PISTON ENGINES

Part 3

Types of Piston Engine

IntroductionPiston Engine Layouts

Generally speaking,

the more cylinders there are,

the more power the engine will produce

and the smoother the engine will run.

The only limit to the variety of layouts

is the designers imagination,

except to say it is uneconomical (in manufacturing costs, capacity and use)

to design and build a 4 litre V8 layout engine

when a 2 litre V6 would do the job.

Introduction

Single

Piston Engine Layouts

Inline 3

Inline 4

Inline 5

Vee Twin

Vee 5

Vee 6

Vee 8

IntroductionPiston Engine Layouts

Horizontally Opposed(or flat) 4

Vee 8

Firing Order: -

1 – 4 – 3 – 2 1 – 8 – 4 – 3 – 6 – 5 – 7 – 2

As its name suggests,

the operating cycle of this engine

is completed in two strokes,

down and up. i.e. one complete revolution of the crankshaft.

Port A – Crankcase Inlet

Port C – Exhaust Outlet

Port B – Cylinder Inlet

The Two-Stroke Cycle

The Two-Stroke Cycle

Stroke 1Piston rising pulls fuel/air mixture into crankcase;(Induction)

Compression is now causing combustion

Stroke 2Piston pushed downforces fuel/air mixtureinto cylinder;

and out of the Exhaust valve

Port A – Crankcase Inlet

Port C – Exhaust Outlet

Port B – Cylinder Inlet

Mechanical ArrangementThe Petrol Engine

Inlet Exhaust

The Diesel Engine

Same mechanicalset-up as the petrol engine

BUT without anignition systemor spark plugs

This means that ignition is timed exactly when required without relying on the timing of a spark.

The Diesel Engine

Mechanical Arrangement

Combustion is initiated by

the temperature increasein the compressed

air/fuel mixture.

Inlet Exhaust

Indirect Injection

Direct Injection

Fuel needs to be injected to obtain thecorrect supply rate.

Fuel is injectedIndirectly into the

inlet manifold, or

Directly into thecylinder.

Mechanical ArrangementThe Wankel Engine

Casing Rotating Triangular

‘Piston’

Fixed (non-rotating)

Pinion

Rotating ‘Crankshaft’

Spark Plug

Output Shaft

The piston rotates around the fixed pinion.

This motion drives therotating crankshaft.

Which in turn drives the output shaft.

The piston shape and the casing make the piston move up & down by a small amount as well.

Points of contact

Inlet Port

Exhaust Port

Mechanical ArrangementThe Wankel Engine

Chamber A

Chamber B

Chamber C

Inlet Port

Exhaust Port

There are 3 chambers formed by the triangular rotor and the casing.

The mixture is ignitedby the spark plug

in chamber B;(Combustion/Power) the expanding gases then force the rotor

round.

As Chamber A rotates it draws in fuel/air(Induction) the chamber then gets smaller

(Compression).

As chamber C rotates,the exhaust port opensand the gases forced out.

(Exhaust)

Mechanical ArrangementRadial/Rotary Engines

Crankcase

Valve Gear

Propeller Mount Bolts

Valve Pushrods

Cylinders

Spark Plugs

Radials and Rotary engines look similar; but in Radial engines, the crankcase and cylinders are stationary,

and the crankshaft rotates the propeller.Whereas in Rotary engines, the crankshaft was stationary

and the crankcase and cylinders rotated to drive the propeller.

Mechanical ArrangementRadial/Rotary Engines

(viewed from the front) (viewed from the side)

RotaryRadial

Aircraft Nose

Aircraft Nose

Radial and Rotary engines were used commonly during WW2 in various transports, bombers and fighters.

Rotary engines, whilst the best for power to weight ratio at the time,suffered some disadvantages -

Gyroscopic effect – rotating such a large mass caused aircraft handling problems.

Oil system – it was difficult to recirculate the oil,which literally splashed everywhere after leaving the engine.

Mechanical ArrangementRadial/Rotary Engines

(viewed from the front) (viewed from the side)

RotaryRadial

Aircraft Nose

Aircraft Nose

Model aero engineRadial Powered Motorbike

28 Cylinder Radial Engine

But making an engine obsolete does not mean it disappears -

Check of Understanding

What is the limit to the variety of cylinder layouts?

No limit

12 cylinders

36 cylinders

24 cylinders

What is the operating cycle of a two-stroke engine?

2 rotations of the crankshaft

¼ rotation of the crankshaft

1 rotation of the crankshaft

½ rotation of the crankshaft

Check of Understanding

What happens on the down stroke of a 2-stroke engine?

Exhaust

Induction

Combustion/Power

Compression

Check of Understanding

Which of the following statementsdoes not apply to a diesel engine?

Fuel needs to be injected

Same mechanical set-upas a petrol engine

It has no spark plugs

Ignition cannot be timed

Check of Understanding

In a diesel engine,where is fuel directly injected?

Into the cylinder

Into the inlet manifold

Into the piston head

Into the exhaust valve

Check of Understanding

In a Wankel engine,How many chambers are formed

by the rotor and casing?

Three

Five

Seven

One

Check of Understanding

In a Wankel engine,what happens in chamber A?

Exhaust

Only Induction

Induction and Compression

Only Compression

Check of Understanding

Which of the following statementsapplies to a radial engine?

The crankshaft is stationary

The crankcase rotates

The crankshaft rotates

The cylinders rotate

Check of Understanding

PISTON ENGINES

End of Presentation