18-05-2013, 11:27 AM
Technical Statement on the Use of Oxygenated Gasoline Blends in Spark Ignition Engines
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INTRODUCTION
The Engine Manufacturers Association (“EMA”) is an international membership
organization representing the interests of manufacturers of internal combustion engines.
Increased worldwide interest in reducing reliance on petroleum-based fuels and
improving air quality has prompted broadened use of alternative, renewable fuels, including
gasoline blended with various oxygenates. Regulatory agencies around the world have adopted
plans requiring the use of renewable fuels, and international standard-setting bodies have
approved specifications regarding their use. Understanding the importance of developing new
technologies without compromising emission or performance benefits, EMA and its members
have actively participated in many of these public and private initiatives.
This Technical Statement sets forth EMA’s position on the use of gasoline blended with
ethanol1 (gasoline ethanol blends) in current engine technologies. While this Technical
Statement primarily focuses on issues relevant to small nonroad spark ignition engines, a
significant amount of the information included is applicable to other categories of engines or
vehicles intended to operate on conventional gasoline. However, it should be noted that EMA’s
current position is limited by the general lack of available research on the use of gasoline ethanol
blends containing greater than 10 volume percent ethanol (E10) in products designed to comply
with stringent emission regulations (not including flexible fuel vehicles intended to operate on
blends containing up to 85 volume percent ethanol (E85)).
EMA recognizes that interest in reducing greenhouse gas emissions, such as CO2, has
resulted in increased analysis of the life cycle emission characteristics of fuel blending
components such as ethanol. However, this Technical Statement does not address the direct or
indirect effect of ethanol production or use on greenhouse gas emissions.
ETHANOL FEEDSTOCK
Ethanol has been used for many years as a blending component for gasoline at a
maximum of 10 volume percent. Such use has historically been on a seasonal basis, and has
been centered primarily in regions required to meet U.S. EPA reformulated gasoline
requirements. Ethanol can be derived from a broad variety of renewable sources such as corn,
cellulose and sugar cane. The source, or feedstock, used to produce ethanol varies by region.
For example, corn based ethanol is common in the United States, while sugar cane based ethanol
is common in Brazil. In addition, in an on-going effort to improve the economics and
greenhouse gas emission benefits of the use of ethanol as a gasoline blending component,
alternate feedstocks, such as cellulose, continue to be investigated. Regardless of the feedstock,
finished ethanol is a single molecule product with consistent chemistry.
ETHANOL and BLEND SPECIFICATIONS
Several international organizations have adopted and continue to revise ethanol
specifications and guidelines. One such specification is ASTM International D4806: Standard
Specification for Fuel Ethanol for Automotive Spark-Ignition Engines. Current ASTM
specifications are limited to blends below E10 (ASTM D4814), and blends between E70 and E85
(ASTM D5798). In March 2009, the Worldwide Fuel Charter Committee (WWFC), of which
EMA is a member, published Ethanol Guidelines for E100 ethanol used in E10.2 Adherence to
such specifications and guidelines is crucial to the effective use of gasoline ethanol blends in
engines.
ETHANOL - GASOLINE BLENDS
Ethanol has a single molecular compound and therefore a single temperature at which
liquid fuel vaporizes. Petroleum based gasoline is a blend of a number of different hydrocarbons
that vaporize at significantly different temperatures (this is often referred to as a “distillation
curve”). The vapor pressure created at a defined temperature and the percentages of the fuel
vaporized at any given temperature are critical parameters that determine the performance of the
engine. Initial vapor pressure is critical for cold engine starting. Mid-range or T50 distillation
characteristics significantly influence engine warm-up and acceleration, and high-end or T90
distillation characteristics have a significant influence on crankcase dilution. As ethanol content
is increased when blended with traditional gasoline, the initial vapor pressure is increased.
However, the mid-range distillation characteristics are lowered. To counter these tendencies a
special type of petroleum gasoline, known as blendstock, is used in the blending process.
Depending on the desired ethanol content, the appropriate blendstock is used in order to assure
that the finished fuel blend has similar characteristics as conventional gasoline.
ENGINE OPERATION, PERFORMANCE AND DURABILITY
The energy content of neat ethanol (E100) is about thirty-five percent (35%) lower than
that of petroleum-based gasoline (on a volume basis). Actual power loss and fuel economy
reduction associated with ethanol blends will vary depending on the percentage of ethanol
blended in the fuel and the engine’s ability to adjust combustion control parameters.
Adjustments to the engine in service made to compensate for such power loss or fuel economy
reduction is a real concern and may result in a violation of EPA’s anti-tampering provisions. To
avoid such illegal tampering, as well as potential engine problems that may occur if the engine is
later operated with petroleum-based gasoline, EMA recommends that users not make such
adjustments.
Higher percentage ethanol blends (greater than E10) can cause a variety of engine
performance problems as a result of (i) the enleanment effect associated with the oxygen content
of such blends on a volume basis; (ii) changes in ignition and combustion parameters; and (iii)
the differences in fuel properties. The differences in fuel properties increases the corrosion of
metals and swelling of elastomers, both of which increase further with increasing ethanol
content. These problems are avoided in flex-fuel vehicles through the use of (i) feedback control
systems that adjust fuel delivery and ignition timing; and (ii) materials that are compatible with
high ethanol content fuels. Products that are either designed to operate on higher ethanol blends
or not required to meet stringent exhaust emission requirements (such as products designed to
operate using E25 in Brazil) are able to avoid such problems.
EMISSION CHARACTERISTICS
Multiple agencies have published reports on the emission effects of ethanol-gasoline
blends. The majority of these reports apply only to light-duty vehicles that have some form of
combustion feedback control for both fuel delivery and ignition timing. The most
comprehensive report covering nonroad engines and equipment was conducted by the Orbital
Engine Company4. In addition, a recent report published the results of testing conducted for the
U.S. Department of Energy (DOE)5 which included testing for selected nonroad engines (“DOE
Report”). However, EMA members have significant concerns with the DOE Report’s data
analysis and conclusions. Such concerns are specifically outlined in EMA’s comments to the
Growth Energy Waiver filed with EPA on July 20, 2009.
Ethanol blends traditionally were used in place of petroleum-based gasoline to reduce
hydrocarbon emissions in various regions during certain seasons. The enleanment affect of the
ethanol reduced overall hydrocarbon and carbon monoxide emissions while increasing NOx
emissions from engines without feedback controls, and provided higher exhaust gas temperatures
that enhanced oxidation type aftertreatment system performance, particularly on cold engine
starting. The value of these ethanol blends diminished as light-duty engine designs incorporated
more advanced closed loop control systems and aftertreatment systems were modified to
improve cold start emissions.
HEALTH & SAFETY
Ethanol blended with gasoline generally results in lower hydrocarbon and carbon
monoxide emissions from engines operating richer than stoichiometry, however, these same
engines typically have increased NOx emissions and increased emissions of several other
compounds such as aldehydes. The influence of such emissions is altered, sometimes
significantly, by the use of closed loop fuel controls and three-way catalytic converters typical of
current light-duty vehicles.
While ethanol blends alter the vapor and distillation characteristics of traditional
petroleum gasoline, such changes do not significantly alter the inherent safety requirements
associated with the storage and/or handling of the fuels.
WARRANTIES
Engine manufacturers are legally required to provide consumers with an emissions
warranty on their products (which are certified to EPA’s gasoline fuel specifications). Engine
manufacturers also typically provide a commercial warranty. Individual engine manufacturers
determine what implications, if any, the use of ethanol blends has on the manufacturers’
commercial warranties. It is unclear what implications the use of unapproved ethanol blends has
on emissions warranty, in-use liability, anti-tampering provisions, and the like.
ECONOMICS
The cost of ethanol blend stock varies depending on the basestock, production process,
geographic area, variability in crop production, government tax incentives, and other factors.
Although the cost of ethanol blend stock may be reduced if relatively inexpensive feedstock,
such as cellulosic material, is used instead of corn or sugar cane, the average cost of ethanol
blend stock nevertheless exceeds that of petroleum-based gasoline. In addition, ethanol price
volatility mirrors gasoline price volatility in the commodities markets.
CONCLUSIONS
In summary, EMA has drawn the following conclusions with respect to the use of
gasoline ethanol blends in current engine technologies:
• Regardless of the biomass feedstock or the process used to produce the fuel, E100 blend
stock should be required to meet the requirements of ASTM D4806.
• Ethanol blends up to a maximum of E10 should not cause engine or fuel system
problems, provided the E100 used in the blend meets the requirements of ASTM D4806
and the finished fuel meets ASTM D4814.
• Ethanol blends ranging from E70 up to E85 should be required to meet the requirements
of ASTM D5798 and only be utilized in vehicles (or engines) identified as flex-fuel
vehicles (or engines).
• Oxygenated gasoline blends should meet the fuel requirements specified by the
engine/vehicle manufacturer for the product they are used in.
• Dispensing pumps should be required to use separate pump systems for blends up to a
maximum of E10 and blends ranging from E10 up to E85.