Page 9 - Automotive Engineering Powertrain Chassis System and Vehicle Body

1.1
Chapter 1.1

Piston-engine cycles

of operation

Heinz Heisler

1.1.1 The internal-combustion
engine

The piston engine is known as an internal-combustion
heat-engine. The concept of the piston engine is that
a supply of air-and-fuel mixture is fed to the inside of the
cylinder where it is compressed and then burnt. This
internal combustion releases heat energy which is then
converted into useful mechanical work as the high gas
pressures generated force the piston to move along its
stroke in the cylinder. It can be said, therefore, that
a heat-engine is merely an energy transformer.
To enable the piston movement to be harnessed, the
driving thrust on the piston is transmitted by means of
a connecting-rod to a crankshaft whose function is to
convert the linear piston motion in the cylinder to
a rotary crankshaft movement (Fig. 1.1-1). The piston
can thus be made to repeat its movement to and fro, due
to the constraints of the crankshaft crankpin’s circular
path and the guiding cylinder.
The backward-and-forward displacement of the Fig. 1.1-1 Pictorial view of the basic engine.
piston is generally referred to as the reciprocating motion
of the piston, so these power units are also known as
reciprocating engines.
harness the working gases. It also provides a jacket to
contain a liquid coolant.
1.1.1.1 Engine components and terms Cylinder head This casting encloses the combus-
tion end of the cylinder block and houses both the inlet
The main problem in understanding the construction of and exhaust poppet-valves and their ports to admit air–
the reciprocating piston engine is being able to identify fuel mixture and to exhaust the combustion products.
and name the various parts making up the power unit. To Crankcase This is a cast rigid structure which sup-
this end, the following briefly describes the major ports and houses the crankshaft and bearings. It is usually
components and the names given to them (Figs. 1.1-1 cast as a mono-construction with the cylinder block.
and 1.1-2). Sump This is a pressed-steel or cast-aluminium-
Cylinder block This is a cast structure with cylin- alloy container which encloses the bottom of the crank-
drical holes bored to guide and support the pistons and to case and provides a reservoir for the engine’s lubricant.
Vehicle and Engine Technology, ISBN: 9780340691861
Copyright Ó 1998 Heinz Heisler. All rights of reproduction, in any form, reserved.