The gas engines used in industrial applications are unique; they regularly function with constantly high loads, are subject to high temperatures for long periods of time, often in inaccessible locations with minimum supervision.
The high loads and temperatures present in the engines provoke oxidation, making the use of oils with a high stability against oxidation essential.
Gas engines are more susceptible to the wearing of valves and their seats. This is due to the dry and clean nature of the combustion inside the engine and to the lack of soot or lead compounds which normally lubricate the valves.
For this reason, the level of sulphated ash is much more critical than in petrol or diesel engines. High levels of ash deposits can cause premature fires. The presence of dirt on spark plugs may cause defective ignition, burned valves, etc.
However, the formation of ash can also be beneficial. A layer of metal salts on the surface of the valve can provide protection against direct exposure to harmful elements in the fuel gas and against high temperatures and heat corrosion. They can also lubricate the valve seats and reduce their deterioration.
Generally, it is recommendable to use an oil with a low ash content, especially when the corresponding engine works with natural gas or non-aggressive biogas.
When they work with natural gas, the oils for motors do not require the same level of detergency as petrol or diesel engines. This said, the use of oils with a higher level of detergency (a higher TBN) is required, understood as an alkaline reserve, when biogas is used, especially waste gas.
Something that is becoming more and more important is the question of air emissions. This has forced some manufacturers of gas engines to use catalytic converters to eliminate and control emissions. The use of catalytic converters limits the content and composition of the additives which should feature in the formulation of the lubricant.
