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Submitted by Neville Lee Archer of Lee Archer &
Co
Background
The petrol used today is different in characteristics and components used as compared to the petrol in the recent past. Current unleaed fuel is vastly different to leaded fuel of the past.
Two factors are present to shorten the shelf life of
fuel:
- Economic: stretching the amount of petrol available
from a barrel of crude oil
- Environmental: addition of oxygenating ingredients
in an attempt to improve overall air quality.
Both of the above factors result in fuel which has
shorter shelf life, is harder on soft components (elastomers)
and leaves deposits (gum, tar, varnish) at a far more
rapid rate than for fuels of the past.
In the 1950s, approximately 28% of a barrel of crude
oil was refined into petrol. This was known as straight-run
petrol. As the most lucrative high-volume product of
crude oil is petrol, petroleum companies have developed
ever-more exotic refining and cracking methods to pull
more petrol from a barrel of crude oil. Today, that
28% has been increased to over 45% and, depending on
the source of the crude, can go to as much as 75%. The
negative effect in the more exotic refining processes
is that they create olefins and diolefins which shorten
shelf life due to oxidation and promote the rapid development
of tars, gums and varnishes. For this reason, most OPE
manufacturers recommend 30 days as the recommended shelf
life for petrol. If used in extreme high temperature
conditions and stored in an aboveground fuel container
(plastic petrol container), we would shorten that to
1 week maximum.
Note: shelf life of petrol can be extended by use of
an oxidation reduction compound known as fuel stabiliser.
Several manufacturers offer this compound; among the
most commonly used world-wide is Sta-Bil (tm) . Use
of these compounds as directed can extend the shelf
life of petrol as long as 1 year.
Note (Update 2011): Many service stations are blending Asian sourced fuels which are of lesser quality to Australian fuels, which may have an adverse effect on small engines. Reliability and "startability" may be effected.
It is our position that use of a fuel stabiliser for
engines that will be stored for a period of time is
superior to draining fuel and running the carburettor
dry. The potential for damage to diaphragms and gaskets
is far greater as those components dry out.
Oxygenated Fuel
Environmental concerns and subsequent regulations
for improved air quality have lead to the use of oxygenated
fuels; fuels containing and oxygen-bearing component.
Though not present,
12 Property Care Industry
adding an oxygenate will provide a lean mixture; improving
overall emissions. These compounds also improve octane;
something drastically reduced when lead was removed.
At the same time, this is also a method to extend the
quantity of petrol available from a barrel of crude
oil. To the petroleum companies, this has become a very
popular practice. The regulations, economics, concern
for diminishing supplies and need to keep octane levels
high have made use of oxygenates very attractive.
The three most common oxygenating ingredients are:
methanol, ethanol and MTBE; a derivative of methanol.
Methanol is produced from natural gas or petroleum
and is commonly known as wood alcohol.
Ethanol is produced from corn or grain and is known
as grain alcohol and is commonly found in spirits, beer,
wine etc. As it comes from a renewable resource, it
is looked upon in high regard by environmental groups
and the agriculture industry in countries with air quality
problems.
All of these components are not without undesirable
characteristics. Alcohols (methanol and ethanol) are
chemically unstable in petrol. Specifically, they do
not want to stay mixed due to the hygroscopic effect
when water is present. Alcohol is naturally attracted
to and readily absorbs water; to the extent that it
will combine with water and, then as the heavier component,
it sinks to the bottom of the tank. This process is
called phase separation and is a serious concern when
alcohol levels are high. As the alcohol/water combination
is a the bottom of the tank, it goes inside the engine
first and sometimes at a level that poses the potential
for engine seizure. The alcohol also acts as a degreasing
agent and washes the protective lubrication film off
of components; leading to rust, corrosion and the potential
accelerated wear. In addition, when used in high ratios,
they can cause deterioration of gaskets, grommets, fuel
lines, etc.
MTBE (methyl tertiary butyl ether) has eliminated the
undesirable effects of straight-run alcohols but has
brought in several of its own negative characteristics.
The sensitivity to detect MTBE is far greater than gasoline;
perhaps by a factor of 10. Simple refuelling in the
US has lead to thousands of complaints of headaches,
dizziness, nausea, burning eyes and sore throats. Even
more of a concern is ground water contamination. In
minute amounts too low to present any health risk, drinking
water will be tainted to the point it is undrinkable.
Once present in ground water, it is extremely difficult
to remove.
MTBE is being phased out as an oxygenating ingredient
in the US. At the same time, the resultant surplus is
being sold as an oxygenating ingredient for petrol production
elsewhere in the world.
As per Power Equipment Australia s October/November 2001 Manganese leaves a red-red brown coating on all internal engine
edition. MTBE has found its way to Australia and is already components and the use of MMT can readily be identified when
being used in petrol Western Australia has already banned its use this condition is present. When used in petrol, if a clear/opaque
due to potential contamination of precious drinking water. A
January, 2001 AAA report supports prohibiting the use of MTB
as well as Methanol and all other derivatives of alcohol (DIPE,
ETBE, TAME, ETAE, etc.)
Another aspect of today 's fuel is octane ratings. With the
elimination of lead in automotive petrol in 1986, other
compounds have been to regain octane ratings. Alcohols do an
effective job of raising octane. 10% methanol can raise the
octane rating by 2-3 points. MTBE is also an effective octane
booster. As petrol has gone away from tetra-ethyl lead as the
most common octane booster, these other compounds are
prevalent. Simple to remember-if lead is out, what is replacing
it?
An additional characteristic of lead for a 4-stroke is that of
providing a cushioning effect for valves to prevent valve scat
recession. Other than as an octane booster, lead is unnecessary in
a 2-stroke. As a result, several compounds have been substituted
as a means of providing this protective layer:
M Mobil: manganese (MMT)
M BP: potassium
M Shell: Phosphorous
fuel container is used, the resultant reaction can
lead to plugged fuel filters.
Potassium has the effect the gumming or sticking valves.
Phosphorous can have a similar effect, as well as leaving
a sooty appearance on all internal engine components.
Sodium is also used in some over the counter octane
boosters, but has been known to corrode internal engine
components in certain high-temperature engine conditions.
Alcohol Shaker Test
To test for the presence of alcohol and the approximate
percentage, a simple shaker test can be done to trigger
phase separation. This can be done with a straight-
sided glass cylinder or beaker with graduations on the
side. Briggs and Stratton s P/NM 100023 Gasohol Test
Kit is a commonly available and inexpensive tester.
In summary, by adding a measured amount of water to
trigger phase separation, the percentage of alcohol
present can be derived by a separation line and the
amount shown above the amount of water that was placed
in the tube. Overall, a 10% ratio is considered acceptable,
but serious problems will be seen if the amount is 20-30%.
Note: This test separates approximately 90% of the
alcohol present. If the test result shows 10%, the actual
is approximately 11 %. Caution: this tester is not effective
if MTBE is present. Only laboratory test apparatus can
be used to arrive at the percentage of
MTBE
OCTANE RATINGS
Australian Octane ratings:
LP (leaded petrol) 89 RON
Super (leaded) 95-96
PLP 98
ULP 91-92
LRP 96
OCTANE RATING SYSTEM
RON research octane number taken at light load and
under acceleration
MON motor octane number taken at high load and RPM
RON rating is used in Australia and NZ
RON+MON formula used in N. America 2
Australia / NZ octane numbers are higher than typical
US numbers, but when the RON + MON method is used, octane
ratings are very similar.
A higher MON number is considered to be a better performing
fuel. RVP ( Reid Vapour Pressure)
A test and rating system used to measure fuel volatility.
Propane and butane gas are commonly added at various
levels to match a historical monthly temperature chart
for each region of a country. Worldwide, this figure
is normally in a range of 48-103 kPa (7-15) psi for
regions with clear seasonal changes for winter and summer.
The less the climatic variation between seasons, the
lower the spread between summer and winter numbers.
The only cause for concern is when an unseasonably warm
day occurs or when fuel blended for a colder area is
transported into a warmer climate.
Note: The standard RVP of Australian petrol is higher
vs. RVP limits in the US, Canada and Japan. These are
also primary markets for 2-stroke equipment, Many times
simply adhering to good maintenance practices (clean
cooling fins, intake passages, etc) will avoid the potential
for vapour lock.
For the future, several air quality proposals are in
process to reduce summer RVP in populated, industrialised
areas such as Brisbane. One would reduce summer RVP
limits to 65 kPa (9.4psi).
Fuel Recommendations
- Use fresh fuel with at least a 91 octane rating
- Recommend your customers use name-brand fuel that
has given good performance in your area.
- Avoid cut rate/economy brands
- Do not store longer than 30 days (1 week in high
temperature conditions).
- Use fuel stabilizer if equipment must be stored
for long periods.
- Keep cylinder fins and cooling air intake areas
clean.
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