5

Natural Gas Vehicles: Impacts and Regulatory Framework

Natural gas (NG) accounts for about 25 percent of all energy use in the United States yet only 0.1 percent is used in transportation, equivalent to about 0.5 billion gallons per year of petroleum fuel. However, in the short time since the release of the report Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles (NRC, 2010), NG has emerged as a viable option for commercial vehicles, driven by the rapid drop in its cost as a result of new technology. Yet, uncertainties exist relative to the extent and quality of reserves, safety and community acceptance, fuel cost and continued availability, sustainability, etc. This chapter starts with a brief review of why NG has emerged as a potentially significant fuel for medium- and heavy-duty vehicles (MHDVs). It then discusses the technology and infrastructure that will be needed for NG-fueled trucks, which can operate on either compressed natural gas (CNG) or liquefied natural gas (LNG). It describes the regulatory framework for greenhouse gas (GHG) emissions (primarily carbon dioxide, or CO2) and fuel economy standards. Finally it presents the key findings and recommendations relevant to NG-fueled trucks.

SUMMARY OF SUPPLY AND DEMAND TRENDS FOR NATURAL GAS FUEL

To better understand what this potential means for the United States and its energy future, the National Research Council’s (NRC’s) Board on Energy and Environmental Systems (BEES) convened a meeting on September 11, 2012, assembling technical experts from private industry as well as representatives of government and academia. The primary goals were to assess the current state of NG development and to identify key research and technological gaps. This effort was augmented by presentations to a meeting of the committee on July 31 and August 1, 2013. This discussion is largely based on those forums.

NG production, driven by shale gas (Figure 5-1), began accelerating in 2005 and is expected to continue to grow (Figure 5-2). There are three key enabling technologies for the current boom: horizontal drilling, which was largely proven in the 1990s; geosteering, the use of real-time, on-site geologic data to guide the well bore; and hydraulic fracturing, or fracking, which involves the use of fracturing fluid (predominately water-based) to fracture the rock and proppants (e.g., sand) to hold the fractures open, allowing the trapped gas to flow through the shale and into the well.1 These technologies have allowed the extraction of NG from huge reserves that previously had been economically inaccessible. The Interstate Natural Gas Association of America expects NG consumption to grow 1.6 percent per year.2

Increased production has driven prices down, which has led to increased demand, in particular for electricity generation and transportation fleet use. It has also benefited residential, commercial, and industrial customers. Manufacturing appears to be on the rebound in this country in part because of the low price of NG, which is used as both a fuel and a feedstock for petrochemicals. Potential NG production levels could exceed growing demand, and the United States could become a net gas exporter by 2015.3 However, low current prices do little to encourage more drilling to expand production, and higher prices will dampen demand. It is not clear where supply and demand will balance.

With the recent, rapid increase in shale gas development has come increasing concern about its environmental impacts, both positive and negative. The substitution of NG for coal for electricity generation has been an important factor in reducing U.S. emissions of GHG. Horizontal drill-

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1 Stephen A. Holditch, Texas A&M University, “Shale gas development,” Presentation to the Board on Energy and Environmental Systems, September 11, 2012.

2 Donald Santa, International Natural Gas Association of America, “Pipelines make it possible,” Presentation to the Board on Energy and Environmental Systems, September 11, 2012.

3 Majida Mourad, Cheniere Energy, Inc. “LNG exports— How much and how soon,” Presentation to the Board on Energy and Environmental Systems, September 11, 2012.



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5 Natural Gas Vehicles: Impacts and Regulatory Framework Natural gas (NG) accounts for about 25 percent of all (Figure 5-2). There are three key enabling technologies for energy use in the United States yet only 0.1 percent is used the current boom: horizontal drilling, which was largely in transportation, equivalent to about 0.5 billion gallons per proven in the 1990s; geosteering, the use of real-time, on- year of petroleum fuel. However, in the short time since the site geologic data to guide the well bore; and hydraulic release of the report Technologies and Approaches to Reduc- fracturing, or fracking, which involves the use of fracturing ing the Fuel Consumption of Medium- and Heavy-Duty fluid (predominately water-based) to fracture the rock and Vehicles (NRC, 2010), NG has emerged as a viable option proppants (e.g., sand) to hold the fractures open, allowing for commercial vehicles, driven by the rapid drop in its cost the trapped gas to flow through the shale and into the well.1 as a result of new technology. Yet, uncertainties exist relative These technologies have allowed the extraction of NG from to the extent and quality of reserves, safety and community huge reserves that previously had been economically inac- acceptance, fuel cost and continued availability, sustainabil- cessible. The Interstate Natural Gas Association of America ity, etc. This chapter starts with a brief review of why NG expects NG consumption to grow 1.6 percent per year.2 has emerged as a potentially significant fuel for medium- and Increased production has driven prices down, which has heavy-duty vehicles (MHDVs). It then discusses the technol- led to increased demand, in particular for electricity genera- ogy and infrastructure that will be needed for NG-fueled tion and transportation fleet use. It has also benefited residen- trucks, which can operate on either compressed natural tial, commercial, and industrial customers. Manufacturing gas (CNG) or liquefied natural gas (LNG). It describes the appears to be on the rebound in this country in part because regulatory framework for greenhouse gas (GHG) emissions of the low price of NG, which is used as both a fuel and a (primarily carbon dioxide, or CO2) and fuel economy stan- feedstock for petrochemicals. Potential NG production levels dards. Finally it presents the key findings and recommenda- could exceed growing demand, and the United States could tions relevant to NG-fueled trucks. become a net gas exporter by 2015.3 However, low current prices do little to encourage more drilling to expand produc- tion, and higher prices will dampen demand. It is not clear SUMMARY OF SUPPLY AND DEMAND TRENDS FOR where supply and demand will balance. NATURAL GAS FUEL With the recent, rapid increase in shale gas develop- To better understand what this potential means for the ment has come increasing concern about its environmental United States and its energy future, the National Research impacts, both positive and negative. The substitution of NG Council’s (NRC’s) Board on Energy and Environmental Sys- for coal for electricity generation has been an important tems (BEES) convened a meeting on September 11, 2012, factor in reducing U.S. emissions of GHG. Horizontal drill- assembling technical experts from private industry as well as representatives of government and academia. The primary 1 Stephen A. Holditch, Texas A&M University, “Shale gas devel- goals were to assess the current state of NG development and opment,” Presentation to the Board on Energy and Environmental to identify key research and technological gaps. This effort Systems, September 11, 2012. 2 Donald Santa, International Natural Gas Association of was augmented by presentations to a meeting of the commit- tee on July 31 and August 1, 2013. This discussion is largely America, “Pipelines make it possible,” Presentation to the Board on Energy and Environmental Systems, September 11, 2012. based on those forums. 3 Majida Mourad, Cheniere Energy, Inc. “LNG exports— How NG production, driven by shale gas (Figure 5-1), began much and how soon,” Presentation to the Board on Energy and accelerating in 2005 and is expected to continue to grow Environmental Systems, September 11, 2012. 52

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Lower 48 states shale plays Niobrara* Montana Thrust Belt Bakken*** Heath** Cody Williston Basin Big Horn Powder River Gammon Hilliard- Basin Basin Baxter- Mowry Appalachian Mancos Michigan Basin Greater Basin Antrim Green Niobrara* River Park Basin Forest Devonian (Ohio) Basin City Basin Illinois Marcellus Uinta Basin Manning Basin Utica San Joaquin Canyon Piceance Denver Basin Mancos Basin Basin Excello- New Hermosa Mulky Cherokee Platform Albany Monterey- Paradox Basin Pierre Temblor Lewis Raton Woodford San Juan Anadarko Fayetteville Basin Chattanooga Basin ArdBasin Monterey m Arkoma Basin Black Warrior Santa Maria, Palo Duro Bend ore Ba sin Basin Conasauga Basin Ventura, Los Floyd- Valley & Ridge Angeles Avalon- Neal Province Basins Bone Spring Barnett Permian TX-LA-MS Miles Basin Ft. Worth Salt Basin Barnett- Marfa Basin Tuscaloosa 0 100 200 300 400 Woodford Basin Eagle Haynesville- Ford Bossier Pearsall Western Gulf Shale plays Current plays Basins Basins * Mixed shale & ± Prospective plays chalk play ** Mixed shale & Stacked plays limestone play Shallowest/ youngest ***Mixed shale & Intermediate depth/ age tight dolostone- Deepest/ oldest siltstone-sandstone Source: Energy Information Administration based on data from various published studies. Updated: May 9, 2011 FIGURE 5-1  Shale gas plays in the continental United States. SOURCE: Energy Information Administration (EIA). Available at http://www.eia.gov/oil_gas/rpd/shale_gas.pdf. Ac- 53 cessed December 23, 2013.

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54 REDUCING THE FUEL CONSUMPTION AND GHG EMISSIONS OF MEDIUM- AND HEAVY-DUTY VEHICLES, PHASE TWO fracturing process.5 At the surface, an integrated manage- ment plan is needed to address the supply, handling, reuse, and disposal of the fracking fluid to ensure sustainability throughout the production cycle. In the electric power sector, the low price of NG has directly caused the closure of coal plants, as it has become more economical to use combined-cycle NG plants (with thermal efficiencies up to 65 percent) for electricity produc- tion. However, fuel price is the dominant contributor to the cost of electricity (55 percent). One analysis concluded that the break-even fuel price is between $4 and $6 per million British thermal units (mmBTUs).6 In the heavy-duty transportation sector, price has a less direct effect on the use of NG as a fuel because delivering and compressing (or liquefying) the fuel account for a large share of the price at the pump. The break-even price of NG relative to diesel fuel is around $6 per million BTU (predeliv- FIGURE 5-2  U.S. natural gas production. SOURCE: EIA (2013a). ery, not at the pump). If the costs of NG vehicles themselves come down relative to the costs of their diesel counterparts (discussed in the next section), the break-even value could be as high as $9 to $12 per million BTU. If, as projected by the Energy Information Administration (EIA), the price of ing causes much less surface disruption than conventional NG in 2035 is about $7 per million BTU (EIA, 2013a), its drilling—for example, Apache Corporation’s Horn River use in the transportation sector will likely depend in part on Development uses a drill pad of just 6.3 acres to recover future technological improvements. gas from approximately 5,000 acres. However, this means Currently, the biggest obstacles to NG use for freight that local pollution (e.g., particulate matter, volatile organic transportation are (1) the lack of widespread and dependable compounds, and nitrogen oxides [NOx]) may be more con- infrastructure, (2) the substantial increase in weight and cost centrated. In addition, NG largely consists of methane, which of the fuel tanks compared to diesel tanks, and (3) the avail- is a powerful GHG. Leakage, most of which is estimated to ability of NG vehicles, although almost all MHDV manufac- come from gas production activities, could negate the hoped- turers now offer a NG engine. More detailed discussion of for climate benefits of reducing CO2 emissions by replacing infrastructure and technology follows in a later section of this other fossil fuels with NG. Methane has a shorter lifetime chapter. Pipeline and infrastructure investment in the United in the atmosphere than carbon dioxide, but its higher radia- States and Canada is likely to exceed $200 billion over the tive forcing—that is, its ability to redirect heat that would next 25 years (see footnote 2). otherwise escape the atmosphere—means that over 100 EIA expects increased production, lower imports, higher years it has 20 times the GHG impact of CO2. One analysis exports, and higher prices, as shown in Table 5-1. concluded that after taking into account current estimates of leakage, converting heavy-duty diesel trucks would have a net negative effect on climate change for centuries.4 One NATURAL GAS ENGINES AND VEHICLES estimate of gas leakage, based on measurements at 190 onshore gas production sites, is 0.42 percent of the total Technology gas production (Allen et al., 2013). Note that this leakage exceeds the amount of NG currently used in transportation. Overview Other estimates of fugitive emissions have been significantly NG internal combustion engines are a well-developed higher (e.g., Howarth et al., 2011). and established technology. There are over 11 million NG Water contamination is a widely discussed concern vehicles worldwide, including passenger vehicles. In the about hydraulic fracturing. This can be divided into two United States, NG-fueled MHDVs, especially transit buses, main issues: (1) underground contamination related to well integrity and (2) disposal of wastewater from the hydraulic 5 Mark Boling, Southwestern Energy, “Forum on Unconventional Natural Gas Issues: Water Quality,” Presentation to the Board on 4 Steven Hamburg, Environmental Defense Fund, “Methane Energy and Environmental Systems, September 11, 2012. 6 Revis James, Electric Power Research Institute, “The Role of leakage from natural gas production, transport and use— Implications for the climate,” Presentation to the Board on Energy Natural Gas in the Electricity Sector,” Presentation to the Board on and Environmental Systems, September 11, 2012. Energy and Environmental Systems, September 11, 2012.

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NATURAL GAS VEHICLES: IMPACTS AND REGULATORY FRAMEWORK 55 TABLE 5-1  Projections of Domestic Production and storage is either by high-pressure (3,600 psi is typical) CNG Prices for Natural Gas and Diesel Fuel Price cylinders or by cryogenic containers filled with LNG. An Year illustration comparing on-vehicle storage of NG with diesel is shown in Figure 5-3. 2012 2025 2040 For the same truck mission, the CNG tank plus fuel Production (quadrillion BTU) 24.59 32.57 38.37 weighs about four times as much as a diesel tank plus fuel. LNG tanks and fuel weigh about twice as much as diesel. The Henry hub price ($) 2.75 5.23 7.65 cost of either CNG or LNG storage adds $40,000 to $50,000 Price delivered to transportation ($) 14.64 15.57 19.67 to the cost of a heavy truck, but with the current low price of Diesel fuel price ($) 8.80 29.02 34.53 NG, the payback period for long-haul trucks is on the order NOTE: Prices are per million BTU in 2012 dollars. Note that a million BTU of only 2 years. is equivalent to about 8 gallons of diesel fuel. Thus, natural gas costs on the There are three general technical classifications of NG order of $2.00 per gallon equivalent, much less than diesel fuel. engines, as shown in Table 5-2. Either CNG or LNG can SOURCE: EIA (2013a). replace gasoline with only modest changes to the spark igni- tion (SI) engine. Compression ignition (CI) engines are more have been incentivized for roughly 20 years in some states complicated; NG can be used in combination with diesel fuel as part of emission-reduction programs. For MHDVs to use (dual-fuel); or it can supply all the energy to a high-pressure natural gas fuel, the most significant differences from cur- direct-injection (HPDI) CI engine, in which a small amount rent vehicles are the onboard fuel storage method and, for of diesel fuel is needed to achieve ignition. compression ignition (diesel-fueled) vehicles, the means of Table 5-2 notes several advantages and disadvantages of introducing and igniting the fuel in the engine. On-vehicle each configuration. FIGURE 5-3  Comparison of diesel and NG fuel tanks. SOURCE: John Wall, Cummins, Inc., “Opportunities and barriers for natural gas: Expanding natural gas in transportation,” Presentation to the Board on Energy and Environmental Systems on September 11, 2012.

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56 REDUCING THE FUEL CONSUMPTION AND GHG EMISSIONS OF MEDIUM- AND HEAVY-DUTY VEHICLES, PHASE TWO TABLE 5-2  Natural Gas Engine Technology Comparison Dedicated NG Dual Fuel HPDI Technology Spark ignition Compression ignition Compression ignition Throttle to control A/F With or without EGR EGR Lean or stoichiometric/EGR Diesel + premixed NG Diesel pilot + in-cylinder NG injection Two-/three-way catalyst A/T DOC DPF+SCR A/T system Not dual fuel—all power from NG DOC DPF + SCR A/T system Advantages 100% diesel substitution Power density similar to diesel Power density similar to diesel Lowest emissions v. other NG Efficiency similar to diesel Efficiency similar to diesel technologies No spark plugs No spark plugs Simple, passive aftertreatment Potentially retrofittable on existing 95% diesel substitution LNG or CNG diesel engine Can run on diesel only Disadvantages Spark plug life Substitution limited to 50-80% High system cost/complexity 10-15% lower efficiency than diesel, Unburned methane emissions Requires both fuels, always better efficiency than gasoline PFI Misfire at light loads LNG + cryogenic in-tank pump for high- Lower power density Knock at high loads pressure injection Knock limited NOTE: A/F, air:fuel ratio; A/T, aftertreatment; DOC, diesel oxidation catalyst; EGR, exhaust gas recirculation; PFI, port fuel injection; SCR, selective catalytic reduction; DPF, diesel particulate filter. SOURCE: Tim Frazier, Cummins Westport, “Cummins Westport Natural Gas-Fueled Engines,” Presentation to the committee on July 31, 2013. These configurations of SI, pilot ignition, and dual fuel can operate as bi-fueled configurations. Bi-fuel indicates have existed for many years, but under very different emis- that vehicles are equipped with both CNG and gasoline fuel sions standards. At least 11 different engine displacements systems; switching from gas to gasoline is automatic. This for CNG/LNG MHDVs are expected to be available by process can significantly extend vehicle range when CNG 2015. As more original equipment manufacturers (OEMs) refueling is not available. Certain of the heavier vehicles are introducing NG options to their product lines, the share are equipped only with CNG fuel systems. Figure 5-4 does of CNG/LNG MHDVs continues to grow. not include aftermarket conversions procured after the sale Details of seven engines are presented in Table 5-3. They of the vehicle. range in displacement from 6.0 L to 12.7 L. The engines As of 2010, the number of medium- and heavy-duty are predominantly SI, capturing the simplicity of fuel/air NG vehicles in the United States is estimated to have been mixing with stoichiometric combustion and facilitating cri- between 30,000 and 50,000, out of roughly 10 million total teria emission control with the similarly simple three-way MHDVs (TIAX for American Natural Gas Association catalyst (TWC). These NG engines typically are based on [ANGA]). diesel engines (not SI) to achieve the durability and reli- ability expected for trucking applications. For example the Fuel Consumption and GHG Comparisons of Natural Gas Cummins-Westport engine has over 80 percent of its parts and Diesel Engines in common with the base diesel-fueled engine (ISX12). However, the SI combustion system is less efficient than CI When a fuel is combusted, its CO2 release per unit heat engines by roughly 15 percent. One manufacturer expects released is a function of its carbon content. Because it has a to offer a HPDI compression ignition model that should relatively low carbon content, NG releases about 28 percent approach diesel engine efficiency. A Westport Innovations less CO2 per BTU of heat than diesel fuel. However, SI 15L-HPDI sold for about 7 years but was taken off the market engine efficiency is considerably lower than that of mature in October 2013; it does not appear in the table. diesel engines, especially at light loads, partially offsetting Figure 5-4 depicts the types of NG-fueled vehicles that the inherent GHG benefit of NG. In addition, unburned are available and the examples of engines for those vehicle methane may be emitted by the vehicle, and upstream emis- classes. The engines shown from Ford and GM are conver- sions from the production and delivery of the NG must be sions of OEM-built vehicles where, upon delivery, customers considered in a well-to-wheels comparison. Methane is a use an OEM-qualified vehicle modifier that supplies the fuel very potent GHG, so if these emissions are significant, NG tanks, lines, and special fuel injectors. Depending on the vehicles could contribute more to GHG emissions than diesel size of the tank, these modifications can cost from $6,000 vehicles. to $9,500. The NG-fueled vehicles offered by Ford, GM, Several studies have compared CO2 emissions of diesel and Chrysler are all derived from gasoline SI engines and and NG vehicles and engines in driving and test cycles.

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NATURAL GAS VEHICLES: IMPACTS AND REGULATORY FRAMEWORK 57 TABLE 5-3  Features of Available Natural Gas Engines Engine Description Vortec 6.0L V8 ISB6.7-G PSI 8.8L-G ISL-G Doosan GL11 ISX12-G D13-LNG gasoline purpose built purpose built purpose built purpose built purpose built diesel derivative conversion diesel derivative diesel derivative diesel derivative diesel pilot Parameters bi-fuel1 Manufacturer GMC Cummins Pow er Solutions Cummins Doosan Cummins Volvo Vehicle Vocational Target CL 2b-6 Van, Trk CL6Westport Intl Trk,SchlBus CL 6-8 Truck Westport CL6-8 Truck, Infracore Am CL6-8 Truck, Westport CL 8 Truck, Bus CL 8 Truck Expected NG form CNG CNG or LNG CNG Bus CNG or LNG Bus CNG CNG or LNG LNG Number ofCylinders V8 6 V8 6 6 6 6 Displacement (L) 6.0 6.7 8.8 8.9 11.1 11.9 12.7 Displ/Cyl (L) 0.75 1.1 1.1 1.5 1.8 2 2.1 Combustion System SI-stoic SI-stoic SI SI-stoic SI-stoic SI-stoic CI Compression Ratio >10.5 12.1 15.6 Electronic Electronic Electronic Electronic Electronic LNG-diesel dual Fuel System Description Port injection throttle body throttle body throttle body throttle body throttle body fuel injectors; mixing mixing mixing injection mixing diesel pilot Air Handling System naturally WG-Turbo; CAC Turbocharged WG-Turbo; CAC Turbocharged, WG-Turbo; CAC VGT; CAC Description aspirated CAC EGR (Y/N) N Y-HPL N Y-HPL Y-LPL Y-HPL Y Aftertreatment Descrptn: TWC TWC TWC TWC TWC DOC,DPF & SCR 2010 Criteria Emissions Rated RPM 5000 2600 3400 2200 2200 2100 1700 Rated kW/L 28.1 36.1 22.7 26.9 22.9 25 27.9 Rated kW(HP) 225'(301) 242'(325) 200'(268) 239'(320) 253'(340) 298'(400) 354'(475) Max Torque N-m(lb-ft) 452'(333) 1017'(750) 1356'(1000) 1356'(1000) 1627'(1200) 1966'(1450) 2373'(1750) Issues & Unique Barriers bi-fuel both fuels, alw ays Production available Y 2015 mid 2014 Y 2014 Y mid 2014 Resource I E F B G B D Notes: 1 bi-fuel means non-simultaneous fuel (natural gas and gasoline) supply to engine While the results differ somewhat, NG engines and vehicles vehicles compared with diesel fuel risks do not appear to be generally emit about 5 to 20 percent less CO2 (Krupnick, appreciably different. However, because the number of NG- 2010; Kamel et al., 2002; Greszler, 2011). The advantage fueled commercial vehicles is small compared with diesel- for NG is very dependent on the drive cycle. One estimate fueled vehicles, that conclusion is uncertain at this time. of the impact of methane emissions, shown in Figure 5-5, is Furthermore, because public crash databases do not contain that they reduce the CO2-equivalent GHG emissions benefit information on fuel type, they cannot provide categorical of NG from 13 percent to only 5 percent. insight on risk. This review of the data comparing diesel and NG engines In tractor vehicles, diesel tanks are often mounted on affirms that the chemical advantage of NG for low GHG the outside of the tractor frame rails beneath the driver and emissions is largely (but not completely) offset by the lower occupant access doors. This location is exposed to side efficiency of most NG-fueled heavy-duty engines. This will impacts from other vehicles, side impacts with objects, truck need to be considered in setting specific GHG and fuel con- rollovers, and opposite direction sideswipe crashes. In single sumption standards for medium- and heavy-duty vehicles unit trucks (SUTs), the tanks are often located below the bed, using NG, as was done in setting different standards for which is more protected. gasoline and diesel engines. If a NG tank is ruptured and the gas is ignited, the fire will be appreciably different from a fire involving diesel fuel. The risk to the driver and occupants from such events Safety: On-Vehicle NG Storage is not well understood due to a lack of data and documented CNG has been used successfully for many years to power crash experience. commercial vehicles operating in limited-range applica- LNG is at much lower pressure and would not ignite so tions, usually in urban areas. With the recent increase in the violently, but the tank shells are more complex to provide availability of low-cost NG, it is anticipated that its use in thermal insulation and may be more vulnerable to puncture long-haul Class 7 and Class 8 trucks will increase, especially than high-pressure CNG tanks. The extreme cold (−260 °F) using LNG as a means of extending vehicle range. Crash- of LNG presents risks of its own. There is little information related safety risks associated with NG storage in larger on accidents involving NG trucks because so few are on the road, but experience with diesel trucks provides some useful

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58 REDUCING THE FUEL CONSUMPTION AND GHG EMISSIONS OF MEDIUM- AND HEAVY-DUTY VEHICLES, PHASE TWO FIGURE 5-4  Available natural gas vehicles and OEM-authorized conversions. SOURCE: NREL. information. In particular, fires (from all causes, not just fuel) composite wrapped.”7 For LNG-fueled vehicles, Dewar flask are involved in accidents responsible for 14.2 percent of all cryogenic tanks are used to keep the fuel in its liquid state. An fatalities and serious injuries in tractors, but only 4.8 percent LNG fuel tank can hold between 56 and 80 diesel-equivalent in SUTs (UMTRI, 2013). These data suggest that protecting gallons. LNG is the preferred form of NG fuel if the daily NG tanks in tractor applications will be very important for operating range is over 400 miles. Given the diversity of safety. Rollovers are the most frequent source of fatalities NG tanks available for the heavy truck market, the crash for both vehicle types, but that is likely to be true no matter characteristics, and associated risks, a review of technical which fuel is used. Heavy trucks are 30 to 40 times heavier standards and safety-related issues appears to be warranted, than passenger vehicles. When crashes occur, they tend to be particularly with respect to tank type, location, and shield- very damaging to cab structures and auxiliary components, ing. At present, there are two SAE-recommended practice particularly when large fixed objects are encountered. There are various NG tank options available for large 7 Kenworth, “Kenworth Truck Company Offers Advice on truck applications. Type 4 CNG cylinders have a “plastic Spec’ing for Natural Gas Power.” Available at http://www.ken- core and are fully wrapped with a composite, such as carbon worth.com/news/news-releases/2011/december/kenworth-truck- fiber. Other less expensive options are Type 2 and Type 3 company-offers-advice-on-specing-for-natural-gas-power.aspx. CNG tanks, which have a steel or aluminum core and are Accessed March 12, 2014.

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NATURAL GAS VEHICLES: IMPACTS AND REGULATORY FRAMEWORK 59 liquefied motor vehicle NG fuel could allow for the design of more efficient and less costly engines. However, a standard for in-use motor vehicle NG could require further process- ing of some pipeline gas before compression or liquefaction. Given the limited demand for motor vehicle NG currently envisioned, compared to nationwide consumption for other purposes such as home heating and power generation, it is not clear if suppliers of NG would invest in the gas cleanup needed for motor vehicle fuel. This could result in NG fueling stations being unavailable in certain areas where pipeline gas does not meet motor vehicle fuel specifications. This could impede the increased use of NG as a motor vehicle fuel. Finally, as noted above, the fuel tank, whether for CNG or LNG, accounts for most of the cost increment for NG vehicles over equivalent gasoline or diesel vehicles. In addition to cost, weight can be an issue. The cheapest solid FIGURE 5-5  Comparison of emissions from natural gas and diesel steel (Type 1) cylinders weigh four to five times as much as engines. NOTE: bhp, brake horse power; g CO2, grams carbon diox- gasoline or diesel tanks of the same capacity; advanced (Type ide. Natural gas emissions were calculated as follows: CO2 engine 3) cylinders with thin metal liners wrapped with composite emissions + [(CH4 engine emissions – CH4 limit) * global warm- weigh about half as much as Type 1 tanks, although they cost ing potential] = 506 + [(1.7 – 0.1) * 25] = 546. The Federal Test Procedure (FTP) was employed. SOURCE: Tim Frazier, Cummins more. Tanks with polymer liners weigh even less, but are Westport, “Cummins Westport natural gas-fueled engines,” Presen- even more expensive. Higher pressure tanks (up to 10,000 tation to the committee on July 31, 2013. psi) could reduce fuel storage space, but at added cost and increased energy required to compress the gas. While tank costs are likely to come down with increased standards for medium- and heavy-duty NG vehicles. SAE and improved production, large cost reductions will depend J2343 focuses on LNG while SAE J2406 addresses CNG. on advanced technology. In the future, it may be possible SAE J2343 refers to tank placement, but neither standard to store CNG at higher density, even at 500 psi (within the covers tank shielding requirements to prevent punctures 200-1,500 psi range for gas in NG transmission pipelines) during crashes. Industry could benefit from best practice in adsorbed NG (ANG) tanks using spongelike materials directives to minimize safety risks associated with NG fuel such as activated carbon. If successful, this technology could tanks on commercial vehicles. allow vehicles to be refueled from the NG network without extra gas compression, reducing cost and energy use and allowing the fuel tanks to be lighter (adapted from NRC, Technology Improvement Opportunities 2013). Also, at lower pressure, the shape of the tank can be Although the engines available today are robust and adjusted as needed to fit the space available, thus minimizing capable, improvements could further increase efficiency and the impact on cargo space (PNNL, 2010). reduce maintenance costs. Areas where further R&D for NG engines would be beneficial are listed in Table 5-4. TABLE 5-4  Technologies for Improvements in Heavy- It has been suggested that in addition to needed advance- Duty Natural Gas Engine Brake Thermal Efficiencies and ments in engines and aftertreatment, a uniform national GHG Emissions for the Phase II Rule standard for NG quality for vehicular use is needed. Higher carbon content hydrocarbons in LNG tanks can lead to fluid Base Engine Aftertreatment stratification, and the composition of CNG tanks can affect Improved air handling Improved three-way catalyst autoignition, combustion behavior, and engine power den- High-efficiency turbo Better methane oxidation Low pressure loss EGR Increased oxygen storage sity. The Engine Manufacturers Association recommends Low restriction ports a minimum methane number of 80 for CNG, a maximum Improved controls inert content of 4 percent, and a 16,200 BTU/lb minimum Higher energy ignition Advanced air/fuel ratio dithering energy content, in addition to limits on contaminants such strategies as water and sulfur compounds, among others (EMA, 2010). Improved combustion Adaptive algorithms New bowl geometry Advanced sensors Activities to support standard setting are in progress in the Lower swirl/higher squish Society of Automotive Engineers (SAE) and the Coordinating Crank case ventilation Research Council (CRC), and ISO-15403 has been published Improved friction and parasitics as a European standard for NG vehicle fuel (Kauling, 2013). SOURCE: Tim Frazier, Cummins Westport, “Cummins Westport natural Assurance of a minimum quality for in-use compressed and gas-fueled engines,” Presentation to the committee on July 31, 2013.

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60 REDUCING THE FUEL CONSUMPTION AND GHG EMISSIONS OF MEDIUM- AND HEAVY-DUTY VEHICLES, PHASE TWO Infrastructure CNG Infrastructure NG is moved throughout the United States in an extensive network of pressurized pipelines. According to the American Gas Association (AGA, undated), there are 1.9 million miles of CNG distribution lines and an additional 300,000 miles of transmission lines. The transmission lines are for long- distance interstate transport and operate at high pressure, from 200 to 1,500 psi. The distribution and service lines to homes operate at low pressure, approximately 50 psi to less than 1 psi. CNG refueling stations for vehicles are connected to points in the distribution pipeline network. The gas indus- try spends over $6 billion per year on the transmission lines and $4 billion per year expanding the distribution system. There are 632 public CNG vehicle refueling locations in the United States (AFDC, undated) and around 1,200 includ- ing stations for private fleets (Weeks, 2013). The number of fueling stations actually peaked in 1997 and then declined FIGURE 5-6  Conceptual diagram of compressed natural gas filling until 2008. The rate of growth of CNG stations has been stations. SOURCE: http://www.afdc.energy.gov/fuels/natural_gas. about 11 percent per year for the last few years (Clay, 2013), html. probably driven more by increased use in trucks than in pas- senger vehicles. The infrastructure hurdle for freight-hauling heavy-duty NG vehicles appears more manageable than for passenger vehicles and for Class 2b vehicles because far is formed by cooling NG to −162°C (−260°F), increasing fewer stations will be needed for servicing trucks. its volumetric energy density about 600-fold and allowing There are two basic types of CNG fueling systems: fast- it to be stored at relatively low pressure in highly insulated fill and time-fill, shown in Figure 5-6 (AFDC, undated). Both containers. The on-vehicle storage volume and weight are capable of filling the on-vehicle tank to approximately advantages compared to CNG are considerable, but diesel 3,600 psi, but as the name implies, the fast-fill can refuel a fuel still has about 1.7 times the volumetric energy density passenger vehicle in a few minutes by supplying gas from of LNG. As shown in Figure 5-3, the approximate range per high-pressure storage vessels that are maintained full by 100 gallons in a long-haul truck is: 650 miles (diesel); 380 compressors. The time-fill system in essence refuels the miles (LNG); and 170 miles (CNG). LNG fueling stations are vehicle over a long period (hours) by the CNG compres- similar in configuration and operation to gasoline and diesel sor’s relatively small direct output, with small storage tanks fuel retail outlets. LNG is delivered to the fueling station in used only for buffering. The time-fill stations are generally tanker trucks, stored there, and dispensed into vehicles with less costly to set up and are likely to be most appropriate cryogenic LNG storage tanks (see Figure 5-7). Many LNG for fleets that can refill overnight. Some stations may have fueling sites supply CNG as well. both systems. The main disadvantage of LNG is that it gradually boils CNG stations are estimated to cost $600,000 to $1 mil- off as ambient heat penetrates the tank no matter how well lion, with time-fills in the lower part of the range and fast- insulated it is. This may not matter much in long-distance fills in the upper (ANGA, undated). These costs will be a considerable hindrance to the growth of CNG as a passenger vehicle fuel. One study estimated that between 16,000 and 32,000 stations would be needed to support a thriving NG vehicle population, with a much smaller number of refueling sites needed for heavy trucks (ANGA, undated). Equipping another 9,000 public stations will cost in the range of $5.4 to $9 billion. LNG Infrastructure LNG use is growing in transportation, especially for Class 8 freight trucks operating over interstate routes. LNG FIGURE 5-7  Conceptual diagram of LNG filling stations. SOURCE: http://www.afdc.energy.gov/fuels/natural_gas.html.

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NATURAL GAS VEHICLES: IMPACTS AND REGULATORY FRAMEWORK 61 trucks that operate almost continually, but it probably pre- as a feedstock. The company also has a demonstration-scale cludes the use of LNG in light-duty vehicles. ethanol plant in Houston, Texas, that uses NG as a feedstock, Only about 40 nonprivate LNG fueling stations are in although Celanese (2013) has noted obstacles to supplying operation in the United States, many of them in California its ethanol for either E85 or E10 in the U.S. market. Cos- (AFDC, undated; TIAX, 2009). Clean Energy Fuels Cor- kata, Inc., is also developing a process for producing ethanol poration has been establishing a cross-country network of from NG. The proprietary Coskata process begins with the LNG fueling stations (“America’s Natural Gas Highway”), reforming of methane to produce synthesis gas, followed by with near-term plans for 100 LNG stations. Shell is working fermentation of the synthesis gas to produce ethanol. Both with TravelCenters of America to offer LNG for highway Celanese and Coskata8 estimate that they can produce etha- trucks and has a joint cooperation agreement on LNG with nol at a substantial discount to gasoline or diesel fuel on an Volvo. LNG is produced at only about 50 to 60 sites in the energy-equivalent basis United States, and there are a few LNG import terminals, Converting NG to liquid hydrocarbons is a well- so transport distance to LNG dispensing stations could be a established technology relying largely on the Fischer- detriment. California boasts the world’s largest facility for Tropsch process developed in the 1920s-1940s. Liquid fuels, producing LNG from landfill gas. especially diesel, from GTL technologies have been shown to be compatible with existing vehicles and can be combined with petroleum products, averting the need for a completely Conversion of NG to Other Fuels new dispensing infrastructure and a new vehicle technology NG can be converted to other fuels using well-known to allow the widespread use of NG for transportation. GTL processes and technology. Each has advantages and disad- plants have been established worldwide where low-cost vantages for storage, GHG impact, and cost: NG is available. To be profitable, the scale of GTL plants is enormous as is the capital investment, and the production • Dimethyl ether (DME) of high-value chemicals in addition to fuel is important. • Methanol Shell and Sasol are the largest GTL producers. Operating • Ethanol since 2011, Shell’s Pearl GTL facility in Qatar is one of the • Gas-to-liquids (GTL) largest such plants in the world (140,000 BPD products), • Ammonia nearly 10 times the size of the demonstration facility Shell • Electricity built in Malaysia in the early 1990s. Products from the Pearl • Hydrogen (for fuel cell vehicles) facility are shipped to the United States. Low-cost NG in the United States gives rise to consideration of domestic GTL DME-fueled truck development and demonstration is production. Companies such as Compact GTL and Velocys being carried out by Volvo with the fuel developer Oberon, are developing relatively small, modular GTL production which has a technology for converting NG or other feed- technology to support operations of, say, less than 5,000 stocks to DME via methanol as an intermediate. DME has BPD. A 1,000 BPD commercial production compact GTL storage characteristics similar to propane and much lower plant is being considered for construction in Pennsylvania, storage pressure and higher energy density than CNG. In a in the heart of one of the large shale gas plays. CI engine its performance is similar to that of diesel fuel. NG is the source for 95 percent of hydrogen production Most methanol produced in the United States is derived in the United States, and fuel cells are candidates for cer- from NG. In the mid-1980s, heavy-duty bus engines that ran tain heavy vehicles such as buses and drayage tractors. In on pure methanol or M85 (a mixture of 85 percent methanol California, fuel cell heavy vehicles are a key option where and 15 per cent gasoline) were produced and emissions- zero-emission vehicles are needed. There are 10 hydrogen certified, but subsequently CNG buses largely replaced them refueling stations in the United States, most of them in (Aldrich, 1995). Passenger vehicles were also produced and California (AFDC, undated). emissions certified to run on M85. A substantial infrastruc- NG is a feedstock for anhydrous ammonia, a feasible ture for dispensing M85 was established for fueling flex-fuel engine fuel that can be stored as a liquid at pressures similar passenger vehicles, especially in California, but the program to propane. Although it has been demonstrated in both SI and came to an end around 2005. Today in China, methanol is CI combustion systems, its toxicity and acute incompatibility blended at low percentages in gasoline. with the human body make its widespread use as a transpor- Although at present motor fuel ethanol comes from fer- tation fuel impractical. mentation of biomass, it can also be produced from petro- About 30 percent of U.S. electricity comes from burn- leum and NG. Recently several companies announced the ing NG (EIA, 2013b), and this fraction is growing rapidly. development of new processes for the production of ethanol Combined-cycle (gas turbine/steam turbine) technology can from NG. For example, Celanese, one of the world’s largest producers of acetic acid from fossil fuels, is building indus- 8 Coskata, Inc. “Natural Gas.” http://www.coskata.com/process/ trial-scale ethanol plants in China and Indonesia using coal index.asp?source=984A0E13-B27D-4267-8411-AA86E0CAA39F.

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62 REDUCING THE FUEL CONSUMPTION AND GHG EMISSIONS OF MEDIUM- AND HEAVY-DUTY VEHICLES, PHASE TWO FIGURE 5-8  Comparison of efficiencies of compressed natural gas vehicles (CNGVs) and battery electric vehicles (BEVs). SOURCE: Curran, 2013. be highly efficient. Some units are over 60 percent efficient, EXPECTED GROWTH IN NATURAL GAS VEHICLE much higher than coal-fired generation. Electric vehicles POPULATION (battery electric or plug-in hybrids) can take advantage of Several forecasts have been made for the growth in NG in this path, thereby displacing petroleum. medium- and heavy-duty vehicles using NG. Figure 5-9 The conversion processes for all of the alternative fuel compares several forecasts of NG penetration in Class 8 options described above emit GHGs. Therefore the processes trucks in the near term. Key factors influencing the decision that produce hydrocarbon fuels will result in higher total to purchase a NG vehicle are the fuel cost savings, initial GHG emissions than NG-fueled engines, which are on par cost premium for the vehicle, and ready access to refueling with or slightly better than comparable diesel-fueled engines. facilities. Only electricity and hydrogen from NG can produce lower The National Petroleum Council (NPC) study produced GHG emissions than direct combustion of NG in engines a longer-term projection to 2050 (Figure 5-10), which esti- due to the inherently high efficiency of battery electric and mated that about 40 percent of Class 7 and Class 8 vehicles fuel cell vehicles. would be fueled by NG by 2050. Figure 5-8 compares the efficiencies from well to wheels of CNGVs and electric vehicles (the figure was developed for automobiles, but the well-to-pump numbers would be the same for trucks). While today’s CNGVs might attain a total well-to-wheels efficiency of 25 percent, the battery electric vehicle could attain 35 percent, which would result in about one-third less GHG emissions.9 This figure assumes efficient (51 percent) gas-to-electric conversion typical of a combined-cycle plant. If heavy-duty vehicles or hybrid passenger vehicles with their relatively high efficiency were to be substituted for the automobile shown, the combustion path would be close to the electric path. 9 FIGURE 5-9  Near-term Class 8 natural gas penetration forecasts. Note that these are not full well-to-wheel estimates since they SOURCE: Citi GPS (Global Perspectives & Solutions), 2013, Ener- include neither leakage at the well nor tailpipe emissions from the gy 2020: Trucks Trains & Automobiles. New York: Citigroup. June. CNGV.

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NATURAL GAS VEHICLES: IMPACTS AND REGULATORY FRAMEWORK 63 tal Protection Agency (EPA) criteria emission requirements and standards (NOx, particulate matter [PM], etc.) for many years. The criteria emission tests and procedures for NG engines are the same as those used to certify gasoline- and diesel-fueled heavy engines. Most engines are certified using a transient engine test, referred to as the heavy-duty Federal Test Procedure (FTP), which is supplemented by additional tests (steady-state and not-to-exceed tests) that cover more engine operating conditions. Medium- and heavy-duty vehi- cle engines fueled by diesel fuel or NG are certified to a NOx standard of 0.20 g/bhp-h. Certification data show similar NOx emission levels for NG and diesel fuel. Evaporative testing is not required of NG vehicles. Some large diesel pickup trucks and vans are chassis-certified based on the vehicle test used to certify cars and light trucks. EPA specifies the properties FIGURE 5-10  Shares of vehicles fueled by natural gas and by diesel to 2050. SOURCE: National Petroleum Council, 2012, of NG for the purpose of certification emission testing. It Advancing Technology for America’s Transportation Future, Part also allows use of alternative test fuel specifications if they One—Integrated Analyses, pp. 3-17. represent fuel the engine would use in normal use, such as pipeline NG. Greenhouse Gas Emission and Fuel Economy Standards for Engines In August 2011 the federal government adopted CO2 and fuel economy standards for new medium- and heavy-duty trucks and engines. The CO2 emission standards for new engines vary by engine type and duty cycle. If the engine is gasoline fueled or uses a spark plug and operates like a theo- retical Otto combustion cycle, it is considered a SI engine. A CI engine is defined as an engine that is not a SI engine. The CO 2 emission standard for a new SI engine is 627 g/bhp-hr, beginning with model year (MY) 2016. For CI engines, the CO2 standard depends on the engine class (light-, medium-, or heavy-duty) and on what type of vehicle FIGURE 5-11  Historic rates of penetration for NG refuse trucks in the engine is used in (tractor or vocational), and it begins with the United States and diesel passenger cars in Europe. SOURCE: 2014 models. The CO2 emission standards for CI engines Data from (1) MacKay & Co. and Ward’s Automotive Group, a are shown in Table 5-5. The 2017 standards represent a 9 to division of Penton Media, Inc., (2) European Automotive Manufac- 23 percent reduction in CO2 compared to a 2010 baseline. turers’ Association (ACEA), and (3) and (4) Westport. Small businesses (fewer than 1,000 employees for truck manufacturers and 750 employees for engine manufacturers) are exempt from the GHG and fuel consumption standards, The growth of refuse trucks fueled by NG is dramatic, although NHTSA and EPA state they plan on reexamining as shown in Figure 5-11. Currently about half of new refuse this in the next rulemaking. trucks are NG-fueled, and that is expected to rise to 90 percent soon, in part because of local, state, and national incentives. However, refuse trucks collectively are not large TABLE 5-5  Engine Emission Standards for New CI consumers of fuel, so the greater opportunity for NG substi- Engines (grams per brake horsepower-hour) tution is in Class 7 and Class 8 tractor-trailer rigs, which use about 20 times as much. HD Engine Engine CO2 Emission Standard Vehicle Type Class 2014 2017 REGULATORY FRAMEWORK FOR NATURAL GAS Tractor, Medium 502 487 ENGINES AND TRUCKS Classes 7 and 8 Heavy 475 460 Vocational Light 600 576 New NG-fueled medium and heavy truck engines have Medium 600 576 been certified by their manufacturers to meet Environmen- Heavy 567 555

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64 REDUCING THE FUEL CONSUMPTION AND GHG EMISSIONS OF MEDIUM- AND HEAVY-DUTY VEHICLES, PHASE TWO Methane and nitrous oxide engine emission standards of Emission and Fuel Economy Standards for Complete 0.10 g/bhp-hr each also apply to all engines regardless of Trucks fuel. Through 2016 models, CO2 emission credits can off- EPA and NHTSA have also adopted GHG and fuel set methane (and nitrous oxide) emissions to provide more economy standards for trucks, with compliance units of flexibility in meeting these additional standards, and the grams/ton-mile and gallons/1,000 ton-miles, respectively. flexibility may help NG engines with high methane emis- The standards vary by truck type (tractor or vocational), sions comply. vehicle class, and roof height of the tractors. These vehicle The test cycle for measuring CO2 emissions from engines standards include no provision unique to NG engines. The used in Class 7 and Class 8 tractors is the supplemental emis- vehicle CO2 standards start in 2014, fuel economy standards sion test (SET). For engines used in vocational vehicles, the start in 2016, and both become more stringent and aligned in test cycle is the heavy-duty transient engine test procedure. 2017. Fuel economy and CO2 fleet average standards were Fuel economy standards for new engines have been also adopted for large pickups and vans, which are chassis- adopted by NHTSA. Compliance with the fuel economy certified. They are patterned after the adopted car and light standard is determined from the CO2 emissions measured by truck CO2 standards, and their numerical values vary by the appropriate emission test. Thus an engine that meets the vehicle attributes such as size. CO2 standard also meets the fuel economy standard, and vice Heavy-duty NG engines are not expected to require versa. The fuel economy standard for diesel engines does significant design changes to meet the current GHG and not begin until MY2017. SI engine fuel economy standards fuel economy standards. CO2 emissions from NG engines begin in 2016. are typically 5 to 20 percent lower than those from compa- rable gasoline or diesel engines, and this is about the same NG Engines reduction required by the current standards. The flexibility of using CO2 reduction to offset methane emissions that are NG engines have to meet the same emission standards as higher than the standard, as discussed in the section on GHG gasoline- or diesel-fueled engines. NG engines are classified emissions and fuel economy standards for engines, suggests for criteria emissions based on the combustion cycle of the the methane standard will not be a barrier to compliance for engine the NG engine is derived from. All larger NG engines NG engines. While NG leakage from a vehicle fuel system (over 7 L) are currently derived from diesel CI engines even is technically possible, manufacturers and operators have if they are converted to SI, and they are treated by EPA as great incentive to prevent this because it would represent a diesel engines for criteria emission certification. EPA also significant safety concern as well as a reduction in range. requires consistent categorization for both criteria and CO2 Fuel consumption certification at the vehicle level for emission compliance. Thus, under current EPA require- the new EPA-NHTSA standards is accomplished by use ments, larger heavy-duty NG engines, even if spark-ignited, of the Greenhouse gas Emissions Model (GEM), a vehicle will have to comply with the CI CO2 standards shown in simulation tool with standard engine maps10 as described in Table 5-5 beginning with the 2014 models. NG engines Chapter 3 of this report. At present, there is no engine map in derived from gasoline engines are subject to the numerically GEM for NG engines, so NG-powered vehicles are included higher SI CO2 standard beginning with the 2016 models. in an alternative certification process under the Advanced Dual-fuel engines and vehicles (such as NG and diesel) Technology and Innovative Technologies categories in the must be tested for CO2 emissions on each fuel. Through 2015 rule. Since NG-powered vehicles are expected to become the test results may be averaged; after 2015, the manufacturer significantly more prevalent in the coming years, future regu- must supply data on actual fuel use of each fuel for the type latory changes should consider modifying GEM to incorpo- of vehicle, and the test results are weighted appropriately. rate them. Using the procedures for Advanced Technology The combined test results must comply with the standards. credits may be replaced by providing a standardized NG Criteria emission standards must be met on both fuels. engine model (SI, stoichiometric, turbocharged) in addition However, separate evaporative testing of the CNG system to a diesel engine model. Otherwise, it could be multiplied is not required. by a factor relating it to a diesel engine. Although some NG The CO2 and fuel economy regulations change the engine engine technologies other than SI may be employed and may classification definitions in a manner that may one day affect offer higher efficiency, the SI model should serve as a base- NG engines. A literal reading of the new definitions suggests line owing to its current and likely future market penetration. that a SI engine derived from a diesel engine would be clas- Several Class 2b pickup and van producers have ques- sified as a SI engine and would have to meet the SI engine tioned the ability of gasoline engines to comply with the CO2 standard, which is less stringent than the diesel engine stringent new rules. Should these gasoline engines be CO2 standard it must meet in 2014. EPA has indicated that it may address this in a future rulemaking, but for now an 10 Engine maps are tables of engine input and output values engine manufacturer may choose to be classified based on determined from calibration tests. They represent how an engine either the new or the old definition. will operate under specific conditions.

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NATURAL GAS VEHICLES: IMPACTS AND REGULATORY FRAMEWORK 65 dropped from production (and probably replaced with diesel The load-specific CO2 emissions from NG engines are engines), the availability of Class 2b NG vehicles would be generally 5-20 percent less than those from comparable die- impacted because the NG engines with displacements of sel engines. NG’s inherent GHG benefit by virtue of its low less than 7 L are generally derived from gasoline engines. carbon content (~28 percent) is partially negated by lower EPA remains confident that technologies developed primar- efficiency in currently available engines and the higher GHG ily for light-duty engines will allow gasoline engines to impact of methane emissions. If the regulations require the remain viable in this class. This issue should be monitored same CO2 levels for trucks using either diesel or NG, then to determine if the availability of NG engines derived from it is conceivable a NG truck could meet the standards with gasoline engines will be impacted, and if this has an effect fewer advanced fuel economy technologies than a diesel on achieving the maximum feasible reduction in fuel use and counterpart. In contrast, a NG leakage correction to GHG GHG emissions. impact could negate the inherent tailpipe CO2 advantage. In summary, the current regulations accommodate NG engines and provide a pathway to their certification. Certi- Recommendation 5.2:  NHTSA and EPA should develop fying the fuel economy of dedicated NG vehicles would be a separate standard for NG vehicles as is presently the case more straightforward if NG engine maps were added to the for diesel- and gasoline-fueled vehicles. Factors the Agencies GEM vehicle simulation. should consider in setting the standard include the maximum feasible ability of NG engines to achieve reductions in GHG emissions and fuel consumption, the uncertainties involved FINDINGS AND RECOMMENDATIONS with the various alternatives, the impact of duty cycles on the Finding:  Most evidence points to a long-term price advan- ability to comply with the vehicle standards, the cost of the tage and abundant supply for NG. Market risks include technology, and rapid growth of the market for NG engines findings on leakage and environmental issues with fracking. and vehicles. This may require additional focused studies. Finding:  NG is a low-carbon fuel with a GHG advantage Recommendation 5.3:  Owing to the economics-driven over diesel and gasoline that varies in magnitude with engine rapid adoption of NG, it is urgent to develop an optimum technology and duty cycles. Being a large domestic resource, solution in Phase II Rule standards for both GHG emissions NG use contributes to national energy security. The use of and fuel consumption (as well as criteria emissions)—that is, NG contributes to the NHTSA energy mission and EPA’s a standard that will accommodate this fuel without artificially goal of reducing climate impacts, unless additional findings disrupting prevailing commercial transportation business of methane leakage alter this vision. models. Such standards need to be expedited to provide certainty to consumers and product developers alike, even as Finding:  NG is also an economical fuel for many applica- current business activities accelerate. As a specific example, tions in medium- and heavy-duty vehicles. By 2025, 20 the GEM certification tools need to include NG engine maps percent of new trucks sold could be fueled by NG, a very fast to more accurately quantify the emissions and fuel economy penetration rate from the current level. However, the regula- of NG vehicles. tory approach and standards themselves are in flux, which could potentially disrupt normal market dynamics. Recommendation 5.4:  To benefit fully from the GHG and petroleum displacement potential of NG, government and Recommendation 5.1:  More studies and data are needed to the private sector should support further technical improve- determine the well-to-tank GHG emissions of NG vehicles, ments in engine efficiency and operating costs, reduction of since current estimates vary significantly regarding quanti- storage costs, and emission controls (as is done for diesel fication of emissions leakage of methane. EPA and NHTSA engines). NHTSA and EPA should also evaluate the need should assemble a best estimate of well-to-tank GHG for and benefits and costs of an in-use NG fuel specification emissions to be used as a context for developing future for motor vehicle use. rulemakings. Finding:  The NG vehicle refueling infrastructure is grow- Finding:  With regard to the option of NG as a broad strategy ing, but the number of retail outlets for fueling medium- and for GHG reduction, NG engines are well-developed and can heavy-duty vehicles is still well short of what is needed. be readily employed in medium- and heavy-duty vehicles, especially with introduction of a 12 L engine for Class REFERENCES 8 trucks. There are areas of technology improvement for engine efficiency and maintenance cost reduction. On-vehi- AGA (American Gas Association). Undated. Available at http://www.aga. org/Kc/aboutnaturalgas/consumerinfo/Pages/NGDeliverySystemFacts. cle storage of NG has high initial cost, economically restrict- aspx. Accessed February 2014. ing NG usage to applications with high fuel consumption.

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