Alternative fuels are derived from resources other than petroleum. Some are
produced domestically, reducing our dependence on imported oil, and some are
derived from renewable sources. Often, they produce less pollution than gasoline
Some alternative fuels that can replace conventional fuel are
3. Natural gas
Ethanol is an alcohol-based fuel made by fermenting and distilling starch crops,
such as corn. It can also be made from "cellulosic biomass" such as trees and
grasses. The use of ethanol can reduce our dependence upon foreign oil and reduce
greenhouse gas emissions.
Cellulosic ethanol, which is produced from non-food based feedstocks, is expected
to improve the energy balance of ethanol, because non-food-based feedstocks are
anticipated to require less fossil fuel energy to produce ethanol. Biomass used to
power the process of converting non-food-based feedstocks into cellulosic ethanol
is also expected to reduce the amount of fossil fuel energy used in production.
Another potential benefit of cellulosic ethanol is that it produces lower levels of
greenhouse gas emissions.
E10 (also called ―gasohol‖) is a blend of 10% ethanol and 90% gasoline sold in
many parts of the country. All auto manufacturers approve the use of blends of
10% ethanol or less in their gasoline vehicles. However, vehicles will typically go
3–4% fewer miles per gallon on E10 than on straight gasoline.
E85, a blend of 85% ethanol and 15% gasoline, can be used in flexible fuel
vehicles (FFVs), which are specially designed to run on gasoline, E85, or any
mixture of the two
Fuel Economy and Performance
A gallon of ethanol contains less energy than a gallon of gasoline. The result is
lower fuel economy than a gallon of gasoline. The amount of energy difference
varies depending on the blend. For example, E85 has about 27% less energy per
gallon than gasoline
Domestically produced, reducing use of imported petroleum
Lower emissions of air pollutants
More resistant to engine knock
Added vehicle cost is very small
Can only be used in flex-fuel vehicles
Lower energy content, resulting in fewer miles per gallon
Currently expensive to produce.
Biodiesel is a form of diesel fuel manufactured from vegetable oils, animal fats, or
recycled restaurant greases. It is safe, biodegradable, and produces less air
pollutants than petroleum-based diesel.
Biodiesel can be used in its pure form (B100) or blended with petroleum diesel.
Common blends include B2 (2% biodiesel), B5, and B20.
Most vehicle manufacturers approve blends up to B5, and some approve blends up
to B20. Check with your owner‘s manual or vehicle manufacturer to determine the
right blend for your vehicle, since using the wrong blend could damage your
engine and/or void the manufacturer's warranty.
Domestically produced from non-petroluem, renewable resources
Can be used in most diesel engines, especially newer ones
Less air pollutants (other than nitrogen oxides)
Less greenhouse gas emissions (e.g., B20 reduces CO2 by 15%)
Safer to handle
Use of blends above B5 not yet approved by many auto makers
Lower fuel economy and power (10% lower for B100, 2% for B20)
Currently more expensive
B100 generally not suitable for use in low temperatures
Concerns about B100's impact on engine durability
Slight increase in nitrogen oxide emissions possible in some circumstances
Using biodiesel reduces greenhouse gas emissions because carbon dioxide released from
biodiesel combustion is offset by the carbon dioxide sequestered while growing the soybeans or
other feedstock. B100 use reduces carbon dioxide emissions by more than 75% compared with
petroleum diesel. Using B20 reduces carbon dioxide emissions by 15%.
Biodiesel is nontoxic. It causes far less damage than petroleum diesel if spilled or released to the
environment. It is safer than petroleum diesel because it is less combustible. The flashpoint for
biodiesel is higher than 150°C, compared with about 52°C for petroleum diesel. Biodiesel is safe
to handle, store, and transpor
Biodiesel improves fuel lubricity and raises the cetane number of the fuel. Diesel engines depend
on the lubricity of the fuel to keep moving parts from wearing prematurely.
Ultra-low sulfur diesel (ULSD) is diesel fuel with 15 parts per million or lower sulfur content.
ULSD combined with advanced emission control technologies is referred to as clean
diesel. Biodiesel is also considered a USLD because it does not intrinsically contain sulfur.
It is a mixture of components, consisting mainly of methane(60-98%) with small
amounts of other hydrocarbon fuel components. In addition it contains various
amounts of nitrogen, carbondioxide, helium, and traces of other gases. Its sulphur
content ranges from very little(sweet) to larger amounts(sour).
Methane=90%,(minimum), ethane=4%(maximum),propane=1.7% c4 and
higher=0.7%, c4 and higher=0.2%,
It is stored as compressed natural gas(CNG) at pressures of 7 to 21 bar and a
As a fuel it works best in an engine system with a single-throttle body fuel injector.
This gives a longer mixing time,which is needed by this fuel.
About 94% of U.S. natural gas used is domestically produced
Roughly 20% to 45% less smog-producing pollutants
About 5% to 9% less greenhouse gas emissions
Less expensive than gasoline
Limited vehicle availability
Less readily available than gasoline and diesel
Fewer miles on a tank of fuel
Propane: Liquefied Petroleum Gas (LPG)
Propane or liquefied petroleum gas (LPG) is a clean-burning fossil fuel that can be
used to power internal combustion engines. LPG-fueled vehicles can produce
significantly lower amounts of some harmful emissions and the greenhouse gas
carbon dioxide (CO2). LPG is usually less expensive than gasoline, it can be used
without degrading vehicle performance, and most LPG used in U.S. comes from
domestic sourcesPropane has a higher octane number, burns more clearly and
saves on maintenance costs.Propane is gaining as a gasoline substitute because it
costs 60% of petrol and gives 90% mileage of its fellow gasoline.
90% of propane used in U.S. comes from domestic sources
Less expensive than gasoline
Potentially lower toxic, carbon dioxide (CO2), carbon monoxide (CO), and
nonmethane hydrocarbon (NMHC) emissions
Limited availability (a few large trucks and vans can be special ordered from
manufacturers; other vehicles can be converted by certified installers)
Less readily available than gasoline & diesel
Fewer miles on a tank of fuel
Hydrogen (H2) is being aggressively explored as a fuel for passenger vehicles. It
can be used in fuel cells to power electric motors or burned in internal combustion
Produced Domestically. Hydrogen can be produced domestically from
several sources, reducing our dependence on petroleum imports.
Environmentally Friendly. Hydrogen produces no air pollutants or
greenhouse gases when used in fuel cells; it produces only nitrogen oxides
(NOx) when burned in ICEs.
High energy content per volume when stored as liquid. This would give as a
large vehicle range for a given fuel tank.
Fuel leakage is not a pollutant.
Hydrogen air mixture burns ten times faster than gasoline air mixture. Hence
it is used in high speed engines.
High efficiency since it has higher hydrogen ignition limits.
It has high self ignition temperature, but very little energy (1/50 th of
gasoline) is required to ignite it.
More difficult to handle
Difficult to refuel.
Poor volumetric efficiency. Any time a gaseous fuel is used in an engine, the
fuel will displace some of the inlet air and poorer volumetric efficiency will
Fuel cost is high
High NOx emissions because of high flame temperature..
In hydrogen engines there is a danger of back fire and induction ignition
which can melt the carburettor. Therefore in hydrogen fuel system, flame
traps, flash back arrestors are necessary. Additionally crank cases must be
vented to prevent accumulation of explosive mixtures.
It is generally produced from dung,sewage,vegetable wastes,poultry droppings, pig
Methane-50 to 60 % by volume
Hydrogen and nitrogen-5 to 10%
H2S and O2 -traces
Possesses excellent antiknock properties(high octane number 120)
Auto ignition temperature is higher than petrol thus it is a safe fuel
Mixes readily with air even at low temperature, therefore there is no need to
provide rich mixture during starting or idling.
Although its calorific value is lesser than petrol.it is possible to use in higher
compression ratios for the same size engine thus producing the same amount
NOx emissions are reduced by 60%
Exhaust gases have less pungent odour.
Flexible-fuel vehicle (FFV)
A flexible-fuel vehicle (FFV) or dual-fuel vehicle (colloquially called a flex-fuel
vehicle) is an alternative fuel vehicle with an internal combustion engine designed
to run on more than one fuel, usually gasoline blended with either ethanol or
methanol fuel, and both fuels are stored in the same common tank. Modern flex-
fuel engines are capable of burning any proportion of the resulting blend in the
combustion chamber as fuel injection and spark timing are adjusted automatically
according to the actual blend detected by a fuel composition sensor. Flex-fuel
vehicles are distinguished from bi-fuel vehicles, where two fuels are stored in
separate tanks and the engine runs on one fuel at a time, for example, compressed
natural gas (CNG), liquefied petroleum gas (LPG), or hydrogen.
A fuel cell by definition is an electrical cell, which unlike storage cells can be
continuously fed with a fuel so that the electrical power output is sustained
indefinitely .They convert hydrogen, or hydrogen-containing fuels, directly into
electrical energy plus heat through the electrochemical reaction of hydrogen and
oxygen into water.
The process is that of electrolysis in reverse.
Overall reaction: 2 H2(gas) + O2(gas) → 2 H2O + energy
Because hydrogen and oxygen gases are electrochemically converted into water,
fuel cells have many advantages over heat engines. These include:
virtually silent operation and,
if hydrogen is the fuel, there are no pollutant emissions.
If the hydrogen is produced from renewable energy sources, then the electrical
power produced can be truly sustainable.
The two principle reactions in the burning of any hydrocarbon fuel are the
formation of water and carbon dioxide. As the hydrogen content in a fuel increases,
the formation of water becomes more significant, resulting in proportionally lower
emissions of carbon dioxide.
The above schematic diagram of an experiment illustrates the basic principle
involved in hydrogen gas production and its consumption. A fuel cell consumes
hydrogen gas and oxygen gas.
Porous nickel and porous carbon electrodes are generally used in fuel cells for
commercial applications. The best electro-chemical catalysts are finely divided
platinum or platinum like metal deposited on or incorporated within the porous
The electrolyte is generally 40% KOH (potassium hydroxide) solution because of
its high electrical conductivity and less corrosiveness compared to acids.
In figure 1.1 (a) the production of hydrogen ( H2 ) gas and oxygen gas (O2 ) is dealt
A beaker is taken with dilute electrolyte inside it and electrodes are inserted into it.
Test tubes are kept inverted on the electrodes which are connected to an external
power source. On passing current through the electrolytic cell electrochemical
reactions occur at the electrodesand the gas are produced.
The electrolyte water splits as ions due to the passage of current. Water requires
the aid of an alkali or acid in ionization. The reaction is :
At anode ( positive electrode) oxidation occurs and thus oxide ions are oxidized to
oxygen gas molecules
O2 + 4 e-
At cathode ( negative electrode ) reduction occurs and hydrogen ions are reduced
to hydrogen gas molecules.
+ 4 e-
Thus the individual gases are produced and stored by displacing the water column
in the inverted test tubes.
The figure 1.1 (b) deals with the consumption of hydrogen ( H2 ) gas and oxygen
gas (O2 ):
On removal of the power source and on connection of a load, the gases that have
been produced are ionized and consumed in the process which results in electricity
generation, heat energy liberation and water production.
The reactions are as follows:
At anode reduction of oxygen molecules occurs resulting in oxide ions formation :
O2 + 4 e-
At cathode oxidation of hydrogen gas molecules to hydrogen ions occurs :
2 H2 4 H+
+ 4 e-
The electrons produced in the above equation travel through the external circuit,
leading to production of electric current in the direction opposite to the flow of
The hydrogen ions and oxygen ions produced react to form water and liberating
heat in the process.
+ 2 O2-
2 H2O + energy
In certain cases the heat energy is used directly if weather conditions are gelid.
Another way of looking at the fuel cell is to say that the hydrogen fuel is being
‗burnt‘ or combusted in the simple reaction
However, instead of heat energy being liberated, electrical energy is produced. The
experiment makes a reasonable demonstration of the basic principle of the fuel
cell, but the currents produced are very small.
The main reasons for the small current are
• the low ‗contact area‘ between the gas, the electrode, and the
electrolyte – basically just a small ring where the electrode emerges from the
• the large distance between the electrodes – the electrolyte resists the
ﬂow of electric current.
To overcome these problems, the electrodes are usually made ﬂat, with a thin layer
of electrolyte . The structure of the electrode is porous so that both the electrolyte
from one side and the gas from the other can penetrate it. This is to give
themaximum possible contact between the electrode, the electrolyte, and the gas.
However, to understand how the reaction between hydrogen and oxygen produces
an electric current, and where the electrons come from, we need to consider the
separate reactions taking place at each electrode.
These important details vary for different typesof fuel cells, but if we start with a
cell based around an acid electrolyte, as used by Grove,we shall start with the
simplest and still the most common type.
At the anode of an acid electrolyte fuel cell, the hydrogen gas ionizes, releasing
electrons and creating H+ ions (or protons).
This reaction releases energy. At the cathode, oxygen reacts with electrons taken
from the electrode, and H+ ions from the electrolyte, to form water.
O2+4e−+4H+→ 2H2 o
Electrode reactions and charge ﬂow for an acid electrolyte fuel cell. Note that
although the negative electrons ﬂow from anode to cathode, the ‗conventional
current‘ ﬂows from cathode to anode.
In an alkaline electrolyte fuel cell the overall reaction is the same, but the reactions
at each electrode are different. In an alkali, hydroxyl (OH−) ions are available and
mobile. At the anode, these react with hydrogen, releasing energy and electrons,
and producing water.
At the cathode, oxygen reacts with electrons taken from the electrode, and water in
the electrolyte, forming new OH− ions.
O2+4e−+2H2O → 4OH−
For these reactions to proceed continuously, the OH− ions must be able to pass
throughthe electrolyte, and there must be an electrical circuit for the electrons to go
from theanode to the cathode.
Also, comparing equations of the chemical rections involved we see that, as with
the acid electrolyte, twice as much hydrogen is needed as oxygen. Note that
although water is consumed at the cathode, it is created twice as fast at the
anode.There are many different fuel cell types, with different electrolytes. The
details of theanode and cathode reactions are different in each case
Single cell, with end plates for taking current from all over the face of the
electrodes,and also supplying gas to the whole electrode.
Two bipolar plates of very simple design. There are horizontal grooves on one side
and vertical grooves on the other.
The arrangement shown in Figurehas been simpliﬁed to show the basic principle of
the bipolar plate. However, the problem of gas supply and of preventing leaks
meansthat in reality the design is somewhat more complex.
Because the electrodes must be porous (to allow the gas in), they would allow the
gasto leak out of their edges. The result is that the edges of the electrodes must be
Sometimes this is done by making the electrolyte somewhat larger than one or both
ofthe electrodes and ﬁtting a sealing gasket around each electrode.Such assemblies
can then be made into a stack .The fuel and oxygen can then be supplied to the
electrodes using the manifolds as shown below. Because of the seals around the
edge of the electrodes, the hydrogen should only come into contact with the anodes
as it is fed vertically through the fuel cell stack. Similarly, the oxygen (or air)
fedhorizontally through the stack should only contact the cathodes, and not even
the edgesof the anodes.
A three-cell stack showing how bipolar plates connect the anode of one cell to the
cathode of its neighbour.
1 The construction of anode/electrolyte/cathode assemblies with edge seals. These
prevent the gases leaking in or out through the edges of the porous electrodes.
Three-cell stack, with external manifolds. The electrodes now have edge seals. It is
called external manifolding. It has the advantage of simplicity. However, it has two
The ﬁrst is that it is difﬁcult to cool the system. Fuel cells are far from 100%
efﬁcient, and considerable quantities of heat energy as well as electrical power are
Internal manifolding. A more complex bipolar plate allows reactant gases to be fed
to electrodes through internal tubes
Fuel Cell Types
The various fuel types also try to play to the strengths of fuel cells in different
ways. The proton exchange membrane (PEM) fuel cell capitalizes on the essential
simplicity of the fuel cell. The electrolyte is a solid polymer in which protons are
mobile. The chemistry is the same as the acid electrolyte fuel cell . With a solid
and immobile electrolyte, this type of cell is inherently very simple.
Solid Oxide Fuel Cells:
Solid oxide fuel cells (SOFCs) use a hard, non-porous ceramic compound as the
electrolyte. Because the electrolyte is a solid, the cells do not have to be
constructed in the plate-like configuration typical of other fuel cell types. SOFCs
are expected to be around 50%–60% efficient at converting fuel to electricity. In
applications designed to capture and utilize the system's waste heat (co-
generation), overall fuel use efficiencies could top 80%–85%.
Solid oxide fuel cells operate at very high temperatures—around 1,000°C
(1,830°F). High-temperature operation removes the need for precious-metal
catalyst, thereby reducing cost. It also allows SOFCs to reform fuels internally,
which enables the use of a variety of fuels and reduces the cost associated with
adding a reformer to the system.
SOFCs are also the most sulfur-resistant fuel cell type; they can tolerate several
orders of magnitude more of sulfur than other cell types. In addition, they are not
poisoned by carbon monoxide (CO), which can even be used as fuel. This
property allows SOFCs to use gases made from coal.
High-temperature operation has disadvantages. It results in a slow startup and
requires significant thermal shielding to retain heat and protect personnel, which
may be acceptable for utility applications but not for transportation and small
portable applications. The high operating temperatures also place stringent
durability requirements on materials. The development of low-cost materials with
high durability at cell operating temperatures is the key technical challenge facing
Scientists are currently exploring the potential for developing lower-temperature
SOFCs operating at or below 800°C that have fewer durability problems and cost
less. Lower-temperature SOFCs produce less electrical power, however, and stack
materials that will function in this lower temperature range have not been
Regenerative Fuel Cells
Regenerative fuel cells produce electricity from hydrogen and oxygen and generate
heat and water as byproducts, just like other fuel cells. However, regenerative fuel
cell systems can also use electricity from solar power or some other source to
divide the excess water into oxygen and hydrogen fuel—this process is called
"electrolysis." This is a comparatively young fuel cell technology being developed
by NASA and others.
Alkaline Fuel Cells
Alkaline fuel cells (AFCs) were one of he first fuel cell technologies developed,
and they were the first type widely used in the U.S. space program to produce
electrical energy and water on-board spacecrafts. These fuel cells use a solution of
potassium hydroxide in water as the electrolyte and can use a variety of non-
precious metals as a catalyst at the anode and cathode. High-temperature AFCs
operate at temperatures between 100°C and 250°C (212°F and 482°F). However,
newer AFC designs operate at lower temperatures of roughly 23°C to 70°C (74°F
AFCs' high performance is due to the rate at which chemical reactions take place in
the cell. They have also demonstrated efficiencies near 60% in space applications.
The disadvantage of this fuel cell type is that it is easily poisoned by carbon
dioxide (CO2). In fact, even the small amount of CO2 in the air can affect this cell's
operation, making it necessary to purify both the hydrogen and oxygen used in the
cell. This purification process is costly. Susceptibility to poisoning also affects the
cell's lifetime (the amount of time before it must be replaced), further adding to
Cost is less of a factor for remote locations, such as space or under the sea.
However, to effectively compete in most mainstream commercial markets, these
fuel cells will have to become more cost-effective. AFC stacks have been shown to
maintain sufficiently stable operation for more than 8,000 operating hours. To be
economically viable in large-scale utility applications, these fuel cells need to
reach operating times exceeding 40,000 hours, something that has not yet been
achieved due to material durability issues. This obstacle is possibly the most
significant in commercializing this fuel cell technology.
Phosphoric Acid Fuel Cells
Phosphoric acid fuel cells use liquid phosphoric acid as an electrolyte—the acid is
contained in a Teflon-bonded silicon carbide matrix—and porous carbon
electrodes containing a platinum catalyst. The chemical reactions that take place in
the cell are shown in the diagram to the right.
The phosphoric acid fuel cell (PAFC) is considered the "first generation" of
modern fuel cells. It is one of the most mature cell types and the first to be used
commercially. This type of fuel cell is typically used for stationary power
generation, but some PAFCs have been used to power large vehicles such as city
PAFCs are more tolerant of impurities in fossil fuels that
have been reformed into hydrogen than PEM cells, which are
easily "poisoned" by carbon monoxide because carbon
monoxide binds to the platinum catalyst at the anode,
decreasing the fuel cell's efficiency. They are 85% efficient
when used for the co-generation of electricity and heat but
less efficient at generating electricity alone (37%–42%). This
is only slightly more efficient than combustion-based power
plants, which typically operate at 33%–35% efficiency.
PAFCs are also less powerful than other fuel cells, given the same weight and
volume. As a result, these fuel cells are typically large and heavy. PAFCs are also
expensive. Like PEM fuel cells, PAFCs require an expensive platinum catalyst,
which raises the cost of the fuel cell.
Molten Carbonate Fuel Cells
Molten carbonate fuel cells (MCFCs) are currently being developed for natural gas
and coal-based power plants for electrical utility, industrial, and military
applications. MCFCs are high-temperature fuel cells that use an electrolyte
composed of a molten carbonate salt mixture suspended in a porous, chemically
inert ceramic lithium aluminum oxide (LiAlO2) matrix. Because they operate at
extremely high temperatures of 650°C (roughly 1,200°F) and above, non-precious
metals can be used as catalysts at the anode and cathode, reducing costs.
Improved efficiency is another reason MCFCs offer significant cost reductions
over phosphoric acid fuel cells (PAFCs). Molten carbonate fuel cells, when
coupled with a turbine, can reach efficiencies approaching 65%, considerably
higher than the 37%–42% efficiencies of a phosphoric acid fuel cell plant. When
the waste heat is captured and used, overall fuel efficiencies can be as high as 85%.
Unlike alkaline, phosphoric acid, and polymer electrolyte membrane fuel cells,
MCFCs do not require an external reformer to convert more energy-dense fuels to
hydrogen. Due to the high temperatures at which MCFCs operate, these fuels are
converted to hydrogen within the fuel cell itself by a process called internal
reforming, which also reduces cost.
Molten carbonate fuel cells are not prone to carbon monoxide or carbon dioxide
"poisoning" —they can even use carbon oxides as fuel—making them more
attractive for fueling with gases made from coal. Because they are more resistant to
impurities than other fuel cell types, scientists believe that they could even be
capable of internal reforming of coal, assuming they can be made resistant to
impurities such as sulfur and particulates that result from converting coal, a dirtier
fossil fuel source than many others, into hydrogen.
The primary disadvantage of current MCFC technology is durability. The high
temperatures at which these cells operate and the corrosive electrolyte used
accelerate component breakdown and corrosion, decreasing cell life. Scientists are
currently exploring corrosion-resistant materials for components as well as fuel
cell designs that increase cell life without decreasing performance.
Advantages and Applications
The most important disadvantage of fuel cells at the present time is the same for
alltypes – the cost. However, there are varied advantages, which feature more or
less strongly for different types and lead to different applications.
These include the following:
• Efﬁciency. As is explained in the following chapter, fuel cells are generally more
efﬁcient than combustion engines whether piston or turbine based. A further
feature of this is that small systems can be just as efﬁcient as large ones. This is
very important in the case of the small local power generating systems needed for
combined heat and power systems.
• Simplicity. The essentials of a fuel cell are very simple, with few if any moving
parts.This can lead to highly reliable and long-lasting systems.
• Low emissions. The by-product of the main fuel cell reaction, when hydrogen is
the fuel, is pure water, which means a fuel cell can be essentially ‗zero emission‘.
This is their main advantage when used in vehicles, as there is a requirement to
reduce vehicle emissions, and even eliminate them within cities. However, it
should be noted that, at present, emissions of CO2 are nearly always involved in
the production of hydrogen that is needed as the fuel.
• Silence. Fuel cells are very quiet, even those with extensive extra fuel processing
equipment. This is very important in both portable power applications and for local
power generation in combined heat and power schemes.
The fact that hydrogen is the preferred fuel in fuel cells is, in the main, one of their
principal disadvantages. However, there are those who hold that this is a major
It is envisaged that as fossil fuels run out, hydrogen will become the major world
fuel and energy vector. It would be generated, for example, by massive arrays of
solar cells electrolysing water. This may be true, but is unlikely to come to pass
within the lifetime of this book.
The advantages of fuel cells impact particularly strongly on combined heat and
power systems (for both large- and small-scale applications), and on mobile power
Honda FCX Clarity:
The Honda FCX Clarity is a hydrogen fuel cell automobile manufactured by
Honda. The design is based on the 2006 Honda FCX Concept. The FCX Clarity
demonstrates electric car qualities such as zero emissions while offering 5 minute
refueling times and long range in a full function large sedan. It first went on sale as
a 2008 model year vehicle.
Mist Lubrication system:
• Mainly for 2 stroke engines-Crankcase lubrication impossible
• Lubricating oil mixed with fuel(3%-6%)
• Oil and fuel mixture is inducted through the carburetor
• Fuel is vaporized and oil in the form of mist goes via the crankcase into the
• Thus oil striking the crankcase walls lubricates the main and connecting rod
bearings,piston,piston rings and cylinder
• No pump required
• No filter required
• Low cost
• CAUSES HEAVY EXHAUST SMOKE due to burning of lubricating oil
• Forms deposits on the piston crown and exhaust ports
• Corrosion of bearing surface as the oil comes in contact with acidic vapours
produced during the combustion
Wet Sump Lubrication system:
• Bottom of the crankcase contains an oil sump from where it is pumped to
various parts of the cylinder
• After lubricating these parts, the oil flows back to the sump by gravity
• Again it is picked up by the pump and is recirculated
• Pressure regulator
Types of wet sump lubrication system:
• Splash system
• Splash and pressure system
• Pressure feed system
• Oil is charged into bottom of the engine crankcase
• Oil is delivered through a distributing pipe extending the length of the
crankcase into splash troughs located under the big end of the connecting
• Troughs are provided with overflows to maintain constant level
• DIPPER-under each connecting rod cap
• It dips into the oil in the trough at every revolution of the crankshaft
• Then oil is splashed all over the interior of the crankcase
• Hole is drilled through the connecting rod through which oil is passed to the
Splash and pressure system
• Oil - supplied under pressure to pipes which direct a stream of oil against the
dippers on the big end of connecting rod
• Bearing cup and the crankpin bearings are lubricated by the splash or spray
of oil thrown up by the dipper
Pressure feed system
• Oil is drawn in from the sump-forced to all the main bearings
• Pressure relief valve –fitted near the delivery point of the pump that opens
when the pressure in the system attains a predetermined value
Dry Sump Lubrication system:
• Oil is carried in an external tank
• Oil pump draws oil from the supply tank and circulates it under pressure to
the various bearings of the engine
• Oil dripping from cylinder is passed through the filter and is fed back to the
• If the filter is clogged, the pressure relief valve opens permitting oil to
bypass the filter
• A separate oil cooler with either water or air as the cooling medium is
provided-remove heat from the oil.