Engine Types and Engine Types and ClassificationsClassifications

Engine Types and ClassificationsAutomobile engine can be classified according to:

Number of cylindersArrangement of cylindersArrangement of valve and valve trainsType of coolingNumber of stroke per cycleTypes of fuel burnFiring orderReciprocating or rotary

Number and arrangement of cylinders In a row In two rows or bank set at an angle (V type)

Three cylinder enginesThe engine has an overhead camshaft and produces 60

horsepower (hp) [45 kW] at 5500 rpm.The camshaft is driven from the crankshaft by a toothed

timing beltThe ignition distributor is driven directly from one end of the

camshaftThe oil pump is on the front of the crankshaftA V belt from the crankshaft drives the alternator and water

pump.

Four cylinder engineFour cylinder engine can be arranged:

In a line In a V shape (V type)

V type engine has set of cylinders in two rows.The two rows are separated by an angle to each others.

The angle could be 60 degrees or 90 degrees or 180 degrees

In a line engine has set of cylinders are arranged in line.The valves in the cylinder head are operated through

valve lifters, pushrods, and rocker arms.An engine with this type of valve train is often is often

V-8 EnginesIt has two 4-cylinders rowsSet at a 90 degree angle.The engine is like two four-cylinder

engines mounted on a single crankcase and using a single crankshaft.

The crankshaft has four crankpins.Connecting rods from opposing cylinders

are attached to a single crankpin.Therefore, each crankpin has two connecting rods attached to it.

Arrangement of valves and valve trainsEngine valve allows the engine to breath.

The intake valve open to admit the A/F mixture to the engine cylinders.

The exhaust valves open to allow burned gases to exit or exhaust from the engine cylinders.

Cam on rotating camshaft operate the valve train, which open the valves.

Location of the camshaft Either on the cylinder head or in the cylinder block.

Types of camshaft drive Camshaft are driven by timing gears, sprockets and timing

chain or sprockets and toothed timing beltTypes of valve train

Two basic types of valve train Overhead camshaft Camshaft in block with pushrod

Number of valves per cylinder Normally each cylinder of the engine has two valves Some have multi-valve cylinder of the engine

PURPOSE of these added valves is to allow the engine to breathe more freely.

Firing orderThe firing order is the sequence of power delivery of

each cylinder in a multi-cylinder reciprocating engine. This is achieved by sparking of the spark plugs in a

gasoline engine in the correct order, or by the sequence of fuel injection in a Diesel engine.

When designing an engine, choosing an appropriate firing order is critical to minimizing vibration and achieving smooth running, for long engine fatigue life and user comfort, and heavily influences crankshaft design.

In a gasoline engine, the correct firing order is obtained by the correct placement of the spark plug wires on the distributor. In a modern engine with an engine management system and direct ignition, the Engine Control Unit (ECU) takes care of the correct firing sequence.

The crankpin and crankshaft arrangement determine the firing order.

Firing orders for the same type of engine may differ.

Two firing orders for in-line 4-cylinders engines are 1-3-4-2 and 1-2-4-3

6-Cylinders engines 1-5-3-6-2-4 The complete firing order of a four-cycle engine represents

two complete revolutions of the crankshaft. This is 720 degrees of crankshaft rotation Firing impulse occurs every 120 degrees of crankshaft rotation

(720/6=120). When piston number 1 is at TDC on the end of compression

stroke, piston number 6 is at TDC on the end of the exhaust stroke.

Classification by cyclesPiston engines operate on either Two-stroke cycle or Four-stroke engine

Four-stroke-cycle enginePower stroke is in every fourth piston stroke

A power stroke during each crankshaft revolutionTwo-stroke-cycle engineEvery other piston stroke has a power stroke

A power stroke during each crankshaft revolution

Two stroke-cycle engine produces twice as many power stroke at the same crankshaft speed (rpm) as the four-stroke-cycle engine.

Piston opens the transfer and exhaust port.Therefore, always mixing some A/F mixture with the

exhaust gases.

Mode of operation of the two-stroke engine

1st stroke: The piston is at the bottom of the cylinder. A pipe at the left side is opened and lets the fuel mixture,

which is already compressed a bit, flow from the lower to the upper part of the cylinder.

The fresh gases expulse now the exhaust through an ejection pipe, which is not closed by the piston at this moment.

2nd stroke: After being hurried upward, the piston now covers the pipe on the left side and the ejection pipe. Because there is no way out any more, the upper, fresh

gas mixture gets compressed now. At the same time in the part below fresh gas is taken in by

the piston driving upward through the open suction pipe. At the upper dead-center, the compressed fuel mixture is

ignited by the sparking plug, the piston is pressed downward while he compresses at the same time the fresh gas below.

The process begins again as soon as the piston arrives at

Mode of Operation of Two- Stroke Engine

Mode of operation of two-stroke engine-continue Intake. The fuel/air 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

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.

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.

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 liter of engine displacement (in

the U.S. also 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.