EPA Mandates Tighter Emissions Standards in 2007
Call and reponse. It’s an ancient form of worship. At the Environmental Protection Agency (EPA), where they worship clean air, it’s a modern technique for compelling manufacturers to create cleaner-burning engines. The EPA calls for ever-more restrictive emissions standards, and manufacturers respond with the technology required to meet those standards. The standards that will be imposed starting in 2007 continue this process. We’ll look at those standards and the technology they will likely require, but first, some history.
Emissions Regulations Began with 1970 Clean Air Act
EPA began regulating on-road diesel emissions as part of the Clean Air Act (CAA) in 1970. The 13-mode, steady-state test procedure initiated then remained in use through the 1983 model-year. The exhaust constituents controlled in those early years are still in the spotlight: hydrocarbons (HC), oxides of nitrogen (NOx), and carbon monoxide (CO). There was, and still is, interest in smoke as measured by opacity under acceleration, lugging, and peak conditions. A particulate matter (PM) standard was added in 1988. Output of emissions is measured in grams per brake horsepower hour (g/bhp-hr).
The reduction in emissions has been dramatic. NOx, for example, was first limited to 10.7 g/bhp-hr. The 2007 emissions standards will cut NOx to 0.20 g/bhp-hr, a reduction of more than 98 percent. PM will undergo a similar drop, from 0.6 g/bhp-hr in 1988 to 0.01 in 2007.
The standards apply to heavy-duty vehicles, which are further divided into three categories by gross vehicle weight rating (GVWR): light heavy-duty, greater than 8,500 lbs. but less than 19,500 lbs. GVWR; medium heavy-duty, 19,500 to 33,000 lbs. GVWR; and heavy heavy-duty, greater than 33,000 lbs. GVWR. Federal Tier 2 standards for light-duty vehicles, phased in starting in 2004, classify vehicles of up to 10,000 lbs. used for personal transportation as medium-duty passenger vehicles. These MDPVs, primarily SUVs and full-size vans, are subject to the emissions standards for light-duty vehicles.
Engine Certification Process Complex and Comprehensive
Although complete vehicles of less than 14,000 lbs. can be chassis-certified as an option, current regulations require certification of the engines themselves. This certification requires testing on an engine dynamometer. The main test is the Transient FTP (Federal Test Procedure), which consists of four distinct phases meant to simulate real-world operating conditions. The procedure is complex and comprehensive, with cold-start and warm-start segments; idling, acceleration and deceleration phases; and a variety of engine speeds. Load factors vary throughout the test and average 20 to 25 percent of maximum engine horsepower.
Beginning in 1998, two additional tests were developed to further refine the testing procedure: the Supplemental Emissions Test (SET) and the Not-to-Exceed (NTE) limits. These tests were introduced for most of the signers of the 1998 Consent Decree between EPA, the Department of Justice (DOJ), and diesel engine manufacturers Caterpillar, Cummins, Detroit Diesel, Mack Trucks, Navistar, and Volvo. The decree required the pull-ahead of 2004 emissions standards of 2.5 g/bhp-hr of total NOx and non-methane hydrocarbons (NMHCs) by 15 months to October 2002.
The genesis of the consent decree was a ruling that engine manufacturers used engine control software that maximized fuel economy but also increased NOx. The EPA considered this an illegal "emission defeat device." The DOJ agreed. The pull-ahead of 2004 standards was part of the settlement. In addition, manufacturers received civil penalties and were required to allocate funds for pollution research. They were required to upgrade existing engines to meet NOx standards. The SET and NTE requirements were introduced, as well, although Navistar gained exemption from some parts of the regulations.
EPA Continues to Refine Testing Procedures
Testing procedures continue to be refined. EPA has grouped all of its engine dynamometer and field testing procedures under one title, "Part 1065: Test Procedures." Additionally, EPA is proposing a manufacturer-run, in-use emissions testing program for heavy-duty diesel trucks. Using portable on-board emissions measuring systems, manufacturers will monitor vehicle performance under real-world operating conditions. This program is the result of a cooperative effort between EPA and the Engine Manufacturers’ Association (EMA). The EMA and some manufacturers had challenged the legality and the technical feasibility of some of the NTE limits, and this program was developed in response to those challenges.
Emissions Control Technology Grows More Sophisticated
The availability of on-board emissions monitoring equipment is just the latest stride in a long march of technology. In the beginning, the technological advances were simple and focused mainly on improving combustion characteristics. One relatively simple fix was to move the top piston ring up higher, nearer the piston crown. This reduced crevice volume, minimizing the space where fuel could hide during the combustion cycle. Unburned fuel trapped in this crevice was released during the exhaust cycle and really spiked emissions output. To further refine the combustion process, manufacturers tweaked the shape and design of piston crowns and cylinder heads.
As emissions restrictions got tighter, emissions control technology got more sophisticated. Some of the most noteworthy changes took place with fuel injection. Injection pressures rose dramatically to ensure that fuel was better atomized and better distributed during the injection phase. Injection timing was altered, too, to control emissions and improve combustion efficiency. And rather than delivering a single, fat squirt of fuel, injectors were programmed to provide smaller bursts before or after the main fuel delivery pulse ("pilot" and "post" injections).
Turbochargers found their way onto more engines, and boost pressures were increased. Manufacturers used either variable geometry turbos or two turbochargers in series. This provided the best performance characteristics of both large and small turbos: the large volume of air required at higher RPMs with quick turbo response at lower engine speeds.
While mechanical innovations played prominent roles in the manufacturers’ quest to meet emissions standards, no area of development saw greater growth than electronics. Although the birthplace and date of engine electronics is open for debate, it’s clear that systems intended for production were in development by the late 1980s.
Technology Produces Benefits, Challenges, and Higher Costs
All these changes brought challenges along with their benefits. Raising the top ring, increasing injection pressures, and jacking up turbo boost resulted in higher heat rejection. Bigger and more efficient cooling systems and air-to-air charge coolers solved the problem, but increased vehicle complexity and maintenance costs. Oil companies poured hours and dollars into the development of lubricants that could meet the demands of these new high temperature engines. Fleet managers were encouraged to perform regular oil sampling to confirm that their PM schedules provided adequate engine protection. In addition, acquisition cost factors often amounted to several thousand dollars per vehicle.
Electronic engine controls were the bright spot in all this. Yes, they added cost and complexity. But they were robust and came with boxfuls of benefits. For one, they greatly simplified diagnostics. The insider’s story is that in the old days, mechanics would spend 80 percent of their time diagnosing a problem and 20 percent fixing it. Armed with a laptop computer, today’s technician has reversed that ratio, and the total time spent servicing an ailing engine has dropped significantly.
Electronics also enabled the development of interfaces with other components. Through the controller area network (CAN) bus, an engine can talk to an electronic transmission or adaptive cruise control to maximize performance and efficiency. And electronics provide oversight of employee conduct. For example, by reviewing logged engine data, a fleet manager can tell if a driver is using progressive shifting. Out-of-range error codes are red flags of abuse.
2007 Standards May Require After-Treatment Options
As mentioned earlier, the 2007 emissions standards will bring about a 98 percent reduction in both PM and NOx as compared to the 1998 standards. The emissions compliance techniques of recent history will not be adequate to meet these exceedingly low levels of emissions, so OEMs are being forced to consider other options. Several have already embraced some form of after-treatment. Some, such as Caterpillar, will be using after-treatment for the first time. (Cat will add a form of exhaust gas recirculation (EGR) to its engines that already have ACERT technology.)
While EGR comes with several stains on its shirt - higher heat rejection, increased soot in engine oil - it has been effective at meeting current emissions standards. But EGR by itself will not be up to the challenge of the 2007 standards. That will require more advanced after-treatment.
There are really two approaches to after-treatment. One is to control NOx with an adsorber or trap, or by selective catalytic reduction (SCR). The other is to control PM with a trap. OEMs must make a choice because control strategies for these two constituents often work in opposition. Lower the NOx, you boost the PM, and vice versa.
There is no clearly superior technique. A plague affecting traps is the accumulation of excessive particles or gases. During idle and at other times when exhaust temperatures are low, the traps aren’t hot enough to light off the gunk they collect. The reduction in exhaust flow affects engine operation. In extreme cases, the accumulation can become so severe that the engine stops running. Even normal operating conditions may not always produce exhaust gas temperatures sufficient to regenerate the after-treatment devices.
New Regulations Include Diesel Fuel Sulfur Content Reduction
Part of the 2007 standards will be a reduction in diesel fuel sulfur content from a maximum of 500 parts per million (ppm) to a maximum of 15 ppm. Since sulfur is a major component of soot, and since soot contributes heavily to the issue of plugged traps, the sulfur reduction should solve some of those plugging problems.
Those who remember the last reduction in sulfur content to 500 ppm may also recall some fuel system problems associated with that change. The severity and scope of the problem was limited to fuel systems with seals of a particular material. Those seals are no longer in use, and this reduction is not expected to usher in any similar troubles.
Adsorbers work by storing NOx during periods of lean operation and releasing it back into the exhaust when conditions are rich, at which time it is catalytically reduced. Adsorbers must be periodically regenerated. Some systems use diesel fuel as a regenerating agent, injecting fuel into the exhaust stream. When the fuel hits the adsorber, it ignites and raises the temperature to that required for regeneration.
SCRs require a urea-based agent for operation. The urea is carried on board the vehicle in a tank. SCRs are effective at reducing NOx, but they have their own problems. One is that there currently is no infrastructure for wide distribution of urea to replenish vehicle tanks. The other difficulty is a phenomenon known as “ammonia slip,” in which a burst of urea is released in the exhaust, leaving the pungent odor of a giant cat box in a vehicle’s slipstream.
Research Costs May Impact Initial Cost of Compliance
The financial impact on buyers won’t be known until OEMs settle on a means of meeting the 2007 standards. It’s possible that the first family of ‘07-compliant engines will have a significant upcharge for the additional equipment as Corning, Johnson Matthey, and others seek to amortize the years of development they’ve put into emissions control technology. But that cost is likely to come down as economies of scale kick in. The aftermarket components should not require servicing in normal use, but they will increase the cost of replacing exhaust systems.
Fuel consumption may go up 2 to 5 percent. Service intervals may have to be adjusted, although PM schedules implemented for EGR engines will probably work for the 2007 engines, as well.
Fleet managers whose vehicles are nearing the end of the line may opt to accelerate their replacement schedule. Others may find it more cost-effective to repower or retrofit their current vehicles, depending on the market in which they operate.
While some of the emissions control strategies leading up to 2007 came with abundant benefits for fleet owners, such as electronic engine diagnostics, this next round will not have a comparable silver lining. Fleet owners will just have to accept the burden of meeting the 2007 standards as part of the cost of doing business. EPA has called, and this is how OEMs have responded.