POLITEKNIK KUCHING SARAWAK

Chapter 1Types of Engines

Mohd Sarhan OthmanDepartment of Mechanical Engineering (Automotive),

Politeknik Kuching Sarawak

Fundamental of the Engine operations

� Engine: is a machine that converts heat energy into mechanical energy.– The heat from burning air-fuel (A/F)

mixture produces power which moves the vehicle.

� Automotive engine are internal combustion (IC) engine because the fuel that runs them is burned internally, or inside the engines.– There are two types of engine

� Reciprocating engine: piston moving up and down, or back and forth

� Rotary engines: have rotor that spin or rotate

– Essential for Engine Operation � The automobile engine has cylinders� Piston moves up and down in each

cylinder– The car moves because the piston

move

� Engine must have available fuel for moving up and down the piston

� Fuel gets into the engine due to the pressure difference.

– Gravity, atmospheric pressure, and vacuum pressure make it possible for the fuel to get into the engine cylinders.

– Fuel burns to produce power.

� Vacuum is the absence of air.� When a piston moves down in

a cylinder, the pistons creates a partial vacuum.

Reciprocating Engine.

Rotary Engine

� Actions in the Engine Cylinder– The intake valve closes after the piston passes it bottom

position and starts to move up again� The bottom position of the piston into the cylinder is called

bottom dead center (BDC).

– The piston moves up, compresses the A/F mixture into a confined space is called combustion chamber.

– The piston reaches the top position and spark plug fire � The top position of the piston into the cylinder is called top

dead center (TDC).– The spark sets the fire to ignite the compressed A/F

mixture.– The temperature of the burning A/F mixture goes up as

high as 33160C.– The high temperature makes the pressure as high as 4140

kPa (1 psi = 6.9 kPa or 1 bar = 100 kPa).

– The 4140 kPa push down the piston of up to 17,792 N� This 17,792 N pushes the piston down� The downward movement, carried through the connecting rod,

rotates the crankshaft� The crankshaft turns the gears and drive shafts to move the

car.

Four Stroke Cycle:1.Intake2. compression3. power4. exhaust

Fundamental of Diesel Engine Operation

� Diesel engines are similar to spark ignition engines in construction, as both have– pistons, with piston rings,

� move up and down in engine cylinders.

– Both type of engines burn fuels in combustion chambers, in the upper parts of the cylinders.

– The high pressure produced by the burning fuel, pushes the pistons down, which rotates the crankshaft.

– The rotary motion is transmitted through shaft and gears, to the drive wheels.

Fundamental of Diesel Engine Operation� The intake valve opens and exhaust valve closes

completely. – The position of the piston into the cylinder is in

bottom dead center (BDC).– Draw the air in to the cylinder.

� Both of the valve close and the piston reaches the top position– The piston moves up, compresses the air into a

confined space is called combustion chamber until reach to the TDC..

– Pressure and temperature increase to its maximum level.

– Injector injects the right amount of fuel to the high temperature air into the combustion chamber. � Fuel burn instantly due to the high

temperature of air.– Develop the high pressure and force to

push the piston down– Create the torque at the crankshaft to

propel the car.– Fuel injectors are controlled by Electronic control

module (ECM)

Petrol Engine and Diesel Engine - comparison

� Major types of engines are petrol and diesel.– The engines required to run with burning petrol and diesel are different

because petrol and diesel are different types of fuel.– Petrol is a highly volatile fuel and gets ignited very easily whereas diesel is

comparatively heavy and dirtier fuel.

Petrol engine Diesel engine

Petrol Engine and Diesel Engine - comparison� Inlet stroke

– In petrol engines, the mixture of air and petrol is drawn in by the falling piston

– In diesel engines, only air is drawn in by the falling piston

� Compression stroke

– In petrol engine, the mixture is compressed.– In diesel engine, only air is compressed.

� Expansion stroke

– In petrol engine, the air and fuel mixture is ignited using a spark plug and burns expanding and forcing the piston down.

– In diesel engine, fuel is injected at a high pressure into the hot, compressed air in the cylinder, causing it to burn and force the piston down. No spark is required.

� Exhaust stroke

– In both petrol and diesel engines, the burned mixture of air and fuel is pushed out of the cylinder by the rising piston.

� Petrol engines are lighter than diesel engines.

� Petrol engine is called spark ignition engine while the diesel engine is called compression ignition engine.

� Diesel engines have better fuel efficiency as compared to petrol due to the fact that they have higher compression ratio.

� Diesel engines don’t need an ignition system, which reduces their complexity. – But they are more noisy and may require frequent maintenance as compared

to petrol engines. – Also they are more durable.

� And now the most important part, fuel economy. Diesel wins in both ways. – Diesel engines give better mileage than petrol engines.– So running on diesel would make you go farther at a lower cost than running

on petrol.

Mode of Operation of Two- Stroke Engine

Mode of operation of two-stroke engine-continue

� Intake. The A/F mixture is first drawn into the crankcase by the vacuum created during the upward stroke of the piston.

� During the downward stroke the poppet valve is forced closed by the increased crankcase pressure. The fuel mixture is then compressed in the crankcase during the remainder of the stroke

� Compression. The piston then rises, driven by flywheel momentum, and compresses the fuel mixture. (At the same time, another intake stroke is happening beneath the piston).

� Power. At the top of the stroke the spark plug ignites the fuel mixture. The burning fuel expands, driving the piston downward, to complete the cycle.

� Transfer/Exhaust.Toward the end of the stroke, the piston exposes the intake port, allowing the compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder. This expels the exhaust gasses out the exhaust port, usually located on the opposite side of the cylinder. Unfortunately, some of the fresh fuel mixture is usually expelled as well.

� Difference between Two-stroke engine and four-stroke engine– The two-stroke internal combustion engine differs from the more common four-stroke

engine by completing the same four processes (intake, compression, combustion, exhaust) in only two strokes of the piston rather than four.

– This is accomplished by using the beginning of the compression stroke and the end of the combustion stroke to perform the intake and exhaust functions.

– This allows a power stroke for every revolution of the crank, instead of every second revolution as in a four-stroke engine.

– Two-stroke engines provide high specific power, so they are valued for use in portable, lightweight applications.� Specific power, which is typically given in kilowatts per litre of engine displacement (or

horsepower per cubic inch).

– Two - stroke engine is always worse than in the four-stroke engine, which loses fresh fuel only because of the "overlap" of the valve times (both valves are open for an instant).

– Beside these performance-technical problems, there are also increasing difficulties with the environment.

– The fuel mixture of the two-stroke engine often gets shifted with a certain quantity of oil because of the necessary lubrication.

– Unfortunately the oil gets burnt partly, too, and harmful gases are expulsed by the engine.

� A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between.

.

GAS TURBINE ENGINE

� The basic operation of the gas turbine:

1) Air flows through a compressor that brings it to higher pressure.

2) Energy is then added by spraying fuel into the air and igniting it, thus the combustion generates a high-temperature flow.

3) This high-temperature high-pressure gas enters a turbine, where it expands down to the exhaust pressure, producing a shaft work output in the process. The turbine shaft work is used to drive the compressor and other devices such as an electric generator that may be coupled to the shaft.

�THE END…