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The Emissions and Energy Outlook for Medium- and Heavy-Duty Vehicles


Medium- and heavy-duty vehicles represent the second-largest consumer of energy in the US transportation sector, behind light-duty vehicles but ahead of every other transportation mode, according to the Energy Information Administration.

By 2030, the transportation sector’s total annual energy consumption will increase 46.5% to an estimated 39,729.9 trillion BTU (40 quads), equivalent to 7.1 billion barrels of crude oil per year, according to EIA’s long-term forecast in the Annual Energy Outlook 2006. (Earlier post.)

During that time, the share of total energy consumption of medium- and heavy-duty trucks will increase by about two percentage points—from about 17% to 19%. In contrast, the share represented by light duty vehicles will decrease by a percentage point from about 59% to 58%.

This makes trucks of particular interest for energy and emissions controls.

For the past 30 years, research and development in heavy-duty vehicles focused primarily on emissions reductions. Successful implementation of the impending 2007/2010 emissions regulations will result in extremely clean heavy-duty diesel systems, with reductions in certain emissions of about 100-fold from the 1960s, when concern about tailpipe pollutants first started to be taken seriously.

The outlook for these systems was the topic of a two-day conference organized by WestStart, the US Army National Automotive Center and the Federal Transit Agency. The general sense of the 6th Annual Clean Heavy-Duty Vehicle Conference was guardedly optimistic.

Engine makers are rolling out their 2007 diesel engine solutions, and are beginning to lock down their design and development plans for their 2010 engines. There was even a sense among a few of the speakers that the industry might be “done” with the emissions issue, and could focus on the two other strategic areas that were emphasized throughout the conference as the necessary next campaign: energy consumption and CO2 emissions.

We are just at the starting point with respect to energy consumption and CO2 emissions...I’m optimistic.

—Michael Walsh, international transportation consultant

Not surprisingly, the energy consumption issue is tied, longer term, to maintaining the emissions reductions currently being put in place. Under a business-as-usual scenario, energy consumption continues to grow rapidly, with the sheer number of vehicle miles travelled overtakes the reductions achieved through the 2007/2010 technologies with aggregate increases in NOx and PM.

As a result, numerous speakers, in presentation after presentation peppered with concern over oil supply (and peaking), fuel prices and climate change, emphasized the need for more efficient heavy-duty vehicle systems, including diesel engines with optimized combustion, hybrids of various forms (hydraulic hybrids are gaining significant momentum) and alternative fuels (gaseous and synthetic).

But while the long view is important, there are still numerous issues to be resolved with actually delivering on the 2010 solutions, with the clock ticking down. These issues range from the cost of the new systems—some estimates pegged the cost of a 2010 diesel engine at twice that of a 2004 diesel—and the concomitant need for other technology approaches that might not be so costly, to driver training, and even to reconfiguring pipeline delivery to prevent sulfur contamination of Ultra Low-Sulfur Diesel.

The industry may be “done” with emissions in theory, but not in the details of operational implementation or deployment.

Background: 2007/2010. In 2001, the EPA finalized a set of regulations for future diesel fuel and heavy duty diesel on-road exhaust emissions. The fuel regulation specified the transition to 15ppm (at the rack) Ultra Low-Sulfur Diesel that is currently underway and will be in place by the end of the year.

Emissions standards were set for 2004 at 2.5g/bhp-hr NOx+NMHC and 0.10g/bhp-hr PM. The 2010 target is 0.2g/bhp-hr for NOx and 0.01g/bhp-hr PM—an order of magnitude reduction for both.

The PM emission standard takes full effect in the 2007 heavy-duty engine model year. The NOx and 0.14g/bhp-hr NMHC standards will be phased in for diesel engines between 2007 and 2010 based on percent-of-sales: 50% from 2007 to 2009 and 100% in 2010.

Most engine manufacturers will likely use the NOx phase-in provisions along with averaging to certify engines to a NOx value roughly halfway between 2.5g/bhp-hr NOx+NMHC and the 0.2g/bhp-hr NOx levels through 2009—i.e., approximately 1.2g/bhp-hr NOx.

The basic 2007/2010 approach. The basic approach to meeting the 2007 emissions standards in the US is to try to reduce engine-out emissions with a number of approaches, including higher-pressure (2,000 bar) injection and improved boosting; to use Exhaust Gas Recirculation (EGR) for NOx reduction; to add a catalyzed diesel particulate filter with active regeneration to the system for the PM; all coupled with the use of ULSD.

The ULSD is critical to keeping the catalyzed diesel particulate filter’s operations—sulfur in the fuel can poison the catalyst. Furthermore, given the use of EGR, sulfur in the fuel can results in recirculated sulfuric acid in the exhaust, to the detriment of the engine internals.

The 2010 approach will see additional efforts on the combustion side, likely through the advent of some partial HCCI regimes; higher injection pressures (2,500 bar); more improvements on boosting; the use of variable valve actuation; and the addition of urea SCR for NOx reduction.

With the aftertreatment that we have, the user has to become more involved when he specifies our truck...Aftertreatment requires a systems approach. It is not an add-on. It has to be considered from the beginning.

—Alan Karkkainen, Director, Future Technologies, Engine Engineering, International Truck and Engine

Alternatives. While diesel is clearly the default approach for many—especially for the long-haul highway applications—other options exist. Compressed natural gas, or hydrogen-compressed natural gas blends (HCNG) delivers an emissions—and perhaps price—benefit. Clean-burning synthetics such as GTL are another option, although given limitations on production, that would likely be in the form of blends.

Other engine approaches are possible, however. Dr. Nigel Gale from Southwest Research Institute gave a presentation on HEDGE—High Efficiency Dilute Gasoline Engine—a consortium-based approach to enabling gasoline engines to meet the performance, durability, and emissions requirements of heavy duty vehicles. (Earlier post.)

The HEDGE consortium, led by SwRI, is exploring the use of high-energy ignition coupled with more sophisticated injection and control to meet 2010 emissions requirements while meeting the power needs of the heavy-duty market.

Should it prove out, one of the benefits would be the cost. While SwRI sees the cost of diesel engines rising from $33/kW for a 2002 engine to $70/kW for a 2010 engine, the cost of a 2010 HEDGE engine would be around $37 or $38/kW. (More on HEDGE in a subsequent post.)

Energy Consumption. The average fuel consumption for heavy-duty vehicles in 2005 was approximately 5.6 mpg of gasoline equivalent for all fuels, according to the EIA. The agency sees a very slow improvement in that figure to 6.43 mpgge by 2030.

By contrast, the DOE’s More Electric Truck research program set a fuel economy target for tractor-trailer combinations of 10 mpg. The approach the DOE is encouraging is to focus on aerodynamic resistance, combustion efficiencies, reduction of parasitic loss and the reduction of idling though electrification of systems and the use of fuel-cell APUs, and thermoelectric waste heat recovery.

Improvements in fuel economy are of immediate interest to any business. The countervailing force to that urge for improvement, however, is concern over the capital cost of new equipment and an aversion to the embrace of what might prove to be risky technologies.

The market works very very well for heavy-duty forces are aligned for improving fuel economy over time.

—Drew Kodjak, Executive Director International Council on Clean Transportation

Hybrids. Hybrids are emerging as an important factor for certain commercial—and military—applications. Just a few days before the conference, UPS announced that it was ordering 50 hybrid package delivery vans from International.

These hybrids are derived from work done by Eaton/International and Ricardo under the DOE’s Advanced Heavy Hybrid Propulsion System (AH2PS), and use a similar hybrid-electric powertrain to the one being deployed in the Hybrid Utility Truck also under development by International. (Earlier post.)

While businesses might in theory be more disposed in higher percentages to a more immediate adoption of hybrid technology than consumers (the fuel cost factor), there are a number of barriers to hybrid commercialization, according to a panel of speakers on the topic at the conference.

The barriers include:

  • The high cost of components;
  • The need for approved testing standards for fuel economy and emissions;
  • Insufficient in-use data;
  • Business case still developing (the price of fuel is not predictable);
  • Rate of acceptance of new technology by customers versus the cost to manufacturers to enter a new market;
  • Component supplier infrastructure and capacity; and
  • Technician training

Although transit buses are a visible application for hybrids, and although the speakers from Seattle and Orange County Transit who spoke on their experiences with the hybrids were “pleased as punch,” the transit market—with 2,000 to 4,000 total new buses per year— is too small to make a significant impact on commercialization. Commercial hybrids need to rely on trucking for a substantive market.

Hydraulic hybrids are gaining significant interest for commercial application—a surprise to those who might have dismissed it as a curiosity a few years ago.

We are extremely pleased with the hydraulic technology. We believe there will be significant demand for this technology...we believe we will have hydraulic hybrids in the low 1,000s by 2010.

—Merrilyn Zaw-Mon, Director of Compliance and Innovative Strategies Division, US EPA

Eaton is targeting 20-30 vehicles this year with its Hybrid Launch Assist technology (earlier post). The company is committed to commercializing its HLA hybrids with 18–24 months. The “end game” for hydraulic hybrids, however, is a series-hybrid configuration.

In that configuration—which is what the EPA is working on in conjunction with its partners for UPS (earlier post), the engine powers a hydraulic pump rather than a motor.

Margo Oge, Director of EPA’s Office of Transportation and Air Quality, believes that the series hybrid will deliver a 70% reduction in fuel consumption in certain urban applications.

Separately, Dana and Permo-Drive are working on a hydraulic hybrid application for the military. (Earlier post.)

In the commercial market, everything is application-specific, requiring different technologies. There is no one solution that works in a commercial application because you have these application-specific requirements.

—Ed Greif, VP Intelligent Hydraulic Drive Products, Dana



Even though such transportation accounts for approximately 40% of U.S. fuel consumption, this is a very important topic because it intrinsically is linked to our national economy.

Joseph Willemssen

That was very informative. People should point to it when they have questions about commercial transportation and/or diesel. Time and again I hear biodiesel advocates wondering why there aren't more diesels on the light vehicle market right now, and this is one of the clearer explanations I've seen about the new diesel rules being phased in.

This site is really a cut above. Kudos.


Do you know by any chance why auto companies choose electric hybrids over hydraulic hybrids??
The only explanation that I can think of is that its easier to connect fuel cell to electric hybrid rather then hydraulic hybrid


Hydraulics have greater mechanical efficiency but much lower energy density; they are good for low-speed start-stop operation, like buses and garbage trucks.  They are not so good for general use, and cannot store enough energy for engine-off cruising.


Poet, how do they compare in terms of reliablility? Would a hydraulic system also be more likely to have problems due to more moving parts and mechanical action?


Tripp, hydraulics are old technology. As a mode of transmitting power, they are and were used in fork lifts, heavy off-road equipment. One of the reasons that they were used over other methods is because of high reliability. Case point is good old Citroen DS with its hydropneumatic system.
I red somewhere that those systems were unbreakable because all the pipe connections were made without any seals. So if done right, hydraulic hybrid might run for decades before breaking.

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