National Academies Press: OpenBook

Alternative Fuels in Airport Fleets (2017)

Chapter: CHAPTER FOUR Airport Experience with Alternative Fuels By Fuel Type

« Previous: CHAPTER THREE Overview of Alternative Fuel Use in Airport Fleets
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Suggested Citation:"CHAPTER FOUR Airport Experience with Alternative Fuels By Fuel Type." National Academies of Sciences, Engineering, and Medicine. 2017. Alternative Fuels in Airport Fleets. Washington, DC: The National Academies Press. doi: 10.17226/24868.
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Suggested Citation:"CHAPTER FOUR Airport Experience with Alternative Fuels By Fuel Type." National Academies of Sciences, Engineering, and Medicine. 2017. Alternative Fuels in Airport Fleets. Washington, DC: The National Academies Press. doi: 10.17226/24868.
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Suggested Citation:"CHAPTER FOUR Airport Experience with Alternative Fuels By Fuel Type." National Academies of Sciences, Engineering, and Medicine. 2017. Alternative Fuels in Airport Fleets. Washington, DC: The National Academies Press. doi: 10.17226/24868.
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Suggested Citation:"CHAPTER FOUR Airport Experience with Alternative Fuels By Fuel Type." National Academies of Sciences, Engineering, and Medicine. 2017. Alternative Fuels in Airport Fleets. Washington, DC: The National Academies Press. doi: 10.17226/24868.
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Suggested Citation:"CHAPTER FOUR Airport Experience with Alternative Fuels By Fuel Type." National Academies of Sciences, Engineering, and Medicine. 2017. Alternative Fuels in Airport Fleets. Washington, DC: The National Academies Press. doi: 10.17226/24868.
×
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Suggested Citation:"CHAPTER FOUR Airport Experience with Alternative Fuels By Fuel Type." National Academies of Sciences, Engineering, and Medicine. 2017. Alternative Fuels in Airport Fleets. Washington, DC: The National Academies Press. doi: 10.17226/24868.
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19 CHAPTER FOUR AIRPORT EXPERIENCE WITH ALTERNATIVE FUELS—BY FUEL TYPE This chapter presents information gathered from airports during the survey and interviews about each fuel type used. It also includes information on fuel infrastructure and cost. Notable highlights include the following: • Airports have observed that biodiesel’s cold weather performance improves with the use of a winter additive. • Airports report unique issues encountered with CNG, such as expensive and unexpected replacement of tanks. • Airports have experienced difficulty securing funding for electric vehicle infrastructure because it typically is not included or anticipated in vehicle procurement budgets. BIODIESEL Nine of the 33 airports that participated in the survey reported using B20 fuel derived from soybean feedstock, and an addi- tional four reported using B5. Of those airports using B20, eight (or 89%) reported being “satisfied” or “extremely satisfied” with the fuel (Figure 10). B20 is popular because it balances several benefits—low cost, low emissions, cold weather perfor- mance, materials compatibility, and ability to act as a solvent. FIGURE 10 Surveyed airports’ overall level of satisfaction with biodiesel. By total volume, biodiesel is the most common diesel replacement fuel in the United States, with 2 billion gallons con- sumed per year across all on- and off-road vehicles (EIA 2016). Pure biodiesel made from soybeans (the most common feedstock) reduces GHG emissions by 12% compared with conventional diesel (ANL 2016a). Biodiesel produced from other pathways, such as from waste oils, can reduce GHG emissions by up to 88% on a life-cycle basis, but these types are not com- mon (ANL 2016a). Most diesel fuel in the United States is blended with up to 2% biodiesel by volume—known as B2. The next most common blends are B20 (6% to 20% biodiesel) and B5 (2% to 5% biodiesel). B100 (pure biodiesel) is rarely used in its pure form. To qualify as an alternative fuel under the Clean Air Act of 1970, the blend must be B20 or higher (DOE 2016b).

20 The most commonly cited issue with biodiesel is the clogging of fuel filters (reported by three airports in the survey). Pure biodiesel from soybeans begins to form ice crystals when the temperature drops below 0°C (32°F), whereas diesel fuel does not form crystals until it reaches −45°C to −7°C (−49°F to 19°F) (DOE 2016b). Biodiesel also begins to gel in cold weather. Multiple airports reported that the use of a winter additive prevents gelling. Lambert–Saint Louis International Airport uses biodiesel in its fleet of snow management vehicles (Figure 11). One airport reported not using the fuel in Airport Rescue and Firefighting vehicles because of reliability concerns. Last, survey respondents noted that biodiesel tends to have more main- tenance requirements and is slightly more expensive per gallon than diesel fuel. FIGURE 11 Biodiesel snowplows and blowers (Source: Lambert–Saint Louis International Airport). Most airports that use biodiesel reported having only one refueling station on site. Minneapolis–Saint Paul International was the only exception with two refueling stations. Almost all reported that their on-airport biodiesel dispensers were private stations. Little Rock International Airport was the only respondent to report using a public station for B20 refueling. RENEWABLE DIESEL Renewable diesel is a hydrocarbon fuel that offers performance similar to that of conventional diesel, but it is produced from such renewable feedstocks as fats and oils. As a “drop-in” fuel, renewable diesel requires no replacement of infrastructure or engine, and can be blended with diesel at ratios of up to 100% (Ernst 2016). Life-cycle analyses suggest that renewable diesel reduces GHG emissions by as much as 80% compared with emissions for conventional diesel, reduces nitrogen oxides (NOx) by 14%, and reduces particulate matter by a small fraction. Across the United States, approximately 560 million gallons of renewable diesel were used in 2016, representing less than 1% of road transportation fuel use (EIA 2016). Today, renewable diesel is being used at San Francisco International Airport (SFO) at blends of 99% (i.e., 99% renewable diesel, 1% diesel) in all formerly diesel-powered vehicles. The airport reported being “extremely satisfied” with the fuel’s performance, cost, and emissions. The city of San Francisco and several neighboring cities also use renewable diesel in their city fleets, so they already have a foundation of knowledge and distribution from which airports can learn. However, availability is much more limited outside California, owing to a lack of incentives and limited distribution. This limited availability appears to contribute to a general lack of knowledge among airport fleet managers about renewable diesel. Most of the airports interviewed for this report could not define renewable diesel and could not distinguish it from biodiesel. COMPRESSED NATURAL GAS CNG is the most commonly used alternative fuel in airport-owned and airport-operated vehicles. Of respondent airports, 71% reported using CNG in at least one vehicle type—typically buses and shuttle buses. DOE estimates that GHG emissions resulting from CNG are 11% lower than those emitted by diesel (ANL 2016a). However, another key advantage of CNG over diesel is the reduction in local air pollutants, namely NOx and particulate matter. Across the United States, CNG accounts for just 2% of road transportation fuel use (EIA 2016).

21 Overall, 76% of the airports that use CNG reported being “satisfied” or “extremely satisfied” with the fuel (Figure 12). The most commonly cited advantages of CNG versus diesel are lower fuel costs, less intensive maintenance requirements, reduc- tions in criteria pollutant emissions, more predictable fuel prices, greater existing infrastructure and distribution, reduced odor from exhaust, and reduced noise from the engine. FIGURE 12 Surveyed airports’ overall level of satisfaction with CNG. Many airport fleets also discussed limitations of CNG, such as the following: • Slow-fill CNG stations take much longer for refueling, so planning around the duty cycle is required. • Few vehicle models are available on the market. • Low energy density relative to other fuels necessitates larger storage tanks to achieve the same range. This size differ- ence creates problems for vehicles that lack excess space capacity, such as some vocational vehicles. • Compared with gasoline vehicles, engine spark plugs in CNG-fueled vehicles require more frequent replacement because of a higher combustion temperature. • CNG pickup trucks, sedans, SUVs, and facility and maintenance vehicles require aftermarket conversion. • If the on-airport refueling station is out of commission, drivers must refuel several miles away, adding to labor and fuel costs. • Onboard CNG fuel tanks typically expire at the midpoint of the vehicle’s lifetime, imposing substantial downtime and replacement costs (up to $15,000 per shuttle bus). • Airports report difficulty finding replacement parts for CNG engines. Last, a key benefit of CNG vehicles that airport respondents identified was that many vehicle types can be bi-fuel, meaning that they can run on CNG or gasoline/diesel. Airports found that the ability to use either of two fuels provided the following advantages over a dedicated fuel system: (1) vehicle operators could drive longer distances off-airport if needed, including to places without CNG refueling stations; (2) vehicles could continue normal operations if an airport CNG station became temporarily inoperable; and (3) vehicles could continue operation if repair parts for the CNG engine were unavailable. RENEWABLE NATURAL GAS Renewable natural gas is a renewable substitute for fossil-based natural gas. It is made from waste gases at landfills, municipal solid waste facilities, dairy farms, and water treatment facilities. After it is processed, renewable natural gas uses the same distribution pipeline and dispensing stations as CNG. Limited environmental assessments of renewable natural gas have been performed, but the current literature suggests that the fuel can achieve promising reductions in GHG emissions. For example, recent analyses for the State of California estimate that some renewable natural gas pathways achieve greater than 100% reductions in GHG emissions by displacing methane emissions at the production sites and displacing fossil fuel in vehicles (CARB 2016). However, other studies note that, owing to data limitations, many uncertainties exist about the fuel’s environmental benefits (Han et al. 2011).

22 As with renewable diesel fuel, producers of renewable natural gas receive incentives for selling fuel in California (CARB 2016). These incentives appear to influence a fuel’s availability in non-California regions. In an interview, Seattle–Tacoma International Airport reported briefly starting a renewable natural gas program, but the program quickly ceased when the fuel distributor moved all fuel to California markets. SFO was the only airport surveyed that uses renewable natural gas. Its program began in 2014; SFO now uses renewable natural gas in 26% of its airport-owned and airport-operated vehicles. SFO allows the use of waste products in the production of renewable natural gas (by an off-airport producer). Only 28% of airport respondents reported being “interested” or “extremely interested” in using renewable natural gas as fuel in the future. More than half said they were “not interested”—the highest degree of disinterest among all the fuel types. LIQUEFIED NATURAL GAS LNG is rarely used in airport fleets; it is typically reserved for specialized equipment. Of the airports surveyed, only 26% said they were “interested” or “extremely interested” in using LNG in the future. As described by DOE, the main barriers to using LNG are the higher fuel cost compared with CNG (DOE 2016a) and the need for special storage tanks capable of maintaining the cryogenically cooled fuel in liquid form. Additionally, the life-cycle emissions and petroleum consumption of LNG are higher than those of CNG because of the compression stage. Airports at which LNG may make economic sense are those near marine terminals where LNG is already imported or exported. This proximity eliminates the need for the airport to compress the fuel. Overall, however, the prospects for greater LNG expansion in airport fleets appear to be limited because of low inter- est and high costs compared with other fuels. LIQUEFIED PETROLEUM GAS The use of LPG, also known as propane, is limited at airports. Of the 33 airport respondents, LPG was used only in forklifts and other material-handling equipment. Availability of vehicles remains a primary barrier to greater adoption of this fuel. According to DOE (2016a), in U.S. markets the only types of LPG vehicles are forklifts, buses, and garbage trucks, which are used in a limited number of city fleets. Although some airports in the survey expressed interest in LPG fuel, one respondent (Denver International Airport) noted that LPG cannot be used in tunnels because of fire codes. Additionally, LPG fuel costs are higher than those of diesel—since 2000, LPG has averaged about $0.20 more per gallon of diesel equivalent. Overall, the prospect of greater LPG use in airport fleets is limited. HYDROGEN Hydrogen fuel has zero tailpipe emissions and the potential for zero life-cycle emissions if the hydrogen is created from renew- able energy. Therefore, hydrogen fuel has great potential for supporting a long-term strategy for mitigating emissions and petroleum use. However, the technology is still in relatively early stages, and fuel and vehicle availability remain key barriers. Other barriers and costs have been detailed elsewhere by DOE (2016a) and others. Of the airports surveyed for this report, only SFO reported using hydrogen in its vehicle fleet—specifically, in two mobile lighting structures that were partially funded by DOE. The airport fleet manager reported that the fuel is expensive and cur- rently delivered in bottles, but the airport is seeking access to a hydrogen fueling station off-airport, which could lower costs and enable airport personnel to also fuel other vehicle types. However, the airport fleet manager also stated that he did not think hydrogen was practical in large vehicles owing to the high vehicle and fuel costs. ELECTRICITY Survey responses showed that electricity was the fastest-growing alternative fuel over the previous 5 years. Forty-five percent of surveyed airports reported having battery-electric vehicles (BEVs), whereas 18% of airports reported having PHEVs. As detailed elsewhere (e.g., DOE 2016a), two key advantages of these powertrains over petroleum-fueled vehicles are the low fuel costs and stable fuel prices. Additionally, BEVs and PHEVs have zero tailpipe emissions when running on batteries, which can be a major benefit in areas where vehicles operate near airport workers and passengers. On a life-cycle basis, the amount of GHG emissions caused by BEVs and PHEVs depends largely on the source of the electricity, but it is lower than petroleum

23 fuels in every U.S. state (DOE 2016a). Additionally, BEVs have the potential for zero emissions on a life-cycle basis if the electricity is produced by renewable resources. Overall, 55% of airports reported being “extremely satisfied” or “satisfied” with their BEVs and PHEVs. However, 11% reported being “unsatisfied” (Figure 13) and several airports also reported challenges with the vehicles. The main concern expressed by airports is the higher upfront vehicle cost of BEVs and PHEVs compared with traditional vehicles. Although some airports said that employees were enthusiastic about BEVs, others reported barriers to employee acceptance. Addition- ally, the electric charging stations are not typically covered under fleet expenses, meaning fleet managers must be creative in finding financing solutions. A BEV at the Port of Seattle is shown in Figure 14. FIGURE 13 Surveyed airports’ overall level of satisfaction with battery-electric. FIGURE 14 Battery-electric vehicle (Source: Port of Seattle) One airport expressed concerns about unanticipated costs from the BEVs’ lengthy refueling time. Specifically, the airport managers said that BEVs can be out of service for an entire day if drivers or maintenance personnel forget to plug in the vehicle overnight, creating problems for fleet readiness. PHEVs, which can run on gasoline or electricity, would mitigate this concern. FUTURE INTEREST IN ALTERNATIVE FUELS The final question in the online survey asked airports about their future interest in each alternative fuel over the next 5 years. Respondents expressed the greatest interest in electricity, with about 80% of airports saying they were “interested” or “extremely interested” (Figure 15). The next-highest amount of interest was shown for CNG, with 67% of airports indicating that they are “interested” or “extremely interested.”

24 FIGURE 15 Surveyed airports’ interest in future use of alternative fuels.

Next: CHAPTER FIVE Airport Experience with Alternative Fuels By Vehicle Type »
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TRB's Airport Cooperative Research Program (ACRP) Synthesis 85: Alternative Fuels in Airport Fleets is designed to assist airport operators in analyzing complex procurement, operational, and environmental decisions when considering alternative fuels in airport fleets.

Airports own and contract fleets to transport passengers, staff, and goods by on- and off-road vehicles. Although most transportation fuels are consumed by aircraft, using alternative fuels in airport fleets is one opportunity airports have to control emissions and fuel costs and potentially reduce maintenance.

The report compiles information on eight alternative fuels, including biodiesel, renewable diesel, compressed natural gas, renewable natural gas, liquefied natural gas, liquefied petroleum gas, hydrogen, and electricity.

Ethanol and hybrid-electric vehicles (HEVs) are not included in this report because the driving experience and refueling operations associated with ethanol and HEVs are well understood and documented elsewhere.

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