Diesel Oils Must Multitask.
Diesel oils are faced with challenges from exhaust aftertreatment devices in addition to the severe challenges inherent to protecting diesel engines.
Formulating motor oil for use in heavyduty diesel applications has changed in recent years. The most recent diesel oil specification, API CJ-4, had a dramatic impact on the way diesel oils are designed, forcing them to address new emissions control devices while still keeping engines clean, protected and running efficiently.
"Heavy-duty diesel oils must stand up to a number of severe conditions…"
Heavy-duty diesel oils must stand up to a number of severe conditions, including high levels of shear, aeration, soot contamination, varnish build-up and extreme temperatures. They are designed to provide resistance to these key areas and hold up for the duration of the advertised drain interval.
Laboratory Bench Testing
The API CJ-4 specification requirements include laboratory bench tests that focus on shear stability, corrosion protection, foaming, volatility, soot control, seal compatibility and emissions system protection. There are also a number of other engine tests used to qualify CJ-4 oils for use in specific applications, including the Mack T-11 and T-12, Cummins ISB, Caterpillar 1N, Caterpillar C13, engine oil aeration, roller follower wear and Sequence IIIF tests. These tests provide additional insight as to an oil’s performance in areas from soot control and ring wear to hot stuck rings and roller follower pin wear.
Bringing Change to Diesel Oils
One of the most drastic changes implemented with the API CJ-4 category was the strict EPA-mandated limits for onhighway diesel vehicle emissions. CJ-4 includes maximum limits for sulfated ash, phosphorus and sulfur (SAPS). These limitations were put in place to protect emissions aftertreatment systems on 2007 and newer engines. The maximum limits are 1.0 percent, 0.12 percent and 0.40 percent respectively for sulfated ash, phosphorus and sulfur.
Diesel Particulate Filters
In 2007, the first wave of emissions reductions focused on particulate matter and required the use of a diesel particulate filter (DPF) to capture what we all know as sooty black smoke by trapping it in a ceramic honeycomb filter. Because soot accumulates in the filter quickly, it needs to be cleaned on a periodic basis or it will plug and shut down the engine. The technique for cleaning DPFs is called regeneration and is categorized as either passive or active.
Regeneration of DPFs
Active regeneration typically uses a charge of diesel fuel or some other type of heating source to light off or burn the accumulated soot in the filter, allowing the filter to continue to trap soot. The heating source ignites soot trapped in the DPF to make room for more. Active regeneration can be problematic to diesel oil if diesel fuel is delivered via the exhaust stroke through the pistons; the diesel fuel can make its way past the piston rings and dilute the oil, which can lead to a reduction in oil viscosity and increased oxidation. Class 8 trucks use a separate fuel injector positioned just ahead of the DPF to deliver diesel fuel to regenerate the DPF, which does not generally cause any oil-related issues. SAPS in diesel oils carries through the exhaust system, does not burn and accumulates in the diesel particulate filter. This is a slow process, but when ash levels become excessive, the DPF must be removed from the vehicle and cleaned. The API CJ-4 specification has a 1 percent maximum sulfated ash level to maximize time between cleanings.
Exhaust Gas Recirculation and Selective Catalytic Reduction
In 2010, another wave of emissions limits were implemented targeting nitrogen oxides (NOx), which are also harmful to humans and animals. The two primary methods used to limit the amount of NOx emitted to the atmosphere are exhaust gas recirculation (EGR) and selective catalytic reduction (SCR). Each of these systems has positives and negatives affecting engine operation and maintenance. EGR reduces the amount of NOx generated during combustion by recirculating some of the engine’s exhaust back into the intake area. This reduces diesel fuels’ peak-flame temperature and reduces NOx production during combustion. High levels of exhaust gas recirculation can shorten diesel oil life through higher operating temperatures, higher levels of soot and potentially higher acid levels. Selective catalytic reduction is also used to reduce NOx levels but works by injecting urea, or diesel exhaust fluid (DEF), through a doser which reduces NOx gases to nitrogen gas and water. While selective catalytic reduction does not increase oil stress, it does complicate maintenance issues for diesel vehicle owners because it requires an additional fluid to maintain.
Conquering All Challenges for Heavy-Duty Diesel Oil
AMSOIL carefully designs and tests all CJ-4 heavy-duty diesel oils to meet or exceed all these requirements in addition to extending drain intervals. With the range of complicated, expensive equipment in the field that depends exclusively on a thin layer of oil for engine protection and prolonged engine life, proper formulation is an enormously important task.