THERMAL ENGINEERING:

Alternative Fuels

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 or diesel.

Some alternative fuels that can replace conventional fuel are

1. Ethanol2. Biodiesel3. Natural gas4. Hydrogen5. Propane

Ethanol

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 (gasohol)

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

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

Advantages

Domestically produced, reducing use of imported petroleum Lower emissions of air pollutants More resistant to engine knock

Disadvantages

Added vehicle cost is very small Can only be used in flex-fuel vehicles Lower energy content, resulting in fewer miles per gallon Limited availability. Currently expensive to produce.

Biodiesel

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.

Advantages

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%) Biodegradable Non-toxic Safer to handle

Disadvantages

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%.

Safety

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

Engine Operation

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.

Clean Diesel:

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.

Natural Gas

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).

Ideal composition:

Methane=90%,(minimum), ethane=4%(maximum),propane=1.7% c4 and higher=0.7%, c4 and higher=0.2%, cabondioxide+nitrogen=0.2%,hydrogen=0.1%,carbonmonoxide=0.1%,oxygen=0.5%,sulphur=10%ppm

It is stored as compressed natural gas(CNG) at pressures of 7 to 21 bar and a temperature around

-1600c

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.

Advantages

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

Disadvantages

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.

Advantages

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

Disadvantages

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

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 engines (ICEs)

Benefits

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.

Disadvantages

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 result.

Fuel cost is high Can detonate. 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.

BIO GAS:It is generally produced from dung, sewage, vegetable wastes, poultry droppings, pig manure etc.Composition: Methane-50 to 60 % by volumeCarbondioxide-30to45%Hydrogen and nitrogen-5 to 10% H2S and O2 -tracesPROPERTIES:

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 of power.

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.

FUEL CELL

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:

high efficiency,

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 material.

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 with.

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 electrodes and 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 :

H2O2 H+ + O2-

At anode ( positive electrode) oxidation occurs and thus oxide ions are oxidized to oxygen gas molecules

2 O2- O2 + 4 e-

At cathode ( negative electrode ) reduction occurs and hydrogen ions are reduced to hydrogen gas molecules.

4 H+ + 4 e- 2 H2

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- 2 O2-

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 electrons.

The hydrogen ions and oxygen ions produced react to form water and liberating heat in the process.

4 H+ + 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 electrolyte.

• 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 the maximum 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 types of 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).

2H2→ 4H+4e−

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.

2H2+4OH−→ 4H2O+4e−

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.

Construction:

The arrangement shown in Figure has 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 sealed.

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 major disadvantages.

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 generated

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 this technology.

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 identified.

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 to 158°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.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 buses.

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 all types – 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 advantage.

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 systems,

TOYOTA CONCEPT:

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.

Lubrication :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 cylinder

• Thus oil striking the crankcase walls lubricates the main and connecting rod bearings, piston, piston rings and cylinder

Advantages

• No pump required

• No filter required

• Simplicity

• Low cost

Disadvantages

• CAUSES HEAVY EXHAUST SMOKE due to burning of lubricating oil partially

• 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

Components:

• Pump

• Strainer

• Pressure regulator

• Filter

• Breather

Types of wet sump lubrication system:

• Splash system

• Splash and pressure system

• Pressure feed system

Splash 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 rods

• 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 bearing surface

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 supply tank

• 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.