Lubricants

Development of Next-Generation Engine Oils

Research and Development for Ultra-Low Viscosity Engine Oils

Fig. 1 - Engine oil viscosity standards (SAE viscosity grades)

The pressing need to reduce CO2 emissions from automobiles has created a need for engine oils with much better fuel-saving performance. One effective means of improving fuel-saving performance is to lower the viscosity of the engine oil. The list of SAE viscosity grades now includes lower viscosity grades (Fig. 1), and a growing number of automobiles are able to use low viscosity engine oils. Japan is one country where the shift toward lower viscosity engine oils started earlier than in many others.

Fig. 2 - Relationship between engine oil viscosity and temperature

Looking ahead to the next generation, we're currently working on development of ultra-low viscosity engine oils with even greater fuel-saving performance. A critical piece of the puzzle for creating such an engine oil is a high viscosity index (VI). Figure 2 shows the relationship between temperature and viscosity in an engine oil. As you can see, the engine oil is more viscous at lower temperatures, which increases drag inside the engine. An oil with a high viscosity index will have a lower viscosity at low temperatures, which translates to higher fuel-saving performance. The primary component of any engine oil is the base oil. To create an ultra-low viscosity engine oil with a high viscosity index, it is critical to use a base oil with a high viscosity index. Using WBASE, an ultra-high VI base oil technology developed in our own labs, we're working to develop high-VI, ultra-low viscosity engine oils with outstanding fuel-saving performance. (Fig. 2)

ZP Technology

Without ZP
With ZP

Fig. 3 - Deposits inside engine head cover (after testing engine 200 hours)

ZP is one of many additives we use in our engine oils. Using ZP not only reduces deposits of sludge and varnish inside the engine, but also extends the service life of the engine oil. In fact, our engine oils made with ZP provide detergency for twice as long as conventional products.

How ZP Differs from Conventional Additives

Fig. 4 - Difference in molecular structures of ZDDP and ZP

For decades, engine oils were formulated with a multi-function additive called ZDDP, which has antioxidant and anti-wear properties. The problem is that ZDDP molecules contain sulfur (S), which leads to increased deposits in the engine and shorter oil life. In ZP, the sulfur atoms found in ZDDP have been replaced with oxygen (O).

Discovery of ZP

Fig. 5 - Hydrolysis of ZDDP

ZP was discovered through research on the decomposition mechanism of ZDDP. A detailed study on how ZDDP decomposes revealed that during combustion in the engine, ZDDP is oxidized and broken down into ZP and sulfur compounds such as hydrogen sulfide. The sulfur compounds react with water to become a strong sulfuric acid, causing the basic detergents in the engine oil to be consumed and reducing the cleaning performance of the oil. ZP contains no sulfur, which meant no sulfur compounds would form when it broke down. We thought that if ZP could be used in place of ZDDP, we could avoid the problems caused by formation of sulfuric acid and enable the detergents to function longer.

Fig. 6 - ENEOS SUSTINA

The thing is, the sulfur in ZDDP also plays a positive role in engine oil performance. What we did was combine ZP with other additives to create a technology that equals or outperforms oils formulated with ZDDP. We then paired this ZP technology with the fuel-saving WBASE base oil to develop ENEOS SUSTINA engine oil.

Development of JAST: JXTG Ash Softening Technology

Diversification in Marine Cylinder Oils and Marine Fuels

An engine oil serves several functions. Among them, one important role is to protect the engine against corrosion by neutralizing the sulfuric acid that forms through reactions involving sulfur in the fuel. This acid is neutralized by alkaline components (mainly calcium carbonate) contained in additives called metallic detergents. Marine cylinder oils in particular are formulated with higher levels of metallic detergents, because marine engines often run on fuels (heavy oil) with high concentrations of sulfur.

Meanwhile, amid growing concern for protecting the marine environment, restrictions on the sulfur content of fuels have gotten tighter. Currently, there are restrictions on sulfur content for fuels used in open seas, and even stricter restrictions that apply to areas designated as Emission Control Areas (ECAs). Because the upper limits on fuel sulfur concentration differ in open seas and emission control areas, ships carry both high sulfur and low sulfur fuels, and switch between them as the situation dictates. If the marine cylinder oil doesn't contain enough metallic detergents to handle the high sulfur fuel, the sulfuric acid will not be fully neutralized, leading to corrosion and wear to the engine. Conversely, with low sulfur fuels, an excess of metallic detergents in the cylinder oil can lead to formation of hard deposits of ash on the pistons, which are a cause of wear (polishing). This means it is necessary to switch from one cylinder oil to another, each with a different level of acid neutralizing performance, when using fuels with different sulfur concentrations in marine engines.

JAST: JXTG Ash Softening Technology

We're working on original technologies that make it possible to use a single type of marine cylinder oil even in ships using both high- and low-sulfur fuels. One such example is JAST (JXTG Ash Softening Technology). Used in a marine cylinder oil, this technology acts to soften ash deposits, which are normally quite hard. When the ash is soft, it crumbles easily and does not accumulate on the moving pistons, which helps prevent damage from polishing. This JXTG technology has been proven effective in actual engines and shown to keep pistons clean in long-term operation.

Esso and Mobil are trademarks of Exxon Mobil Corporation, used under license.