Experimental and Modeling Study of the Flammability of Fuel Tank Headspace Vapors from Ethanol/Gasoline Fuels Phase 3: Effects of Winter Gasoline Volatility and Ethanol Content on Blend Flammability; Flammability Limits of Denatured Ethanol D.P. Gardiner and M.F. Bardon Nexum Research Corporation Wendy Clark National Renewable Energy Laboratory NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. Technical Report NREL/TP-5400-52043 July 2011 Contract No. DE-AC36-08GO28308 Experimental and Modeling Study of the Flammability of Fuel Tank Headspace Vapors from Ethanol/Gasoline Fuels Phase 3: Effects of Winter Gasoline Volatility and Ethanol Content on Blend Flammability; Flammability Limits of Denatured Ethanol D.P. Gardiner and M.F. Bardon Nexum Research Corporation Wendy Clark National Renewable Energy Laboratory Prepared under Task No. FC08.0073 NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. National Renewable Energy Laboratory Technical Report 1617 Cole Boulevard NREL/TP-5400-52043 Golden, Colorado 80401 July 2011 303-275-3000 • www.nrel.gov Contract No. DE-AC36-08GO28308 NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Available electronically at http://www.osti.gov/bridge Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from: U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831-0062 phone: 865.576.8401 fax: 865.576.5728 email: mailto:[email protected] Available for sale to the public, in paper, from: U.S. Department of Commerce National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 phone: 800.553.6847 fax: 703.605.6900 email: [email protected] online ordering: http://www.ntis.gov/help/ordermethods.aspx Cover Photos: (left to right) PIX 16416, PIX 17423, PIX 16560, PIX 17613, PIX 17436, PIX 17721 Printed on paper containing at least 50% wastepaper, including 10% post consumer waste. Foreword The U.S. Department of Energy (DOE) supports efforts to increase the use of ethanol-rich transportation fuels such as “E85” (51 to 83 percent ethanol). Furthermore, the mission of the DOE’s Clean Cities program is to advance the energy, economic, and environmental security of the United States by supporting local decisions to adopt practices that reduce the use of petroleum in the transportation sector. However, infrastructure compatibility and safety have historically been among the most difficult deployment hurdles to address when introducing a new transportation fuel. The proximity in the fuel supply chain of self-serve fuel dispensers and underground storage tanks to the consumer elevates concerns regarding potential unintended consequences. The physical and chemical properties of ethanol-rich fuels are different from those of conventional transportation fuels; therefore, it is critical to evaluate the situation to ensure safety. In addition to testing that led to Underwriters Laboratories listing of dispensers (http://www.nrel.gov/docs/fy11osti/49187.pdf), the National Renewable Energy Laboratory undertook the testing described in this report and two previous reports (http://www.nrel.gov/vehiclesandfuels/npbf/pubs_ethanol.html) to assess the difference in headspace flammability between typical summertime gasolines, which have accepted levels of safety, and these new high-ethanol content fuel blends. The results apply to vehicle fuel tanks as well as to underground storage tanks. This project evaluated the effects of ambient temperature and fuel formulation on the headspace vapor flammability of ethanol/gasoline blends. When a fuel tank is partially filled with liquid fuel, the remaining space (i.e., the headspace) is filled with fuel vapors and air. Depending on the degree of tank filling, fuel type, and ambient temperature, the fuel vapors can be flammable or non-flammable. Vapors in fuel tanks containing pure gasoline generally are too rich (i.e., the ratio of fuel vapor to air is too high) to be flammable except when ambient temperatures are extremely low. However, fuels containing high percentages of ethanol blended with gasoline can be less volatile than pure gasoline and thus can produce flammable headspace vapors at common ambient temperatures. The study is also intended to provide knowledge to support the refinement of fuel ethanol volatility specifications and to show the potential consequences of using fuels that do not comply with such specifications. A risk analysis/hazard assessment will be required to fully judge the safety implications, if any, of the introduction of these new fuel blends into the hands of the public. The results show that in general “E85” is flammable at low temperatures whereas denatured ethanol is flammable at warmer temperatures. If both fuel types are stored in separate tanks at the same location, one or both of the tanks’ headspace vapors will be flammable over a wide range of ambient temperatures. This is relevant to the issue of splash-blending ethanol and gasoline at fueling stations and allowing consumers to blend ethanol and gasoline themselves. Fuels that are compliant with volatility specifications in ASTM D5798 are relatively safe, but the field samples of “E85” tested in this work indicate that at least some of the ethanol fuels currently available when ASTM D5798 Class 3 conditions (-5°C and below) exist are likely to produce flammable vapors within the ambient temperature range where they are used. Whether or not flammable headspace vapors represent a significant hazard to the public is unknown at this time. i Acknowledgments This project was funded by the Department of Energy Office of Vehicle Technologies (Dennis Smith, Clean Cities Program Manager, and Kevin Stork, Fuels Technologies Team Lead) through the National Renewable Energy Laboratory. Executive Summary Background The flammability of a fuel blend in the head space of a storage tank is controlled by the vapor pressure of the blend. Conventional gasolines are so volatile that the headspace vapors are normally too rich to sustain combustion at most ambient temperatures. Only under very cold conditions does the vapor-air mixture in the tank become flammable. Because of its different vapor pressure and stoïchiometry, pure ethanol produces vapor-air mixtures in the tank that are flammable over a wide range of ambient temperatures. Blends of ethanol and gasoline form non-ideal mixtures in which the gasoline components render the vapor-air mixture in a tank too rich for combustion at warm temperatures. Like gasoline, as temperature drops, the vapor-air mixture becomes leaner and eventually falls into the flammable region. However, the mixture becomes flammable at higher temperatures than conventional gasoline, and so presents a hazard over a greater range of conditions if a suitable ignition source is present. Objectives of the Work Reported The mission of the US Department of Energy’s Clean Cities program is to advance the energy, economic, and environmental security of the United States by supporting local decisions to adopt practices that reduce the use of petroleum in the transportation sector. Part of this program includes the replacement of petroleum by alternative and renewable fuels. Introduction of fuels that have chemical and physical properties different from petroleum must be done with the safety of the public foremost in mind. Since even perceived safety issues can be barriers to deployment, analytical testing is needed to ensure that decisions are based upon scientific knowledge rather than assumptions about potential issues. This flammability study is part of the research into the properties of ethanol blends to address, understand, and quantify the issues involved in the deployment of a new fuel. This project was comprised of an experimental study to measure the flammability of fuel vapors at low ambient temperatures, and further development of a mathematical model to predict the temperatures at which flammable vapors were likely to form. The fuels investigated in the current project were provided by Marathon Petroleum Company. The fuel samples were produced in a laboratory to systematically investigate the effects of varying ethanol content on the volatility and flammability of the resulting blends. There were three sets of ethanol/gasoline blends (including the partial set originally evaluated during the ii Phase 2 study [2]), which were all provided and characterized by Marathon Petroleum Company, and are referred to throughout this report as “laboratory samples”. The blend matrix was comprised of three gasoline vapor pressure levels (83.0 kPa (12.04 psi) DVPE, 89.2 kPa (12.94 psi) DVPE, and 101.2 kPa (14.68 psi) DVPE) and seven different blend levels (E0, E15, E55, E60, E68, E75, and E83). The three gasoline vapor pressure levels were intended to represent low, typical, and high levels for available winter gasoline. Investigations involving these fuels were intended to provide information to guide future fuel specifications. Such specifications could be developed based upon knowledge of the compromise between avoiding flammable mixtures at low ambient temperatures and maximizing the ethanol content of the fuel.