HeatEnginesVol 1 Chapter 10 RS - 10 COMBUSTION INTERNAL...

10
INTERNAL COMBUSTION
ENGINES - RECIPROCATING
Heat engine in which the combustion of.fuel takes place in the engine cylinder is
known as internal combustion engine. As the combustion takes place inside the engine
cylinder, very high temperature is produced in the cylinder. It is therefore, necessary to
abstract or remove some of the heat from the cylinder to prevent damage to the metal
of the cylinder, by circulating water through jacket, surrounding the cylinder. The cylinder
of a motor cycle or an aero-engine is cooled by atmospheric air. It may be noted that
the cylinder of a steam engine requires to be heated by supplying steam (from the
boiler) in the jacket surrounding the .cylinder to reduce condensation of steam in the
cylinder.
The thermal efficiency of an internal combustion engine is much higher than that
of a steam engine plant, as in I.C. engine there is no apparatus corresponding to boiler
and no losses corresponding to the boiler losses. A best modem I.C. engine converts
about 30 to 35 per cent of the heat of combustion of fuel into work (i.e. the thermal
efficiency is about 30 to 35 per cent), whereas an ordinary steam engine plant converts
only 8 to 10 per cent and a best modem steam turbine plant converts .only 15 to 25
per cent of heat of combustion of fuel into work, i.e., the overall efficiency of a modem
steam plant (boiler and turbine combined) is about 15 to 25 per cent.
Reciprocating internal combustion engines are most , commonly single-acting whereas
reciprocating steam engines are nearly always double-acting. All large size I.C.'engines
and marine I.C. engines are double-acting.
As the combustion of fuel takes place inside the engine cylinder of internal
combustion engine, they are relatively smaller in size as compared to steam engine
plant. A steam engine plant needs a boiler, a condenser, * and an economiser. Internal
combustion engine can be started quickly within a short time, whereas a steam engine
plant will require much more time as steam has to be generated in the boiler before
the steam engine can be started.
Around 1878, many experimental I.C. engines were constructed. The first really
successful engine did not appear, however, until 1879, when a German engineer Or.
Otto built his famous Otto gas engine. The operating cycle of this engine was based
upon principles first laid down in 1860 by a French engineer named Mr. Bea be Rochas.
The majority of modem I.C. engines operate according to these principles.
The development of the well known Diesel engine began about 1893 by Mr. Rudolf
Diesel. Although this engine differs in many important aspects from the Otto engine,
the operating cycle of modern high speed Diesel engines is thermodynamically very
similar to the Otto engines.
10.1 Introduction

302
ELEMENTS OF HEAT ENGINES Vol.l
Internal combustion engines may be classified according to the :
- Type of fuel used - Diesel oil engine, Petrol engine, Gas engine, and Light oil (Kerosene)
engine.