Click to enlarge.

These technologies include, but are not limited to, advanced aftertreatment and waste heat recovery; lean-burn plus lean-NO_x emissions traps; integration of zero-emission miles technologies; further refinements in reducing friction and parasitic energy losses; and widespread utilization of renewable and natural gas and hydrogen blends.

Background. California policy makers face challenges in devising a pathway that can simultaneously help the state achieve NO_x and GHG reduction targets. Compared to the 2010 “Business as Usual” scenario—which includes all adopted emission control measures for the South Coast—NO_x levels must be reduced by 65% and by 75% to meet the 2023 and 2032 ozone standards, respectively. An 80% reduction of GHG emissions is targeted for 2050, relative to 1990 levels.

California’s two worst non-attainment areas need rapid, significant NOx reductions sooner. Click to enlarge.		California’s Climate Protection Strategies do not help meet NAAQS Standards. Click to enlarge.

According to the GNA report, heavy-duty diesel trucks are the largest contributors to the NO_x inventories of the South Coast and San Joaquin Valley ozone non-attainment areas. They are also major producers of toxic air contaminants and GHGs.

To meet federal deadlines for attainment of ozone and fine particulate matter (PM_2.5) standards, these regions must expeditiously phase in heavy-duty vehicles that emit at, or below, the equivalent of “zero-emission” battery-electric vehicles when accounting for pollution from base load electricity generation. This constitutes a NO_x reduction of approximately 90 percent below the current federal heavy-duty engine standard of 0.2 grams per brake horsepower-hour (g/bhp-hr).

Since the advent of the first Low-Emission Vehicle regulations in 1990 and the passage of California Assembly Bill 32 (AB 32) in 2006, the California Air Resources Board (ARB) has attempted to address the state’s air quality and climate goals by requiring development of motor vehicles that do not directly emit NO_x or other criteria pollutants. Policy makers have emphasized policies that compel the manufacture and/or purchase of vehicles that emit zero-emissions at the tailpipe. These “technology forcing” requirements, which direct manufacturers to phase-in sales of battery-electric vehicles or large transit fleets to buy zero-emission buses, have not resulted in the commercialization of zero-tailpipe emission vehicles as quickly as air quality regulators hoped or planned for. Zero emission vehicle mandates have, however, spurred tremendous innovation by the manufacturers of internal combustion engines, emission control equipment, and advanced vehicle drive trains. The resulting technological transformations have dramatically increased the menu of options available to policy makers to meet the state’s air quality and GHG reduction goals.

… The use of heavy-duty engines powered by natural gas offers a unique, viable and complementary “pathway” to help meet California’s aggressive reduction goals for NO_x and GHG emissions.

—“Pathways to Near-Zero-Emission Natural Gas Heavy-Duty Vehicles”

Technologies. With steady application of known and proven engine and control technologies, the GNS report notes, it is widely believed by engine manufacturers and other researchers that heavy-duty natural gas engines can meet a NO_x emission level of 0.05 g/bhp-hr—75% below today’s standard. This, industry observers believe, can be achieved in the near term, and certainly prior to the 2023 deadline to achieve the 80 ppb ozone NAAQS.

In the longer term, the GNA report suggests, a 90% reduction in NO_x emissions from 2010 standards is achievable, which will enable heavy-duty NGVs to emit no more NO_x from the tailpipe than would be emitted by power plants providing electricity to equivalent heavy-duty BEVs.

This presents a very important point: today’s very low-emitting natural gas HDVs are more than just “bridge technologies” to the future of California’s near-zero-emission heavy-duty transportation sector. These technologies can and should be a foundation of that future. Thousands of heavy-duty NGVs are on California’s roadways logging millions of miles with very low emissions, even as the technology steadily evolves toward power plant emissions-equivalency. If the near zero technologies outlined in this paper are developed in the time frame described herein, they will dramatically enhance the state’s ability to meet air quality standards and climate protection objectives. Coupled with other strategies for light duty vehicles, area sources, and the stationary sector, increased use of natural gas in the heavy-duty sector is a fast, cost- effective, and deployable fuel and technology combination.

—“Pathways to Near-Zero-Emission Natural Gas Heavy-Duty Vehicles”

There are five overarching technology pathways for heavy-duty NGVs to meet progressively lower NO_x and GHG emissions, the report says:

1. Advanced Engines. Starting with near term improvements in more finely controlled high-pressure fuel injection and other technological improvements including variable-spray nozzles and piezo-electric nozzles, the report moves on to note the potential for new engine types and new or enhanced combustion cycles.

   Examples of these advanced combustion cycles include low-temperature combustion (LTC), homogeneous charge compression ignition (HCCI), and premix charge compression ignition (PCCI). According to a recent draft final report prepared for the California Energy Commission cited by GNA, natural gas-fueled technologies that can achieve reduced NO_x levels of 0.02g/bhp-hr include cam-less engines and HCCI.

   Improved accessories, sensors and controls will also play an important role. To reduce power demand, some accessories can be converted to electric power. Some accessories can also be better regulated so that their operation is restricted except when needed. Another way this can reduce power consumption is that accessories can be run at speeds independent of engine speed. Enhanced sensors and controls enable the utilization of electric-powered accessories in a way that can improve fuel economy.

   A 2010 National Academy of Science (NAS) study cited by GNA found that a 3-5% fuel consumption reduction is possible through the integration of improved accessories, sensors, and controls.

   Waste heat recovery technology also provides an opportunity. All totaled, engine heat accounts for 26% of the fuel consumed, and exhaust heat accounts for another 24%. Technologies and techniques exist or are emerging that can recapture this wasted heat and help reduce vehicle emissions as well as fuel consumption.

2. Advanced After Treatment. There are three primary kinds of exhaust after treatment relevant to the report: Selective catalytic reduction (SCR); Lean NO_x absorber catalyst; and Three-way catalyst (sometimes referred to as “non-selective catalytic reduction” or NSCR).

3. Hybridization. Numerous heavy-duty engine and vehicle manufacturers are now working on hybrid vehicle platforms that integrate in heavy-duty natural gas engines. These include US Hybrid’s work on a Class 8 drayage truck that features a plug-in hybrid drive train with a CNG-fueled Cummins Westport ISL G engine; Capstone Turbine Corporation working on a series of hybrid drive systems that use microturbines fueled by natural gas to achieve very low-NO_x and low-GHG emissions; and other companies such as ICR Turbine Engine Corporation working on similar concepts. Transpower is working with Siemens Corporation to build and to demonstrate hybrid drayage trucks that will be zero-emission when driven along a catenary electric system, and near-zero-emission off the catenary through the utilization of a very clean heavy-duty natural gas engine such as the Cummins-Westport ISL-G).

4. Vehicle Integration. Several strategies exist to reduce the amount of energy required by a vehicle to perform a given task. In the on-road heavy-duty sector, examples of these technologies include improved vehicle aerodynamics, rolling resistance reductions, and vehicle weight reductions.

5. Fuels, Storage, and Infrastructure. In the long term, the report suggests, two of the best strategies to obtain the final increments of GHG reduction in NGVs will be increasing the use of methane that results from biological sources, such as digester or landfill gas, as well as increasing the hydrogen content of natural gas.

Example pathway to zero-NOx equivalency for the drayage trucking sector. Click to enlarge.		Example pathway to zero-NOx equivalency for the long-haul trucking sector. Click to enlarge.

Policy implications. The report also calls on California policy makers to enact policies and programs to encourage the development and commercialization of these ultra-low-emission motor vehicle technologies, which will accelerate replacement of the existing diesel-fueled heavy-duty vehicle fleet with advanced engine technologies.

Presently, diesel-fueled heavy-duty on- and off-road vehicles and equipment are the largest sources of smog-forming gases and airborne toxic soot. California’s air quality regulators recognize that current plans to meet air quality deadlines will fall short of Federally-mandated deadlines and that more must be done for the state to achieve these smog-reduction and long-range climate protection goals.

In the heavy-duty vehicle sector, which has lagged behind the light-duty sector in both low-emissions regulations and technological innovation to reduce emissions, the best approach for achieving very aggressive emissions-reduction goals will involve greater flexibility for manufacturers to achieve near zero emissions.

Heavy-duty natural gas engines are well along the path to achieve a 90 percent NO_x reduction from the existing heavy-duty engine NO_x standard, while also becoming increasingly fuel efficient to reduce GHG emissions. Widespread deployment of these near-zero and power plant emission-equivalent heavy-duty natural gas vehicles (NGVs) are needed to meet tough air quality and climate protection goals. To realize these benefits, supportive public policies and public-private partnerships are needed that continue to encourage the development, demonstration, and deployment of critical natural gas-fueled heavy-duty vehicle technologies.

Furthermore, research indicates that heavy-duty NG engines are on a trajectory to be certified at a NO_x level of 0.02 g/bhp-hr, an emissions level so low that it equates to the power plant emissions that would result from charging an electric vehicle.

California’s policy makers can encourage this development with three actions: 1) Implement policies that fund the research, development, and demonstration of these crucial “pathway” technologies; 2) Support modifications to the state’s already robust air quality incentive programs that promote the commercialization of near-zero and power plant emissions-equivalent heavy-duty vehicles; and 3) Develop new and innovative requirements for the use of “pathway” technologies throughout the state. Coupled with continued promotion of zero-emission technology, particularly in those sectors of the vehicle population in which the most progress is being made, an air quality plan that encourages the rapid development and massive deployment of near-zero and power plant emissions-equivalent NGVs can propel California down the path to a cleaner, more climate-friendly future.

—“Pathways to Near-Zero-Emission Natural Gas Heavy-Duty Vehicles”

The GNA report further suggests that the most technically sound and cost-effective approach for HDVs is for California to establish a new “near-zero-emission” and/or a “power plant equivalent” emission standard. Such a standard would be the functional equivalent to ARB’s current ZEV standard for an HDV (no direct vehicle emissions), but would take into account the emission of criteria pollutants associated with the generation of electricity from a new generation, natural gas-fueled power plant necessary to recharge a comparable heavy-duty BEV.

The proposed emission standard should also take into account full fuel-cycle GHG emissions of various HDV fuels and technologies. Such a new standard would enable manufacturers to pursue a greater menu of fuel and technology pathways, e.g., natural gas or hydrogen internal combustion engines, as long as they achieve ZEV equivalency. It would provide greater long-term market choices for fleet owners. Most importantly, it would help state and local air quality regulators to accelerate progress towards meeting air quality goals for ozone NAAQS attainment and mitigation of climate change.

In order to meet stringent air quality targets, regulators can expand the menu of options available to the market. Heavy-duty natural gas engines are on a trajectory to achieve ultra-low-emission levels that will provide air quality planners with a crucial tool in their efforts to restore clean air to California sooner. By combining advanced, near zero emission natural gas technologies in the heavy-duty sector with innovations already being deployed in the light-duty sector (electric drive, plug-in hybrids, fuel cells, and near-zero emission natural gas vehicles), a strategy becomes available to bring California more expeditiously towards achieving ambient air quality standards.

—Cliff Gladstein, President of GNA and one of the authors of the report

Resources

• Pathways to Near-Zero-Emission Natural Gas Heavy-Duty Vehicles