Be careful of extended oil drains with the newer diesel engines
It came as no surprise to anyone attending the recent summer meeting of The Maintenance Council of ATA in Indian Wells, Calif., that diesel engines have changed significantly in the last few years and that tomorrow's engines will bring even more changes.
Because modern diesels have to meet an ever-growing range of tests to demonstrate environmental compliance, engine manufacturers must now design for tighter control of all gaseous emissions, regardless of operating conditions, while recognizing that NOx control is the primary challenge, says Steve Berry, manager of advanced engineering at Mack Trucks. And OEMs must apply new technologies to provide the fuel efficiency and engine durability that fleets demand.
How will these goals be achieved? Berry looks to retarded engine timing, improved fuel systems, better turbocharging, and use of exhaust gas recirculation and aftertreatment systems.
The amount of NOx produced drops as engine timing is retarded, Berry notes. That's the good news; the bad news is that retarded timing leads to increased amounts of soot as unburned fuel impinges on the cylinder walls. Soot, Berry points out, is an abrasive carbon compound that contributes to engine wear, and elevated soot levels tend to raise an oil's viscosity and restrict its flow.
To address soot concerns, engine manufacturers have several weapons in their arsenal. Berry mentions increased injection pressures (to shorten injection duration), spray-angle adjustment, modifications in piston-bowl geometry, and increased sump capacity. He recognizes that although engine-oil suppliers have already improved their formulations to handle soot, even further improvements may be needed.
One fundamental technology for the diesel engine industry in its efforts to meet the 2002 NOx standard, says Berry, is exhaust gas recirculation (EGR), in which a portion of the exhaust gas is recirculated into the combustion charge, thereby reducing localized combustion temperatures and reducing NOx. Again, there is some bad news: Soot loading goes up somewhat and exhaust stream acids react with sulfur in the fuel to generate corrosive sulfuric acids.
Berry warns that by 2002 oils and filters may not be the commodity products they are today, and that premium products may be required.
Another viewpoint - that of an oil-additive-package supplier - was offered by John Martin, executive engineer-R&D for Lubrizol. Martin notes that although API service classification CH-4, which addresses valvetrain wear control, is only a little more than a year old, several engine manufacturers are already asking for an oil with higher performance, especially for extended service intervals.
Some of the newest specs reflect these needs, says Martin. Cummins CES 20076, for example, requires a premium HD oil (exceeding minimum CH-4) for 1999 and older engines, and Mack EO-M Plus approved oils are required for extended (50,000 mi.) drain intervals in Mack engines. In Europe, ACEA E5-99 (due 10/99) specifies a premium HD oil, highly refined or partially synthetic, for Euro 3 low-emission engines; and, in North America, PC-9 (due 4/02) will focus primarily on the higher soot caused by EGR.
For fleets, Martin recommends the following:
*Use the highest quality HD oil available. API CH-4 should be the minimum spec.
*Be careful of extended drains. Play it safe and easy by using OEM-recommended intervals.
*Re-establish drain intervals by using oil analysis and do so through 2002 as engines change.
*Monitor oil analyses carefully and pay close attention to contaminants, wear metals, soot, and sufficient TBN (total base number) to neutralize acids.