|Standard for API CI-4 Diesel Oil
On Time, On Target
by Jim McGeehan
The EPA has committed to controlling emissions of oxides of nitrogen
(NOX) from diesel engines on the highway. Committee D02s 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 NOx. Particulate is composed of soot and sulfate bound with water
and unburned oil. NOx 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 NOx 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 NOx
In October 2002, there will be no change in particulate limits,
but NOx 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 NOx formation, engine manufacturers could use either severe retarded
timing or cooled exhaust gas recirculation to control NOx. 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 NOx formation. Researchers have observed 30 to 75 percent reductions
in NOx by using 5 to 25 percent of EGR.
Although there are a number of technical papers explaining the
effects of EGR on lowering NOx, 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 NOx 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 thats
burning is not only heating up the air and the fuel in the normal
process, its 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
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 NOx 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
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 manufacturersMack 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
Three oil companiesChevronTexaco, 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
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
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
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
High Temperature/High Shear Viscosity
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
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
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 ASTMs ability to deliver new engine oil
to meet customers and engine manufacturers needs in a timely manner
and within budget. //
Copyright 2002, ASTM