What's ahead for diesels?
If curbing NOx is such a hassle, why push it? EPA explains that NOx
reduction provides a uniform, one-step (albeit partial) solution to a variety
of local, regional, state and national air-quality compliance problems.
Basically, environmentalists want to nix NOx because it reacts with other
atmospheric pollutants to form acid rain and health-threatening smog/ozone.
A. Exhaust Gas Recirculation(EGR) System
What will it ultimately take to clean-up diesels? For 2004, EGR supplemented with cooled intake air remains a potentially-necessary strategy. There's no getting around the fact that EGR works. Researchers at the University of Wisconsin at Madison have observed a 30 to 75% NOx reduction at EGR rates of 5 to 25%.
There's disagreement over how EGR works its magic, however. According to one theory, EGR dilutes the air/fuel mixture and displaces oxygen, thereby lowering peak cylinder temperatures, which reduces NOx. Passavant explains that combustion temperature also is reduced because inert exhaust gas absorbs heat when fed into an engine. To compensate for oxygen depletion, higher turbo boost pressures are required.
Predictably, seating EGR on one end of the seesaw causes PM to rise, especially at high engine loads.
In theory, EGR boosts PM because cooler combustion can't burn it up. Next, EGR shovels abrasive PM and sulfuric acid into the engine and its crankcase where it can foul-up everything, attack lube oil and promote engine wear.
B. Multi-Point Injection System
There is, however, a new way to counteract EGR's soot production. Today's diesels only inject fuel toward the end of the compression cycle. In contrast, it's been demonstrated by the University of Wisconsin at Madison that combining 6% EGR with sequenced, triple-dose fuel injection (using a single-cylinder version of a Cat 3408) can simultaneously cut NOx to 2.2 g/bhp-hr and bring PM down to 0.07 g/bhp-hr. That's according to Technical Paper 950217, published by the Society of Automotive Engineers (SAE), Warrendale, Pa. Even greater NOx reductions could be achieved, we're told, by delaying injection beyond top dead center (TDC).
Notably, Southwest Research Institute (SwRI), San Antonio, Tex., has prototyped a double-dose, two-point injection system. Early in the combustion cycle, the main injector provides a lean, premixed shot of fuel and air. Next, before the piston retreats far from TDC, a secondary injector introduces a hot "energetic" jet of fuel that boosts combustion rate.
SwRI's better-injection mousetrap zaps NOx and PM simultaneously, and very dramatically, according to Daniel Dickey, manager of engine development and controls for the engine and vehicle research department.
SwRI also is working on so-called "non-thermal plasma methods" of passive exhaust aftertreatment (i.e., no internal, soot-purging toaster required) that simultaneously lower NOx and PM.
Providing the big picture, here's EPA's laundry list of basic NOx killers:
For some insight, CCJ interrogated Blaine Johnson, national chairman of the Truck & Bus Council of SAE, and maintenance director of Miami-based Ryder Truck Rental. Mr. Johnson is noted for keeping his crystal ball brightly polished.
Johnson's fearless forecast
Johnson advises fellow fleetmen to stop speculating about the imminent
introduction of engines from space, or drinkable diesel fuel. He contends
that alternative fuels like natural gas and methanol have limited appeal.
Good old No. 2 diesel remains the fuel of the future, he firmly proclaims.
No medium/heavy-duty EGR or exotic innovations stolen from low-emitting demonstration engines will appear on the road in 1998. And only a few, medium-duty diesels will be offered with aftertreatment. At worst, he says, most diesel makers will continue the productive, electromechanical modifications used to aid 1994 compliance. For that matter, engines relying on NCPs and/or credits for 1998 compliance need not change.
There's absolutely no chance that the petroleum industry will provide cleaner diesel fuel to aid compliance, he says. Still suffering chest pains from the 1994 sulfur reduction, refiners won't be swayed by suggestions for more refinements, he claims. That's not to say that individual companies won't market premium, extra-clean-burning diesel fuels laced with additives.
Passavant notes that EPA has the authority (imparted by the Clean Air Act) to require the nationwide production of cleaner No. 2 fuel, if it would provide a "cost-effective" way to reduce stack emissions. But that's extremely unlikely, industry sources report.
In theory, any 1998 engine whose timing is severely retarded to lower NOx will produce more soot and suffer from diminished fuel efficiency. But Passavant says that timing won't be retarded to the detriment of oil change intervals or fuel efficiency in 1998. Instead, he says, engine makers will rely primarily on fine-tuned electronic controls and "precision fuel/air management" to manipulate stack emissions. But he agrees with Johnson that some low-horsepower ratings will bite the dust.
Johnson explains that "progressively-higher horsepower ratings, including hefty dual ratings, didn't just materialize to brighten a driver's day. The thing that's really driving-up horsepower is the fact that more horses aid emissions compliance, which is determined on the basis of grams per brake horsepower-hour." In effect, higher-horsepower engines run more efficiently and statistically dilute pollutants.
Johnson concludes that contending with EPA's 1998 limits will be painless compared to dealing with the huge NOx reductions initially scheduled for 2004. Even then, however, EPA will soften the blow.
Beware of 2004 (maybe)
Echoing Johnson's 1998 forecast is Al Schaeffer, vice president of
environmental affairs for the American Trucking Associations, Alexandra,
Va., and a confidant of top-level EPA staffers.
"As Blaine said, there won't be any EGR in 1998, and only a few, medium-duty engines will use aftertreatment. But lower hp ratings definitely will be curtailed," Schaeffer says.
Despite smooth sailing through 1998, fleetmen should keep a wary eye on the road ahead, Schaeffer warns. "In model year 2004, it's possible that EGR could descend upon us. On the other hand, there won't be widespread use of NOx aftertreatment, or changes to diesel fuel. Most engineering efforts will remain focused on improving engine-out compliance," he says.
Don't get the impression that the petroleum industry doesn't care about Mother Nature, Schaeffer cautions. Admittedly, EMA's data suggests that better diesel fuel could reduce emissions notably. On the other hand, Schaeffer points to extensive research, conducted by SwRI, indicating that "changes in fuel composition have a relatively small effect on exhaust emissions" from today's diesels
2004: the Big Deal
What's the big deal about 2004 compliance? EPA explains that Uncle
Sam, the California Air Resources Board and diesel makers have signed a
cooperative agreement to slash diesel NOx to 2.0 g/bhp-hr by 2004.
That's a 50% reduction, compared with 1998's limit of 4.0 g/bhp-hr. Yet SwRI notes that NOx levels of 2.5 g/bhp-hr already have been demonstrated, "with minimal impact on fuel consumption and engine durability."
Sounds encouraging, right? On the other hand, it's relatively easy for a test engine to clean up its act. The real-world challenge is to exceed minimum requirements enough to compensate for production variables and in-service degradation of stack emissions.
Signatories to the cooperative industry agreement include: Caterpillar, Cummins, Detroit Diesel, Ford, General Motors, Hino, Isuzu, Mack Trucks, Mitsubishi, Navistar International, and Volvo. Conspicuous by their absence are any representatives of the fuel industry.
In a few years, EPA will review the agreement and "if needed, may make limited adjustments to the level and timing of the standards." The potential for adjustment is clear, since signatories to the agreement "recognize that fuel improvements may be essential in reaching low NOx levels." If essential improvements to fuel quality aren't determined to be cost-effective, however, EPA proposes that NOx standards for 2004 be relaxed slightly.
The cooperative agreement also pushes for long-term research to exceed 2004's emission reductions. And a big chunk of that cooperative research will be coordinated by SwRI, which hopes to reduce NOx to 1.0 g/bhp-hr.
Phase II of SwRI's Clean Heavy-Duty Diesel Engine project already is focused on: the effects of higher injection pressure, smaller nozzle holes and injection rate/timing on injector life; passive particulate traps; reformulated diesel fuel, including water/fuel emulsions; the negative effects of EGR.
Participants in SwRI's Phase II research (which is independent of the industry's cooperative agreement) include: several component suppliers; Cummins; DAF; Detroit Diesel; Hino; Iveco; John Deere; Mack Trucks; and Volvo Truck Corporation.
Expanding credit lines
Will failure to comply with 2004's limits force a lot of diesel families
from the marketplace? Nope. Relatively few engines are likely to disappear,
because EPA proposes to ease compliance, for example, by killing all limitations
on credit life.
Other changes proposed by EPA would be far less transparent to fleetmen. For example, EPA will push for development of on-board diagnostic systems to monitor the health of emissions- related items.
Beginning in 2004, EPA also wants to require that all heavy-duty
diesels (not just urban bus engines) be rebuilt with components providing
the same emission-control capability as a new engine.
D. Engine Oil - Sorry, no CH-4 for 1998
Once upon a time, fleetmen anticipated that a new breed of oil for 1998 diesels - to be labeled American Petroleum Institute (API) CH-4 - would arrive in time to handle potential problems ranging from more crankcase soot to increased ring/liner wear and piston deposits. The current API spec for four-cycle diesels using low-sulfur fuel is CG-4.
Sadly, API CH-4 still languishes as proposed category PC-7 and may not mature into a full-blown service category by early 1998. At least, that's the unsettling forecast of Ralph Timmerman, director of product formulation and quality assurance for Dryden Oil Co., a Baltimore-based provider of heavy-duty vehicle lubricants that's owned by Castrol North America.
Timmerman is one of 15 persons in an advisory committee jointly established by API and EMA. Basically, he supports the previously-noted forecasts of Johnson and Schaeffer. That is, don't expect any earth-shaking design changes, such as EGR, in 1998. And don't look for cleaner diesel fuel, even in 2004.
He expects that, some time before 2004, API and EMA will return to the drawing board to propose a PC-8 oil for contending with EGR's potential to "play havoc with ring and liner wear." A new oil also is needed to protect against 2004's higher compression ratios and injection pressures, which will place "tremendous loads" on valve trains, bearings and crankshafts.
In addition, Timmerman forecasts, a piston's top ring will sneak even closer to its crown, to eliminate "dead space" where unburned fuel can hide. Such pistons will be tougher to lubricate, due to higher operating temperature. They'll also be more prone to form ring-pack deposits. So an oil's general durability, and resistance to oxidation, will become an increasingly critical concern.
Conclusion - No aspirin needed
In the final analysis, there's no reason to question the future of heavy-duty diesels and conventional fuel.
In fact, University of Wisconsin researchers Pierpoint, Montgomery and
Reitz cite long-range predictions that the environmentally-friendly "engine
of the future" will be (begin the drum roll, please) a turbocharged diesel
with electronically-controlled injection, electronically-controlled EGR
and catalytic aftertreatment.