Why Natural Gas?

The drivers behind increased uptake are simple, according to Welton. Natural gas is clean, abundant and secure, and it offers a level of social credibility. On their own, none of these would be enough to move fleets toward the use of natural gas, said Welton. But when fleet managers consider these benefits along with cost, they begin to incorporate natural gas vehicles into their fleets.

Natural gas engines are 35 to 50 percent less expensive to run than diesel engines, and they are supported by tax subsidies in Europe. One gallon of natural gas, compared to the cost of a diesel-equivalent gallon, Welton said, is between U.S. $1 and $1.50 lower, on average.

Security of fuel supply also contributes to growth in natural gas vehicles. With the shale gas boom in North America, and the United States emphasis on reducing its reliance on imported oil, the region is a champion for sour gas uptake. However, the adoption of natural gas fleets in North America is still hindered by the lack of a strong network of refueling stations and engines capable of long hauls.

Instead, China, India and Europe lead the charge and will be the most significant incorporators of natural gas vehicles in the coming years. Europe, for example, boasts 3,000 compressed natural gas refueling stations, and a wider replenishing network for liquefied natural gas is coming.

Original equipment manufacturers see huge potential in both heavy-duty and light-duty engine segments, Welton continued, although light-duty natural gas engines havent quite caught the publics imagination. While OEMs are rapidly developing technology for the passenger car segment, speed of uptake in the light vehicle market is largely dependent on infrastructure and upfront costs, and the publics perception of safety when it comes to driving with a compressed gas cylinder in the vehicles trunk.

Therefore, the highest growth in coming years will continue to be in medium- to heavy-duty vehicle fleets, with approximately 930,000 units expected to be sold worldwide between 2012 and 2019.

Lube Challenges

As more and more vehicles fueled by natural gas take to European highways, oil formulators must work harder and harder to accommodate the growth. When [additive and lube companies] formulate for natural gas engines, [they] are dealing with a very different type of stress environment, Welton said. The difference is simple: Gas is going into the engine, and air and fuel mixes more easily and efficiently and provides much better combustion and much more heat. With more heat, however, comes higher oxidative stress, higher nitration stress and higher foam stress.

What does that mean for the oil? Because the gaseous fuel itself does not provide lubrication, its up to ash derived from detergent and antiwear additives to protect the valves.

One of the key factors when formulating natural gas engine oils is striking the right balance for sulfated ash content, he emphasized. Formulators must walk a fine line. Too much ash, and deposits could form, resulting in preignition and valve torching. Too little, and insufficient acid neutralization and valve recession results, and the valves are not sufficiently protected.

Valve torching is probably the main concern for natural gas engines, Welton said. When too much deposit forms on the valve face and it cannot close properly, exhaust gas escapes, causing three major problems. First, the engine loses power. Second, it raises emissions. Third, [the exhaust gas] can cut through the valve and the valve stem, hence the phrase torching.

Oil formulators must take a vastly different approach to formulating oils for natural gas engines than they would for diesel engines, for instance. But they also must try to accommodate fleet managers who attempt to use the same oil in the different engine types, while attempting to navigate and leverage each engines different OEM specifications.

Lets be very clear – when formulating for diesel vs. natural gas, were dealing with a very different type of oil, Welton pointed out. And its going to have to face very different challenges because of different stresses in the hardware.

Diesel vs. Natural Gas

Diesel engine oil formulators must focus more on fuel economy and soot handling. We dont need to worry about either of those … when it comes to natural gas engines – fuel economy isnt a concept that has really driven natural gas oil formulation yet. In addition, there is very little, if any, soot to deal with in a natural gas engine.

Fleet managers with a mixed fleet of diesel and natural gas engines, and with a single oil supplier, are most likely going to run the whole fleet on diesel engine oils, Welton noted. But when oils formulated for diesel engines are used in natural gas engines, as they often are, he said, natural gas engines are working with too much ash in the oils. This creates preignition problems, along with hot spots and deposits in the combustion chamber.

So we see a logistical challenge in mixed fleets coming in with existing diesel engines and new natural gas engines, and fleet operators wanting to go with one oil, he said. In that case, something must give, and its usually the performance of the natural gas vehicles. We believe that many natural gas engines are running at suboptimal performance on diesel engine oil, raising emissions and not working as efficiently as they could because they are forming these deposits and requiring extra maintenance.

As hardware evolves in both natural gas and diesel engine categories, formulators that have both engine oil types in their portfolio are faced with another challenge: meeting divergent OEM specifications. For example, Cummins CES 20074 calls for ash content of 0.4 to 0.6 percent, while Detroit Diesel Corp. specifications set ash content at 0.8 percent. Such parameters would fall well outside of upcoming heavy-duty diesel engine oil performance categories such as PC-11.

It is possible that the two types will converge, Welton posited. Either way, he said, its up to oil formulators to adapt. We have to look at the hardware evolution, get with the OEMs, oil companies and fleet operators to see whats working, what limits we can push and how we can move forward.

But the challenge for formulators doesnt stop there. As natural gas engines become more efficient, they demand more from the oil, Nick Burton, an EMEA regional marketing manager for Infineum said, continuing the discussion at the companys presentation before the Uniti Mineral Oil Technology Congress in Stuttgart, Germany, in April.

To meet industry requirements for improved power output, efficiency and reliability, as well as reduced emissions, OEMs are increasing compression ratios and turbocharger pressures while improving combustion control and valve timing. [And they] are changing piston materials from aluminum to steel to cover the higher pressures now present in the combustion chamber, Burton said. The resulting high-efficiency engines, which also have smaller oil reservoirs and lower oil consumption rates compared with their conventional counterparts, present even greater lubrication challenges – particularly in terms of oil life and hardware protection.

Burton noted that changes in piston design put the lubricant much closer to the engines combustion zone, which spikes oxidation and can rapidly deplete the oils base number, lowering its ability to neutralize combustion acids. Additives can make a real difference in this growing and increasingly challenging market segment, he added.

Understanding the benefits that each component can deliver, their positive and negative interactions, and striking the right balance of component types to offer sufficient protection is absolutely essential, Burton said. Todays formulator must also recognize the impact that working with different base stocks can have so that the final lubricant is harm-free and maintains performance throughout its lifetime in the engine.

Other Segments

Growth in natural gas engines extends to railroad, marine vessels and construction vehicles as well, Infineum pointed out. Catepillar, for example, said that they were all-in, when it comes to embracing the technology. The U.S. construction vehicle company said that for every model and engine type it makes, it will also create a natural gas equivalent, according to Infineum.

Formulators must also look beyond transportation segments to accommodate the booming growth in stationary natural gas engines. By far the biggest driver for gas growth, certainty in terms of volume, is the demand from power generation and industrial applications in large stationary reciprocating engines, Burton continued. In Europe, the stationary gas engine market is becoming increasingly complex, he added, as a growing number of natural gas types – such as landfill and biogas – are being adopted as ways to secure sustainable power sources and reduce operating costs.

Gas engines used in both power generation and gas compression applications present a number of unique formulation challenges as well, Burton said. First, the operating conditions are very tough. If you imagine commuting to work by car for ten years without changing the oil, you will have some idea of what we expect from a gas engine oil.

Nitration is often the most critical factor in stationary natural gas engines, as opposed to oxidation in gasoline and soot in diesel, he added. Gas engine oils must not only protect the engine by preventing deposits, corrosion and wear, they must also minimize engine downtime and continue to deliver protection over extended drain intervals so that operators can maximize output and reduce running costs.

A lot of unanswered questions remain with regard to natural gas engine growth, Welton concluded. But with changes lurking just over the horizon, its up to additive companies to ensure that formulators can provide the right type of oil in this rapidly expanding market.