Who Needs Monogrades?

2012-06-08   来源：润滑油情报网 网友评论 0 条

Trouble is, there now is no category that supports single-grade heavy-duty engine oils.

Some may doubt that’s very important since the bulk of modern engine oil development has been in multigrade products. API categories are all backwards compatible, so it is reasonable to assume that API CD, CF and CF-2 needs could be covered by API CH-4 oils. In addition, many buyers can simply use the multigrade product in their applications calling for single grades and move on.

The change will go unnoticed by passenger car and light truck drivers, as no automaker recommends single grades for use in their engines. They prefer multigrades to maximize fuel economy while maintaining wear control and emissions performance. Heavy-duty diesel builders serving the trucking market also face tough emissions and fuel economy pressures, and don’t recommend single-grade engine oils, so it’s not surprising that the Engine Manufacturers Association agreed to the elimination of the older categories.

However, Dan Larkin, longtime lubrication expert with Detroit Diesel and now an industry consultant, has a very different view. He has concerns about the loss of any first intent single-grade engine oil category — especially in light of the number of older engines still specifying API CD, CF or CF-2 oils.     These categories continue to dominate many heavy-duty markets — Asia, Africa and Latin America — and play a role in North America as well.

Larkin polled several large engine manufacturers regarding their estimates of how many engines requiring single-grade engine oils of at least API Service CD or CF quality are still in use. From his research, he said it would not be overstating the case to say there are a million engines in service today worldwide that still require single-grade CD or CF quality oils. Here are a few examples:  

^• MTU Detroit Diesel builds and rebuilds special duty twocycle engines, used in such applications as off-road construction, mining, military, power generation, marine propulsion and more. The company was formed in 2000 from the off-highway engine operations of Detroit Diesel and Germany’s Tognum AG. It has built 3.5 million large twocycle engines since the 1940s, and estimates that some 300,000 “classic” units are still in service worldwide. Sources at MTU Detroit Diesel say that those numbers do not include additional standby generators and other installations.

^• Both Fairbanks Morse Engine and ALCO (American Locomotive Co.), both now part of EnPro Industries, also have decades-old engines in service, some having logged 40-plus years. ALCO has   some 15,000 locomotives in service, from railyard switchers to mainline diesels. Fairbanks Morse engines are found on tugboats, dredges, merchant ships and navy vessels, as well as in nuclear power plants and water pumping stations.

  ^• Representatives of Finnish engine builder Wartsila simply said that “thousands” of their older engines are still in service.

Larkin noted that many of these engines have oil sumps holding anywhere from 50 to 300 gallons, not the 10 to 15 gallons used in over-the-road truck engines. If his one million engine figure is accurate and the engines average at least 50 gallons per sump, that suggests a need for a significant volume of oil including makeup. Some of these engines can be served by railroad-type engine oils, not API CF or CF-2 oils, but that market too is moving towards multigrade oils from the traditional single grades.  

Change Not Wanted

Why is the continued life-support of single-grade oils so important?

First, there is the question of approvals. Many engine builders state a preference for a particular API category designation and SAE viscosity grade, based on their experience with these oils in their engines and applications. In order to change from one   type of oil to another a great deal of test work, both laboratory and field, is required.

Fairbanks Morse/ALCO (FM/ACLO) has what might be considered a typical procedure for approving a new oil in its engines, as detailed in the MI-12009N specification. The process requires that the oil first must meet certain physical and chemical   requirements, including being an SAE 40 grade and API CD/CF. When that is documented, a field test is then required. Two engines must be run on the candidate oil for at least one year. All moving parts are rated for wear and photographed. FM/ALCO then will evaluate the data and either approve or reject the oil. From that point forward, approved oil is OK for use — but the formulation cannot be changed without additional field testing.

 “The above evaluation program is the complete responsibility, both financially and otherwise, of the oil supplier and/or the user,” a company bulletin advises. “FM/ALCO will assist in carrying out analysis of test data and act only in an advisory capacity.” The cost in time and dollars to run such a test is significant and most oil companies or equipment operators are reluctant to spend the money to gain a new approval.

Even with a new approval in hand, changing an in-ser- vice lubricant can be an issue for end-users, especially in critical applications such as power plants. The Electric Power Research Institute has been addressing this issue for some time. EPRI consultant Howard Adams commented to Lubes’n’Greases that a sudden change in lubricant name, composition or recommended use causes a great deal of difficulty in plant operations, especially nuclear power plants.

Nuclear plants are licensed by the Nuclear Regulatory Commission in accordance with the Code of Federal Regulations, Title 10 part 50. It spells out exacting requirements that must be followed when making physical changes to a licensed facility. It applies varying amounts of  rigor when changing lubricants, based on the importance of the equipment’s design function, Adams noted.

For example, changing an “environmentally qualified” (EQ) lubricant requires the highest rigor and resources. EQ lubricants must be tested and shown to be capable of withstanding harsh accident environments. In these tests, lubricants are artificially aged and then subjected to postulated accident levels of radiation, temperature, pressure and moisture. Throughout the test, the equipment must be capable of performing its design function. Once a lubricant is environmentally qualified, the product cannot be altered in any way without invalidating the test report.

“Safety-related” lubricants are used in equipment   required to safely shut down the plant in an emergency. Like EQ lubricants, safety-related lubes are purchased commercial grade and dedicated on-site. To change a safetyrelated lubricant, a much simpler design process called a Replacement Parts Equivalency (RPE) may be used, but even this requires a fair amount of resources to complete.

Regardless of the lubricant classification, all lubricant changes must be reviewed for impact on the facility’s licensing basis. 10 CFR 50.59 establishes the conditions under which licensees may make physical changes to the facility without prior NRC approval. This evaluation and documentation takes time and resources.

According to David Efron, maintenance engineer at the   Diablo Canyon Nuclear Power facility in San Luis Obispo County, Calif., the engine oil used in standby emergency diesel generators is a safetyrelated issue. These diesel generators are required to provide electrical power to safety-related equipment in the event of a total loss of offsite power. Redundancy is provided by having three diesel generators for each of the plant’s two nuclear power units, although only two are needed to safely shut down the plant. These generators must be capable of going from standby to rated speed/voltage and ready to load within 13 seconds.

Bottom line, Efron added, the diesels are deemed very important with respect to protecting the public health and safety. Inappropriately chang-     ing the engine oil could affect all the engines and the ability to safely shut down the plant. Making changes to oil chemistry or qualifications will have a deep impact on these lubricant customers, and others.

Multigrade? No Thanks

There are also issues related to the performance of singlegrade vs. multigrade engine oils. Detroit Diesel two-cycle engines are notorious for their dislike of multigrade engine oils. It wasn’t until the 92 series engines came out that Detroit Diesel felt comfortable even recommending SAE 15W-40 engine oils.

This discrimination is particularly evident in larger displacement engines such as the DD 149 series. In a set of experiments at an open-pit copper mine in Arizona, a   Detroit Diesel 16V-149 engine in an electromotive ore hauler was dynamometer tested to determine maximum horsepower at a set RPM and at maximum power (stall).

The results are shown in the table on  page 20  . As can be seen, compared to the straight-grade SAE 50, the SAE 25W-50 produced 4 percent less power at constant RPM and 2 percent less power at maximum. While not large numbers, these do represent a loss of carrying power when bringing ore out of the pit. The SAE 25W-50 was formulated with an extremely shearstable viscosity index improver, typically used in gear oils. All three oils used the same base stock source.

  Danny Larkin sees a breakdown on the single-grade issue in two areas. First on   the heavy-duty oil side, where the Diesel Engine Oil Advisory Panel is a major driver for API and its oil categories. Naturally, their focus is on-highway vehicles and their related emissions.

Second, he said, the Engine Manufacturers Association, which has a big voice in the DEOAP, does not have as close communication with the builders of large displacement engines for stationary and specialized uses as it does with the on-road engine builders. Each specialized OEM tends to do its own thing with approvals, field qualifications, etc. That also applies to the smaller engine builders, like Brigg & Stratton, Tecumseh, Toro, Honda and so on, who mainly produce engines of 15 hp or less.  

Both API and EMA have stated that when they polled industry they found little interest in developing a single-grade standard for engine oil. The biggest concern was the time and cost to develop a new standard, coupled with the apparent lack of need from the much larger over-the-road marketplace, where multigrade oils are the norm.

However, the specialty, stationary and off-road markets still need qualified singlegrade oils to cover their equipment. The challenge, as Larkin admitted, is to develop a new set of approvals and standards that cover these engines with current quality level engine oils — preferably multigrade but with the single-grade option available.  

Strong Arguments For Monogrades

Power Output With DD 149 Engine In One Hauling Service