double Coin announces new original equipment, national account manager

In his most recent role, Tim Kelly was a national fleet manager for Bridgestone and has held multiple roles in the field.

Tim Kelly Double Coin