Combuston engine, as used in the car as well
as the VeloSoleX S 3800,
is a major cause of environmental
pollution contributing as much as 50% to all
Carbon Monoxide, Nitrogen Oxide and Hydro-Carbon emissions in the US
(Source: US Department Of Energy, 1992).
The 3 Primary Emissions of a car are:
N2 - Air is 78% Nitrogen gas and most
of this passes straight through the car engine
Dioxide CO2 - Carbon in the fuel bonds with
oxygen in the air
- Water Vapour H2O
in the fuel bonds with oxygen in the air
Apart from Carbon
Dioxide, which is thought to contribute to global
warming, 3 other Harmful Secondary
Emissionsare also produced:
Carbon Monoxide CO - A poisonous, colourless
and odourless gas
- Hydro-Carbons HC
and Volatile Organic Compounds
VOC - Mainly produced from unburnt fuel that evaporates
and react with Nitrogen Oxides to create ground-level
Ozones O3 which a major component of smog
Oxides NO and NO2 - Known to contribute to smog and
acid rain and to cause irritation to human mucus membranes
These 3 last harmful emissions are what Catalytic
Converters were primarily designed to reduce and the reason why
they are sometimes called 3-way Catalytic Converters.
CONVERTERS typically have a 2-Stage Ceramic Honeycomb
Structure (to provide a large surface area) coated with
the expensive metals of Platinum, Rhodium and Palladium.
The 1st stage Platinum-Rhodium Reduction Catalyst
holds on to the Nitrogen molecule of NO or NO2 freeing
oxygen as O2. This Nitrogen molecule bonds with other
Nitrogen molecules already present to produce Nitrogen
N2 which is the major component of air.
2nd stage Platinum-Palladium Oxidation Catalyst works
by burning (oxidizing) unburnt Hydro-Carbons and Carbon
Monoxide using the Oxygen remaining in the exhaust gas
to primarily produce Carbon Dioxide CO2.
An Oxygen (Lambda) Sensor
upstream of the Catalytic Converter can measure the amount
of Oxygen present and tell the engine computer to increase
or decrease the amount of Oxygen in the exhaust gas
by adjusting the air-fuel mixture ratio, while not changing it
too much from the ideal stoichiometric air-fuel mixture
14.6 : 1.
Catalytic Converters are used on modern 4-Stroke
and 2-Stroke mopeds. Catalytic Converters require a
temperature in the range of 300°C to 600°C to work properly, so for the VeloSoleX S
(which is often used for short trips), it must be located as close as possible to the engine manifold
to enable a quick warm-up. This unfortunately can result in reduced
life expectancy for the Catalytic Converter. Another
cause of reduced life expectancy for the Catalytic Converter
is unburnt fuel in the exhaust gas which unfortunately
is how the VeloSoleX S
often tuned, since a slightly
rich mixture helps to prevent the air-cooled engine
from overheating while still giving good acceleration.
Converters use Variable-Conductance Vacuum Insulation
(VCI) to keep the temperature of the catalysts above 300°C
for at least 24 hours after stopping the engine thus
them to work immediately the vehicle is started the
As far as failures are concerned, when a Catalytic Converter fails the only way of knowing
about it may be by a total lack of engine power or the
engine overheating because of blocked exhaust gases.
These days, shaking it and listening for loose or broken pieces
may not be a reliable indicator anymore.
SINCE the 1920's, fuel has been 'Leaded' (the Alkyl
compound Tetra Ethyl
Lead was added to fuel) to allow
engines to use higher compression ratios and hence
without the problem of engine detonation
"pinking"). Lead also had a secondary benefit of reducing
Valve Seat wear on 4-Stroke engines. Typically, 100
RON Premium Leaded Fuel of the 1970's had
about 0.7 - 0.8 grams per litre and 94 RON Regular
Leaded Fuel about 0.6 - 0.7 grams per litre.
From the 1970's, because of increasing
smog levels in cities, laws were passed so that Catalytic Converters had
to be fitted to cars. At the same time, action
tried to get Tetra Ethyl Lead removed from fuel believing
that the Lead was ending up
in people's blood and affecting their health. The average
Catalytic Converter was very quickly damaged by Lead in fuel and so
Leaded Fuel was conveniently targeted as the main culprit
and was phased out as Unleaded Fuel was phased in.
Since then, there have been a number
of reports suggesting that the removal of Lead from fuel, which
was so eagerly
pounced on, has
notquite resulted in the reduction of Lead
levels in blood expected.
Since the Lead scavengers Ethylene
Dibromide and Ethylene Dichloride, also required in Leaded Fuel, could react with Hydro-Carbons to produce
highly toxic Organo-Halogen emissions such as Dioxin, even if catalysts were
removed or Lead-tolerant catalysts discovered, Alkyl Lead compounds would
still remain banned because of their toxicity and toxic emissions.
Sulphur inhibits the octane-enhancing effect
of Lead and can damage Catalytic Converters, so from the
beginning it was advantageous for motorists to have
Sulphur reduced to an absolute minimum particularly
the 1970's with the introduction of Catalytic Converters.
Since Sulphur Dioxide is widely associated
with pollution, many fuel distributors capitalize on this
and proudly boast
of Low-Sulphur Content to attract environmentally-concious
motorists while not mentioning too much about the undesirable
effects of the other fuel components which may have
WHEN Tetra Ethyl Lead was reduced
from about 0.6 - 0.7 grams per litre in
Leaded Fuel to about 0.015 grams
per litre in Premium and Super Unleaded Fuels, the percentage of Fuel Aromatics increased because
they were used to replace
Lead as the Octane Enhancer and anti-knock
The typical percentage of the some
important Fuel Aromatics in
Leaded Fuel is:
- 10 % Toluene
- 5% Benzene
- 5% Xylene
- 1% Ethyl Benzene
There has been mounting
evidence to suggest that Fuel Aromatics have the opportunity
to escape at filling stations and tanker spills. Benzene as well as 1,3 Butadeine combustion by-products
are known to be highly carcinogenic. So to reduce the escape of
these Fuel Aromatics, many countries
have had special fuel pumps installed to prevent the escape of fuel vapours at
The carcinogenic effects of the other
30 or so components of fuel are still being investigated.
Using Unleaded Fuel without a Catalytic Converter or
using a defective Catalytic Converter is widely
believed to introduce many new pollutants into the atmosphere
than when Leaded Fuel was used.
Unleaded Fuel is seasonally
adjusted to compensate for changing ambient temperatures and fuel
volatility. Consequently fuel sold in summer does not have
same composition as fuel sold in winter.
On the topic of pollution,
it should be noted that 10%
of all Carbon Monoxide polluters produce over 50% of
the pollution. Hence, it may make more sense to focus
on these polluters than to spend large amounts of money
on researching how to further improve the emissions
of the modern car.
HIGH Octane Fuel Aromatics can produce disproportionate amounts of Carbon Dioxide CO2
and Hydro-Carbons HC
in exhaust emissions.
In the US, the Clean Air Acts forced manufacturers to produce Re-Formulated Gas (RFG) from 1995 onwards to reduce pollution.
Re-Formulated Gas contains less Benzene, evaporates
slower and contains more Oxygenates. High blending octane
Oxygenates began to be used
increasingly as the levels of the high octane Fuel Aromatics were reduced.
was some early evidence to suggest that Oxygenates might
reduce the smog-forming tendencies of exhaust
fumes if the Hydro-Carbon fraction is carefully modified.
Oxygenates include the alcohols and ethers such
as Methyl Tertiary Butyl Ether (MTBE), Tertiary Amyl
Methyl Ether (TAME) or Ethyl Tertiary Butyl Ether (ETBE).
Fuel typically contains as much as 15% MTBE.
The major concern with Oxygenates at present is not
with atmospheric pollution but with their carcinogenic
properties, water solubility and very slow biodegradability
in groundwater. There has been some pressure since the
1990's to replace MTBE
with the alcohol Ethanol as it may be less carcinogenic
(although more expensive).
TYPICALLY, Premium Unleaded Fuel contains
some or all of the following additives:
- Anti-Oxidants to inhibit gum formation and improve fuel
- Corrosion Inhibitors to prevent fuel from corroding storage tanks
- Deposit Modifiers to reduce deposits, spark-plug fouling and
- Dyes to colour fuel for safety or regulatory purposes
- Freezing-Point Depressants to prevent icing
- Metal De-Activators to inhibit gum formation
and improve fuel stability
- Octane-Enhancing Additives to improve the octane rating
- Surfactants to prevent icing, improve vapourisation, inhibit deposits
reduce Nitrogen Oxide emissions
THE two main Octane Ratings
are currently RON and MON:
- RON (Research Octane Number)
is determined by typically using the Cooperative Fuels Research (CFR)
ASTM D2700-92 612cc [cm³] Single Cylinder Test Engine using the fuel to be tested.
The engine is run at 900 RPM, the inlet air
temperatrure is set to 38°C and the ignition
timing is varied from 14° to 26° BTDC as the
is varied from 4 : 1 to 18 : 1 (by moving the
cylinder head) until
detonation (measured by a Magneto-Restrictive Detonation Sensor
in the Combustion Chamber) reaches 50 on a scale of 0 to 100 of a Detonation
Meter. Next, a reference fuel
mixture of Heptane and Iso-Octane is used in
the engine and
their ratios altered until 50 is
reached once again on the Detonation Meter. Heptane and Iso-Octane
were chosen as reference fuels because they
have similar boiling points and therefore less likely
to introduce spurious effects. Heptane ignites
easily when compressed; Iso-Octane ignites
with great difficulty. The percentage of the
used gives the Research Octane Number (Octane
Rating) of the fuel being measured (eg: 95%
Iso-Octane used means 95 RON).
- MON (Motor Octane Number) is determined
by typically using the
Cooperative Fuels Research (CFR)
ASTM D2699-92 Test Engine (actually a similar test engine as that used to measure RON but set
up differently to better represent an engine
in the real-world).
Here, the engine is run at 600 RPM, the inlet
air temperatrure is set between 20°C and 52°C (depending
on barometric pressure) and the ignition timing
is fixed at 13° BTDC. These conditions tend
to give lower Iso-Octane numbers (eg: 85% Octane
used means 85
The difference between the RON and
MON numbers is known as the Fuel
Sensitivity. If the Octane Ratings of a test
fuel varies a lot with changes of inlet air temperature
or ignition timing (which is typical for highly cracked
fuels), it is said to be more sensitive.
The US AKI
(Anti-Knock Index) is the Average of
the RON and MON numbers and is the figure
shown on US
fuel pumps while RON is shown on European fuel pumps.
So, if one uses the examples above (RON = 95,
MON = 85) the AKI would be:
Generally, the closer the AKI Number
rating to the fuel's RON number,
the more reliable the AKI rating.
OXYGENATES have been known toswell or shrink
Elastomers depending on the level of
Fuel Aromatics (Arenes)
also in the fuel. Elastomers are
used for the SPI Lip Seal
on the VeloSoleX S 3800 crankshaft
and also sometimes as a seal on one or both sides
of the Crankshaft Roller Bearing depending
on the type.
Oxygenates may also lead to
increased Spark Plug fouling
in 2-Stroke engines that were designed a long time ago.
Since reliable information
on the levels of Oxygenates, Fuel Aromatics and Olefins
is not readily available for the various fuels in use
around the world it is NOT RECOMMENDED
to use the higher octane Premium and Super Unleaded Fuels
in the VeloSoleX S 3800
until more information becomes available on the subject.
The recommendation at the moment is
to use only Regular Unleaded Fuel (eg:
95 RON or US Pump 89