The automotive industry has been recently faced with unprecedented changes and new challenges. As increasingly strict fuel economy limits have proliferated across the globe, automakers have shifted to new engine technologies in order to keep the pace.

Specifically, gasoline direct injection (GDI) technology has been identified as one of the most reliable means to boost fuel efficiency in passenger cars on a broad scale. The market for these fuel efficient engines is widely anticipated to expand dramatically over the next several years. By 2020, it’s estimated that 39 percent of all cars produced globally will run on GDI engines.

As the marketplace shifts this way, the collective knowledge of traditional engines doesn’t directly apply. It necessitates new approaches to engine oil formulation and additive chemistry, accounting for the unique operation of GDI hardware.

Nowhere is the need for new approaches clearer than the case of GDI soot, a carbonaceous byproduct and oil contaminant that is formed under the operating conditions of GDI engines. Not quite traditional soot and not quite sludge, GDI soot falls somewhere in between, and it has been identified as a contributing factor to the most pressing issues facing GDI technology. But first: what is GDI soot, and how are OEMs and oil marketers addressing the associated challenges?

Understanding GDI Soot

Understanding GDI soot and its implications begins with understanding the operating conditions of GDI engines. GDI engines achieve greater fuel economy by spraying fuel directly into an engine’s cylinders, which allows for increased torque and compression ratios. This enables engine downsizing; a 4-cylinder GDI engine can generate the same torque as a traditional 6-cylinder engine. Fewer cylinders providing the same amount of power is a direct route to greater fuel economy.

However, it’s through this unique method of introducing fuel to the engine that high amounts of GDI soot can be formed. And while the GDI soot phenomenon is yet very new, industry experts and researchers including those within Lubrizol Additives have begun the investigation into the hows and whys.

So far, it has been established that the new substance falls somewhere between traditional soot and sludge, while yet maintaining several unique properties. A strong understanding of both traditional soot and sludge has helped Lubrizol understand the fundamental differences between those materials and GDI soot.

• Appearance GDI soot simply looks different than either traditional soot or sludge. Traditional soot maintains a turbostratic structure, meaning the substance’s carbon planes appear in a logical pattern. GDI soot, meanwhile, is far more amorphous and doesn’t maintain a firm structure.
• Chemistry At the chemical level, GDI soot is more aromatic than traditional soot, and is slightly more polar. For both of these reasons, GDI soot has been found to interact with lubricants in certain ways that have not been previously witnessed. Specifically, the material can interfere with lubricant additives and the ways in which those additives perform their intended functions–primarily the lubricant’s ability to provide the robust protection that GDI engines require. Traditional soot is commonly responsible for lubricant thickening–while this problem exists to some extent with GDI soot, oil marketers and OEMs are far more concerned with the non-traditional engine wear associated with GDI soot.

Combined with acids and fuel dilution from incomplete combustion, GDI soot has been found specifically to contribute to accelerated wear on an engine’s timing chain, a vitally important component connecting the engine’s crankshaft to the camshaft. Also responsible for valve timing, the timing chain’s connection must remain precisely accurate. Unchecked chain wear can effectively cause the chain itself to elongate, which negatively alters valve timing, and can lead to major engine damage.

This issue is being addressed within the ongoing development of the proposed GF-6 specification. A new test is being developed that seeks to evaluate a lubricant’s ability to help mitigate chain wear, and Lubrizol has been closely involved with that development.

Seeking a Solution

Lubrizol is on the forefront of developing a firm understanding of GDI soot. In order to help solve the associated issues, Lubrizol has taken a holistic approach as GDI technology grows more prevalent throughout the passenger car market. Through its investment in testing and research, Lubrizol can thoroughly understand GDI soot, its properties and characteristics, and its ramifications for formulators. With this knowledge, Lubrizol along with its partners can deliver the advanced additive chemistry required to enable advanced hardware technology for a more fuel-efficient future.

For more information contact your Lubrizol account manager.