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- 1 

## Chapter 13: **Natural Gas Ve**  **hicles and Engines**  **13.1 Detailed Life**  **- Cycle Analysis**  We conducted a review to assess the lifecy cle impacts of natural gas used by the heavy
duty truck sector. We also present the results of an anal ys is by the Energy

I nformation Administration projecting the future use of natural gas b y heav y - dut y trucks. Finally, we list a number of potential technologies which could help to reduce the methane emissions from natural gas trucks
. 

### 13.1.1 **Upstream Emissions** Upstream methane emissions , occurring in the natural gas production, natural gas processing, transmission, storage and distribution sectors , are estimated and summarized in an annual report “ Inventory

of U.S. Greenhouse Gas Emissions a nd Sinks ” (GHG Inventory ) for the United Nations Framework Convention on Climate Change (UNFCCC). 1 As a basis for estimating the life
- cy cle impact of natural gas use by heavy
- dut y trucks, we used the year 2012 methane emission estimates in the most recent GHG Inventory , published in 2014. The GHG Inventory also includes the quantity of carbon dioxide which is co
- produced with methane throughout the natural gas sy stem and emitted to the atmosphere through venting, flaring, and as fugitive emissions. Th e GHG Inventory

is updated annuall y to account for new emission source s ( e.g., new natural gas wells ), updated data, emission factors and/or methodologies, and to account for changes in emissions due to changes in policy , regulat ions and industry practices
. The GHG Inventory reflects emission reductions due to existing state regulations, National Emission Standards for Hazardous Air Pollutants (NESHAP) promulgated by EPA in 1999, the New Source Performance Standards (NSPS) promulgated by EPA in 2012, and N atural Gas Star ( a flexible, voluntary

partnership that encourages oil and natural gas companies to adopt proven, cost - effective technologies and practices that improve operational efficiency and reduce methane emissions) E mission estimates in the GHG Inventory are generally bottom
- up estimates which are per - unit (compressor, pneumatic valve, etc.) emission estimates based on measured or calculated emission rates from such emission sources
. In addition to the national
- level data available through the GHG Inventory , facility
- level petroleum and natural gas sy stems data is also available through EPA’s Greenhouse Gas Reporting Program (GHGRP). These data represent a significant step forward in understanding GHG emissions from this sector and EPA expects that this data will be an important tool for the Agency and the public to anal yz e emissions, and understand emission trends. For some sources, EPA has alread y used GHGRP data to update emission estimates in the GHG inventory, and EPA plans to continue to leverage GHGRP data to update future GHG Inventories. The natural gas which comprises CNG is expected to be off
- loaded from the natural gas sy stem where the vehicles using CNG are refueled. This is because the natural gas used as CNG***** E.O. 12866 Review**

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13
- 2 is compr essed at the retail stations and fleet facilities which fuel the CNG vehicles. To get the natural gas to the CNG retail facilities, the natural gas must be shipped through the distribution sy stem downstream of the natural gas transmission sy stem. When th e natural gas is transmitted through the distribution system, the methane emissions are higher because the methane emissions from the distribution sy stem are added to the rest of the upstream methane emissions. Because LNG plants are located separate fro m the retail facilities, they can be located to access the lowest cost feedstock. This means the natural gas for LNG can be sourced from the larger natural gas transmission pipelines which are upstream of the distribution pipelines. This provides two adv antages for LNG: 1) by avoiding the natural gas distribution sy stem, the natural gas is priced lower, and 2) avoiding the natural gas distribution sy stem avoids the methane emissions which occur from the distribution sy stem. Table 13
- 1 c ontains the 2012 m ethane e missions e stimate for the UNFCCC d ocument.

**Table 13**  **- 1**  **Me thane Emissions from**  **the Natural Gas System in 2012**  EMISSION POINT FROM NG FACILIT IES METHANE EMISSIONS (G IG AGRAMS ) Field Production 1858 NG Processing 892 Transmission and Storage 2071 Subtotal without Distribution 4821 Distribution 1231 Total with Distribution 6052 The GHG Inventory

also includes the quantity of carbon dioxide which is co
- produced with methane throughout the natural gas s ys tem and emitted to the atmosphere through venting, flaring, and as fugitive emissions. This quantity is summarized in Table 13
- 2
. **Table 13**  **- 2**  **Carbon Dioxide**  **Emissions from the Natural Gas System in 2012**  EMISSION POINT FROM NG FACILIT I ES CARBON DIOXIDE EMISS IONS (GIGAGRAMS) Production 13,659 NG Processing 21,469 Transportation and Storage 63 Distribution 37 Total 35,228 In the GHG Inventory , EPA assessed the amount of uncertainty with its emission estimates and provided a lower and upper bound estimate for its emission estimates. The lower***** E.O. 12866 Review**

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- 3 bound emission estimate is 19 percent lower than the best case estimate in Table 13
- 1 and the upper bound estimate is 30 percent higher than the best case estimate. In the Climate Action Plan , EPA projects that methane emissions will increase in the future due to increases in natural gas production. 2 Table 13
- 3 summarizes the projected increase in US methane emissions from the Climate Action Plan and the projected increase in natural gas production referenced from the proposed power plant rulemaking , 3 which is likely the most consistent natural gas production es timate with the projections made in the Climate Action Plan. **Table 13**  **- 3**  **Projected Natural Gas Production Volume and Methane Em**  **issions (g/million BTU)** YEAR 2012 2020 2025 Methane Emissions Teregram CO 2 eq. 145 140 151 Natural Gas Production (dry) trillion cubic ft 24. 1 26.6 29.3
As Table 13
- 3 shows, methane emissions from natural gas facilities are expected to increase from 145 teregram CO 2 eq. in 2012 to 151 teregram CO 2 eq. in 2025, about a 4 percent increase. At the same time, natural gas production of dry natural gas is expected to increase from 24. 1 trillion cubic fee t in 2012 to 29.3 trillion cubic feet in 2025, about a 2 2 percent increase. When estimating the meth ane emissions on the same natural gas production basis, the methane emissions are projected to be 14 percent lower in 2025 than 2012. A In the GHG Inventory , emissions associated with powering the units or equipment (i.e., compressors, pumps) used in natu ral gas production, processing, transmission and distribution are aggregated with all the other fossil fuel combustion activities
. Rather than attempt to disaggregate those specific GHG emissions from the rest of the process emissions in the GHG Inventory , we instead use d the estimated emissions f o r these sources provided by GREET. 4 Table 13
- 4 summarizes the process energy consumed to produce and process natural gas.

A The 14% reduction figure is calculated by multiplying the methane emissions estimate in 2025 by the ratio of 2012 natural gas production over the 2025 natural gas production (151x24.1/29.3) and the resulting value is 115, which is 85.5% of 145, or 14% le ss.***** E.O. 12866 Review**

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- 4 **Table 13**  **- 4**  **Process Energy Dem**  **and by the Natural Gas System (BTU/million BTU)**  FUEL TYPE PRODUCTION NATURAL GAS PROCESSING TRANSMISSION/

DI STRIBUTION TO TAL Conv Wells Shale

Wells Weighted

Avg Natural Gas 22,016 20,955 21,307 26,123 0 47,430 Diesel 2816 2680 2725 272 0 2997 Electricity 256 244 248 816 0 1064 Gasoline 256 244 248 0 0 248 Resid 256 244 248 0 0 248 Totals 25,600 24,367 24,777 27,211 0 51,988 Table 13
- 5 contains the factors we used to convert the GREET process energy demands used to operate the equipment used to produce, process and distribute natural gas to carbon dioxide emissions for those process fuels. 5

**Table 13**  **- 5**  **Carbon Dioxide Emission Factors for Process Fuel Consumption** 

PROCESS FUEL GCO2/BTU Natural Gas 0.0398 Diesel 0.0555 Electricity 0.1549 Gasoline 0.0535 Resid 0.0563 Table 13
- 6 summarizes the total estimated methane and carbon dioxide emissions emitted by the up stream natural gas sy stem. Two estimates are provided, one of which includes the emissions from the distribution sy stem representing the upstream emissions for CNG. The second estimate summarizes the emissions excluding the emissions from the distributio n sy stem representing the upstream emissions for L NG , since it is expected to access the natural gas from the transmission portion of the natural gas sy stem.***** E.O. 12866 Review**

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- 5 **Table 13**  **- 6**  **Summ ary of Year 2025 Emissions from**  **t he Natural Gas System (grams/million BTU)**  METHANE EMISSIONS CARBON DIOXIDE CNG Analysis (includes CH 4 emissions from the distribution system) 242 3881 LNG Analysis (does not include CH 4 emissions from the distribution system) 192 3881


### 13.1.2 **Dow nstream**  **Emissions** The GHG Inventory does not estimate the methane emissions for natural gas once the natural gas is diverted for use by the transportation sector, thus, we obtained information from other sources. Natural gas can be used b y vehicles either as a co mpressed gas (CNG) or as liquefied natural gas (LNG). We discuss the emissions of both. 

### 13.1.2.1 Compressed Natural Gas ( CNG ) To make CNG available to trucks, the natural gas must be compressed from the pressure that it is available from the distribution pipeline s to a pressure over 3600 psi to enable filling the truck CNG storage tanks. We used the compression energy available from GREET for this step which reflects national
- average emissions for electricity generation. 6 The emissions associated with natural ga s compression for CNG are summarized in Table 13
- 7
. **Table 13**  **- 7**  **Estim ated Emissions for Electricity Generated to Power CNG Compressors (g/m**  **illion BTU)**

METHANE CARBON DIOXIDE NI TROUS OXID E Emissions 6.9 3988 0.06 An important advantage that CNG has over LNG is that only a single facility , the retail outlet, is required for distributing CNG, while LNG requires both a liquefaction plant and a retail outlet. The simplified logistics of providing CNG also provides fewer opportunities for emissions and leakage to the environment
. We are aware of the following two t ypes of emissions for CNG which are not estimated in the lifecy cle anal ys is due to lack of quantifiable data
. The first is CNG refueling emissions. CNG trucks are refueled at the retail stations providing CNG. When the refueling hose is disconnected from the connection fitting on the vehicle, a small amount of natural gas is released to the atmosphere. This CNG refueling vented gas has not been estimated and therefore not included in the lifecy cle anal ys is. The second is fugitive emissions from small leaks in the CNG fuel storage sy stem. While CNG has an advantage over LNG because it is contained in a sealed s ys tem , the very high pressure at which CNG is stored dramatically increases fugitive emissions if a fitting pipe were to develop a leak. The level of fugitive emissions for a certain sized hole is directly proportional to the pressure. We do not have an y data on the fugitive emissions from CNG trucks, theref ore, in our lifecy cle anal ys is, we assume that CNG fugitive emissions are zero which likely underestimates the methane emissions from CNG trucks.***** E.O. 12866 Review**

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- 6 

### 13.1.2.2 Liqu e fied Natural Gas (LNG) The first step in making L NG available to trucks is the liquefaction step. As discussed above, t h e liquefaction plant is likely to be constructed near natural gas transmission pipelines to access the natural gas at the lowest price point. The liquefaction step involves the remova l of heat from the natural gas until it undergoes a phase change from a gas to a liquid at a low pressure. Once the natural gas is liquefied, it is stored in an insulated storage tank to keep the LNG liquefied. LNG plants are configured depending on the ir ultimate capacity . World class LNG plants produce 5 million metric tons, or more, per y ear of LNG and the economy of scale of these large plants support the significant addition of capital to reduce their operating costs. An LNG plant solely

producing LNG for truck fuel is expected to be significantly smaller than the world class LNG export plants and so the capital invested is expected to be much lower, thus, their operating costs would be expected to be much higher, and their energy efficiency much l ower on a percentage basis. The California Air Resources Board estimates the liquefaction plants used for producing truck LNG fuel are 80 percent efficient, compared to 90 percent efficient for world class LNG plants. 7 In our lifecycle anal ys is of LNG as a truck fuel, we also assumed that LNG plants are 80 percent efficient. For our GHG analy sis, we estimate the carbon dioxide emitted when 20 percent of the natural gas is combusted to provide the energy required to liquefy the natural gas to L

NG. The upstream emissions associated with the natural gas used in the liquefaction process must be accounted for and added onto the LNG produced b y the plant. These emissions are included as indirect emissions. Table 13
- 8 summarizes the GHG emissions attributed to the liquefaction plant.

**Table 13**  **- 8**  **LNG Liquefaction Plant Emissions (g/million BTU)** 

METHANE CARBON DIOXIDE Direct Emissions 0 15,175 Indirect Emissions 48 970 Total Emissions 48 16,145 To transport the LNG to the retail station, the LNG is loaded into an insulated horizontal trailer designed specifically for transporting LNG. If the LNG in the trailer were to warm sufficiently

to cause the LNG to reach the pressure relief valve venting pressure, there would be boil
- off emissions from the trailer. However, since the LNG is super cooled, boil off events are likely to be rare. We used a CARB estimate of boil
- off emissions for LNG transportation between the LNG plant and retail ou tlets. 8 Table 13
- 9 c ontains the estimate of boil off emissions and the emissions from the vehicle transporting the LNG to retail.***** E.O. 12866 Review**

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- 7 **Table 13**  **- 9**  **Boil -**  **Off Em issions Estimate for LNG Transportation to Retail (g/m**  **illion BTU)**

METHANE CARBON DIOXIDE NI TROUS OXIDE Fuel Use (Diesel Fuel) 0.45 378 0.009 Methane Boil Off Emissions 0.43 0 0 Total 0.88 378 0.009 LNG is stored in the insulated storage tank at the retail facility . Heat gain in the storage tank could eventuall y lead to boil
- off emissions. Service stations with little LNG demand are at a higher risk of boil
- off emissions compared to service stations which have a significant throughput volume. LNG stations could be configured to avoid boil
- off events to the atmosphere, such as venting to a co
- located CNG facility , or venting to a nearby natural gas pipeline. We used a CARB emission estimate to provi de an estimate of the boil
- off emissions from LNG retail facilities. 9 Table 13
- 10 summarizes the estimated boil off emissions for L NG retail facilities.

**Table 13**  **- 10**  **Boil -**  **Off Em issions Estim**  **ate for LNG Retail Facilities (g/m illion BTU)**  METHANE EMISSIONS LNG Retail Boil
- Off Emissions 1 1
. 1 The total well to tank emissions for CNG and LNG are summarized in Table 13
- 12
. These emissions represent the total of upstream and downstream emissions which includes delivering the fuel to the truck fuel storage tank.

**Table 13**  **- 11**  **Total Well to Tank Emissions Estimate for CNG and LNG (g/million BTU)**

METHANE CARBON DIOXIDE NI TROUS OXIDE CNG 249 7869 0.07 LNG 251 20,405 0.009 

### 13.1.3 **Vehicle E**  **missions** 13.1.3.1 Vehicle Configurations There are several different way s that diesel heav y duty engines can be configured to use natural gas as a fuel. The first is a spark ignition natural gas (SING), Otto cy cle SING heavy duty engine burns the fuel stoichiometric al ly and uses a three
- way

catal ys t and some also add an oxidation cataly st to provide the greatest emissions reduction
. Stoichiometric combustion is used in most light
- duty

SING engines. Problems with thermal stress and low power density have favored the use of the lean
- burn combustion sy stem in heavy dut y engines. The use of cooled EGR provides further potential to increase the engine output and, at the same time , decreases NO X emissions
. In this case the engine compression ratio is reduced similar to that of a gasoline***** E.O. 12866 Review**

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- 8 engine, about 12 to 1 or more , and thus its thermal effi ciency is lower than a diesel
- like engine by about 10
- 15 percent , depending on the driver
. The second is a direct injection natural gas (DING), d iesel cy cle. The DING engine uses a small quantity

of diesel fuel (pilot injection) or a glow plug as ignition sources. As the injection sy stem for the diesel fuel does not have the capability of greater injection quantities, this option has no dual
- fuel properties. On the other hand, an optimization of the pilot injection can be made to achieve lower emissions. An advanced high pressure direct injection (HPDI) fuel sy stem combining the injection of both diesel fuel and natural gas can be used for lean b urn combustion. This enables the engine to maintain the efficiency advantage of a compression ignition engine while running mainly CNG/LNG. The third is a mixed
- fuel natural gas (MFNG), d iesel cy cle. In a mixed
- fuel engine, natural gas is mixed with int ake air before induction to the cy linder and diesel fuel is used as ignition source. Mixed
- fuel vehicle/engine means any vehicle/engine engineered and designed to be operated on the original fuel(s), or a mixture of two or more fuels that are combusted to gether. Mixed
- fuel sy stem means that a diesel engine works with two ty pes of fuels together. In fact the engine is a diesel thermody namic cy cle and the energy is given by

the diesel and the natural gas fuel. In mixed
- fuel conversion the original engine i s not modified in any way , a conversion s ys tem is installed in order to permit the engine to run on both fuels
. The conversion of the engine is totally

reversible, in fact it is possible to choose the mode how to run the engine (diesel / mixed
- fuel). Whe n the engine runs in diesel mode, the engine runs in the same way as per the original configuration. Engine results showed that the efficiency of the engine could decrease b y about 2
- 5 percent in mixed
- fuel mode compared to diesel mode and that the diesel replacement was approx imately 40
- 60 percent efficient
. Each of these natural gas engine ty pes has its merits. The SI NG engine is less costly , but is less fuel efficient and because of the lower compression ratio it has less torque than the two diesel cy cle engines. The DING engine is likely the most expensive because of the special natural gas/diesel fuel injection sy stem and large required amount of natural gas (LNG or CNG) storage since the truck must run on natu ral gas. However, because the truck can run almost completely

on natural gas, the DING engine has the potential to more quickly pay down the higher investment cost of the natural gas truck. The MFNG engine provides the truck owner the flexibility to oper ate on natural gas or diesel fuel, but at the expense of a slower natural gas investment pay down rate because it can operate at most 50 percent of the time on natural gas. An important advantage of LNG is the increased energy densit y compared to C NG. At present, CNG stored at its maximum storage pressure is only 25 percent of the energy

density of diesel fuel, while LNG contains about 60 percent of the energy density of diesel fuel. Because of its higher energy

densit y, L

NG is favored over CNG fo r long
- haul trucking. An adsorbent for natural gas (ANG) material technology B called metal organic framework (MOF) for storing CNG

B Menon, V.C., Komarneni, S. 1998 “Porous Adsorbents for Vehicular Natural Gas Storage: A Revie w”, Journal of Porous Materials 5, 43
- 58 (1998); Burchell, T “Carbon Fiber Composite Adsorbent Media for Low Pressure Natural Gas Storage” Oak Ridge National Laboratory***** E.O. 12866 Review**

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- 9 has been invented and is being tested for large scale use. The technology involves filling the CNG tank with a specially de signed substance which looks similar to a pelletized cataly st. The substance establishes a matrix which causes the methane molecules in natural gas to become better organized and store the same quantit y of natural gas in a smaller volume at the same press ure, or store the same density of natural gas at a lower pressure. This MOF could improve the energy

density of CNG which would make it a better candidate for natural gas storage for long range combination trucks, while avoiding the boil
- off events that a re a risk with using LNG. 

### 13.1.3.2 Tailpipe Emissions When assessing the methane emissions from both CNG and LNG trucks, it is important to separate those trucks built or converted before 2014 to those built or converted in 2014 and later. The trucks built before 2014 are onl y required to meet a nonmethane hy drocarbon (NMHC) standard, which means that the methane emissions from these trucks are unregulated. Our certification data shows that the methane tailpipe emissions from these trucks/buses ranges from 2

– 5 g /bhp
- hr for both spark ignition (gasoline ty pe) and compression ignition (diesel t ype) engines. For 2014 and later OEM compression ignition natural gas trucks or natural gas conversions of 2014 and later diesel trucks , the trucks must meet a 0.1 g/bhp
- hr methane emission standard in the case of a larger truck engine tested with an engine dy namometer, and a 0.05 g/mile methane emission standard in the case of smaller trucks tested on a chassis dy namometer. For spark ignition (gasoline sty le) engines, the standards take effect in 2016. 10 The natural gas truck manufacturers are allowed to offset methane emissions over the standard by converting the methane emission exceedances into CO 2 equivalent emissions and using CO 2 credits. For the initial natural gas engine certifications that EPA received for 2014, the truck manufactures chose to continue to emit high levels of methane (around 2 g/bhp
- hr) and use carbon dioxide credits to offset those emissions. We don’t know if this practice of using CO 2 credits to offset high methane emissions will continue in the future, however, for evaluating the lifecy cle impacts of natural gas heav y - duty vehicles , the 2014 and later natural gas heav y - dut y trucks may

in fact have an emissions profile more like the pr e - 2014 trucks and not like the 2014 and later trucks as depicted below in the figures
. Furthermore, our emissions analy sis assumes that these trucks are emitting GHG emissions as designed. In cases when these trucks experience an increase in emissions du e to deterioration or malfunction of the engines, fuel supplies or associated emission control devices on these trucks, the methane emissions could be high er than estimated
. Table 13
- 12 summarizes the emission standards and the estimated methane emissions from heav y - duty

trucks assumed in the anal ys is
.***** E.O. 12866 Review**

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- 10 **Table 13**  **- 12**  **Methane Em**  **ission Standards and Estimated Emissions fr om**  **Heavy -**  **Duty Trucks** PRE
- 2014 2014 AND LATER Methane Standard None g/bhp
- hr Estimated Emissions g/bhp
- hr 2

– 5 0.05 g/ million BTU 214

– 534 5.3 

### 13.1.3.3 Boil
- off, Venting and other Fugitive Emissions Truck drivers requiring LNG fuel drive up to an LNG retail outlet or fleet refueling facility and fill up with LNG fuel. When the refueling nozzle is disconnected from the LNG tank nozzle, a small amount of methane is released to the environment. In addi tion, prior to refueling it may be necessary

or advantageous, due to high pressure in the truck’s LNG tank, to reduce the pressure in the truck’s LNG tank to speed up the refueling process. In some cases the retail station is equipped with another hose an d associated piping to vent the excess gas to the retail stations’ storage tank, or perhaps to a natural gas pipeline. However, for those retail outlets without such vent lines to the storage tank, the truck driver may simpl y vent the truck’s storage tank to atmosphere. As part of a sensitivity anal ys is for our lifecy cle analy sis, we estimate the emissions for venting an LNG tank prior to refueling. A major GHG issue for LNG trucks is boil
- off emissions from the trucks themselves. When the liquefied natu ral gas is pumped into the truck LNG tanks, it is “supercooled,” meaning that the temperature of the LNG is well below the boil
- off pressure and temperature. If the truck is driven extensively

the drawdown of liquid level will cause some of the fuel to bo il off and thus cool the rest of the liquid in the L NG storage tank. I t is possible that the fuel would maintain its supercooled temperature or possibly even cool further below its supercooled temperature all the time until the LNG is completely consumed. If the truck is not driven or is driven very little, the very

low temperature LNG warms through ambient temperature gradient through the tank wall causing the temperature and pressure of the LNG to rise. When the pressure reaches a maximum of 230 psi there is a safet y release valve on the LNG storage tank which releases the methane gas directl y to the atmosphere until the pressure drops to 170 psi, the pressure at which the safet y release resets. There are two industry standards used to design tanks t o reduce the temperature increase, one for a 3 day hold time C and one for a 5 day hold time. D Hold time is the minimum time elapsed between when the truck’s LNG tank is refueled and when it begins to vent. If there is a boil
- off event, a large amount of methane would be released. If aware of the impending boil
- off such as when the truck is being maintained, the truck driver could hook up the L NG tank to a hose which would vent the natural gas emissions to a CNG sy stem which

C National Fire Protection Association 52, Compressed Natural Gas (CNG) Vehicular Fuel System Code, 2002 Edition D SAE International (2008) SAE J2343: Recommended Practice for LNG Medium and Heavy
- Duty Pow ered Vehicles. Warrendale, Pennsylva nia.***** E.O. 12866 Review**

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- 11 would reuse the boil
- off natu ral gas as CNG, or vent the natural gas emission to a natural gas pipeline. Otherwise the boil
- off emission would simply vent to the atmosphere. When an L

NG fuel tank venting (refueling venting or boil
- off) incident occurs, there are two separate proces ses which occur that contribute to methane emissions during the venting. The most obvious process is the pressure drop, from 230 to 170 psi, in the gaseous space above the liquid. The volume of gas vented is proportional to the reduction in absolute pres sure in the tank. Since the drop in absolute pressure is 244 to 184 psi (14.7 psi is added to the 230 and 170 psi gauge pressure), about 25 percent of the gas in the tank is vented (184 psi is 25 percent of the way from 244 psi to zero pressure). The sec ond process is the vaporization of liquid during the pressure reduction in the LNG tank. The boiling point of any liquid decreases as the pressure decreases. Thus, when the LNG undergoes the pressure reduction during a venting/boil
- off, the boiling point of the methane decreases and to balance the s ys tem, some of the liquid methane must boil off to cause the cooling of the liquid. The quantity liquid methane which must boil off from the liquid is calculated from methane’s heat of vaporization over the bo iling point temperature change, which drops from
- 178 F to
- 189 F as the pressure drops from 230 to 170 psi. The amount of natural gas which boils off during a venting event varies based on the quantity of liquid in the LNG storage tank. The greatest am ount of natural gas which is lost during a venting/boil off event occurs when the tank is closest to being full. For a 200 gallon tank sy stem, each boil off event has the potential to release on the order of 3
- 9 gallons or 5,300

– 15,800 grams of CH 4 whic h translates to 132

– 400K grams of CO 2 - equivalent emissions, assuming methane has global warming potential (GWP) of 25 over a 100 year lifetime. If the vehicle continues to sit after boil
- off events begin to occur with boil
- off events each day and up to several boil
- offs per day , as much as million grams of CO 2 - equivalent emissions may be emitted over the twent y or so day s at which point the vehicle LNG tank would be completel y empty . Table 13
- 13 summarizes the starting and ending conditions and the loss from the tank for venting incidents (200 gallon L NG tank decreases in pressure from 230 to 170 psi) when the LNG tank is 90 percent, 50 percent and 10 percent full. A refueling venting event is more likel y to occur when the tank is mostly empty , so the 50 and 10 percent case s are the most likely cases to consider
. **Table 13**  **- 13**  **Estim ated Quantity of Boil**  **- Off from**  **a 200 Gallon LNG Fuel Tank for a Single Boil**  **- Off Event** 

PERCENT FULL (INIT IAL) PERCENT FULL

(FINAL) LI QUID LOSS

(GALS) TO TAL MASS

LOSS (LBS) Boil
- off Scenarios 90 83.2 13.6 38.7

50 46.2 7.6 24.8 10 9.3 1.5 11.0 Table 13
- 13 shows that if a truck had 200 gallon of LNG storage capacit y, the estimated quantity of liquid boil
- off volume would range from 2 to 14 liquid gallons of LNG depending on the fill level of th e LNG tank. When the quantity of LNG gas loss is included, the total loss ranges from 11 to 39 lbs.***** E.O. 12866 Review**

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- 12 The quantity

of LNG tank boil
- off or venting per distance driven b y the truck depends on the frequency

of boil
- off or venting incidents. As described ab ove, a truck’s driving profile play s a key

role in determining the boil
- off risk from L NG trucks. Fleets which purchase LNG trucks do so with the intent of driving the LNG truck extensively to pay off the much higher purchase price of the LNG truck. For this reason, there is likely to be few boil
- off incidents, except for cases when the truck is forced out of its routine. Examples of when the truck might be sidelined include times when the truck is being maintained, the immediate period after the truck i s involved in an accident or perhaps when the owning compan y experiences a loss of workload or files for bankruptcy . We have no data which would allow us to estimate the frequency when these sorts of incidents would occur, and even if we did, we still cou ld not estimate the frequency of boil
- offs that occur in these cases. As the truck ages, it likely would be sold by

the company

which originally purchased the truck to avoid having to deal with the increased maintenance that occurs with older trucks. Figure 13
- 1 shows the estimated vehicle miles traveled by class 8 trucks as they

age (the data is from the MOVES Model.

**Figure 13**  **- 1**  **Vehicle Miles Traveled by Com bination Trucks in 2014**  Figure 13
- 1 shows that the mileage driven b y combination tr ucks decreases as they

age. By the time that a combination truck is about 17 years old, it is driven about half the number of miles per y ear as a new truck. I t would seem that the risk of boil
- off incidents increases with these older trucks. Venting inci dents during refueling can occur at any time, and there is an incentive to do so when it is time to refuel. The decision to vent an LNG tank in most cases is solely up to the truck driver who is often under pressure to complete his work in less time to ma ximize profits. There is a lot of uncertainty in estimating the quantity of boil
- off and venting from an LNG truck. To reflect this uncertaint y, we assume two different boil
- off/venting emission estimates. The low estimate assumes that 35 grams per mil lion BTU of fuel consumed is

0 20,000 40,000 60,000 80,000 100,000 120,000 140,000

1995 2000 2005 2010 2015MilesDrivenperYear



### Tr uck Y ear***** E.O. 12866 Review**

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13
- 13 emitted , which is from GREET. The high estimate assumes a boil
- off event and a venting event each time the truck is refueled and before that tank full of LNG is used up , and this quantity is estimated to be 734 g per million B TU of fuel consumed
. The crankcase of these engines receives leakage from across the piston rings, which can contain methane. The crankcase of the spark ignition engines is normall y vented into the intake of the engines, thus, an y methane emissions f rom the crankcase which is not combusted in the engine would be accounted for in both the engine
- out and tailpipe emissions. For compression ignition engines, however, the crankcase emissions are t ypicall y vented into the exhaust pipe downstream of the aftertreatment devices although they are accounted for in addition to the engine
- out emissions during certification
. E ngine
- out emissions are subjected to deterioration factor s based on well
- established pro cedure , which may make them more robust than deterioration factors for vented crankcase emissions . Moreover, deterioration of crankcase emissions may

be more variable. Thus, sealed crankcase s would achieve more robust control of methane emissions
. Another potential source of methane emissions from CNG and LNG trucks is leaks from the fuel piping which to the engine which is another source of fugitive emissions. Thus, either while parked or operated, the vehicle fuel and engine sy stems could leak methane to the environment. We do not have nor did we attempt to estimate this ty pe of methane fugitive emissions from CNG or LNG trucks
. Table 13
- 14 summarize the estimated tailpipe emissions for CNG trucks, and Table 13
- 15 summarizes the estimated tailpipe and boil
- off and venting emissions for LNG trucks.

**Table 13**  **- 14**  **Estim ated**  **Tailpipe Emissions for CNG Trucks (g/mmbtu)** METHANE CARBON

DI OXIDE NI TROUS

OXIDE 2014 and Later Direct 5.3 60,702 2

Indirect 0.1 3 0 Total 5.4 60,705 2 Pre
- 2014 Direct 374 60,702 2

Indirect 6 189 0 Total 380 60,891 2
**Table 13**  **- 15**  **Estim ated**  **Tailpipe and Boil**  **- Off**  **Emissions for LNG Trucks (g/mmbtu)**  METHANE CARBON

DI OXIDE NI TROUS

OXIDE 2014 and Later assuming low Venting and Boil
Off Emissions Direct 5.3 60,702 2

Indirect 0.07 5.5 0 Total 40.4 60.707 2 2014 and Later Assuming High Venting and Direct 5.3 60,702 2

Indirect 0.07 5.5 0 Total 739 60,707 2***** E.O. 12866 Review**

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13
- 14 Boil
- Off Emissions Pre
- 2014 Assuming Low Venting and Boil
- Off Emissions Direct 374 60,702 2

Indirect 4.8 386 0 Total 413 61,088 2



### 13.1.3.4 Thermal Efficiency While not an emission source per se, the thermal efficiency of the natural gas engine also play s a role in the lifecy cle emissions of the truck. Thermal efficiency is defined by

the amount of energy that is obtained to propel the truck compared to the ene rgy consumed by

the engine. If a fuel
- engine is less thermally efficient, then it consumes more fuel, or more BTUs, to travel the same distance, thus, emitting more carbon dioxide per distance traveled, or work performed. We estimate that SI

NG engines c an be as much as 15 percent less efficient than compressed ignition engines which operate on diesel fuel. Conversel y, DI NG and MFNG engines which operate at a higher compression ratio, are estimated to be 5 percent less energy efficient compared to a dies el engine. In our lifecycle anal ys is, we provide two different sensitivities for natural gas vehicles assuming that they may be 5 percent and 15 percent less efficient. 

### 13.1.4 **Results of Life Cycle Analysis**  To estimate the lifecy cle impact of natural gas used by heavy
- dut y trucks, we totaled the carbon dioxide, methane and the nitrous oxide emissions for the upstream and downstream portions of the natural gas sy stem. The methane and nitrous oxide emissions are converted to carbon dioxide
- equivalent emissions usi ng global warming potential s ( (GWP s ) ; these are a measure of the relative contribution of global warming of emissions of a given gas in comparison to that of carbon dioxide over a given time period) . The GWP s EPA is currently using is from the AR 4 (2007) IPCC report for 100 ye ar timeframe, which is 25 and 298 for methane and N 2 O , respectivel y. To establish the impacts of natural gas use in the heav y - dut y fleet, it was necessary to compare the lifecy cle impacts of natural gas against its replacement, whic h is a diesel fueled heav y - dut y truck. The lifecy cle impact diesel fuel was estimated by the National Energy Technology Laboratory (NETL) for the production and use of diesel fuel in 2005. EPA used this lifecy cle assessment for the Renewable Fuel Standar d Rulemaking. We used this NETL diesel fuel lifecy cle estimate for the baseline for comparison with the natural gas lifecy cle assessment. The vehicle nitrous oxide and methane emissions are from the MOVES vehicle model developed by EPA. Table 13
- 16 summarizes the lifecy cle emissions for diesel fuel estimated by NETL. **Table 13**  **- 16**  **Estim ated**  **Diesel Fuel Lifecycle Greenhouse Gas Emissions (g/million BTU)******* E.O. 12866 Review**

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13
- 15 CARBON DI OXI DE METHANE NI TROUS OXIDE TO TALS

CO 2 EQ * Well to Tank 15,838 98 0.3 18,377 Tank to Wheels 78,308 1 2 78,929 Well to Wheels 94,146 99 2.3 97,306 Note: *T he totals are calculated using 25 and 298 for the GWPs for methane and nitrous oxide, respectively. NETL is in the process of updating its lifecy cle analy sis from the 2005 analy sis y ear to 2009 as the anal ys is y ear. While the revised lifecy cle anal ys is is not y et available, one of the author s of the analy sis explained that the 2009 analy sis appears to b e quite similar to the 2005 anal ys is. 11 To illustrate the relative full lifecy cle impact of natural gas
- fueled heavy
- duty vehicles versus diesel fueled heavy
- dut y vehicles, we assessed a couple different scenarios. The first scenario is a conversion of a diesel engine to use CNG . Of the tens of thousands of heav y - duty natural gas trucks currently in use, over 90 percent are of this t ype. These are conversions of older trucks so they

are not regulated by

the 2014 methane standard. For future y ear heavy
- duty trucks, we also estimated the lifecy cle emissions if the trucks were meeting a 0.1 g/bhp
- hr or a 0.05 g/mile methane tailpipe standard. We provide two estimates for the lower thermal efficiencies of CNG trucks, one assumes that the truck is 5 percent less thermally efficient and the second assumes that the truck is 15 percent less thermally efficient (10 percent less efficient than the 5 percent less thermally efficient case). The estimated lifecy cle emissions of CNG trucks, assuming projected upstre am emissions in 2025, is summarized in Table 13
- 17
.***** E.O. 12866 Review**

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13
- 16 **Table 13**  **- 17**  **Full Lifecycle Analysis of a CNG Truck (g/million BTU)**  TRUC K TYPE EMISSION

CATEGOR Y CARBO

N DI OXI D E METHAN

E NI TROU

S OXIDE TO TA

L CO 2 EQ.* THERMAL

EFFICIENC Y 5% AND 1 5 % CO 2 EQ.* TO TALS

INCLUDING THERMAL EFFICIENC Y IMPACT CO 2 EQ. * Pre
2014 CNG Truck Well to

Tank 7869 249 0.07 14,107 705 2116 14,812

16,223 Tank to Wheels 60,891 380 2 70,98 0 3 548 10647 74, 528

8 1 , 627 Well to Wheels 68,760 628 2 85087 4254 12,763 8 9,379

9 7 , 8 50 2014 or Later Truck Well to

Tank 7869 249 0.07 14,107 705 2116 14,812

16,223 Tank to Wheels 60,704 5 2 61,436 30 7 2 9 215 64, 508

70, 651 Well to Wheels 68574 254 2 75,544 3 7 77 11, 331 79, 321

8 6 , 875 Note: *T he CO 2 eq. totals are calculated using 25 and 298 for the GWPs for methane and nitrous oxide, respectively. The CNG lifecy cle assessment relative to a diesel truck lifecy cle anal ys is is shown in Figure 13
- 2
.

**Figure 13**  **- 2**  **Full Lifecycle**  **Analysis of a CNG Truck**

**( Projected**  **Upstream Methane Emissions**  **in 2025, Methane**  **GWP of 25**  **)** In the first two bars of Figure, it shows that based solely on tailpipe emissions (with and without thermal efficiency adjustments and assuming no increased methane emissions at the 0 20,000 40,000 60,000 80,000 100,000 120,000

Diesel

Tailpipe CNG

Tailpipe Diesel CNG pre2014 CNG 2014 and later**E m** **i s** **s i** **o n** **s (** **g C** **O 2** **e q** **/ m** **m B** **t u** **)** Thermal High

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13
- 17 truck), natural gas trucks are estimated to emit about 20 percent less GHG emissions than diesel engines. But this advantage decreases if the natural gas engine is less thermally efficient. The three full lifecy cle anal ys es represented b y the right three bars in the figure shows that pre
- 2014 CNG trucks are estimated to emit a bout the same GHG emissions as diesel trucks, although if their thermal efficiency

is much lower or if a higher GWP for methane were used, they would likely be somewhat higher emitting in GHG emissions. When such trucks are compl yi ng with the 2014 and lat er methane emission standards, their methane emissions are much lower and these trucks are expected to be lower emitting than diesels, even considering if they are less thermally efficient. The second scenario is a combination truck which is assumed to be in compl iance with the 2014 methane standard. Because it is high mileage truck , the truck most realistically must use LNG as a fuel to provide the necessary range for the dedicated natural gas engine. We make two different assumptions with respect to refueling and boil off emissions. I n the natural gas average case, we assume a modest quantity of refueling and boil
- off methane emissions which is equal to the combined boil
- off emissions from the liquefaction, transportation and retail station as estima ted b y GREET. The second boil
- off emission estimate is based on venting the LNG storage tank to the atmosphere each time the driver refills his tank, and one LNG boil
- off event between each time the driver must refuel his tank. As we discussed in the dis cussion about refueling and truck boil
- off emissions, we don’t expect this to be as common practices for newer trucks that are operated regularl y. However, as the use of these trucks decreases as they age and are sold into the secondary market, the risk f

or refueling and boil
- off emission events increases

– this estimate provides a simple sensitivity emission estimate. The estimated lifecy cle emissions of LNG trucks, assuming projected upstream emissions in 2025, is summarized in Table 13
- 18 **.**

**Table 13**  **- 18**  **Full Lifecycle Analysis of an LNG Truck (g/m illion BTU)**  TRUCK TYPE EMISSION

CATEGOR Y CARBO

N DI OXI D E METHAN

E NI TROU

S OXIDE TO TALS

* CO 2 EQ. THERMAL

EFFICIENC Y 5% AND 15% CO 2 EQ.* TO TALS

INCLUDIN G THERMAL EFFICIENC Y IMPACT CO 2 EQ.* Pre
- 2014 LNG Trucks assumin g low Venting and Boil
Off Emission s Well to

Tank 20,405 251 0.01 26,693 1334 4004 28,027

30,697 Tank to Wheels 61,088 413 2 72,896 3645 10,934 76,542

83,831 Well to Wheels 81,494 665 2 98 , 732 4 935 14 ,807 1 03 , 668

113 , 540

2014 and Later LNG Trucks assumin Well to

Tank 20,405 251 0.01 26,693 1334 4004 28,027

30,697 Tank to Wheels 60,707 40 2 62314 3116 9347 65,429

71,661 Well to 81,113 291 2 89,024 4450 93.475***** E.O. 12866 Review**

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13
- 18 g low Venting and Boil
Off Emission s Wheels 13 , 350 102,375

2014 and Later LNG Trucks with High Venting and Boil
Off Emission s Well to

Tank 20,405 251 0.01 26,693 1334 4004 28,027

30,697 Tank to Wheels 60,707 990 2 86,037 3035 9106 89,072

95,143 Well to Wheels 81,113 990 2 112,720 4370 13 , 109 117,090

125,829

Note: *T he totals are calculated using 25 and 298 for the GWPs for methane and nitrous oxide, respectively. The LNG truck lifecy cle anal ys is relative to a diesel truck lifecy cle analy sis is shown in Figure 13
- 3
.

**Figure 13**  **- 3**  **Full Life**  **c ycle Analysis of an LNG**  **Truck (Projected**  **Upstream Methane Emissions in 2025, Low and High Refueling and Boil**  **- Off**  **Em ission**  **, M**  **ethane GWP**  **of 25 )**  Figure 13
- 3 shows that LNG trucks have about the same greenhouse gas foot print as diesel trucks when we assume a low quantity of refueling and boil
- off emissions. I n comparing CNG to L NG, the LNG trucks appear higher emitting than CNG trucks because of the low

0 20,000 40,000 60,000 80,000 100,000 120,000 140,000**E m** **i s** **s i** **o n** **s (** **g C** **O 2** **e q** **/ m** **m B** **t u** **)**

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13
- 19 thermal efficiency

of the small liquefaction facilities. If these LNG trucks emit high levels of methane when refueling and by experiencing boil
- off events, their GHG emissions can potentially

be much greater than that from diesel trucks. It is important to point out the uncertainties associated with the lifecy cle estima tes provided Figures 13
- 2 and 13
- 3 . As discussed above, there is uncertaint y in both the upstream and downstream methane emission estimates for natural gas facilities and equipment, and the trucks that consume natural gas. In the GHG Inventory , EPA estim ates a range of natural gas emissions from the upstream natural gas production sector. The range varies from
- 19 percent to +30 percent relative to the principal estimate. To illustrate the impact the range has on the relative life cy cle impacts of natur al gas versus diesel trucks, Figure 13
- 4 shows the impact on the relative life cy cle emissions for CNG trucks when the low and high methane emissions are compared to the best estimate case we used in the above analy ses for a CNG truck compl yi ng with the methane emissions standards
.

**Figure 13**  **- 4**  **Full Lifecycle**  **Analysis of a CNG Truck -**  **Low, Avg and High Upstream Me**  **thane Emissions**

**(Projected Upstream**  **M ethane**  **E mi**  **ssions in 2025, Methane**  **GWP of 25**  **)** Figure 13
- 4 shows that higher and lower upstream emissions , based on the uncertaint y factors provided in the GHG Inventory , does impact the relative GHG lifecy cle impact of CNG trucks, but the effect is quite modest relative to the other emissions effects depicted in the figures presented earlier
. As new methane emission information becomes available, we will update our methane emission estimates which would reduce the uncertainty
. In ad dition to the new methane emissions information from the GHG Reporting Program, there will likely be other studies as well. For example, a number of studies are being conducted to quantify the methane emissions and life cy cle impacts of natural gas by Env ironmental Defense Fund (EDF). The final reports for these studies have not y et been released but we will review them once they are available. T he GWP s used to assess the relative climate impacts of methane and nitrous oxide can also effect the relative life cy cle impacts natural gas trucks compared to diesel trucks. The 0 20,000 40,000 60,000 80,000 100,000 120,000

Diesel

Tailpipe Nat Gas Tailpipe Diesel Nat Gas

Low Nat Gas Avg Nat Gas High Thermal High

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13
- 20 GWPs of methane and nitrous oxide vary based on the timescale assumed
. To illustrate this point, we added two more sets of figures as sensitivities for comp aring the life cy cle impacts of CNG and LNG natural gas trucks to diesel trucks if the greenhouse gas emissions are evaluated over a different lifetime . The GWPs that we use are the two alterative GWPs reported by I PCC in its 4 th Assessment Report evaluat ed at 20 y ear and 500 y ear GHG lifetimes
. Table 13
- 19 summarizes the GWPs at the different lifetimes along with the GWPs used in the pri mary anal ys is summarized above
. **Table 13**  **- 19**  **Summary of GWPs** PRIMARY ANALYSIS SENSITIVITY ANALYSES 100 Year 20 Year 500 Year Methane ( CH 4 ) 25 72 7.6 Nitrous Oxide ( N 2 O ) 298 289 153 It is important to point out that while there are fairly significant differences in methane emissions between the various natural gas cases being studies and compared to diesel trucks, the nitrous oxide emission s var y ver y little across all the cases. Therefore, when comparing the relative lifecy cle impacts using different GWPs, the impact on relative lifecy cle emissions is almost exclusively

due to changes in the methane GWP. Figures 13
- 5 through 13
- 8 show the relative lifecy cle effect s of natural gas trucks compared to diesel trucks when the GWPs used are based on 20 ye ar and 500 y ear lifetimes.

**Figure 13**  **- 5**  **Full Lifecycle**  **Analysis of a CNG Truck (Projected**  **U pstream**  **M ethane**  **E mi**  **ssions in 2025, Methane**  **GWP of 72**  **)**

0 20,000 40,000 60,000 80,000 100,000 120,000 140,000

Diesel

Tailpipe CNG

Tailpipe Diesel CNG pre2014 CNG 2014 and later**E m** **i s** **s i** **o n** **s (** **g C** **O 2** **e q** **/ m** **m B** **t u** **)** Thermal High

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13
- 21 **Figure 13**  **- 6**  **Full Life c**  **ycle Analysis of an LNG truck (Projected**  **Upstream Methane**  **Emissions in 2025, Low and High R**  **efueling and Boil -**  **Off Em ission,**  **methane GWP**  **of 72 )** 

**Figure 13**  **- 7**  **Full Lifecycle**  **Analysis of a CNG Truck (Projected**  **Upstream M**  **ethane E**  **mi ssions in 2025,**  **Methane GWP of**  **7 .**  **6 )** 

0 20,000 40,000 60,000 80,000 100,000 120,000 140,000 160,000 180,000 200,000**E m** **i s** **s i** **o n** **s (** **g C** **O 2** **e q** **/ m** **m B** **t u** **)**

Thermal High Thermal Low CH4:&N2O CO2

0 20,000 40,000 60,000 80,000 100,000 120,000

Diesel

Tailpipe CNG

Tailpipe Diesel CNG pre2014 CNG 2014 and later**E m** **i s** **s i** **o n** **s (** **g C** **O 2** **e q** **/ m** **m B** **t u** **)** Thermal High

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13
- 22 **Figure 13**  **- 8**  **Full Life c**  **ycle Analysis of an LNG truck (Projected**  **Upstream Methane Emissions in 2025,**  **Low and High Refueling and Boil -**  **Off Em**  **ission, Methane**  **GWP of 7.6**  **)** Figures 13
- 5 through 13
- 8 show that when evaluated over a shorter timescale, the higher GWP for methane increases the relative lifecy cle impact of natural gas trucks compared to diesel trucks. Conversel y, when evaluated over a longer timescale, the lower GWP for methane decreases the relative lifecy cle impact of natural gas trucks compared to diesel trucks. We compared our lifecy cle emission estimates for natural gas, relative to diesel fuel, with the estimates provided by th e California Air Resources Board (CARB) for its L ow Carbon Fuel Standard (LCFS). For our emissions estimate used in the comparison we used the carbon dioxide
- equivalent ( CO 2 eq) emissions estimated for 2014 and later engines, which must comply with a metha ne tailpipe emissions standard, and assumed that the engine was 5 percent less thermally efficient than a comparable diesel engine. Both analy se s used GWPs based on 100 ye ar timescale (i.e., a GWP of 25 for methane and 298 for nitrous oxide) . For the CAR B emissions estimates, we used the estimates made for what it terms purposes” using the 2013 version of the CARB GREET model as published in August, 2014. 12 CARB estimates that CNG engines emit 76 percent of the CO 2 eq emissions as a diesel truck , while our anal ys is estimates that CNG engines emit 81 percent of the CO 2 eq emissions as a diesel truck . The most likely explanation for CARB’s lower estimated CO 2 eq emissions for CNG engines is that a much larger portion of the electricity

used to compress natural gas is renewable in California than the rest of the country . CARB estimates LNG engines emit 94.5 percent of the CO 2 eq emissions, as a diesel truck while our analy sis estimates LNG trucks emit 96 percent of the CO 2 eq emissions as a diesel truck
. CARB as sumes no boil
- off or venting emissions from LNG trucks and for this comparison, we used our more modest boil
- off and venting assumption, as described above, 0 20,000 40,000 60,000 80,000 100,000 120,000**E m** **i s** **s i** **o n** **s (** **g C** **O 2** **e q** **/ m** **m B** **t u** **)**

Thermal High Thermal Low CH4:&N2O CO2***** E.O. 12866 Review**

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13
- 23 which is close to CARB’s. Overall, our estimates are very similar to those estimated by CARB and w hen there are differences, the differences are as expected. E A UC Davis report recently released estimated that CNG and LNG trucks using spark ignition engines (SING) emit about the same amount of CO 2 - equivalent emissions, and these emissions are slightl y higher than that of diesel engines. 13 The HPDI engines (DING) fueled b y LNG are estimated to be the lowest emitting of the several scenarios anal yz ed by the study
. Because the stud y did not discuss vehicle boil
- off emissions, it is likely that the study either assumed that these emissions are zero or assumed the default vehicle boil
- off emission estimates made b y GREET. It is likely that the stud y assumed that the liquefaction plants are 90 percent efficient as this is the default assumption in GREET, wh ich leads to lower GHG emissions by LNG trucks. 

### 13.2 **Projecting Natural Gas use in HD Trucks** EPA reviewed several information sources and projections to estimate how much natural gas is currentl y being used and is projected to be used by heav y - dut y trucks. An obvious set of projections to review was the set of projections provided in the National Academ y of Sciences ( NAS ) report. 14 The NAS report attached a figure, sourced from Citi Research, which provided projections by

ACT, PACCAR, Frost and Sullivan and the National Petroleum Council. 15 This figure is reproduced below as Figure 13
- 9
.

E Per Anthy Alexiades of CARB: CARB is planning to propose a new draft lifecycle analysis for CNG and LNG trucks at an April 2015 public meeting. While the CNG lifecycle is expected to be about the same, the LNG lifecycle analysis is expected to hav e lower emissions based on using a 90% efficiency for liquefaction plants instead of the 80% efficiency it w as using previously. Lifecycle emissions for both CNG and LNG trucks will be adjusted to be 10% higher if using a spark ignition engine to account for their low er thermal efficiency. These estimates are solely for hypothetical analyses. LCFS credits are aw arded based on GHG emissions for each specific application.***** E.O. 12866 Review**

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13
- 24 **Figure 13**  **- 9**  **Near -**  **Term Class 8 Natural Gas Penetration Forecasts**  The first observation we can make about all these reports is that they start out assuming that natural gas use is 2 percent of the Class 8 heavy dut y truck fleet in 2012. However, that level of natural gas vehicle penetration of the heavy
- dut y fleet is not supported by other data sources. In the Energy

I nformation Administration’s Annual Ener gy Outlook 2014, EIA shows natural gas use comprising about onl y 0.2 percent of total heav y dut y fuel consumption in 2012, and na t ural gas use b y Class 8 trucks is under 0.1 percent . 16 In 2014, AEO 2014 shows natural gas comprising about 0.4 percent of tot al heav y - duty fuel demand and about the same for Class 8 heav y - dut y truck demand. One estimate of the number of natural gas trucks supports this level of fuel demand made by EIA . In a meeting with the Natural Gas Vehicle for America (NGVA), NGVA present ed their estimate that 62,000 heav y - dut y trucks are fueled b y natural gas. The M OVES data base estimates that there are 12.4 million heavy
- dut y trucks in 2014. Combined, the NGVA and M OVES numbers estimate that natural gas heav y - duty trucks comprise 0.5 percent of the heavy
duty truck population. We also evaluated the growth rates for natural gas trucks, including reviewing two of the studies reference d in the NAS report. The ACT Research study shows the most aggressive***** E.O. 12866 Review**

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13
- 25 growth rate for natural gas heav y - dut y trucks. The ACT Research projection did not seem to consider the economics of natural gas versus diesel fuel. Instead, the ACT projection seemed to be based on a consumer acceptance profile of a new technology , presumably assuming that the technol ogy

is already

economically

competitive. In a recent ACT press release for a more recent report, it was acknowledged that the growth rates ACT projected earlier were too aggressive and a more modest growth rate is more likely
. 17 The NPC projection shows a similar growth rate as that estimated by

ACT Research, but NPC’s projection for increased uptake of the natural gas technology

begins in 2015 instead of 2012. In its study , NPC assumed that the increased capital cost for a natural gas truck compared to a diesel truck study decreases from $60,000 to $20,000 by 2040. 18 This cost decrease seems excessive, and it is likely an important reason why the NPC study shows such a large increase in natural gas use by heavy
- dut y trucks. We did not have access to core assumptions used in the PACCAR and Frost and Sullivan projections to assess their viability
. We searched for the Citigroup report on the Web and in addition to the figure provided in the NAS report, we found Citi Group’s projection shown in the context o f the other projections referenced b y NAS from the Citi bank report in Figure 13
- 10
. 19 Citi Group’s projection is less optimistic than the ACT projection, but is more optimistic than the NPC reference case projection.***** E.O. 12866 Review**

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13
- 26 **Figure 13**  **- 10**  **Long -**  **Term Class 8 Natural Gas Penetration Forecasts**  In its Annual Energy

Outlook, EI A projects the use of different fuels by the transportation sector. 20 This projection was not referenced in the NAS report, but our review found it to be especiall y credible. First, as described above, EIA estimates that natural gas fueled 0.4 percent of the energy use of heav y - dut y trucks in 2014 and this estimate is consistent with the fraction of heav y - dut y fleet which are fueled b y natural gas. Second, the EIA projection is based on an economic anal y sis which considers the increased cost of manufacturing a natural gas truck over a diesel truck, the fuel savings for using natural gas instead of diesel fuel, and whether the payback time of the fuel savings against the increased truck cost would trigger purchases of natural gas trucks. As part of this analysis, EIA assumes that lighter heavy
- dut y trucks would use CNG which is a lower cost technology suited for the shorter driving distances for these trucks. The long haul trucks, however, require larger stores of fuel to extend the driving range which is satisfied by storing the natural gas as a liquid. LNG has about 60 percent of the energy density of diesel fuel, compared to CNG which has onl y 25 percent of the energy

density of diesel fuel. To satisf

y the long driving range of the long haul***** E.O. 12866 Review**

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13
- 27 trucks, EIA assumed that they would use LNG as a fuel. The assumptions used by EIA for conducting its economic anal ys is all seem reasonable. Third, EIA is one of the several well
- respected organizations in the wo rld for collecting and anal yz ing today ’s fuel prices and projecting future fuel prices. According to t he Alternative Fuels Data Center , o ne of the most important assumptions in projecting the future use of natural gas in the transportation sector is the r elative price of natural gas to the price of diesel fuel. Figure 13
- 11 summarizes the total retail prices and the cost components that make up the final average ye ar 2014 retail prices of diesel fuel, CNG and LNG, whose prices are expressed on a diesel gallon
- equivalent basis.

**Figure 13**  **- 11**  **Relative Retail Cost of CNG and LNG to Diesel Fuel ($/gal dge)**  In 2014, the natural gas price purchased b y industrial users was about $6 per million BTU , which c or

r esponds to $0.60 per diesel gallon equivalent. The price of crude oil has been volatile du ring 2014 as the Brent crude oil price started at about $110 per barrel ($2.38/gallon), but decreased to under $ 5 0 per barrel towards the end of 2014. From EIA’s website, the average retail diesel fuel price in the first part of 2014 was about $3.80 cents per gallon. When comparing the natural gas spot market price on a diesel equivalent basis to the diesel fuel price, it appears that natural gas is priced about one quarter of the diesel fuel price. However, if used as compressed natural gas, the natural gas must be distributed through smaller distribution pipeline sy stem that exists in cities, which dramatically increases the price of the natural gas to $1.15 per DGE. Then the natural gas must be compressed and stored at a retail outlet which adds anoth er $1.30 per DGE. The estimated retail price of CNG is $2.35 on a diesel gallon equivalent basis (DGE), or about $1.45 DGE less than diesel fuel. Similarly , if natural gas is converted to LNG, the resulting retail L NG price is much higher than the raw n atural gas price. LNG liquefaction plants are assumed to be located close to large transmission pipelines away from cities, thus, they would likel y pa y t he same low price as industrial users. However, for producing LNG, the natural gas must be liquefied which adds about $0.75 DGE. When the L NG is transported to retail outlets and marked up, the LNG is***** E.O. 12866 Review**

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13
- 28 priced $60 per DGE higher. The tax applied to LNG is on a per gallon basis, thus, is much more than on a DGE basis because of LNG’s lower energy density
. All these steps add substantially to the price of the LNG and the estimated retail price of LNG is $2.65 DGE, or $1.15 DGE less than diesel fuel. In its projections, EIA estimates that crude oil prices in the upcoming ye ars will decline modestly until aft er 2020 when they start increasing until they reach $140/bbl in 2040. Natural gas prices are expected to only slightl y increase over this period. The f ifth reason wh y the EIA projections seem reasonable is because the pay back hurdle assumptions assumed for truck fleet owners seem reasonable. EIA projects that natural gas trucks begin to be purchased when the pay back times are 4 ye ars or less based on a survey conducted b y the American Trucking Associations. The ATA s urvey found that 24 percent of responde nts would choose natural gas trucks over diesel trucks if the pay off is 4 y ears, another 57 percent would choose natural gas if the pay off is 3 y ears, the next 15 percent would choose natural gas if the pay off is 2 y ears and the last 5 percent w ould choose natural gas if the pay off is 1 y ear or less. 22 This is consistent with some conversations we have had with some fleet owners
. The NAS cites the pay

back for the extra cost of natural gas trucks as 2 y ears, but other sources report a longer return closer to 4 y ears. F The results of EIA’s economic anal ys is and projected natural gas use in heavy dut y trucks presented in the 2014 Annual Energy Outlook is presented in Figure 13
- 12
. 23

**Figure 13**  **- 12**  **EIA Projection of Fuel Prices and**  **Natural Gas Use by HD Engines** Figure 13
- 12 shows, as we discussed above, that natural gas currentl y supplies only about 0.5 percent of total heavy
- duty truck fuel demand and it expected to continue to do so until about

F Early LNG Adopters Experience Mixed Results; Truck News, October 1, 2013 0 1 2 3 4 5 6 7 8 9

0.00% 1.00% 2.00% 3.00% 4.00% 5.00% 6.00% 7.00% 8.00% 9.00%

2010 2015 2020 2025 2030 2035 2040Cost($/gal)NaturalGasPercentoftotalHDDemand



### Ye ar NG percent of HD Demand NG Price DGE Diesel Price***** E.O. 12866 Review**

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- 29 2023. Starting in 2023, EIA estimates that the rising price of diesel fuel relative to that of natural gas, which begins to change about 2019, creates the economic inc entive to purchase natural gas trucks. As expected, the EIA projection that the price differential between natural gas and diesel fuel continues to increase results in the effect that the uptake of natural gas use in the heav y - dut y truck fleet accelerates as the price differential increases. A very interesting conclusion of the EIA projection is the natural gas penetration differences between the different heav y - dut y truck classes. Figure 13
- 13 summarizes the projected use of natural gas by the AEO for different truck classes.

**Figure 13**  **- 13**  **EI A**  **Projection of NG use by Truck Weight Class** Figure 13
- 13 shows that the only heavy
- dut y sector which is projected to see a large penetration of natural gas is the heav y, heav y - dut y sector which increases to 10 percent by 2040. The light and medium classes of the heav y - dut y tru ck fleet onl y show modest increases in natural gas use. The likely reason EIA’s anal ys is shows little CNG or L NG use by

light and medium heav y - dut y trucks is because they are driven far less and their use does not justify the higher purchase price. Accor ding to the Vehicle Inventory and Use Survey, light and medium heav y dut y trucks average less than 1/3 rd the annual mileage of the heaviest trucks. 24 EI A is using a distribution of VMT for new class 7 and 8 trucks as shown in Figure 13
- 14
.

0.00% 2.00% 4.00% 6.00% 8.00% 10.00% 12.00%

2005 2010 2015 2020 2025 2030 2035 2040 2045Percentage

Year Heavy HD Medium HD Light HD***** E.O. 12866 Review**

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13
- 30 **Figure 13**  **- 14**  **Percent of Class 7 and 8**  **Truck Fleet by Annual Miles Traveled** Figure 13
- 14 shows that although about half of class 7 and 8 trucks are driven less than 60 thousand miles per y ear, the other half is driven from 60 thousand to over 200 thousand miles pe r year. It is these high mileage long haul trucks which are prime candidates for using LNG because of their abilit y to pay down the high marginal natural gas truck cost. Since EIA does not report the pay back times as an output of its projections, we con ducted our own anal ys is of sample pay back times solel y for illustrative purposes
. We assessed the time required for the lower fuel cost of LNG to pay back the incremental truck cost of using LNG assuming that a truck averages 120,000 miles per year . There were several important aspects of the pay off anal ys is that we conducted. First, based on the EIA anal ys is which found that the heav y, heav y - dut y trucks sector is the only one which will see natural gas use increase dramaticall y, we solely studied the pay back of natural gas in this truck sector. Second, as concluded b y EIA, we also assume that the higher energy densit y of LNG will make it the most likely natural gas fuel t yp e used b y the heav y, heavy
- dut y trucks. Third, the higher natural gas truck cost was approximated from the anal ys is EIA conducted for its Annual Energy Outlook. Fo u rth , t he analy sis presents a simple pay back as well as a discounted pay back using a 7 percent discount factor . F ifth , we evaluated the pay back in 2014, and we also assessed what the pay back might be in 2020 and 2030 and assume some changes in the future y ears as discussed in some example evaluation cases b e low.

0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00%

0 50 100 150 200PercentageofTruckFleet



### Annual Miles T raveled (thosand miles)***** E.O. 12866 Review**

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- 31 **Table 13**  **- 20**  **Payback Analysis** CASE 1 2014 DUEL FUELED CASE 2

2014 HPDI CASE 3

2020 HPDI CASE 4

2030 HPDI Miles per Year 120,000 1 2 0,000 120,000 120,000 Miles per Gallon 6.7 6.7 7.1 7.2 Incremental NG Truck Cost 55,000 70,000 65,000 60,000 Incremental NG Maintenance Cost per year 970 1613 1935 1935 Diesel Fuel Price ($/gal) 3.80 3.80 4.16 5.65 Natural Gas Price ($/gal DGE) 2.64 2.64 2.66 2.83 Diesel Fuel Cost per Year 68,263 56,886 70,608 94,167 Natural Gas Fuel Cost Per Year 60,062 43,978 50,614 53,810 Lower NG Efficiency (%) 5% 5% 5% 5% Vehicle NG Use (%) 50% 95% 95% 95% Simple Payback (years) 6.7 4.5 3.3 1.5 Discounted Payback (years) 9.1 5.5 3.7 1.6 We evaluated two different cases for 2014. Case 1 assumes an LNG fueled, heav y - dut y truck which exceeds 26,000 gross vehicle weight rating and averages 120,000 miles per year. It is a mixed
- fuel (MFNG) natural gas truck and is assumed to operate 50 perce nt on natural gas and 50 percent on diesel fuel
. B ut because this truck can operat e on diesel only , the truck can manage with a more modest storage quantit y of LNG, thus reducing the cost of L NG storage. When this truck is fueled by L NG, it is estimated to be 5 percent less thermally efficient. The fuel costs are consistent with the prices during the first part of 2014. Accounting for the fuel cost savings based on the average fuel econom y and also accounting for the increased maintenance cost for opera ting on LNG, G this truck only achieves a discounted pay back time of 9.1 y ears for pay ing down the $55,000 increased cost for this truck. The second case we evaluated for 2014 is a direct injection natural gas (DING) truck. Because this truck must fuel o n LNG or be parked (the diesel fuel is simply used to enhance the combustion process), there must be more LNG storage capacity and the truck purchase price is estimated to be $70,000 more than a diesel truck. This case also assumes 1 2 0,000 miles accumulat ed per ye ar. The discounted pay back time is 5.5 ye ars, which is less than the first case because the truck runs more of the time on natural gas. If we used the lower diesel fuel prices that we experienced later on in 2014 and earl y 2015 ($2.90/gallon) , th e pay back time would be much longer. Even on a simple pay back basis, the pay back time is over 20 y ears for both Case 1 and Case 2. For Case 3, we assessed a 2020 case using EIA fuel price projections. L ike the second case, the truck is a DING truck, but because it is six y ears later, we assumed a modest cost

G FPInnov ations estimates that natural gas truck maintenance costs are $0.01/per kilometer more than diesel trucks.***** E.O. 12866 Review**

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13
- 32 reduction due to a learning curve. Due to the large price spread between diesel and natural gas, this truck’s discounted pay back time is 3.7 y ears. For Case 4, we assessed a 2030 case using EIA fu el price projections. L ike the previous two cases, the truck is a DING truck , and we assumed a further modest cost reduction due to a learning curve. This truck is also assumed to accumulate 120,000 annual miles fueled on LNG. Due to the even larg er pri ce spread between diesel and natural gas, this truck’s discounted pay back time is 1.6 y ears. The pay back time for both 2014 high mileage heavy
- dut y truck cases we evaluated are over 4 years. Since fleets become interested in purchasing natural gas trucks purchased when the pay back times are 4 y ears or less, it explains the low penetration of natural gas in the heavy
- dut y sector. Given the apparentl y poor pay back times for natural gas vehicles in 2014, it suggests that existing subsidies for natural gas likel y pla y an important role in encouraging its use. According to EI A, half the natural gas consumption by cars and trucks is in California and may be partially due to subsidies and other incentives California off ers. California subsidies the purchase price of natural gas vehicles, and also offsets the cost of natural gas dispensing stations. The Low Carbon Fuel Standard (LCFS) in place in California also incentivizes natural gas use because natural gas is considered to cause less of an impact on the climate than petroleum
- based gasoline and diesel fuel. The majority of the other half of the NG fleet is also in s tates which subsidize the natural gas truck or service st ation costs. Based on the EIA projections for crude oil and natural gas prices, the pay back time of LNG trucks is expected remain long (more than 4 years) until sometime around 2020 when crude oil prices are projected to begin increas ing . Thus, natural gas use b y heav y - duty trucks is not projected to increase above 1 percent of the heav y - duty fuel demand until after 2025. Even if the economics improve for using CNG and LNG in the heav y - dut y fleet, another hurdle is fuel availability

since these fuels ar e not alread y widely available. Figure 13
- 15 shows the number of CNG and LNG public and private service stations relative to the number of gasoline and diesel fuel se rvice stations and truck stops, respectively
.***** E.O. 12866 Review**

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- 33 **Figure 13**  **- 15**  **CNG and LNG Availability at Service Stations** As Figure 13
- 15 shows, CNG and LNG fuel availability at service stations is 1 percent or less of the availability

of gasoline and diesel fuel. Even if a business owner finds the purchase of one or more new natural gas trucks an attractive investment, if the fuel is not availab le in the area, the business owner may have to forgo purchasing the natural gas trucks. A fleet owner might be in the position to also install a n atural gas service station or establish a contract with a third party

fuel provider to provide the fuel, but that may require making a large purchase of trucks to justify

the installation of the service station or the establishment of the contract. If the fleet owner would need to build a CNG or LNG refueling station to enable purchasing the natural gas trucks, then the combined cost of the service station installation and the natural gas trucks purchase could make the prospect uneconomic even if the natur al gas truck purchase b y itself is justified. L

NG availability

is particularly

challenging because in addition to an LNG service station, a L

NG liquefaction plant would be needed as well. If the economics turn favorable for using natural gas in the truck fleet, the conversion to natural gas is likely to be slow due to the need to build out the fuel availability
.

0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000

Number of Service Stations Selling CNG Total Number of

Service Stations Number of

Trucks Stops Selling LNG Total Number of

Truck Stops**N u** **m b** **e r** **o f** **S e** **r v** **i c** **e S** **t a** **t i** **o n** **s a** **n d** **T r** **u c** **k S** **t o** **p s** 

PlannedAbout1%ofServiceStations ~150,000 total Service Stationslessthan1%ofTruckStops***** E.O. 12866 Review**

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- 34 

### 13.2.1 **Dimethyl Ether** Although NAS focused its recommendations on natural gas, it also discussed d imethy l ether (DME) , which is a potential heavy
- dut y t ruck fuel sourced from natural gas. Dimethy l ether has a high cetane number (more than 55), although its energy density is about 60 percent of that of diesel fuel. Dimethy l ether is a volatile fuel, like liquid petroleum gas, that can be stored as a liqu id at normal ambient temperatures under moderate pressure. Ty pical DME fuel tank s would be designed to prevent an y significant evaporative emissions. A DME fueled truck is only modestly more expensive than a diesel fuel truck. The fuel tank is more expensive than a diesel fuel tank, but much less expensive than an LNG tank since it does not need to be heavily insulated. The engine modifications to ena ble using DME are also modest. B ecause DME does not have carbon
- carbon bonds that form particulate particles during combustion, the particulate filter, which is normally installed on recent y ear diesel trucks, can be eliminated
. This offset s some of the increased DME engine and fuel tank costs. Although DME is sourced from cheap natural gas, the conversion of natural gas to DME and moving the fuel to retail outlets greatly increases the cost of the fuel. As Figure 13
- 16 shows, DME i s more expensive than LNG, but still lower in cost than diesel fuel. Similar to Figure 13
- 11 , the diesel fuel price used in Figure 13
- 16 is based on crude oil prices in earl y 2014.

**Figure 13**  **- 16**  **Relative Retail Cost of DME to CNG, LNG and Diesel Fuel ($/gal dge)**  DME is estimated to cost $3.50/ DGE, or $0.30 DGE less than diesel fuel. Because there is very

little DME use in the US (there is onl y a very small fleet of DME trucks being contemplated in California), we did not conduct a lifecy cle assessment of DME. We will, however, discuss a few aspects of a lifecycle anal ys is for DME. First, since DME is sourced from natural gas, the upstream methane emissions from the natural gas industry would 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00

CNG LNG Diesel DMECost($/gal)

Raw Fuel Cost/Crude Oil Liquifaction/Refining Distribution and Marketing Taxes***** E.O. 12866 Review**

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13
- 35 st ill be allocated to DME. Second, there are not venting issues associated with DME as with LNG or CNG refueling. Third, but very significantly , DME ’s global warming potential is estimated to be 0.3 when assessed over a 100 ye ar lifetime, which is about 1 percent of methane’s GWP
. 25 

### 13.3 **Natural Gas Emission Control Measures** 13.3.1 **Proposed Control Measures** E PA is proposing some control measures to reduce potential methane emissions from natural gas vehicles. The cost discussion for each is below. 

### 13.3.1.1 Crankcase Emission s The proposal would require that all natural gas engines have closed crankcases, rather than continuing the provision that allows compression
- ignition engines to separately measure and account for crankcase emissions that are vented to the atmosphere. T his allowance has historically

been in place to account for the technical limitations related to recirculating crankcase gases with high PM emissions back into the engine’s air intake. Natural gas engines have inherently

low PM emissions, so there is no t echnological limitation that would prevent manufacturers from closing the crankcase and recirculating all crankcase gases into the engine’s air intake. The methane standard that was introduced in Phase 1 of this rule accounts for crankcase emissions by

re quiring methane in crankcase emissions be measured and included. However , there can be significant deterioration with respect to volatile crankcase emission such as methane, and it is difficult to ensure that all deterioration is fully reflected in the ma nufacturer’s deterioration factor. W hen the s ys tem is sealed and emissions are routed to the engine intake, crankcase emissions are zero and deterioration ceases to be a concern . See the Preamble Section II. D. for a description of the proposed requiremen t. M ost ( if not all ) NG engines are derived from either a gasoline engine or a diesel engine
. Since it is alread y required for gasoline engines to seal the crankcase , it is not necessary to propose an y crankcase changes for gasoline
- derived engines
. Diesel engines are not required to seal the crankcase , but are required to include the crankcase emissions in the emissions test
. Many OEMs alread y close the crankcase for their engines , and EPA projects the average costs to comply with this proposed requirement would be negligible
. 

### 13.3.1.2 Require 5 Day

Hold Time Boil
- off emissions from LNG vehicles were not addressed nor accounted for in Phase 1 of this rule. As more testing has been done in this area since that time for this emerging issue, a minimal requirement EPA is propos ing a s described in the Preamble Secti on XII is to require manufacturers to follow current industry recommended practice , SAE J2343 for five day hold time to limit boil
- off emissions from L NG vehicles
. The ANSI standard for NG vehicles was adopted in 1994 when we required evaporative standard s for NG vehicles (59 FR 48472 September 21, 1994). This was updated to the more recent ANSI NGV1
- 2006 in the Tier 3 Rule***** E.O. 12866 Review**

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- 36 (79 FR 23414, April 28, 2014) to the proposal would adopt the analogous requirements for LNG, found in SAE J2343 in Section 4.2. The specifications of this safet y related standard will only affect new LNG vehicles to prevent boil
- off initially

and does not address aging vehicles as their insulating properties diminish such as loosing vacuum over time and may eventuall y result in much sh orter hold times
. The SAE J2343 test is done at 72 o F, therefore it is reasonable to assume that hold times will be shorter for very

hot summer day s and high solar loading. Since the majority

or all of the NG vehicles are already compliant with the NFPA 52 and SAE J2343 recommended practices for 3 and 5 day hold times, there would appear to be zero to minimal costs for the requirement for a 5 day hold time. 

### 13.3.2 **Potential Controls** EPA is also investigating additional controls to further reduce potential methane emissions from natural gas vehicles. There are not well defined cost estimates for man y of these options since they are ideas that will require research and development. 

### 13.3.2.1 Update to CO 2 

### Credits Program The P hase 1 H eavy - dut y vehicle rulemaking establishing greenhouse gas emission standards included a compliance alternative allowing heavy
- dut y manufacturers and conversion companies to comply

with the respective methane or ni trous oxide standards by means of over
comply ing with CO 2 standards (40 CFR 85.525 (ii)). The heav y - dut y rules allow averaging only between vehicles or engines of the same designated ty pe (referred to as an “averaging set” in the rules)
. Specifically , t he P hase 1 H eavy - duty rulemaking added a CO 2 credits program which allowed heav y - duty manufacturers to average and bank pollutant emissions to comply with the methane and nitrous oxide requirements after adjusting the CO 2 emission credits (generated from t he same averaging set) based on the relative GHG equivalents. To establish the GHG equivalents used by the CO 2 credits program, t he P hase 1 H eav y - duty vehicle rulemaking incorporated the I PCC Fourth Assessment Report GWP values of 25 for CH 4 and 298 for N 2 O , which are assessed over a 100 year lifetime. Since the Phase 1 rule was finalized, a new IPCC report has been released (the Fifth Assessment Report), with new GWP estimates. This is prompting us to look again at the relative CO 2 equivalency of methane and to seek comment on whether the methane GWP used to esta blish the GHG equivalency value for the CO 2 Credit program should be updated to those established by

I PCC in its Fifth Assessment Report. The Fifth Assessment Report provid es four 100 y ear GWPs for methane ranging from 28 to 36 . Therefore, we not only request comment on whether to update the GWP for methane to that of the Fifth Assessment Report, but also on which value to use from this report. The costs for changing the GWPs used for the CO 2 Credits Program can be estimated by the cost to the manufacturer for reducing CO 2 emissions. If for example the GWP of methane is***** E.O. 12866 Review**

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13
- 37 increased from 25 to 34, then the number of CO 2 credits that will be necessary to offset methane emissi ons above the standard can be calculated b y this change . The cost involved would be the cost per ton of CO 2 for the diffe rence in CO 2 credits. See chapter 7 for a discussion of our estimated cost per ton of CO 2 credit. 

### 13.3.2.2 Deterioration Factors for NG Tailpipe Emissions The current deterioration factors are based on diesel technology
. 

### 13.3.2.3 Vehicle Boil
- Off Warning A simple means to help limit boil
- off emissions would be to require that natural gas truck drivers be alerted to expected near
- future boil
- off events. S uch an alert could be in the form of a warning light and associated alarm that would indicate that the LNG storage tank is approaching a pressure which would require that the tank vent. Knowing this, the truck driver could take evasive action to prevent s uch a release. A second alarm could be required when the LNG tank is venting. This would alert the truck driver to take action to avoid the potential for an explosive environment forming from the vented natural gas emissions. To alert for a boil
- off event a pressure sensor integrated with the vehicle’s horn would cost on the order of $5. 

### 13.3.2.4 Extend 5 D ay H old T ime The specifications of the proposed 5 Day Hold Time SAE 2343 safet y related standard will only affect new LNG vehicles to prevent boil
- off initi ally and does not address aging vehicles as their insulating properties diminish such as loosing vacuum over time and may eventuall y result in much shorter hold times
. LN G tank manufacturers are further developing their technologies for improvement of hol d times and reducing boil
- off from L NG storage tanks on trucks. These improvements can be incorporated by requiring longer hold times. It may be possible using these improvements in technology to extend the hold times to ten day s or longer
. One example o f an existing technology t o address boil
- off emissions has shown a 10 day or more hold time depending on ambient temperatures and solar loading experienced by the vehicle. Westport Innovations, I nc . Ice Pack technology H is an integrated vehicle design whi ch requires low pressure, lower temperature fuel, referred to as “blue” fuel, for the longer hold times. The sy stem does accept the ty pical LNG fuel which is higher pressure and temperature, referred to as “green” fuel, at the expense of shorter hold time s. Fleet owners of these innovative vehicles have installed refueling stations which service their own fleets. The Ice Pack technology

used by Westport has been on the market since 2007 and has gone through several

H Reiskin, Jonathon S. “Expensive Fuel Tanks, Systems Drive High Price of Nat
- Gas Trucks”, Transport Topics Special Report “Alternative Fuels” Decem ber 2013***** E.O. 12866 Review**

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- 38 revisions to work out issues. The tech nology involves a pump at the bottom of the tank which pumps the liquid fuel to the engine. Through a series of pressure changes and pumps, vapor is fed to the engine. At the same time a purge s ys tem takes the high pressure warming vapor in the fuel tank through a series of valves and feed it to the engine using the pressure. This purge sy stem reduces the pressure of the fuel tank which further extends the hold time. The range of enhancements necessary to achieve extended hold time of at least 10 day s wi ll range in cost from $5000 to $20,000 per vehicle
. I Ic e Pack technology used by Westport is on the higher end of that range due to the additional vehicle pump and complicated engineering sy stem which depressurizes the L NG for use in the engine while purging the gas during engine operation and keeping the LNG in the tank cold. Other approaches used by OEMs include increasing the vacuum size between the interior and exterior tank walls to maximize the insulation, keeping heat transfer to a minimum. The colder the LNG stay s, the longer the hold time. 

### 13.3.2.5 Captur ing and/or Converting Methane Refueling o r Boil
- Off Emissions A methane canister using adsorbents such as ANG (adsorbed natural gas) could be added to capture the methane which otherwise would be released to the environment during a refueling or boil
- off e vent. Once captured, steps could be taken to route the methane to the engine intake once the vehicle is operating again, or to take steps to converting the methane to less GHG
potent CO 2 . ANG has been a patented technology since the 1950’s
. J The Departm ent of Energy (DOE) Advanced Research Projects Agency (ARPA
- E) has awarded over $10 million in 2012 to four different projects to develop new sorbent materials for on
- board natural gas storage. Gas Technology

I nstitute (GTI), a research and development or ganization which serves energy and environmental markets has been utilizing the grant to develop lightweight, affordable, natural gas tanks for natural gas vehicles. Methane will adsorb more efficiently with high pressure such as a boil
- off event onto thi s material. As shown in Figure 13
- 17 , f or a 115 gallon LNG tank which would boil off completely in approximately

35 day s K the boil
- off methane emissions would be on t he order of 18 lb s over two day s, and close to 50 lbs in 5 day s. This would require a canister of approximately 15
- 50 gallons of the adsorbent material for a 2
- 5 day hold time , L as show in Figure 13
- 18
. A methane canister using adsorbents such as ANG will need to be on the order of 15
- 50 gallons for 2
- 5 day

hold time. I t is still earl y to say what the costs for this application will be bec ause there is so much engineering development and testing y et to do, but it is estimated that the casing and adsorbents for this size of canister will range from $1 , 5 00
- $ 8 ,000.

I As per confidential discussions with OEM’s, June 27, 2014, and November 20, 2014. J Menon, V.C., Komarneni, S. “Porous Adsorbents from Vehicular natural Gas Storage: A Revie w”, Journal of Porous Materials 5, 43
- 58 (1998) K Pow ars, Charles A. “Bes t Practices to Avoid LNG Fueling Station Venting Losses”, St. Croix Research for Brookhaven National Laboratory, 2010 L LNG
- ANG Venting Calculations Spreadsheet, “LNG
- ANG Venting Calcs.xlsx”***** E.O. 12866 Review**

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- 39 **Figure 13**  **- 17**  **Boil Off Rat e for a 90% Filled 115 gallon LNG Tank with 18 Watts of Heat Input** 

**Figure 13**  **- 18**  **ANG Control of 115 gallon LNG Tank with 18 watts of Heat Input** If being discharged to the environment, the methane potentially could be burned to CO 2 using a burner. Another potential option would be to convert the methane capture d in a canister to CO 2 over a catal ys t. If a catal ys t were to be developed, it would have to be designed to transform an y escaping methane into carbon dioxide to reduce the global warming potential of methane down to that of carbon dioxide
. A methane catal ys t for a boil
- off event on a vehicle has not yet been designed. We acknowledge that this would be a challenge and expect a good deal of engineering will be required for this application which will include an external heat source to be triggered upon a boil
- off event initiation, possibly a pressure sensor which notices when the pressure builds to close to 230 psi when boil
- off occurs.***** E.O. 12866 Review**

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- 40 

### 13.3.2.6 Reduc ing Refueling Emissions In addition to the boil
- off issue is the recurrence of manual venting at refueling by LNG truck operators. Under high pressure circumstances, such as when the vehicle has been sitting for some time period in warmer temperatures, i t is necessary to decrease the pressure in the fuel tank before new fuel can enter the tank. The recommended practice is to transfer the extra vaporized fuel to the gas station or natural gas pipeline, but this can take extra time. I n some areas i t has turned into common practice to just vent to the atmosphere to keep the down time at the refueling station to a minimum. In other areas there is an incentive to reroute the gas into the station storage tank or natural gas pipeline with credit towards the fuel purchase. One option would be to require a s ys tem for rerouting back to fuel storage tank, whether it is to a CNG tank, a CNG pipeline or re
- liquefy ing s ys tem for an LNG storage tank
. There are opinions within the industry that the technology

a t the refueling station and the vehicles are advancing so that the newer pumps and vehicles will automatically vent any pressurized gas back through the refueling nozzle which will quickly cool with LNG in the fuel line and go back into the vehicle as a li quid which ultimately

lowers the pressure with the drop in temperature. Most LNG refueling stations are alread y equipped with a vent line to take excess vapors back to the station storage tank before refueling with the cold liquid fuel. For the older LNG stations which are not equipped with a vent line, there would be an overhead cost of approximately $10,000
- $15,000 to install a vent line sy stem at each pump. Advancing this feature to tie into a NG pipeline for monetary credit would add another overhead of similar magnitude. The technology exists to install a very

small methane liquefaction facility at a retail station which would allow the retail outlet to re - liquefy the vented gas and put it back into their storage tank. Another option would be to con trol refueling emissions for LNG trucks with an on
- board vapor recovery refueling sy stem similar to light duty gasoline vehicles. This would likely involve a canister with carbon designed to adsorb methane specificall y. See discussion in 13. 3.2.5 .4
. Onbo ard refueling will require research and development for an onboard canister with methane adsorbents with a canister sized to take the vapors from a refueling event. The resulting canister and therefore costs will likely be similar to the discussion in Sec tion B4.2.4. The recentl y promulgated Tier 3 rule requires use of the ANSI
- NGV1
- 206 standard practice to meet the evaporative emissions refueling requirement. Small puffs of up to 200 cc/hr (which equates to 72 grams of methane per hour) of leakage are a llowed with these tests. For CNG the current recommended practice for refueling involves a vent line taking a small amount of NG away

from the operator for safet y reasons, but this small amount is generall y released to the atmosphere. Multiplied out for all of the refueling events of the CNG fleet this small amount can add up quickl y especially with projected fleet expansion. When it is again multiplied by the methane GWP it would be worth investigating options for a s ys tem that would recompress the gas and reroute back into the CNG storage tank or pipeline. Rerouting the vent line from a CNG refueling event will be a slightly more complex endeavor due to the mixing of air involved. In order to reroute the vent line to a NG pipeline for credit or to compr ess for usage will both require some engineering and development. This will be an overhead cost for the station.***** E.O. 12866 Review**

**– REVISED** 

**– Do Not Cite, Quote, or Release During Review ** ***

13
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### 13.3.2.7 OBD Requirements for Fuel Sy stem Methane Leak Detection Onboard diagnostics (OBD) are required to detect and provide a warning for when meth ane leaks occur due to wear of connections and components of the CNG or LNG fuel sy stem. Methane leaks occur due to wear of connections and components of the fuel s ys tem just as in gasoline or diesel sy stems. This can result in cracks, holes or structura l breaks in the components. The HD OBD Rule requires comprehensive component monitoring with rationality and functionality

checks for all HD vehicles including NG, b y 2013. By 2019 all HD vehicles , including NG , must verify that their emissions control sy stems are functioning (74 FR 8310 February 24, 2009 . T he implementation schedule is found in 86.010
- 18(o))
. The requirements are alread y in place for methane leak detection
. T herefore there would be minimal additional costs to include a pressure senso r and warning light for impending boil
off. The OBD code should alread y be programmed to record all associated methane leak events and keep a running record. Therefore adding accounting for boil
- off venting should be minimal. There would be additional har dware and programming involved to detect whether the operator is venting high pressure gas to the refueling storage tank or to the atmosphere. Depending on the amount of engineering development required for a system of pressure and temperature sensors thi s approach could be relatively cost effective. The incremental costs for a vehicle with an OBD s ys tem alread y in place would be minimal, on the order of $5
- 10
.***** E.O. 12866 Review**

**– REVISED** 

**– Do Not Cite, Quote, or Release During Review ** ***

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## References 1 US Greenhouse Gas Emissions and Sinks: 1990
- 2012, US Environmental Protection Agency, April 15, 2014 (EPA 430
- R
- 14
- 003). 2 United States Climate Action Report 2014, First Biennial Report of the United States of America, Under the United Nations Framewor k Convention on Climate Change. Table 5.2. 3 Regulatory Impact Analysis for the Proposed Carbon Pollution Guidelines for Existing Power Plants and Emission Standards for Modified and Reconstructed Pow er Plants, US Environmental Protection Agency, June 2014 , Table 3A
- 4. (EPA
- 542/R
- 14
- 002) 4 GREET1 Model, Argonne National Laboratory, 2012. 5 Inventory of US Greenhouse Gas Emissions and Sinks: 1990

– 2012, Annex 2, Tables A
- 34 and A
- 35, April 15, 2014. 6 GREET1 Model, Argonne National Laboratory, 2012. 7 Detai led California
- Modified GREET Pathw ay for Liquefied Natural Gas (LNG) from North American and Remote Natural Gas Sources, Version 1.0, July 20, 2009. 8 Detailed California
- Modified GREET Pathw ay for Liquefied Natural Gas (LNG) from North American and Remot e Natural Gas Sources, Version 1.0, July 20, 2009. 9 Detailed California
- Modified GREET Pathw ay for Liquid Natural Gas (LNG) from North American and Remote Natural Gas Sources, Version 1.0, California Air Resources Board, July 20, 2009. 10 The emission stan dards w ere required by the rulemaking named “ Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium
- and Heavy
- Duty Engines and Vehicles” published September 15, 2011. 11 Conversation with Timothy J. Skone P.E., National Energy Technolo gy Laboratory, Department of Energy, June 2014. 12 Lo w Carbon Fuel Standard Reconsideration: CA
- GREET Model Update, California Air Resources Board, August 22, 2014. 13 Jaffe, Amy Myers, Exploring the role of Natural Gas in U.S. Trucking, NextSTEPS Program, UC Davis Institute of Transportation Studies, February 18, 2015. 14 Reducing the Fuel Consumption and Greenhouse Gas Emissions of Medium
- and Heavy
- Duty Vehicles, Phase Tw o: First Report, National Research Council, National Academy of Sciences, 2014. 15 Ene rgy 2020: Trucks, Trains and Automobiles, Citi GPS: Global Perspectives and Solutions, June 2013. 16 Annual Energy Outlook 2014 w ith projections to 2040, US Energy Information Administration, April 2014. (w ww.eia.gov/forecasts/aeo) 17 Natural Gas Adoption Increases Slowly, ACT Reports, HDT Truckinginfo, www.truckinginfo.com , September 17, 2014. 18 Advancing Technology for America’s Transportation Future, Summary Report, National Petroleum Council, August 1, 2012. 19 Energy 2020: Trucks, Trains and Automobiles, Citi GPS: Global Perspectives and Solutions, June 2013. 20 Issues in Focus: Section 6 ̈ Heavy
- Duty Natural Gas Vehicles, Energy Information Administration, Annual Energy Outlook 2012, June 25, 2012. 22 Conversation with Nicholas Chase, Energy Information Administration, October 2014. 23 Annual Energy Outlook 2014 w ith projections to 2040, US Energy Information Administration, April 2014. (w ww.eia.gov/forecasts/aeo) 24 U.S. Department of Commerce, Bureau of the Census, 2002 Vehicle Inventory and Use Survey, Microdata, CD, 2005. (Additional resources: www.census.gov/ svsd/www/tiusview.html) 25 Good, D.A et al, Lifetimes and global w arming potentials for dimethyl ether and for fluorinated ethers: CH3OCF3, CHF2OCHF2, CHF2OCF3, Journal of Geophysical Res, Vol 103, Pages 28,181

– 28,186, November 20, 1998.