Heavy-duty diesel engines today are emitting about a third less carbon dioxide than gas engines and 70 per cent fewer nitrous oxides. Nevertheless, diesel engines continue to be the focus of ever more...
Heavy-duty diesel engines today are emitting about a third less carbon dioxide than gas engines and 70 per cent fewer nitrous oxides. Nevertheless, diesel engines continue to be the focus of ever more stringent regulations from the U.S. Environmental Protection Agency, which sets the stage for the regulations we will live by in Canada. The next big emissions reduction date is October 2002, when the regulations stipulate that diesels can emit no more than 2g of nitrous oxides (NOx) or half the current amount allowed. And so the race is on, from OEMs to lube and additive manufacturers, to build the engines and corresponding lubes to meet these requirements.
“During the establishment of the last engine lube CH-4 category, OEMs were dragging their heels on improvements, so the CH-4 process dragged out and OEMs were fined. Engine calibration had to be re-computerized. OEMs were under the gun. Now they are under strict guidelines and they want to make sure that they don’t run into glitches,” says Crawford Smyth, category manager, with Shell Canada.
The process of retarded injection timing was used to address the EPA’s 1998 emission demands, and the CH-4 category of engine oils targeted those systems. Retarded injection lowered peak combustion chamber temperatures, but at a small cost to fuel efficiency. To further reduce NOx to the proposed 2002 levels, the technology of EGR, or exhaust gas recirculation, will have to be applied to heavy duty diesel engines. In diesel engines, NOx emissions rise as the peak flame temperatures go up. So to reduce NOx, the exhaust gas needs to be cooled down.
“Cold EGR” technology is the method currently considered to have the best chance to achieve this. It’s basically a reinjection of hot exhaust air (from four per cent to as much as 15 per cent) into the combustion chamber of the engine. Hot exhaust air gets drawn through an intercooler to bring its temperature down (from about 1200F to 250F). It is then mixed with cooler inlet air (at 110F). With EGR, fuel injection timing can be optimized for best power and economy, with the recirculated gas taking care of excessive combustion chamber temperatures, as well as re-burning some of the inevitable unburned hydrocarbons left over from the combustion process.
The American Petroleum Institute licenses oil companies to display the service classifications of engine lubes on their packaging. And the American Society of Testing and Materials committee on heavy duty engine oil will set the limits and verify the testing on these classifications.
CH-4 oils would not work in an EGR engine because the drain intervals would be much shorter. So the next step up from the current CH-4 category is PC-9, (Proposed Category 9, which will likely be renamed CJ-4 according to protocol). The ASTM is now in the process of defining the procedures for running the tests required by each of the OEM specs. The process should be final by May or June of this year, with PC-9 oils expected on the market nine months to a year later, i.e. April to June 2002, months in advance of the deadline for the new engines.
But to get there motor oil makers must deal with the rough impact EGR technology has on lubes. “The process itself impacts oil in four basic areas: an increase in corrosive acids, an increase in soot levels, higher oil oxidation levels, and an increase in abrasive wear,” says Michael Dargento, senior marketing manager, commercial automotive market segments, Chevron Products Company.
The new classification of lubes will have to call on higher alkaline reserves (Total Base Numbers) to protect crankcase oil against the sulphuric acid that will come from the exhaust back into the combustion chamber, better soot dispersancy to prevent filter plugging, and better oxidation control or high temperature protection.
“NOx can form nitric and sulphuric acid, which impact oil and the engine. So the (new) oil must effectively neutralize acids. But it’s not just a case of dumping oil in. We have to think of where the acids are hitting the oil first. Although we may see the first effects on the soft metals, it affects the hard metals too,” says Michael Ragomo, product advisor, commercial vehicle lubricants, Exxon Mobil Corp.
Because the intercooler is cooled by the same on-board cooler capacity that the engine has, the engine runs hotter and this puts greater stress on oxidation resistance of oils. Also, the higher the levels of exhaust gas recirculated, the more loss because the intake charge is diluted. And this could mean a harder duty cycle for the oil.
“EGR technology is the most severe technology that an engine will have had to face to date. But all we have right now to work with are the EGR test engines. They tend to be more severe and handle the worst case scenario in the field. Engines will see higher temperatures and because of the nature of combustion, we expect to see more soot, which thickens the engine oil. Current engines, using retarded timing, produce one to three per cent soot. Test engines are producing as much as 10-11 per cent soot. The ability of engine oil to disperse this level of soot will be extremely important,” says June Li, category manager, commercial and industrial lubricants, Petro-Canada.
Increased soot presence will also have implications at start-up, says Ragomo. “We’re looking at not only the effect of soot at operational temperatures but also at start-up temperatures. And we’re pleased to see the industry is finally recognizing this as a contributing factor,” he says.
Li says that the composition of the actual base oils used in the PC-9 lubes also has a major effect on performance.
“The importance of the actual base oils used will be more important than before around soot dispersion. Solvent refined base oils are not as pure (analogous to a sifting separation process to remove impurities). Hydrocracking involves converting or obliterating base oil impurities through a severe chemical reaction. The hydrocracked base oils are higher quality in their ability to disperse soot and not thicken up, and additives work better with them,” says Li.
Lube manufacturers know what they will be targeting in terms of effects, but expect tolerances to be officially defined during the course of 2001.This involves a multi-step process with many players.
There are three new engine tests for the PC-9 category, developed to address the needs required in each operational environment of engines.
Mack T-10 with EGR is a 300-hour test for piston liner durability at elevated temperatures and will look at oil oxidation and the effect of corrosion on ring weight and cylinder liner wear. Cummins M11 EGR is a 300-hour test that will vary between soot-generating cycles, then an engine wear mode. Each cycle will last 50 hours.
“This test will end up with 8.5 – to 9.5 per cent soot at the end. This will mean just 90 per cent lubricant remaining. And too much solid material that doesn’t have lubricant ability. What they may consider is all their parameters: sludge formation, valvetrain wear, filter premature pressure increase, and plugging,” says Ragomo.
CAT 1Q with EGR is the final test and will look for upper piston deposits and oil consumption. This is a single cylinder test, and it is the largest one of the category, to run for 504 hours, over 20 days.
While the goal of PC-9 is to maintain 30-40,000 mile drains for EGR engines, there is no consensus so far on how probable this will be. “Engine oil has to cover the most severe applications and you formulate around that. But the intent is to maintain all service levels where they are today,” says Smyth.
While drain intervals may change, if the effects of EGR aren’t properly addressed, you’re looking at viscosity breakdown or a failed additive package, and even more resulting downtime for your fleet.
“I think there’s going to be compromised engine life if you go beyond the recommended drain interval. We do like to build a lot of robustness into the lubes so there’s no breakdown if they go beyond. But there’s no false economics behind engine drains. We take a holistic approach on th
e total cost of ownership, and engine durability. And for pricing, it may be a bit too soon to tell, but there will be more opportunities for fleets to extract more value out of high-quality lubricants – and have a service interval advantage,” says Ragomo.
Lube manufacturers have a vested interest in the whole emissions reductions process, says Dargento. “In terms of benchmarks, we have to keep pace with the industry. The ASTM panel is made up of our research engineers, engine manufacturers, and lube and additive manufacturers. And it’s very expensive to run these tests. It could, if you don’t get good results in initial tests, cost you millions of dollars to test your oils,” he says.