Lubes em Foco

Lubes em Foco Magazine – issue 98

Click on the magazine and read, download, or share the articles:

By: Isabela Magri, Especialista de Aplicação
Jorge Perrotta, Engenheiro de Aplicação

The presence of water in lubricating oils compromises the performance and lifespan of mechanical and hydraulic systems. Water accelerates oil oxidation, promotes corrosion of metal surfaces, alters viscosity, and contributes to the depletion of additives and the formation of sludge. In hydraulic oils and transmission fluids, water is also associated with component wear. Therefore, controlling the water content is a central parameter in quality control, in the analysis of oils in use, and in predictive maintenance programs.
The Karl Fischer titration is the established reference method for quantifying water. It is recognized for its sensitivity at low levels and remains widely used. In parallel, instrumental evolution has brought a physical alternative: the determination of water by relative humidity sensor. The method eliminates the need for chemical reagents, generates less waste, and delivers results in a few minutes, characteristics aligned with modern laboratories and sustainability goals.

Principle of the relative humidity sensor method

The method is physical and is based on the controlled vaporization of water. The sample is contained in a vial with a septum and heated in an oven at adjustable temperatures from 25 °C to 300 °C. Heating releases the volatiles present in the sample. A dry carrier gas transports these volatiles from the vial to the sensor block.
The block contains a polymer capacitor-type relative humidity sensor. The sensor responds specifically to water. The measurement is not a direct reading from the sensor. The result integrates three variables, processed by a microprocessor: the signal from the relative humidity sensor, the temperature of the sensor block, and the flow of the carrier gas. It is this combination of parameters, and not the isolated reading from the sensor, that allows the determination of the water content in matrices of varying composition. The specificity of the method stems exclusively from the sensor’s response to water, and not from the nature of the transported volatiles.
Before analysis, a purging step removes residual moisture from the vial. An apparently dry vial retains microscopic droplets of water on its walls and traps ambient moisture when closed. Tests indicate that, under normal conditions, this contribution varies from 200 to 400 µg, depending on the ambient humidity. A purge of 30 to 45 seconds reduces this contribution before measuring the water content of the sample.

Karl Fischer Method

The Karl Fischer titrator is the dedicated instrument used for this water determination technique, which is widely standardized and recognized for its high sensitivity at low moisture levels. The Karl Fischer titration system promotes a stoichiometric chemical reaction between water, iodine, sulfur dioxide, and a base in an alcoholic medium. The instrument dispenses the reagent until the reaction endpoint is reached, and the result is calculated from the amount of reagent consumed, which is directly proportional to the water content present in the sample.

Difference compared to the relative humidity sensor method

The relative humidity sensor method does not promote a chemical reaction with the sample. The determination is exclusively physical, based on vaporized water detected by the sensor. This difference has practical consequences. The physical method eliminates reagent preparation, frequent standardizations, and the disposal of chemical waste. It also reduces the risk of error associated with reagent contamination by atmospheric humidity.

Selectivity and interfering factors

Karl Fischer titration can be affected by interference from compounds that react with the titrating reagent, such as ketones, aldehydes, and amines. In oils with certain additives, this requires method adaptations. The relative humidity sensor method does not depend on chemical reaction and is less susceptible to this type of interference.
The physical method, however, has its own interferents. Ammonium hydroxide, ethanol, methanol, and acetone are incompatible with the sensor and should not be included in the sample. In lubricating oils, these substances are rare, which favors the application of the method in this class of products.

Operational and environmental advantages

The absence of reagents simplifies the operation and reduces the need for specialized training. The method eliminates the handling and disposal of alcoholic solvents, iodine, and sulfur dioxide. This reduces occupational exposure and the generation of hazardous waste. Maintenance is less: unlike Karl Fischer titration, which requires periodic cleaning of electrodes and replacement of reagents, the physical method has no electrodes or reagents to replace. Calibration uses capillary tubes traceable to NIST and is verified in a few minutes.
Speed ​​is a significant advantage in routine use. The analysis time varies according to the matrix and the temperature applied, generally from a few minutes to about 16 minutes. In high-volume laboratories, this represents a gain in productivity.
Performance and correlation with Karl Fischer titration
There are instruments based on this technology available on the market capable of detecting water contents as low as 10 ppm, with a resolution of 1 ppm and an accuracy of ±5% at 1000 µg of released water. Repeatability, expressed by the coefficient of variation, is typically less than 10% for contents above 0.1% and less than 15% for contents below 0.1%.
The following results compare the average values ​​obtained by the two methods in three matrices, as an example. The analyses by relative humidity sensor were performed on a Computrac® Vapor Pro® XL analyzer (AMETEK Brookfield). The analysis times refer to the relative humidity sensor method.
The relative difference between the methods was below 2% in the three matrices: 0.3% in hydraulic oil, 0.1% in diesel oil and 1.5% in transmission fluid. This is a point-by-point comparison, of an illustrative nature, and not a validation study. The analytical equivalence between the physical method and the Karl Fischer titration is established by the ASTM D7546 standard and the documented correlation with ASTM D6304. The capacitive sensor detects small variations in relative humidity in the carrier gas, which provides good repeatability and reduces the variability associated with the manual preparation of reagents.

Comparison between the methods

Normalization

The relative humidity sensor method applies to new and used lubricating oils and additives according to ASTM D7546, which describes the determination of moisture in these products using a relative humidity sensor. The same principle extends to other petroleum fluids. The results correlate with the industry-standard Karl Fischer titration method, ASTM D6304, applicable to petroleum products, lubricating oils, and additives by coulometric titration. This correlation supports the adoption of the physical method in quality control and predictive maintenance routines.

Conclusion

Water control in lubricating oils can be conducted using different techniques. Karl Fischer titration is widely used, and the relative humidity sensor method has been adopted by laboratories in Brazil and worldwide for the analysis of water in new and used lubricating oils, providing fast and reproducible results that correlate with standardized reference methods. Because it eliminates the need for reagents and generates no chemical waste, this physical method directly addresses the sustainability goals of laboratories. In this context, it establishes itself as a modern, clean, and productive option, aligned with the future of analysis in the lubricants sector.

Lubes em Foco Magazine – issue 98

Click on the magazine and read, download, or share the articles:

By: Leticia Lazaro

Rheology studies properties such as viscosity, plasticity, elasticity, and the flow of matter. For flow to occur, a force in the direction of flow is necessary. This force divided by the area over which this force is applied is called shear stress.
In Figure 1, we identify shear stress as the force F divided by the area. In the case of liquids, they do not resist the application of this force and deform rapidly, flowing. This flow is related to the viscosity of the fluid, which is its internal resistance to flow. The higher the viscosity, the greater the shear stress required for flow to occur. In Newtonian fluids, such as lubricating oils in general, this stress is proportional to the deformation (shear rate).

In addition to Newtonian fluids, there are other rheological classifications (Figure 2) such as:

• Bingham plastic – require an initial shear stress to begin flowing. When they reach this stress, they behave like a Newtonian fluid (example: gel-based cosmetics)
• Pseudoplastic fluid – as shear stress increases, viscosity decreases and the fluid flows more easily (example: ketchup)
• Dilatant fluid – as shear stress increases, viscosity increases and the fluid has more difficulty flowing (example: cornstarch with water)

Lubricating oils exhibit Newtonian behavior at usual application temperatures. However, at low temperatures and/or with the use of Viscosity Index Improvers (polymer-based additives), it is necessary to use other methods to evaluate the flow of these oils because they no longer behave as Newtonian fluids.
Brookfield viscosity (ASTM D2983 or ABNT NBR 14541) and CCS (cold cranking system – ASTM D 5293 or ABNT NBR 14173) are tests adopted to better predict the performance of these oils in combustion engines at lower temperatures. These two properties are measured in rheometers and under conditions in which the oil does not behave as a Newtonian fluid. For this reason, these viscosities are called apparent viscosity because it varies with the test conditions, especially with shear stress. It’s important to remember that Newtonian fluids exhibit constant viscosity with variations in shear stress.

Greases are not Newtonian fluids.

Greases are a mixture of lubricating oils with thickeners and do not behave like Newtonian fluids under any conditions. They behave like a pseudoplastic fluid that requires a minimum shear stress to flow. This means that if the stress is less than the minimum stress required for flow, the grease behaves like a solid and does not flow. When the stress exceeds this minimum stress, the grease flows, and as the stress increases, it flows more easily (viscosity or resistance to flow decreases).
The study of this behavior through rheology provides more information about how the grease works, for example in a bearing, than worked penetration, a more common test to characterize the consistency of greases.
Another property that can be evaluated through rheology is the ability of the grease to recompose its original structure when the stress that makes it flow ceases, for example, when the bearing stops rotating. This recovery capacity is fundamental for the grease to adequately lubricate the equipment.
Overworked penetration helps to identify the resistance of the grease structure to work. It differentiates how well products withstand the work or not, in a more qualitative way. Rheology can determine the boundary conditions under which a given grease recovers its initial structure or not.

The rheology of greases as a tool

The growing importance of this topic is evident in the existence of standards that describe the methodology for measuring these properties, thus standardizing them. The ISO (International Organization for Standardization) published two standards related to the rheology of lubricating greases in 2025. One of them establishes a correlation between rheological properties and the consistency of a grease.
Grease rheology is still a tool that is being increasingly adopted in the research environment, but it is very promising for future adoption as a specification limit, for example.
In future articles, this topic will be explored in greater depth, defining the most important rheological properties, how they are measured, the types of rheometers used, etc.
Follow the next editions of Lubes em Foco magazine to better understand grease rheology. Until then!

Lubes em Foco Magazine – issue 98

Click on the magazine and read, download, or share the articles:

As the efforts to reach net zero emissions intensify, the appeal of using alternative low and zero carbon fuels in internal combustion engines (ICEs) is growing. Hydrogen is an attractive option for larger applications, although it comes with a new set of challenges, with pre-ignition being the primary concern for OEMs. Carina Foster, Infineum Commercial Vehicles New Specifications Technologist, talks to Insight about recent lubricant development work that is helping to minimise the number of pre-ignition events in ICEs running on hydrogen.
To meet their greenhouse gas emissions reduction commitments, OEMs in the transportation industry are looking to transition away from burning fossil-based fuels towards low and zero carbon energy sources. In the commercial vehicle segment, where powertrain electrification is challenging, there is a growing interest in using hydrogen in conventional internal combustion engines (H2ICE). This set up can provide the power, efficiency and the load carrying capacity these applications need, and its advantages mean it is already moving into the testing and commercialisation phase. While lack of refuelling infrastructure and availability of green hydrogen have been the biggest barriers to its adoption, significant investment is being made in these areas.

Investment in capacity and infrastructure

In the past five years the Hydrogen Council reports steady growth of operational clean hydrogen, with most volumes being produced in North American and China.
The US is currently focused on producing low carbon hydrogen, often referred to as ‘blue hydrogen’, driven by the Inflation Reduction Act (IRA) and associated tax credits. In Europe, a large number of projects are dedicated to renewable ‘green’ hydrogen’ capacity growth, driven by regulation and policy. The Asia-Pacific region, led by China and increasingly India, is emerging as the fastest growing in terms of operational green hydrogen facilities.
The rapid growth of green hydrogen production in China stems from several factors. These include high capacity for electrolyser manufacturing (approximately 60% of total production) and the economies of scale, as well as low-cost renewable energy. Importantly, this is underpinned by strong government policy aimed at achieving carbon neutrality and decarbonisation of industrial processes. As a result, the price of green hydrogen in China is approximately three times lower than elsewhere, and the country is expected to produce more green hydrogen than the rest of the world combined in 2026.

According to the Hydrogen Council, 9–14 mtpa of clean hydrogen capacity could feasibly come online by 2030, which is split evenly across renewable and low carbon capacity. However, the ultimate volumes will depend on how much of that capacity can secure stable, likely policy–backed, offtake. Without secure demand, the Council says supply projects will remain stranded.
In the past five years, there has also been a steady increase in the number of hydrogen refuelling stations (HRS).

Looking out to 2030, although there is a high level of uncertainty, analysts suggest there could be more than 6,000 HRS across the world. These continued investments in supply and infrastructure mean that the use of hydrogen in the commercial vehicle sector is increasingly viable.

Lubrication requirements

One of the key advantages of developing internal combustion engines that enable commercial vehicles to run on hydrogen is hardware familiarity – making current operational experience and servicing skills relevant well into the future. However, although the lubrication requirements of internal combustion engines running on diesel fuels are well understood, the use of hydrogen means lubricant formulators will need to address a new set of lubrication challenges.

Water accumulation, durability, wear and aftertreatment compatibility are all important factors to consider. However, OEMs are telling us that pre-ignition is the most significant challenge that needs to be overcome to facilitate the successful deployment of H2ICE into the market.

What is pre-ignition?

The very low ignition energy of hydrogen means that H2ICE can experience spontaneous ignition of the fuel ahead of a spark event, which also results in high in-cylinder pressures. This phenomenon, known as pre-ignition, is more prevalent under the high speed and high load conditions encountered in commercial vehicle applications.
The challenges associated with pre-ignition include:

• • • Reduced engine power output
    • Reduced fuel economy
    • Poor engine performance
    • Inferior vehicle operator experience.

However, by far the most important issue is that severe pre-ignition events can damage engine components and potentially lead to engine failure.
Pre-ignition can result from multiple hardware and operational sources, such as hot spots within the combustion zone, residual hot gases and sub-optimal mixing of hydrogen and air. In addition, the lubricant can play a notable role, with lubricant-derived deposits having the potential to insulate metal surfaces and create hot spots.
However, the main source of lubricant-derived pre-ignition is thought to arise from lubricant droplets that are ejected from the piston rings into the combustion chamber. These droplets can act as an ignition source via exothermic chemical reactions, such as chemical degradation of additive compounds. The released energy is sufficient to ignite the hydrogen/air mixture, which means combustion occurs ahead of the spark event.

Direct combustion of the lubricant itself is not thought to be a leading cause of pre-ignition. In research, neither the autoignition temperature nor the flashpoint of the oil have shown a correlation with the rate of pre-ignition. The chart below shows that despite the limited variation in both flashpoint and autoignition temperature of five test oils, a large variation in pre-ignition rate between them was observed. This testing suggests that the chemical composition of the lubricant has a more significant impact on pre-ignition than its physical properties.Pre-ignition shows little correlation to the physical properties of the oils tested

Optimising the test methods

Test selection is a key element of gaining a clear understanding of the impact of lubricants on pre-ignition. It is important, for example, to ensure that tests can minimise hardware-derived pre-ignition since lubricant optimisation is unlikely to overcome, or substantially mitigate, deficiencies in hardware or engine operation. Infineum has used two pre-ignition test methods to investigate the impact of lubricant composition on pre-ignition. The tests differ in a number of ways including engine size and type, operating conditions and most notably the candidate oil delivery method.
In one test method, lubricant-derived pre-ignition occurs as a result of the ejection of oil into the combustion zone from the ring pack (‘natural oil transport’). In the other test, known as the oil dosing test method, the candidate oil is artificially introduced into the combustion zone of the engine via the air intake manifold. Both test methods have been shown to be statistically repeatable and capable of clear and comparable differentiation between lubricant formulations.

Hydrogen pre-ignition is new

While they are similar phenomena, pre-ignition in H2ICE is not the same as gasoline low-speed pre-ignition (LSPI), which has been studied extensively. Hydrogen pre-ignition occurs under a wider range of engine conditions and the lubricant formulation responses are not the same as observed for LSPI. This means that a lubricant formulated to minimise gasoline LSPI cannot be expected to offer the same protection in a hydrogen engine, and vice versa. In our view, it is vital that a dedicated hydrogen pre-ignition test is developed to ensure lubricants are optimised to deliver the required protection in H2ICE.

Using existing gasoline LSPI approaches may result in a lubricant with very poor H2 pre-ignition

Infineum has undertaken extensive pre-ignition testing. Through fundamental research our technologists have built up a deep understanding of the different contributions of various additive, base stock and viscometric combinations. This knowledge enables optimised lubricants to be designed across a wide composition map. Benchmarking of existing heavy-duty lubricant technology has shown a broad range of capabilities, with some existing formulations exhibiting strong ability to minimise pre-ignition. However, bespoke development and reformulation can ensure optimal pre-ignition performance.

Lubricants with optimised pre-ignition can be formulated across a broad composition map

While base stock type can have a significant impact on pre-ignition rate, optimisation of the additive formulation is critical. A strong additive technology can reduce the negative impact of a weaker base stock; thus allowing flexibility in base stock selection, which may be driven by availability, price or other performance criteria.

Lubricant development approach

While the market for H2ICE is still nascent it is difficult to predict what the industry will require and value in lubricants developed specifically for this new application. Infineum has been investigating three key approaches: bespoke, boosted and suitable for use.

In our view it is essential that lubricants intended for use in H2ICE are assessed for their pre-ignition capability. Existing heavy-duty engine oils, designed for diesel ICEs, may well be able to provide acceptable performance in H2ICE. However, it is likely that, as hydrogen engines become more widely established in the market, there will be a growth in demand for lubricants specifically formulated for this application. Infineum will be ready with the chemistries needed to support the roll out of hydrogen-powered engines.
This however is not the complete story regarding H2ICE lubrication. Infineum is also working to assess other performance benefits that lubricants can deliver in this new environment.