One area for potential improvement is lubrication. traditionally many operators have used engine oils that were not specifically designed for their equipment. industry insiders say its possible to design oils that are better suited for the evolving conditions of gas engines. doing so should allow operators to extract more energy and heat – an attractive prospect during these times of high energy prices.

Gas Gaining Popularity

Stationary engines fueled by natural gas or biogas are mainly used in power or heat generation plants or to move gas through pipelines. Smaller versions are used to provide emergency electrical power in homes or in hospitals, in transportation or to supply on-demand power for stabilization of electrical grids.

In Europe, emissions regulations and government incentives for sustainable energy encourage increased use of natural gas for power generation. As a result, the continent today is the leading global buyer of gas engines for power generation, according to Infineum.

It is much cheaper to build gas-fueled plants than to develop expensive and environmentally risky coal or nuclear plant projects, Infineums sales manager for Europe, the Middle East and Africa, Katie McTavish, told RPIs Lubricants Russia conference in Moscow in November.

When conventional fuel prices are very high, using gas engines can lower [production costs] per unit of energy, compared to the costs of diesel or gasoline engines, while distributor generators reduce transmission loss, said McTavish, who is based in Oxford, England. Infineum also found that deregulation of some energy markets drives the growth of smaller plants that generate a combination of heat and power.

Against the backdrop of these changing market conditions, engine design and lubrication technology are evolving, too. Increases in compression ratios and the pressures achieved by turbochargers have allowed greater power output along with improved efficiency. But these design changes also raise operating temperatures, elevating heat and oxidation stresses on the engine lubricant.

McTavish and others agreed that the time is ripe to raise performance of natural gas engine oils. OMVs Franz Novotny-Farkas told Januarys OilDoc conference in Rosenheim, Germany, that a focus on power density and electrical efficiency [have] further pushed the performance demands on stationary gas engine oils. It means lubricants should have improved efficiency and durability, better emission reduction [and be able to withstand] higher compression rates and higher turbocharger pressure.

Novotny-Farkas, who is based in Vienna, explained the reason for designing oils that help improve fuel economy. The average overall efficiency of electricity or heat generation by conventional systems powered by large gas engines is 48.7 percent, he said. The main areas of energy loss that have to be addressed with advanced lubrication are the liner and piston parts, journal bearings and the oil pump.

Room for improvement

At present, monograde oils hold the biggest share in the gas engine oils market, and original equipment manufacturers complain that they are a poor fit for the application and that this leads to problems that were often ignored in the past. Large gas engines are a challenging environment for the lubricants. Operating temperatures are high (according to some measurements, temperatures in a gas engine crankcase can be 165 to 225 degrees C hotter than in diesel engines), and gas engines run at nearly full load for long periods with infrequent interruptions. This puts a great deal of stress on the lubricant.

Biogas and gas from landfills are commonly used as alternatives to natural gas for fueling stationary gas engines, and this complicates the job of the engine oil. Biogas comes from plant or animal waste, so it is a renewable resource, and proponents say it is neutral in its effect on the environment because it only releases carbon dioxide that was previously bound up in plants. Like natural gas, biogas is a mixture of gases – 50 to 60 percent methane and the remainder consists of carbon dioxide and small amounts of nitrogen and oxygen. But the chemical makeup of biogas is sufficiently different to affect the engine oils operating environment.

In cases where biogases are used, lubricants have to neutralize combustion acids and disperse silica to prevent deposits, McTavish said.

Germany is unchallenged world market leader in stationary gas engines operating on biogas, with around 7,500 combined heat and power generation units, according to Leuna, Germany-based lubes manufacturer Addinol. A very big disadvantage to the engine is the formation of hydrogen sulfide or water vapor, but they can be reduced to negligible levels with help of desulfurization and drying processes, Addinols research and development head, Juergen Deckert, told the OilDoc conference.

Because of the preferred use of cleaned biogas today, Deckert called for development of synthetic low-ash gas engine oils, saying these could improve engine performance by a measurable amount. Modern [biogas fueled] gas engines require oils of highest performance, he said. Oils of this performance level can be realized only with smaller amounts of … sulphated ash in order to reduce the ash deposits in the combustion chamber, at sparking plugs, at valves and at other components, compared to deposits created by engine oils [designed] for motor vehicles.

Increasing Efficiency

Regardless of what gas is used, industry insiders said that operation of stationary gas engines could also benefit from other advances to the lubricant, as well as from improved engine design. Antiwear performance, oil consumption and drain intervals are all areas that could stand improvement, they say. On the equipment side, improved combustion control, adjustments in the timing of miller valves and a better fuel injection system would all make a difference.

New products should have lower viscosity index to help keep engines cool and clean, as well as better exhaust compatibility and longer service life, OMVs Novotny-Farkas said, adding that lower viscosity at high operating temperatures would aid pumpability and increase specific heat capacity to improve cooling performance and filterability. Better pumpability and filterability result in higher compression and oil pump power and fewer impurities, he said.

Efforts to developing engine oils for gas engines will focus on maximizing productivity, which of course has a direct bearing on profitability. Drain intervals need to coincide with routine maintenance to reduce engine down-time, cut maintenance costs, lower waste disposal costs and maximize earning potential, Infineums McTavish said.

Addressing energy efficiency will require introduction of formulations with lower viscosity, as well as additives that are tailored to the functional needs of gas engines. Formulators should rely on the practices and advanced knowledge gained from the automotive [lubricant] area, Novotny-Farkas noted.

Excellent oxidative stability and control over nitration are essential to good performance of gas engine oils, and formulators can gauge for these properties using used oil tests.

Some of the key requirements for modern gas engine oils are to reduce valve wear, to disperse ash and prevent formation of deposits, to control oxidation and nitration and improve viscosity and base number retention, McTavish observed.

Effect on Bottom Line

Two thirds of respondents in an ExxonMobil customer survey indicated that the energy efficiency of their industrial lubricant impacts gas engine operating costs from a moderate to a great extent. In the drive for increasing productivity and in the face of rising fuel costs and rigorous emission reductions, it comes as no surprise that respondents cited energy efficiency as a primary concern, said Gilles Delafargue, industrial product technical advisor for ExxonMobil, speaking at the OilDoc conference.

Premium base stocks generally have not been used much in gas engine oils to date, but they are well-suited for todays performance needs and deserve to be used extensively in new formulations, OMVs Novotny-Farkas said. The base oil quality of stationary gas engines has been acknowledged as critical issue, and it is getting more and more important. he said. OMV found that base stocks with greater chemical homogeneity and stability could yield huge benefits for performance. Such base stocks have longer service life and generate fewer deposits.

Farkas said that efforts to develop higher performing gas engine oils could also benefit from adoption of international product standards. Such an undertaking should divide oils into different categories and define test methods for performance characteristics.