Well Oiled Machines

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Tribologists are important folks these days. No, they’re not social historians studying the Bushmen of the Kalahari Desert. They’re the technical wizards who work so hard to create the oil your engine needs to live longer than a mile or two. And they’ve never been busier. Thanks to increasingly stringent emissions regulations, which are going to get tougher still, engine makers have had to make huge changes to the way combustion occurs and especially to the way its byproducts are dealt with. It’s astonishing that, over the past couple of decades, heavy-duty diesel engines have gotten better in just about every way, not just in terms of pollution. They’re making more useable power than ever, they’re easier to drive, and they’re almost infinitely programmable. If you want a flat torque curve from 1100 all the way to 1700 rpm, no problem. They also last an awful lot longer.

On the emissions front, modern diesels produce a third less carbon dioxide than gasoline engines. Today, NOx emissions have been reduced by 70%. Particulates have been reduced by 90% during the last 10 years. And, better yet, diesel emissions will be reduced by an additional 50% over the next decade.

“Compared to alternate power sources, the environmental impact of diesel already is minimal, and it’s only going to get better,” says John Campbell, performance engine products manager at Caterpillar. And, of course, diesels are more efficient than ever. Your trucks can still get 4.0 miles per gallon if you allow them to be driven that way, but it’s no great challenge to cut that consumption in half. Or better.

All that progress is pretty obvious. But every major change in emissions regs, with its attendant change in combustion engineering, also brings the need for a new engine lubricant. That’s a much more subtle matter, but it’s no less remarkable.

“The whole lubricants industry is being driven more and more towards higher standards, where yesterday’s premium-grade capabilities become today’s minimum standards,” says Peter Mack, manager of automotive products marketing at Petro-Canada Lubricants.

Lube refiners have their work cut out for them now, with the work that 2002 emissions regs have forced on them.

“Our industry has seen more successive emission regulations in the past 10 years than we saw in the prior 40 years,” says Don Carver, legendary oil expert and program co-ordinator for ExxonMobil’s “Smartlube” program. “And we’ll see many more changes again in the next six to 10 years.”

For 1999, engine makers could only meet lower nitrous-oxide (NOx) demands by retarding injection timing, but that meant reduced combustion temperature and hence substantially higher levels of soot added to the crankcase oil. It’s not hard to fathom why. Retarding the injection allows the piston to advance down the cylinder a little before combustion is complete. The actual amount is only around 30 thousandths of an inch, but the out-of-the-combustion-bowl process means trouble by way of soot. It’s basically unburned fuel, and it’s nasty.

Soot levels increased by 100% or so in those retarded engines-going up to a whopping 600% in some cases-which demanded a new oil classification even beyond the American Petroleum Institute (API) CH-4 standard introduced in late 1998. The key challenge: keeping that soot in suspension.

Two engine makers had already developed their own more stringent oil specs by then. The Mack EO-M and Cummins CES 20071 tests improved oil’s ability to keep soot in suspension. Then they went one better to create the EO-M Plus and CES 20076 tests, aiming to further ensure long-term engine durability. They’re tough enough that the oil industry itself has gone on to worry about the effects of the 2002 regulations (see sidebar).

The rigorous Cummins M11 high-soot test, for example, measures the wear on the valve bridge where the rocker bears. As the rocker presses down on the bridge, it slides across the surface, and a lube oil heavily laden with soot will act as an abrasive on engine surfaces unless the soot is well dispersed. Similarly, soot contamination will clog filters and leave sludge deposits on the rocker cover. These are elements of the Cummins M11 test and they quickly reveal shortcomings in an oil’s additive package.

Oils meeting these new Mack and Cummins standards have become known as CH-4+. Compared to earlier CG-4 oils, they offer better control of soot-induced wear, improved filter performance, better viscosity control, and easier low-temperature pumping, among other gains.

Straight CH-4 oil can manage a maximum soot content of 5%, Don Carver notes, and the newest CH-4+ oils go to 7.5%. Previous API classifications handle progressively less-1994’s CG-4 can manage 3% and CF-4, from 1991, just 1.5%. Earlier oils were CE and CD, from 1988 and 1970 respectively. Note that we’ve seen four API classifications in the 1990s.

The American Petroleum Institute is the agency that decides when a new lube-oil category is required. The process starts with a request from engine manufacturers; extends through a review that determines whether circumstances have changed to such an extent that the category is really essential; and leads to a task force design of the testing and performance requirements that oils complying with the category must meet.

John Holuk, technical advisor/lubricants, at Shell Canada, explains the process of determining the specifics of a proposed new standard. First off, lube refiners learned long ago that they couldn’t go their own way.

“It probably costs an oil company between $250,000 and $500,000 to run the tests that get a heavy-duty engine oil approved if there’s been any significant change to the standard,” he explains. “So it certainly made sense to develop a set procedure to handle the evolution of standards. “Each engine manufacturer, as their models change, will become aware of the various ‘nuances’ in how those power plants operate-their strengths and weaknesses, if you will-and they’ll release a set of performance criteria that they feel the lubricant industry must meet in order to adequately address the needs of that engine.

“And each engine maker will propose certain engines to use as test beds,” Holuk notes. “These engines nowadays usually are found at certain commercial test facilities around the United States, rather than in-house at each oil company. It’s more cost-efficient to contract with these test centres: you send them a quantity of your lubricant; they’ll run the desired tests to a very structured protocol that they use for every client; and then they’ll send you the results.

“The consensus of performance criteria that becomes a standard like CH-4 will last perhaps three or four years, but even that’s not the end of it,” he says. “The various engine manufacturers typically also establish their own standards, much of which will be incorporated into something like CH-4, but they’re not necessarily identical. If an engine maker feels that they need to have something out on the street to protect a given engine they’re producing, and the current API-sanctioned standard has some gaps in it-or the latest version isn’t ready yet-then they’ll issue their own standard.”

Once the criteria are published, API allows a year for all lube suppliers to complete testing and certification before it licenses the supplier to use the API ‘donut’ on its labels, with the category number inside the ring to show that lube oils meet the new category definition.

It’s the American Society for Testing and Materials (ASTM) that actually develops the testing and performance criteria for heavy-duty oil classifications. It includes oil, additive and engine manufacturers.

To qualify for any category, oil is run in certain kinds of engines under exacting test conditions. Oils failing to meet performance levels can be denied certification or, somewhere along the line, stripped of certification if makers don’t make corrections. Each refiner formulates its oil to meet a classification’s minimum performance requirements, so two oils that have earned the CH-4 or any other label may not be equal in performance. Formulations-and performance-will differ among refiners.

To put all this in a practical context, the Cummins recommendations for 1999 N14 Plus engines in normal duty (5.5 to 6.5 mpg and under 80,000 pounds gvw) allow 20,000 miles between oil changes with CG-4 lube, 30,000 with CH-4/CES 20071, and 35,000 with CH-4+/CES 20076. A 1999 Signature engine can go out to 40,000 miles with CES 20076 oil.

Incidentally, the “C” in CH-4 means compression ignition, as in diesel, and the “4” refers to four-cycle, the type of diesel this oil is designed for. The “H” denotes progression from one standard to the next.

The next oil type, tentatively called PC-9 (PC stands for Proposed Category) and likely to get the CJ-4 name formally, will be needed for the heavy-duty diesels due out in October 2002. By U.S. decree, they’ll produce about 50% less NOx than current engines. All of them will need cooled exhaust-gas recirculation (EGR) to do it, and that means the oil refiners are mighty busy.

Some engine makers feared that they couldn’t pull this off, and it’s not a done deal yet, but the lube test requirements have been established and all ASTM labs now have test engines. Formal testing will start this month and end some time in early 2001, with the CJ-4 standard likely ready for market in early 2002. It looks like there will be three separate engine tests-the Mack T10, Cummins M11 with EGR, and the Caterpillar 1Q by name.

Details are scarce, but it seems that a typical 2002 EGR system will siphon a small amount of exhaust gas from the turbo, run the gas through a special water-to-gas heat exchanger, and then mix it with clean inlet air in the charge-air cooler. From there the cooled air-gas mixture will go to the engine’s combustion chambers where it will help cool the combustion flame, by excluding a portion of the oxygen, to reduce NOx.

How much exhaust gas will be recirculated? It’s not known, but some industry experts are suggesting 12% to 15%. Injection pressures will be higher still.

For heavy-duty diesels, cold EGR presents major challenges. For one, there’s the problem of getting the gas to go into the turbocharged inlet stream-a bit like getting balls to roll uphill. For another, there’s the need to cool the gas from its 1000° F or so temperature down to around 200°.

Neither problem exists with current EGR applications in gasoline engines, so there’s little technology to draw from, either in designing the engines or the lubes that will allow them to live at the same durability levels as today’s diesels.

ExxonMobil’s Don Carver is pessimistic about all this. “Cold EGR maintains fuel economy, but you have to be careful not to cool too far and get condensed sulphuric acid,” he says. “So it’s more complicated than previous changes. EGR brings top ring and liner wear, resulting in a dramatic decrease in engine durability. Also, high EGR means rapid Total Base Number degradation and a four-times soot increase. That results in oil thickening.” Given the very early results of EGR test engines, it’s evident that Carver’s prediction will be borne out. There will be increased corrosive acids in the oil, a marked increase in soot, and increased injector slider wear.

Also, since the engines will have to cool the exhaust gas, with predictions of anything up to an additional 40% increase in heat rejection, engines and engine compartments are expected to run hotter. That will lead to increased oxidation in the oil. To handle all the anticipated changes and to gain a measure of comfort against the EGR demands, additional testing is included in PC-9, bringing the total to 13 to satisfy the needs for oil certification.

Dan Arcy, Pennzoil’s product manager for heavy-duty engine oils, points out the limit for the maximum soot in diesel lube was pegged at just 1.5% in 1993 when CF-4 came in. The 2002 standard has a requirement to carry up to 10% soot. “Imagine if you have a crankcase with 11 gallons of oil, at 10% soot, one gallon of crankcase capacity is soot,” he says. “This would be a worst-case scenario-stop-and-go city traffic-but it shows the great improvements in oil over just the last few years.” Arcy notes that CJ-4 oils should be backward-compatible, meaning they would be useable in pre-2002 engines. Perhaps surprisingly, apparently there would be no degradation in drain-interval capability with CJ-4 oils. Other experts, however, are less confident.

Work is already underway on the next emissions hurdle, set for 2007. This one is so challenging that some industry engineers have referred to it as a new paradigm. The proposed emissions levels, published in April, will likely require a continuation of EGR with additional particulate trap and NOx catalyst technologies.

To have lubes ready for 2007, ASTM is already working on PC-10. The demands of those technologies may well mean the end of backwards compatibility for new premium oils, says Arcy.

Lube oils are an increasingly important part of the total emissions strategy and a key engine component, fundamental to the durability of an engine’s pistons, rings, and bearings. At the same time, however, truck users have been looking for performance gains as well, especially in longer drain intervals. The fact that oils have managed to allow stretched intervals, while meeting all those other challenges, is really quite remarkable. But it does mean that this is no time to try to save a buck on cheap oil. A lube oil’s additive package, most notably the detergents and dispersants that keep soot from building up on engine surfaces, has to be awfully good.

The demands of engines today also dictate that the category of oil you use has to be matched precisely to the level of your engine’s technology. Engines from 1998 need CH-4 oils, and 1999 models need CH-4+ oils. By 2002, you’ll have to be using PC-9/CJ-4 if you want the same level of engine reliability and durability you’ve enjoyed over the last decade.

You may be concerned about the rising cost of engine lubes, but you’ll appreciate that the rocketing price of crude oil has had an affect on both oil base stock prices-they’ve doubled-and on oil-derived additives used in blending top-quality lubes. Other non-crude-based chemicals have been affected by tightening supply, which drives up their price.

Premium oil marketers have also raised prices to help pay rising research costs for next-generation lubes. For instance, a normal Cummins M11 test that ran 200 hours now requires 300. The cost of meeting Mack and Cummins specs has increased as much as $60,000 to $80,000 US per test. Some of the upcoming tests may require 500 engine hours or more, we’re told.

But more than ever, when you choose an engine oil, you’re going to get what you pay for.

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Rolf Lockwood is editor emeritus of Today's Trucking and a regular contributor to Trucknews.com.

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