As gas engines are increasingly filling a need for power flexibility, we asked two leading lubricant manufacturers how they are keeping pace with this trend

Sharanie Patterson, PetroCanada

A reliable and well-maintained gas-powered engine which performs consistently and continuously can lead to a healthier bottom line for operators.

Lubricants play a critical role in engine reliability and in order to achieve strong plant efficiencies and profits, operations and service managers need to focus on how to minimize engine downtime, maximize drain intervals and optimize performance. The gas engine oil (GEO) used to lubricate the engine is one key component that can address each of these objectives. Lubricant can be viewed as part of the engine design and is sometimes referred to as the “lifeblood” of the engine.

By going beyond today’s standards with lubricants that maximize service life, engine cleanliness and wear protection, engine operators can reduce unnecessary maintenance costs and downtime. In contrast to other fuel types, gas engines traditionally burn cleaner, hotter, and operate at a constant speed. This means GEOs must be specifically formulated to address these unique characteristics.

Drain intervals and reliability

Drain interval – or oil change frequency – is closely linked to engine reliability. GEOs with extended drain capability can withstand factors that break down the oil and cause it to degrade. Longer oil life allows the engine to perform consistently, reduces maintenance cycles and provides cost savings.

Drain service intervals are designed to provide maximum engine protection under various conditions. Also referred to as ‘drain time’, it is measured as the number of hours an engine can efficiently run before the oil needs to be changed. The timing of the oil drain is determined by the results of a used oil analysis. The limits for the used oil are defined by the original equipment manufacturer (OEM) of the gas engine. These intervals vary due to factors such as mechanical design of equipment, application, environment, and condition of gas. Optimal drain intervals allow the engine to run for an extended period before oil change is necessary without compromising engine durability.

Yesterday, 8000 hours between drains in such an engine was unthinkable. Suddenly, anything less could be unacceptable.

Sentron LD 8000, a revolutionary new GEO from Petro-Canada Lubricants, shatters the accepted drain interval standard. The breakthrough technology in Sentron LD 8000 helps operations extend drain intervals by up to 300 per cent when compared to the leading global conventional competitor GEO. (In a field test conducted on a Caterpillar G3500TALE gas engine, Sentron LD 8000 reached up to 8000 hours in a gas compression application with pipeline gas quality, under high load (>90 per cent) conditions).

Sentron LD 8000 meets and exceeds the standards of many different OEMs. For instance, a typical drain recommendation for a Waukesha F3521 GSI engine is 500 hours (based on conventional products, engine appetite and application). During a six-month test period, Sentron LD 8000 achieved over 4500 hours before being drained (cogeneration service with pipeline gas quality fuel).

GEOs that offer extended drain intervals reduce the need to change oil as frequently, which results in reduced downtime and increased uptime. As there is a strong correlation between continuously operating engines and a plant’s bottom line, minimizing downtime is a key objective for operators of gas-powered engines.

As the oil degrades, it takes on certain characteristics; as it reaches specific maximum levels that are dictated by the OEMs, the oil is condemned and needs to be changed. Several factors cause oil to degrade. These can include oxidation, acid formation, nitration, trace metals and other contaminants found in used oil.

Oxidation and oil degradation

Oxidation occurs in engine oils when oxygen molecules chemically join with oil molecules. This causes the oil to thicken, form acids and lose fresh oil qualities. Oxidized oil can lead to deposits on pistons and valves, threatening engine life.

As with most chemical reactions, oil oxidation is accelerated by heat and pressure so oxidation is often an issue for gas-powered engines – both older engine types and new lean burning engines in high temperature, high pressure operations.

Heat speeds up the oxidation process. Engine loads also influence the levels of oxygen and pressure within the engine, which can accelerate acid formation, corrosion, viscosity (oil thickening), deposit formation and, ultimately, wear.

Acid formation

The concept of oxidation is closely tied to acid, which forms as a result of the combustion process. Oxidation reduces the oil life and its ability to neutralize acid. If not neutralized, acid can attack metal engine parts, threatening service life and durability. GEOs need strong acid neutralization capability (total acid number – TAN) and good base retention (total base number – TBN). As it relates to engine reliability, increased acid control contributes to longer drain intervals and minimizes wear. Total base number (TBN) retention is another measurement that helps define an oil’s acid neutralization properties. Put simply, the greater the TBN retention, the greater the ability of the oil to neutralize acid. By neutralizing the amount of acid attacking the metal of the engine, the formation of deposits can be minimized – as could pitting and corrosion.

Sentron LD 8000 also offers better TBN retention with pipeline gas quality fuel, under high loads (>90 per cent) in gas compression service in a Caterpillar G3500TALE engine compared to leading conventional competitors.

Nitration

Nitration is another factor that contributes to oil life and drain interval. This naturally occurring process results when oil is exposed to heat, oxygen and nitrogen oxides (NOx). In gas-fueled engines, nitration occurs when the oil comes in contact with nitrogen oxide compounds. The result is the formation of sludge, varnish and deposits, which could cause wear and reduce engine efficiency. These deposits also cause oil rings to stick, increase oil consumption, and shorten engine component life.

Since oil type can define nitration resistance, it’s important to select a high quality oil that is able to resist breakdown caused by temperature, nitrogen oxides and other contaminants.

In some engine designs, the NOx created in combustion is much higher since there is stricter air/fuel ratio control (stoichiometric conditions). This leads to greater creation of NOx and, as a result, there is greater likelihood of condemnation based on nitration or nitric acid formation. Sentron LD 8000 is equipped to effectively control nitration in these particular environments, minimizing their impact on the oil.

Trace metals, coolant leaks, dust, dirt and contaminants found in used oil also affect drain interval. Metals such as iron, lead and copper come from metal-to-metal contact or metal corrosion/erosion. As a high-performing lubricant, Sentron LD 8000 protects the engine from these harmful contaminants which can reduce drain intervals and minimize downtime. Any excessive levels of contaminant ingress needs to be addressed as soon as possible; steps taken to control, reduce or potentially eliminate this ingress ensures longevity of the engine.

Deposit control and cleanliness

The formation of deposits (including sludge and varnish) leads to reduced engine efficiency and increased wear. These deposits can also increase oil consumption, and shorten engine component life.

A top-performing GEO can play a significant role in minimizing deposits and wear on valves, ports, pistons, liners and rings, and can also help extend engine life, promote engine cleanliness and minimize de-rating of engines. When an engine is de-rated, it is not performing at optimal levels. This is often due to the presence of deposits. As a result, there is additional stress on the engine and output is reduced. As an engine is de-rated, temperatures are lower, resulting in incomplete combustion and more formation of deposits onto the metal surface that remain on the engine.

Engine oils that offer extended drain intervals reduce the need to change oil as frequently

Credit: PetroCanada

Gas-powered engines are designed to run at 100 per cent under optimal pressures and temperatures. As they work, however, deposits inevitably grow in the engine. As gas engines operate at a constant speed and temperature, they are also prone to creating deposits. The type of engine duty cycle and the environment in which it operates also play a role in deposit formation.

When engines are burdened with deposits, engine efficiencies are impacted which could result in even higher engine temperatures, loss of energy to either create power or compress gas, pre-detonation, and engine damage. Due to this potential engine damage, operations de-rate the engine and reduce loads. This reduction of load will reduce engine outputs and may affect the bottom line.

Deposits can also cause pre-combustion, which creates instability in the engine. This robs an engine of its efficiency. For example, if pistons can’t move freely up and down, more energy is utilized. The result is that the engine has to work harder to achieve the same result, consuming more energy in the process, which could add to operating costs.

Not all deposits are unwanted and harmful. Some deposits, in the form of ash, are needed to protect valves and prevent valve recession (the premature compression and wear of the valve seat in the cylinder head and valve tulip). Ash residue, which remains after the oil is burned during operation, helps to prevent premature valve recession by forming a protective, sacrificial layer on the valve seat and valve tulip to absorb the impact of the two coming into contact.

A new standard

As the industry designs new engines, innovative lubricants are also developing to protect them. Plant operators need high-performing products that have a proven track record of successful use under a wide range of conditions.

From extended drain intervals to deposit control and engine reliability, advances in gas engine oil mean that the industry is changing and what was once thought of as unattainable – up to 8000 hours between drains – will soon be the new standard.


Jarmo Vihersalo, ExxonMobil

Research shows that for more and more companies, while production targets remain important, safety is paramount in the power industry.

Across the wider industrial landscape, companies continue to be faced with rising energy costs and challenging environmental goals. Adding to this, different engine types require individual lubrication needs. For example, gas engines have higher combustion temperatures and higher engine loads than those of conventional diesel or petrol engines, which impacts their lubrication requirements.

Advanced lubricants can help to improve the performance of gas engines by helping to mitigate potential injury risks, minimizing the impact on the environment in some ways, and increasing overall productivity for owners and operators of natural gas engines.

Safety first

Safety is a fundamental concern and the number one priority for power generation companies.

By extending oil drain intervals and extending equipment and component life, advanced lubricants contribute to reducing employees’ exposure to hazardous maintenance procedures.

Maintenance procedures carried out on gas engines during both scheduled and unscheduled downtime have the potential to put operators at risk by direct contact with equipment.

High-quality advanced lubricants, particularly synthetic lubricants, can help extend equipment life, increase power output and extend oil drain intervals. The balanced formulations used in the development of Mobil-branded industrial lubricants are designed specifically with these benefits in mind.

For example, Mobil SHC synthetic oils are designed to work at higher operating temperatures than mineral oils, helping to extend equipment life (compared with mineral oils) and therefore maximize the productivity of gas engines.

Additionally, the advanced technology used in the Mobil SHC Pegasus series is designed to maximize natural gas engine component reliability, and can increase fuel efficiency by up to 1.5 per cent versus mineral gas engine oils.

Productivity… and beyond

While the trend to improve safety and environmental care is growing, productivity remains important. Power operators care about the financial output of running a power plant and continue to look for ways to increase production.

In addition to the benefits outlined above, advanced lubricants can also contribute to enhancing overall power plant outputs by optimizing gas engine performance.

Reduced number of oil changes as a result of extended oil drain intervals, fewer oil purchases, less labour and waste in specific cases, as shown in the example below, help lower operating costs and maximize engine availability, which can bring significant savings and make business more profitable.

Lubricant properties help to reduce gas engines’ envirnomental impacts

Credit: ExxonMobil

For example, following the introduction of Mobil Pegasus 1005 to lubricate gas engines used across five combined heat and power (CHP) plants at a UK district energy company, oil drain intervals (ODI) have increased by 150 per cent when compared against the previous mineral product.

As a result of the extended ODI, safety hazards were significantly decreased with fewer oil changes and lessened employee exposure to maintenance procedures and associated injury risks.

Extended ODI has helped decrease used oil generated for disposal by 52 per cent. Moreover, the annual savings generated were calculated at approximately £21,600 ($33,345) for the five applications as a result of increased equipment availability, reduced annual oil consumption/cost, and lower maintenance and oil disposal costs.

Another company to benefit from extended equipment operation thanks to Mobil Pegasus 1005 is E.ON Hanse Wärme GmbH, one of the major energy companies in Germany, which was looking for a lubricant that would help extend the operating periods of its gas engines.

E.ON Hanse Wärme generates heat in several federal states, and operates and services 200 combined heat and power generators. Following the introduction of Mobil Pegasus 1005, the company observed that the load-bearing parts of the engine were extremely well-protected and stayed cleaner for longer.

The safety risks facing employees as well as the operating costs were lowered by reducing scheduled and unscheduled maintenance.

Supporting power operators

Safety, environmental care and productivity are intrinsically linked. Mobil products and services are designed to help minimize downtime by providing long drain intervals and improving gas engine reliability. They support power industry operators in increasing the safety of their staff; some of the lubricants’ properties also help to reduce some environmental impacts by improving energy efficiency and therefore power output, which helps gas engines deliver operational excellence beyond productivity.