undefined | unit 5 engine systems and alternative fuels

Unit – 5

Engine Systems and Alternative Fuels

Q1) What is Air Cooling engines. Write merits& Demerits of Air-Cooling System.

A1)

Air Cooling:

Air cooled engines are those engines, in which heat is conducted from the working components of the engine to the atmosphere directly.  The cylinder of an air-cooled engine has fins to increase the area of contact of air for speedy cooling.

The amount of heat dissipated to air depends upon:

Amount of air flowing through the fins.

Fin surface area.

Thermal conductivity of metal used for fins.

Merit & Demerits of Air-Cooling System

MERITS:

It is simpler in design and construction.

Water jackets, radiators, water pumps, thermostat, pipes, hoses etc. are not needed.

It is more compact.

It is comparatively lighter in weight.

DEMERITS:

There is uneven cooling of engine parts.

Engine temperature is generally high during working period.

Q2) Explain the liquid cooling system and Merits & Demerits of Liquid Water-Cooling System.

A2)

Liquid Cooling System

A liquid is circulated around the cylinders and absorb heat from the cylinder walls and cylinder head.

Coolant absorbs heat as it passes through the engine and also lubricates the water pump.

Hot coolant enters the radiator in which the heat is passed on to air that is flowing through the radiator.

Merits & Demerits of Liquid Water-Cooling System:

MERITS:

Uniform cooling of cylinder, cylinder head and valves

Specific fuel consumption of engine improves by using water cooling system

If we employ water cooling system, then engine need may not be provided at the front end of moving vehicle.

Engine is less noisy as compared with air cooled engines, as it has water for damping noise

DEMERITS:

It depends upon the supply of water.

If the water-cooling system fails then it will result in severe damage of engine

The water-cooling system is costlier as it has a greater number of parts.

Q3) Explain the properties of lubricants.

A3)

Properties of lubricants

Viscosity:

It is a measure of the resistance to flow of an oil.

It is measured in SayboltUniuniversal Seconds (SUS).

It is expressed in centistokes, centipoises and redwood seconds.

2. Viscosity Index:

Viscosity of oil decreases with increase in temperature.

3. Cloud point:

If an oil is cooled, it will start solidifying at some time.

Temperature at which oil starts solidifying, is called cloud point.

4. Pour point:

It is temperature just above which the oil sample will not flow under certain prescribed conditions.

This property is important for operation of engines and substances at low temperature conditions.

5. Flash point and Fire point

The temperature at which vapour of an oil flash when subjected to a naked flame is called flash point.

Fire point is the temperature at which the oil, it once lit with flame, will burnt steadily at least for 5 seconds.

6. Specific Gravity:

It varies between 0.85 to 0.96.

7. Acidity:

Oil must have low acidity.

8. Carbon residue:

It is quantity of carbaneous residues which remains after evaporation of a sample oil under specific conditions.

9. Oiliness:

It is property of oil to cling to the metal surface by molecular action and then to provide a very thin film under lubrication conditions.

This property affects start of engines.

Q4) Describe the Mist Lubrication System and its advantage and disadvantages.

A4)

Mist Lubrication System

This system is used where crankcase lubrication is not suitable.

In two – stroke engine, as the charge is compressed in the crankcase, it is not possible to have the lubricating oil in the sump. Hence, mist lubrication is adapted in practice.

In such engine, the Lubricating oil is mixed with the fuel. The usual ratio being 3 % to 6 %

The oil and the fuel mixture are inducted through the carburetor.

The fuel is vaporized and the oil in the form of mist goes via the crankcase into the cylinder.

The oil which strikes the crankcase walls lubricates the main and connecting rod bearings, and the rest of the oil lubricates the piston, piston rings and the cylinder.

The advantage of this system is its simplicity and low cost as it does not require an oil pump, filter.

Disadvantages are as below.

1)It causes heavy exhaust smoke, due to busing of lubricating oil partially or fully and also forms deposits on piston crown and exhaust ports which affect engine efficiency.

2)Since the oil comes in close contact with acidic vapors produced during the combustion process gets contaminated and may result in the corrosion of bearing surface.

3) This system calls for a through mixing for effective lubrication. This requires either separate mixing prior to use or use of some additive to give the oil good mixing characteristics.

4) During closed throttle operation as in the case of the vehicle moving down the hill, the

engine will suffer from insufficient Lubrication as the supply of fuel is less.

Q5) Describe the wet sump Lubrication System and explain different varieties of the wet sump lubrication system.

A5)

Wet sump Lubrication System

In the wet sump system, the bottom of the crankcase contains an oil pan or sump from which the lubricating oil is pumped to various engine components by a pump.

After Lubricating these parts, the oil flows back to the sump by gravity.

Again, it is picked up by a pump and recirculated through the engine lubricating system.

There are three varieties in the wet sump lubrication system.

i) Splash System:

This type of lubrication system is used in light duty engines.

A schematic diagram of this system is shown in fig.

The Lubricating oil is charged into in the bottom of the engine crankcase and maintained at a predetermine level.

The oil is drowned by a pump and delivered through a distributing pipe extending the length of the crankcase into splash through located under the big end of all the connecting rods.

These through were provided with overflows and the oil in the through are therefore kept at a constant level.

A splasher or dipper is provided under each connecting rod cap which dips into the oil in the trough at every revolution of the crankshaft and the oil is splashed all over the interior of the crankcase, into the piston and onto the exposed position of the cylinder walls.

A hole is drilled through the connecting rod cap through which oil will pass to the bearing surface.

Oil pockets are also provided to catch the splashing oil over all the main bearings and also over the camshaft bearing.

From the pockets the oil will reach the bearings surface through a drilled hole.

The oil dripping from the cylinder is collected in the sump where it is cooled by the air flowing around the cooled oil is then recirculated.

(ii) The Splash and Pressure Lubrication System:

This system is shown in Fig: where the Lubricating oil is supplied is under pressure to main and crankshaft bearing.

Oil is also supplied under pressure to pipes which direct a stream of oil against the dippers on the big end of connecting rod bearing cup and thus the crankpin bearings are lubricated by the splash or spray of oil thrown up by the dipper.

(iii) Pressure Feed System:

• The pressure feed system is illustrated in fig. in which oil is drawn in from the sump and forced to all the main bearings of the crankshaft through distributing channels.

• A pressure relief valve will also be fitted near the delivery point of the pump which opens when the pressure in the system attains a predetermined value.

• An oil hole is drilled in the crankshaft from the center of each crankpin to the center of an adjacent main journal through which oil can pass from the main bearings to the crankpin bearing.

• From the crankpin it reaches piston pin bearing through a hole drilled in the connecting rod.

• The cylinder walls, tappet rollers, piston and piston rings and connecting rod bearings. The basic components of the wet sump lubrication systems are:

i) Pump ii) Strainer iii) Pressure regulator iv) filter v) breather

Q6) Describe the construction and working of Battery coil ignition system.

A6)

Battery coil ignition system

Construction:

It consists of the following parts:

Battery (Lead Acid type): Stores the Electrical Energy. Charges using the Dynamo driven by the engine.

Ignition switch: Helps in turning the system ON or OFF.

Ballast Resistor: Under prolonged conditions it helps to maintain the temperature of Ignition Coil.

Ignition coil: Steps up the Low Voltage to High Voltage to induce an electric spark in the spark plug.

Contact breaker: Making and breaking the primary circuit.

Capacitor: Prevents the burning and possible welding of metal points.

Distributor: Distributes the Ignition surge to individual spark plugs.

Spark plug: Creates the spark due to ionization of gap.

Working:

Ignition switch is turned on, the current starts flowing through primary circuit. This current sets up a magnetic field around the soft iron core of the ignition coil.

When the breaker points open, the current which was flowing through the contact breaker starts flowing through the condenser

As the condenser charges, the primary current falls and the magnetic field collapses.

This change in the magnetic field induces a current in the primary winding which flows in the same direction as the primary current and changes the condenser to a voltage much higher than battery voltage thus stooping the current flow from the battery.

Due to this, the condenser then discharges into the battery, thus reversing the direction of both primary current and magnetic field.

This rapid collapse and reversal of the magnetic field induces a very high voltage in the secondary winding of the ignition coil.

This high voltage is then carried through the high-tension wires to the distributor rotor, where it passes through one of the ignition harnesses into the spark plug and produces a spark.

Q7) Define supercharging and the method of supercharging.

A7)

Supercharging

Method of supplying air or fuel - air mixture higher than the pressure at which the engine naturally aspirates, by means of boosting device is called the supercharging.

The device which boosts the pressure is called supercharger.

Method of supercharging

Electrical motor driven supercharger

In this type of compressor is driven independently usually by an electrical motor.

The speed of the supercharger can be varied independent of engine speed and therefore control comparatively easier.

2. Ram effect of supercharging.

The Ram effect of supercharging system consist primarily of tuned inlet pipes.

These pipes induce resonant harmonic air oscillations. the kinetic energy of these oscillations provides are ramming effect.

For the efficient operation of this system, the engine Speed must be kept constant.

3. Under piston supercharging.

Under piston method of supercharging has so for been confined too large marine four stroke engine of the crosshead type.

It utilizes the bottom side of the piston for compressing the air.

The bottom ends of the cylinder are closed off and provided with suitable valves.

This system gives an adequate supply of compressed air as there are two delivery strokes to each suction stroke of the cycle.

4. Kadenacy system of supercharging

The Kadenacy system utilizes the energy in the exhaust system to cause depression of pressure in the cylinders.

The depression makes the scavenge air to flow into the cylinder.

A blower may also be used with this system, but it is not an essential.

The Kadenacy system is based on the following principal: when the exhaust ports or valves are opened rapidly during the end of expansion stroke, there is, within the first interval of a few thousands second, an urge or impulse in the gases to escape very rapidly from the cylinder.

The escaping gases leave behind the pressure depression at the above moment, the fresh change of air is allowed to enter the cylinder behind the exhaust gases by suitable timing off the admission valve or ports.

For the best result of proper timing and skillful design of the exhaust system is must.

Q8) Explain the turbo-charging.

A8) Turbo charging

In turbo charging, the supercharger being driven by a gas turbine which uses the energy in the exhaust gases.

There is no mechanical linkage between the engine and the supercharger.

The major parts of turbo charger are turbine wheel, turbine housing, turbo shaft, compressor wheel, compressor housing and bearing housing.

During engine operation hot exhaust gases blowout through the exhaust valve opening into the exhaust manifold.

The exhaust manifold and the connecting tubing route these gases into the turbine housing.

As the gases pass through the turbine housing, they strike on the fins or blades on the turbine wheel when the engine load is high enough, there is enough gas flow, and this makes the turbine wheel to spin rapidly.

The turbine wheel is connected to the compressor wheel by the turboshaft.

As such, the compressor wheel rotates with the turbine which sucks air into the compressor housing centrifugal force throws the air outward.

This causes the air to flow out of the turbocharger and into the engine cylinder under pressure.

In the case of turbo-charging, there is a phenomenon called turbolag.

It refers to short delay period before the boost or manifold pressure increases.

This is due to the time the turbocharger assembly takes the exhaust gases to accelerate the turbine and compressor wheel to speed up.

In the turbocharger assembly, there is a control unit called waste gate.

This unit limits the maximum boost pressure to prevent detonation in SI engine and the maximum pressure and engine damage.

Q9) Explain the different types fuels:

• Biodiesel

• Ethanol

• LPG

A9)

Bio-diesel

Biodiesel refers to a non-petroleum-based diesel fuel consisting of short chain alkyl (methyl or ethyl) esters, made by Transesterification of vegetable oil or animal fat, which can be used (alone, or blended with conventional petrol-diesel) in unmodified diesel-engine vehicles.

"Biodiesel" is standardized as mono-alkyl ester.

Ethanol

• It is commonly called alcohol, ethyl alcohol, and drinking alcohol.

• The principal type of alcohol found in alcoholic beverages, produced by the fermentation of sugars by yeasts.

• It is a neurotoxin, psychoactive drug, and one of the oldest recreational drugs. It can cause alcohol intoxication when consumed in sufficient quantity.

• Ethanol is a volatile, flammable, colorless liquid with a slight chemical odor. • Empirical formula is C2H5OH

LPG (Liquefied Petroleum Gas)

• Liquefied Petroleum Gas (LPG) or Auto Gas is a generic name for mixtures of hydrocarbons (Generally Combination of the gas is 70% butane (C4H10), 30% propane (C3h8)) which exists as vapor under ambient conditions and can be changed into liquid state by applying moderate pressures.

• When stored under pressure it becomes a dense liquid allowing large quantities of gas to be stored in a relatively small space. Energy content similar to gasoline. Inherently clean burning characteristics.

• LPG, known world over as Auto gas, gives you a new life as it brings along multiple benefits. Auto gas is the 3rd most popular automotive fuel and the number # 1 clean fuel alternative in the world.

2 C4H10 + 13 O2 → 8 CO2 + 10 H2O + heat C3H8 + 5 O2 → 3 CO2 + 4 H2O + heat

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