The industrys solution for these challenges has been short drain intervals. Through their choice of base stocks and additives, gas engine oil formulators are working to develop products that last longer, but end users are divided on their willingness to pay the premiums that these oils demand. The end result is that many gas engine oil suppliers feel compelled to offer a range of products.

Dirty Gas

As explained in Part I of this series, natural gas is made almost entirely of methane and contains little or no contaminants. Alternative gases fall into two general categories – landfill gas and biogas – and although their chemical makeup varies from source to source, they do contain contaminants. Most biogases contain hydrogen sulfide and other precursors to the formation of harmful acids. Landfill gases (a type of biogas) also contain siloxanes, which lead to buildup of abrasive deposits in the engine.

Change intervals for conventional gas engine oils vary depending on the gas and oil, but generally they are short compared to other applications. Engines running on clean methane typically require changes at 1,000 hours, and with typical engines operating somewhat more than 8,000 hours a year, this means changes every six or seven weeks. For contaminated gas, oils must be changed more often, and with heavy contamination, intervals may be as low as 150 hours – just six days of operation.

Industry insiders say oil analysis is an important part of determining when oil needs to be replaced. If the customer is used to drain interval of 1,000 hours, we do regular oil analysis every few hundred hours, an analysis of 1,000 hours, look at the oil quality but still drain the oil and then the next oil drain we go to 1,100, look at the results, so just stretch the oil life, said Joris van der List, research scientist at Q8Oils, an Antwerp, Belgium-based subsidiary of Kuwait Petroleum Corp.

Industry insiders say the current situation for gas engine lubrication needs improvement. Regular oil testing and changes work well but do not provide complete engine protection, said Dean Clark, global segment manager for gas engine oil additives at Abingdon, U.K.-based additive supplier Infineum. For example, damage caused by silicon dioxide deposits triggered by the impurities in landfill gas [lead to] frequent and expensive top-end engine rebuilds – which cost 20,000 to 30,000.

Formulators are working to develop oils that extend drain intervals while also providing better engine protection. Selections of base stocks and additives are both in play, but several sources said additives are making a bigger difference because they:

protect against corrosive sub-stances such as acids that form in the oil;

improve upper cylinder and head lubrication, reducing valve recession;

protect against harmful compounds that are abrasive.

Its the secret of that additive package and how it deals with the siloxanes and the hydrogen sulphide that is the unique selling point for gas engine oils, said Andrew Stone, director of energy solutions at U.S.-based engine manufacturer Cummins. Don Wootton, global power systems advisor for Odiham, U.K. oil analysis laboratory Spectro, added, There is definite evidence that in high silicon engines certain additive types can reduce the friction caused by the silicon in the combustion chamber.

Moderating the use of ash-forming additives is one way to deal with contaminants. Operators generally like to minimize ash because it contributes to deposits. For engines operating on landfill gas, however, a moderate level of ash is desirable because it helps combat siloxanes.

Ash is there primarily as one of the safeguards against the acid increase, said David Burke, service director of Clarke Energy, a Liverpool, U.K., gas engine operator and maintenance provider. It adds some absorbency to protect against acid build-up, so that would be the reason why you would normally see a medium-ash oil for a non-natural gas application and a low-ash oil for natural gas.

But as Arevon Energy Asset Manager Mark Woollams noted, there is a downside to ash. Arevon operates 35 landfills in the U.K. The additives introduced to the oil to combat the siloxanes create ash and ash causes problems within the engines.

Generally, the issue is to have as few additives as possible, said Armin Roeseler, product line management head at MWM, a German arm of U.S. engine manufacturer Caterpillar Inc. For instance, with natural gas you should have only the amount of additives that you really need in your oil, as too many can lead to deposits which in turn change your compression ratio and impinge on the running of the engine. We clearly state that with natural gas the ash content must not exceed 0.5 percent, and with biogas it has to be in a range of 0.5 percent to 1.0 percent.

Some oil marketers purchase additives in packages from additive companies, but others buy individual components for formulas that they themselves have developed. Exxon-Mobil (acknowledged by many to be the market leader in gas engine oils) is firmly in the components camp and sees it as a point of difference with competitors. Mobil Pegasus gas engine oils are component based formulations, and therefore we do not deploy additive packages like some of the competition, said Kathleen Tellier, lead gas engine oil formulator for Fairfax, Virginia, U.S.-based ExxonMobil Lubricants and Specialties. This approach allows each additive to be specifically selected and optimized to meet the required performance levels. Types of additives which are selected include, detergents, dispersants, antioxidants, antiwear, metal passivators to name but a few.

Group I or II?

Traditionally gas engine oils have been made using API Group I base stocks, and some suppliers, such as Q8Oils and Lukoil, continue to use only Group I. Conversely, Petro-Canada Lubricants, of Mississauga, Ontario, Canada, produces and uses Group II oils, and Chevron, of San Ramon, California, U.S., has made a strategic decision to move all its gas engine oils to Group II.

Woollams said Arevon is considering a switch to a Group II product. Currently, the whole of our fleet is on Group I products, but were on a trial with Chevron on a Group II product. he said. If it proves successful well move all our fleet onto the Group II because of the future long-term life and availability.

Mainly in gas engine oil its Group I, Group II category, some are using Group III to make it a bit different, said Philippe Poudou, product line manager industrial engine oil specialties for Europe, Africa and the Middle East at additive supplier Chevron Oronite, a subsidiary of Chevron. I would say that Group II oils currently are the bulk of the high performance products in natural gas engine oils.

Q8Oils Senior Product Line Manager Mark Hensen explains his companys preference for Group I. New developments are more related to the thermal stability of gas engine oils, deposit control in combination with good dispersancy, so looking at different components but also different base fluids, thats really critical for the moment…. We know that there are a lot of companies going to the Group II base oils, [but] we think that Q8Oils produces one of the best Group I base oils, with very good oxidation stability and therefore very suitable for gas engines of the newest generation.

The market now includes products that offer significantly longer drain intervals, but not everyone wants them. Some people want highly improved extended drain periods, up to 8,000 hours, and some in the landfill market are content if they can achieve 1,000 hours, depending on the quality of the gas, Chevron Technical Manager Paul Nadin-Salter explained.

Extended life oil is more expensive, and some OEMs believe that changing the oil more frequently makes more financial sense.

Peter Law, operations director at Manchester, U.K. gas power plant operator ENER-G, is not convinced about the premium placed on extended life oil: The cost of an oil that will do 10,000 hours is massive compared to an oil that does 1,000 hours, so you may as well go for an oil which will [last] 1,000 hours, he said We do look at alternative ways of extending the oil life, but we then have to weigh the cost of the oil versus the benefit it provides.

Sunny Outlook

Gas engines can be split into two major power bands, over 5 megawatts which operates almost entirely on natural gas and below 5 MW. The 500 kilowatts to 3.5 MW bands account for 68 percent of all new capacity and it is these power bands where there is the highest use of contaminated gas. Engine designs are evolving, and this – along with growing use of alternative gases – is requiring improvements in lubricant performance. OEMs are pushing towards higher efficiency engines, and this means that temperatures and pressures in the engines will go up, Q8s Henson said. Of course this is also important for the lubricant because if pressure and temperature go up we have to deal with more thermally stable additives.

Most observers agree that demand for various types of gas is likely to continue growing and that demand for gas engines as well as gas engine oils should do likewise.

Gas has become, not just in the U.S., a lot cheaper, and in one or two years the U.S. will become an exporter of gas, said Thoralf Lemke, director of marketing at MWM. Then this lower cost gas will be available outside the U.S. as well. For the future we are very optimistic and expect good growth opportunities.

Hermann Kling, head of gas engine export sales at German engine manufacturer Man, forecasts a 5 percent growth in gas engines sales in Europe, the Middle East and Africa. The biogas share will grow depending on energy politics, and the natural gas share will become more important, he said.

Given expectations that gas supply will remain fragmented, sources agree that oil marketers need five or six products in a gas engine oil portfolio in order to meet all of the various needs, including some with extended life.

The gas market is growing rapidly because it makes compelling financial sense for investors and helps mitigate the risk of electricity shortages. Still to come is the unknown impact of shale gas development which may secure further investment in distributed generation in Europe, using gas engines.

All market sectors interviewed for this article stand to benefit from the projected market growth but gas engine oil companies in particular face the perfect storm. They are secure in the knowledge that oil consumption is increasing faster than the market, because of the rapid growth of biogases in the mix which greatly increase oil consumption. Gas engines have indeed proved to be the stalking horse, silently booming again, some 140 years after they were first invented.