On Time, On Target

by Jim McGeehan

The EPA has committed to controlling emissions of oxides of nitrogen (NO_X) from diesel engines on the highway. Committee D02’s Heavy Duty Engine Oil Classification Panel has played an important role in the effort to make the new API CI-4 oil category available with the timely development of a standard.

The U.S. Environmental Protection Agency (EPA) has mandated on-highway diesel engine emission reductions. The two principle reductions mandated are particulate and NO_x. Particulate is composed of soot and sulfate bound with water and unburned oil. NO_x is formed by oxidation of atmospheric nitrogen in the power-cylinder and is a principle component of smog. As a result of EPA rulings, a 70 percent reduction in NO_x emissions and a 90 percent reduction in particulate emissions have been achieved since the 1980s. This has been achieved through improvement in in-cylinder combustion, use of electronic fuel systems, and reductions in fuel sulfur, which contribute to particulate.

Since diesel engine oils are part of the low emission equation, there has been a stepped increase in the quality of crankcase oils, along with the stepped reduction in exhaust emission. The new API CI-4 oil category developed by ASTM focuses on diesel engine oil quality improvements for the year 2002 for engines that use cooled exhaust gas recirculation (EGR). It should provide adequate engine protection for new EGR diesel engines, and all other existing diesel engines (see Figure 1).

COOLED EGR REDUCES NO_x

In October 2002, there will be no change in particulate limits, but NO_x emissions will be reduced from 4 to 2 g/bhp-hr, requiring the use of cooled EGR on the majority of light- and heavy-duty diesel engines of U.S. manufacturers.

Because peak cylinder temperature is the most influential variable affecting NO_x formation, engine manufacturers could use either severe retarded timing or “cooled exhaust gas recirculation” to control NO_x. EGR, however, has been found to provide 10 percent better fuel economy than the retarded timing strategy. EGR is the most effective means of controlling NO_x formation. Researchers have observed 30 to 75 percent reductions in NO_x by using 5 to 25 percent of EGR.

Although there are a number of technical papers explaining the effects of EGR on lowering NO_x, John Wall, chief technical officer of Cummins, provided in clearer terms the simplest explanation for truck customers: “EGR is all about controlling temperature. If you want to control NO_x in-cylinder, you want to control peak combustion temperature and keep it from getting too high. So you take some exhaust and cool it and put it back in with the intake air. Now the fuel that’s burning is not only heating up the air and the fuel in the normal process, it’s got the extra stuff in the combustion chamber that needs to be heated up as well. Because that soaks up some of the energy, you reduce the peak temperature and you can reduce the NO_x formation.”

As an inert gas is being added to the cooled intake charge, higher turbocharger boost pressures are required because the exhaust is replacing some of the oxygen in the intake. Therefore, more total air mass must be forced into the cylinder to burn the same quantity of fuel and retain the original power. Most engine manufacturers will use variable geometry turbochargers to attain these higher boost pressures. The combination of these factors lowers NO_x and maintains fuel economy at its current levels, but increases peak firing pressures (190 bar (2,800 psi)) and fuel injection pressures (2,400 bar (35,000 psi) in some cases).

INCREASED HEAT REJECTION TO COOLANT AND OIL WITH EGR

Heat rejection to the coolant increases 25 to 35 percent because the exhaust is cooled from 650°C (1200°F) to 120°C (250°F) by the engine coolant in the heat exchanger. This is in addition to the normal block cooling. Consequently, “top tank” radiator coolant temperatures will increase, as it may not be possible to put larger radiators in the trucks due to available space. This increased heat rejection will also mean higher oil temperatures, as the oil cooler uses engine coolant. So there must be sufficient oxidation inhibitor in engine oil to prevent viscosity increases.

INCREASED ACID IN THE POWER CYLINDER WITH EGR

For on-highway trucks in the United States, the fuel sulfur level is currently regulated at 500 ppm (0.05 wt percent) to reduce particulate. The sulfur in diesel fuel burns to form sulfurous (H₂SO₃) and sulfuric (H₂SO₄) acids, and these increase linearly with increasing fuel sulfur levels. Since these acids are relatively low in on-highway trucks, alkaline detergents in the oil successfully neutralize them and prevent corrosive wear.

However, the introduction of cooled exhaust gas, which contains H₂SO₃/H₂SO₄ in the inlet charge, increases the acid in the power cylinder. Consequently, there must be sufficient detergent in the engine oil to neutralize this acid, thereby preventing ring/liner, bearing, and valve stem corrosion. This is particularly critical when engines start or idle at low coolant temperatures, which increases corrosion (see Figure 2).

NEW OIL CATEGORY DEVELOPMENT PROCESS TO MAINTAIN ENGINE DURABILITY WITH EGR

To address the above problems, the Engine Manufacturers Association requested a new oil category. The intent of this oil category is to maintain engine durability, in spite of the application of cooled EGR to lower emissions.

The process for this category development is defined in the new API 1509 Engine Oil Licensing and Certification System and involves the following committees: API, New Category Development Team (NCDT), EMA, American Chemistry Council (ACC), Diesel Engine Oil Advisory Panel (DEOAP), and ASTM International. These committees are all involved in selecting tests, base oils, and additive technologies for matrix testing and in providing the funding for that testing.

The critical driver to the process was the ASTM Heavy Duty Engine Oil Classification Panel. This panel is balanced between engine manufacturers and oil-additive suppliers. They are:

• Seven engine manufacturers—Mack Trucks, Cummins Inc., Caterpillar Inc., Detroit Diesel, John Deere, General Motor, and International Truck and Engine Corp.
• Four additive suppliers— Lubrizol, Oronite, Infineum USA, and Ethyl Corp.
• Three oil companies—ChevronTexaco, ExxonMobil, and Equilon.

The panel started work on the new oil category in January 2000 and delivered on time with an approved ASTM Subcommittee B ballot in December 2001--D 4485, Standard Specification for Performance of Engine Oils. This ensured that this quality of oils would be in the marketplace prior to the introduction of EGR engines (see Table 1).

SEVEN FIRED ENGINE TESTS AND EIGHT BENCH TESTS IN API CI-4

This oil category was driven by two new cooled EGR engine tests operating with nominally 15 percent EGR, with soot levels at the end of the test ranging from six to nine percent. These tests are Mack T-10 and Cummins M11 EGR, which address ring, cylinder liner, bearing, valve train wear, filter plugging, and sludge. In addition to these two new EGR tests, there is a Caterpillar single-cylinder test without EGR for piston deposits and oil consumption control using an articulated piston. This test is called the Caterpillar 1R and is in the existing Global DHD-1 specification.

A precision and base oil interchange matrix was completed in the Mack T-10 and Cummins M11 EGR tests. This involves three different additive technologies, which are blended into one API Group I (solvent refined) and two Group II (hydrocracked) base stocks as SAE 15W-40 oils. A limited precision matrix was conducted on Caterpillar 1R.

In total, there are eight fired-engine tests and seven bench tests covering all the engine oil parameters in the API CI-4 category. The new bench tests include a seal compatibility test for fresh oils and a low temperature pumpability test for used oils containing five percent soot from the Mack T-10 test.

The new tests or existing tests with new limits are:

• Mack T-10 (EGR) (Ring, Liner, Bearing Wear, and Oil Consumption)
• Cummins M11 EGR (Ring, Valve Train Wear, Filter Delta P, and Sludge)
• Caterpillar 1R (Piston Deposits and Oil Consumption)
• Mack T-8E (Soot Dispersancy)
• Sequence IIIF (Oil Oxidation and Oil Consumption)
• Low Temperature Pumpability for Oil Containing five percent Soot
• High Temperature/High Shear Viscosity
• Elastomer Compatibility
• Volatility

The six remaining tests in the category are in the existing API CH-4 category and are carried into API CI-4, making a total of 15 tests. API CI-4 is a backward-compatible category. Simply, if the requirements of API CI-4 are met, oil companies can claim API CH-4, CG-4, and CF-4 without running any further tests (see Figure 3).

ON TIME, ON TARGET, WITHIN COST

This work was completed in October 2001 by the HDEOCP, at a cost of $5.71 million (6.28 million euro) for the engine test matrix. This was followed by a ballot completing ASTM work in December 2001. API requires a nine-month period to qualify oil company products before API-licensed products designated API CI-4 become available in August 2002. This on-time delivery of API CI-4 was achieved by a team effort within the HDEOCP and all the task forces established to quickly resolve problems as the category developed, in addition to the use of “Exit Criteria” ballots on test limits to establish company positions prior to the ASTM B ballot (see Figure 4).

API CI-4 oils are pivotal components in maintaining diesel engine durability using cooled EGR. API CI-4 is a higher quality oil than the previous diesel oil categories, so it will provide engine protection for both existing and new EGR engines. Ultimately, consumers of these high-quality oils are the real winners. Finally, this has demonstrated ASTM’s ability to deliver new engine oil to meet customers and engine manufacturers needs in a timely manner and within budget. //

Copyright 2002, ASTM