TITLE.PM5

INTRODUCTION—OUTLINE OF SOME DESCRIPTIVE SYSTEMS 7

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the charge gets compressed when E.P. (exhaust port) and T.P. are covered by the piston ; thus the

cycle is repeated.

L

E.P. M

V

L

E.P. M T. P.

V

C.C.

L

E.P.

M

T. P.

V

C.C.

T. P.

C.C.

Spark

plug

()i ()ii ()iii

L = Cylinder ; E.P. = Exhaust port ; T.P. = Transfer port ; V = Valve ; C.C. = Crank chamber

(i)(ii)(iii)

Fig. 1.5. Two-stroke petrol engine.

The power obtained from a two-stroke cycle engine is theoretically twice the power obtain-

able from a four-stroke cycle engine.

1.3.5. Compression ignition (C.I.) engines

The operation of C.I. engines (or diesel engines) is practically the same as those of S.I.

engines. The cycle in both the types, consists of suction, compression, ignition, expansion and

exhaust. However, the combustion process in a C.I. engine is different from that of a S.I. engine as

given below :

In C.I. engine, only air is sucked during the stroke and the fuel is injected in the cylinder

near the end of the compression stroke. Since the compression ratio is very high (between 14 : 1 to

22 : 1), the temperature of the air after compression is quite high. So when fuel is injected in the

form of a spray at this stage, it ignites and burns almost as soon as it is introduced. The burnt

gases are expanded and exhausted in the same way as is done in a S.I. engine.

1.4. Gas Turbines

1.4.1. General aspects

Probably a wind-mill was the first turbine to produce useful work, wherein there is no

precompression and no combustion. The characteristic features of a gas turbine as we think of the

name today include a compression process and an heat addition (or combustion) process. The gas