5.2 Why are there seasonal changes?

Only gaseous hydrocarbons burn, consequently if the air is cold, then the
fuel has to be very volatile. But when summer comes, a volatile fuel can
boil and cause vapour lock, as well as producing high levels of evaporative
emissions. The solution was to adjust the volatility of the fuel according
to altitude and ambient temperature. This volatility change has been
automatically performed for decades by the oil companies without informing
the public of the changes. It is one reason why storage of gasoline through
seasons is not a good idea. Gasoline volatility is being reduced as modern
engines, with their fuel injection and management systems, can automatically
compensate for some of the changes in ambient conditions - such as altitude
and air temperature, resulting in acceptable driveability using less volatile
fuel.

4.5 What are oxygenates?

Oxygenates are just preused hydrocarbons :-). They contain oxygen, which can
not provide energy, but their structure provides a reasonable antiknock
value, thus they are good substitutes for aromatics, and they may also reduce
the smog-forming tendencies of the exhaust gases [15]. Most oxygenates used
in gasolines are either alcohols ( Cx-O-H ) or ethers (Cx-O-Cy), and contain
1 to 6 carbons. Alcohols have been used in gasolines since the 1930s, and
MTBE was first used in commercial gasolines in Italy in 1973, and was first
used in the US by ARCO in 1979. The relative advantages of aromatics and
oxygenates as environmentally-friendly and low toxicity octane-enhancers are
still being researched.

They can be produced from fossil fuels eg methanol (MeOH), methyl tertiary
butyl ether (MTBE), tertiary amyl methyl ether (TAME), or from biomass, eg
ethanol(EtOH), ethyl tertiary butyl ether (ETBE)). MTBE is produced by
reacting methanol ( from natural gas ) with isobutylene in the liquid phase
over an acidic ion-exchange resin catalyst at 100C. The isobutylene was
initially from refinery catalytic crackers or petrochemical olefin plants,
but these days larger plants produce it from butanes. MTBE production has
increased at the rate of 10 to 20% per year, and the spot market price in
June 1993 was around $270/tonne [15]. The "ether" starting fluids for
vehicles are usually diethyl ether (liquid) or dimethyl ether (aerosol).
Note that " petroleum ethers " are volatile alkane hydrocarbon fractions,
they are not a Cx-O-Cy compound.

Oxygenates are added to gasolines to reduce the reactivity of emissions,
but they are only effective if the hydrocarbon fractions are carefully
modified to utilise the octane and volatility properties of the oxygenates.
If the hydrocarbon fraction is not correctly modified, oxygenates can
increase the undesirable smog-forming and toxic emissions. Oxygenates do not
necessarily reduce all exhaust toxins, nor are they intended to.

Oxygenates have significantly different physical properties to hydrocarbons,
and the levels that can be added to gasolines are controlled by the 1977
Clean Air Act amendments in the US, with the laws prohibiting the increase
or introduction of a fuel or fuel additive that is not substantially
similar to any fuel or fuel additive used to certify 1975 or subsequent
years vehicles. Waivers can granted if the product does not cause or
contribute to emission device failures, and if the EPA does not specifically
decline the application after 180 days, it is taken as granted. In 1978 the
EPA granted 10% by volume of ethanol a waiver, and have subsequently issued
waivers for <10 vol% ethanol (1982), 7 vol% tertiary butyl alcohol (1979),
5.5 vol% 1:1 MeOH/TBA (1979), 3.5 mass% oxygen derived from 1:1 MeOH/TBA
= ~9.5 vol% of the alcohols (1981), 3.7 mass% oxygen derived from methanol
and cosolvents = 5 vol% max MeOH and 2.5 vol% min cosolvent - with some
cosolvents requiring additional corrosion inhibitor (1985,1988), 7.0 vol%
MTBE (1979), and 15.0 vol% MTBE (1988). Only the ethanol waiver was exempted
from the requirement to still meet ASTM volatility requirements [16].

In 1981 the EPA ruled that fuels could contain aliphatic alcohols ( except
MeOH ) and/or ethers at concentrations until the oxygen content is 2.0
mass%. It also permitted 5.5 vol% of 1:1 MeOH/TBA. In 1991 the maximum
oxygen content was increased to 2.7 mass%. To ensure sufficient gasoline
base was available for ethanol blending, the EPA also ruled that gasoline
containing up to 2 vol% of MTBE could subsequently be blended with 10 vol%
of ethanol [16].

Initially, the oxygenates were added to hydrocarbon fractions that were
slightly-modified unleaded gasoline fractions, and these were known as
"oxygenated" gasolines. In 1995, the hydrocarbon fraction was significantly
modified, and these gasolines are called "reformulated gasolines" ( RFGs ),
and there are differing specifications for California ( Phase 2 ) and Federal
( simple model ) RFGs, however both require oxygenates to provide Octane.
The California RFG requires the hydrocarbon composition of the RFG to be
significantly more modified than the existing oxygenated gasolines to reduce
unsaturates, volatility, benzene, and the reactivity of emissions. Federal
regulations only reduce vapour pressure and benzene directly, however
aromatics are also reduced to meet emissions criteria [16].

Oxygenates that are added to gasoline function in two ways. Firstly they
have high blending octane, and so can replace high octane aromatics
in the fuel. These aromatics are responsible for disproportionate amounts
of CO and HC exhaust emissions. This is called the "aromatic substitution
effect". Oxygenates also cause engines without sophisticated engine
management systems to move to the lean side of stoichiometry, thus reducing
emissions of CO ( 2% oxygen can reduce CO by 16% ) and HC ( 2% oxygen can
reduce HC by 10%) [17], and other researchers have observed similar
reductions also occur when oxygenates are added to reformulated gasolines
on older and newer vehicles, but have also shown that NOx levels may
increase, as also may some regulated toxins [18,19,20].

However, on vehicles with engine management systems, the fuel volume will be
increased to bring the stoichiometry back to the preferred optimum setting.
Oxygen in the fuel can not contribute energy, consequently the fuel has less
energy content. For the same efficiency and power output, more fuel has to
be burnt, and the slight improvements in combustion efficiency that
oxygenates provide on some engines usually do not completely compensate for
the oxygen.

There are huge number of chemical mechanisms involved in the pre-flame
reactions of gasoline combustion. Although both alkyl leads and oxygenates
are effective at suppressing knock, the chemical modes through which they
act are entirely different. MTBE works by retarding the progress of the low
temperature or cool-flame reactions, consuming radical species, particularly
OH radicals and producing isobutene. The isobutene in turn consumes
additional OH radicals and produces unreactive, resonantly stabilised
radicals such as allyl and methyl allyl, as well as stable species such as
allene, which resist further oxidation [21,22].

Issues Raised by the Change to California Phase 2 RFG

Virtually all vehicles using California Phase 2 RFG will perform the same as they have in the past. However, Chevron cannot predict how California Phase 2 RFG will perform in every vehicle or situation. Test programs operate in a relatively narrow environment and cannot accurately duplicate every combination of real-world driver, vehicle, and driving condition. Some vehicles, for example, are poorly maintained, while others are particularly sensitive to specific fuel properties.

Chevron believes it is important to anticipate a range of potential usage situations and to identify any potential consequences of using California Phase 2 RFG. The following sections present Chevron's current assessment of the issues related to the change to the new gasoline.

While this Bulletin mentions potential consequences that other gasoline producers may not discuss, we believe the consequences are not unique to Chevron gasolines. The actual consequences should be the same for all California Phase 2 RFG, because all producers must meet the same ARB specifications.

Issues Overview


General Performance
ARB tests indicate California Phase 2 RFG performs as well as conventional fuel in most vehicles.


Fuel System Parts
Chevron tests indicate that the use of California Phase 2 RFG may result in the failure of some fuel system parts containing elastomers--particularly older or worn fuel system parts in a very small percentage of older or high-mileage vehicles. Some failures may be accompanied by fuel leaks, which, in some circumstances, could result in a fire if a source of ignition is present.


Fuel Economy
The fuel economy of California Phase 2 RFG may be, on average, up to one percent lower than current California winter gasoline.


Odor
The odor of California Phase 2 RFG will be the same as current California winter gasoline.


Cold Starting
Cold starts with California Phase 2 RFG may take longer during unseasonably cold spring days.


Fuel Handling
As with any gasoline, extreme caution must be taken in handling California Phase 2 RFG. In the unusual circumstances described in the "Fuel Handling" section, there may be a change in the vapor space explosibility of summer California Phase 2 RFG at temperatures below 25oF.


Health
The California Phase 2 RFG marketed by Chevron will be oxygenated predominantly with MTBE. Dispensing California Phase 2 RFG requries no additional precautions compared to current gasoline.

Issues Analysis

General Performance

In ARB's cooperative vehicle test program, 829 vehicles in eight government and private fleets were fueled with one formulation of California Phase 2 RFG for six months.1 An additional 637 vehicles in the same fleets were fueled with conventional gasoline. ARB's conclusion is that the California Phase 2 formulation "performed as well as conventional fuel in terms of driveability, starting, idling, acceleration, power, and safety." 1

ARB also arranged for off-road engines and equipment to be tested--including off-road vehicles, marine engines, utility equipment, and lawn and garden equipment. The intent was to evaluate the compatibility, performance, and durability of the equipment when fueled with California Phase 2 RFG. The differences in the design and usage of the equipment required a variety of test programs--some were field tests and others were laboratory tests. ARB's conclusion is that "no problems were experienced...in these engines that could be linked to the fuel." 1

Fuel System Parts

The fuel system parts which may be affected by gasoline are those made from natural or synthetic rubbers, for example, seals, 'O'-rings, and hoses. These rubbers, as a class, are called "elastomers." All elastomers swell when first exposed to gasoline. Changes in gasoline composition can cause more swelling or reduce the initial swelling (but generally not below the original size of the part). Shrinking and swelling can cause worn elastomers that have hardened and lost their elasticity to fail. The elastomers in newer vehicles generally pose less of a problem, being newer and more flexible, and being made from materials more resistant to changes in gasoline composition.

In the ARB vehicle test program mentioned above, three percent of the vehicles fueled with California Phase 2 RFG experienced fuel system problems, some of which were leaks from various elastomeric parts. The fuel system problems occurred in pre-1991 vehicles and, generally, in those with higher mileages. ARB does not attribute these problems to California Phase 2 RFG because: (1) the test vehicles fueled with conventional gasoline experienced similar problems at a similar frequency; (2) the frequency of problems (3%) in the test vehicles was well below the historical frequency of fleet fuel system problems, adjusted for the test time interval (10%).2 ARB's conclusion is consistent with the views of vehicle and engine manufacturers, who are on record that California Phase 2 RFG will not cause incremental maintenance problems.

Chevron conducted its own test. The test involved two 115-vehicle matched sets of privately owned vehicles, fairly representative in make and age of the California population of gasoline-powered vehicles. One set was fueled with a California Phase 2 formulation; the other set was fueled with conventional gasoline. As in the ARB test, both sets of vehicles experienced fuel system problems, some of which were leaks from various elastomeric parts. And, as in the ARB test, it was the older vehicles that had the problems. However, in the Chevron test, the frequency of fuel system failures for the vehicles fueled with California Phase 2 RFG was greater than the frequency for the vehicles fueled with conventional gasoline. Because the difference was statistically significant, Chevron believes that its testing demonstrated a potential for California Phase 2 RFG to affect elastomeric fuel system parts in older or high-mileage vehicles. Chevron has shared these results with ARB and with the oil industry trade association--Western States Petroleum Association.

While both ARB and Chevron test vehicles developed fuel system leaks, no vehicle fires occurred. But fire is always a concern when gasoline is leaking.

It is not certain that California Phase 2 RFG will cause any incremental elastomer failures. However, in light of the fact that Chevron's testing indicated a potential problem, we believe that our customers deserve to be informed, enabling them to make their own decisions based on all the information available.

Chevron recommends that owners of older or high-mileage vehicles consult an auto repair technician about possible repair or replacement of fuel system parts. Owners should monitor their fuel systems for leaks, repairing any leaks immediately. Vehicles never should be operated with a fuel leak.

Chevron also believes that it would be prudent for owners of older, non-automotive gasoline-powered engines and equipment to be alert for fuel leaks. Owners should ask mechanics knowledgeable about their equipment whether preventative fuel system maintenance is advisable. No engine should be operated with a fuel leak.

As part of its customer information effort, Chevron will post a warning label on pumps dispensing California Phase 2 RFG at all our stations.



Fuel Economy

The distillation limit specification of California Phase 2 RFG may result in a small decrease in mileage. This limit excludes higher-boiling gasoline components from California Phase 2 RFG formulations. Since higher boiling components are denser and, thus, contain more energy per gallon, their exclusion may reduce the mileage of California Phase 2 RFG by up to one percent, on average. This decrease should not be noticeable to most consumers, as it represents a mileage change from, for example, 22.0 mpg to 21.8 mpg.

Adding oxygen to gasoline also decreases mileage because oxygenates contain less energy than non-oxygenated gasoline. Compared to the mileage of non-oxygenated summer California Phase 1 RFG, the mileage of California Phase 2 RFG may be on average up to three percent lower. However, since California Phase 2 RFG will be introduced at the end of California's winter oxygenated gasoline season, consumers most likely will be comparing it to oxygenated California Phase 1 RFG, or to federal Phase I RFG, which is oxygenated year round. Since the oxygen content of California Phase 2 RFG will be the same as the oxygen content of these fuels, consumers should not experience any additional decrease in mileage due to the oxygen in California Phase 2 RFG.

Odor

The addition of oxygenates not only impacts fuel economy, but also gives oxygenated gasoline a different odor than that of non-oxygenated gasoline. Since, as explained above, California Phase 2 RFG most likely will be replacing fuels which are already oxygenated, its introduction should not be accompanied by a perceptible change in gasoline odor.

Cold Starting

Starting and warmup driving is more difficult with a lower-vapor-pressure gasoline when the weather is cold because the gasoline does not ignite as easily. In the summer, California Phase 2 RFG vapor pressure limits are not likely to cause slow starting and warmup driving problems. In the winter, the vapor pressures in most areas will continue to be those established by the American Society of Testing and Materials (ASTM) to provide good cold weather engine performance. However, ARB's regulations require that terminals and retail service stations be converted back to low-vapor-pressure summer gasoline by April 1 in Southern California and May 1 in Northern California. To meet these deadlines, producers must start filling the distribution system as early as February. During the February-May transition period, the vapor pressure of gasoline at the pump may be low enough that unseasonably cold weather may result in slower starting and hesitation or stalling during warmup driving for some vehicles.

Fuel Handling

All gasoline is very flammable and must be handled and stored with extreme care. However, under certain unusual circumstances, summer California Phase 2 RFG, because of its lower vapor pressure, may present a potential increased hazard which higher-vapor-pressures gasolines do not.

In any gasoline storage tank or container, the vapor space--the space above the liquid fuel--is occupied by a mixture of gasoline vapor and air. The concentration of gasoline vapor is determined by the vapor pressure of the fuel at the storage temperature. The vapor space above a gasoline with a high vapor pressure contains more gasoline vapor and less air than the space above a gasoline with a lower vapor pressure. The same is true for the vapor space above a gasoline at one temperature compared to the space above the same gasoline at a lower temperature.

Typically, the gasoline vapor in a closed tank or container will not burn at normal ambient conditions because too little air (oxygen) is present. The gasoline vapor/air mixture is described as being "too rich" to burn. If the ambient temperature is cold enough during the spring phase-in of low-vapor-pressure summer California Phase 2 RFG, the concentration of gasoline vapor in the vapor space may become low enough to move the vapor/air mixture into the flammability range. This increases the risk of explosion if a source of ignition is present. The risk of increased flammability and explosion under the above circumstances potentially affects any fuel storage tank or container at a temperature less than 25oF at sea level or 20oF at 6000 feet elevation. (The lower atmospheric pressure at higher elevations increases the vaporization of gasoline and, thus, the concentration of vapor in the vapor space.)

We do not believe California Phase 2 RFG presents any new or increased flammability or explosion risk when handled in a manner consistent with all approved procedures for gasoline. Anyone who handles gasoline should be aware of, and consistently and carefully follow, current safety guidelines. This includes keeping sources of ignition away from gasoline and gasoline away from sources of ignition. While this precaution applies to all gasolines at all temperatures, the above explanation shows that it is especially important for California Phase 2 RFG at temperatures below 25oF. In addition, if California Phase 2 RFG purchased in the spring or summer is stored below this temperature, it may be prudent to keep the container as full as possible to minimize the vapor space.

Health

All gasolines contain chemicals which appear on federal and state lists of toxic materials. Anyone handling gasoline, including California Phase 2 RFG, should take steps to minimize skin contact and vapor inhalation. Common sense precautions usually are sufficient to prevent any adverse health effects. Fuel handlers and customers wanting more detailed health and safety information are encouraged to consult the Material Safety Data Sheet for the appropriate grade of Chevron gasoline3.

The California Phase 2 RFG produced by Chevron will be oxygenated predominantly with MTBE, the oxygenate that has been used most extensively in California to date. Since the introduction of MTBE-oxygenated gasoline, there have been isolated complaints by fuel handlers and consumers of nausea, headaches, and eye or skin irritation. Most of these complaints have originated from a few cities outside of California. After a comprehensive investigation that included epidemiological studies, ambient air analyses and the exposure of volunteers to MTBE vapor, the U.S. EPA concluded that exposure to MTBE does not appear to cause eye and nose irritation or behavioral changes in healthy adults.

Chevron is not aware of any research which indicates that gasoline formulated with MTBE presents a greater health risk or needs to be handled differently than gasoline without MTBE. Nevertheless, If a customer or fuel handler experiences symptoms which they attribute to gasoline exposure, they should see their physician for an evaluation. Physicians may call the Chevron Emergency Information Center 24-hours-a-day at 1-800-231-0623 to obtain more information about the health effects of gasoline exposure.