Classification Of Steam Engine Plants- Basic Thermal Engineering

INTRODUCTION

A steam engine plant shall have boiler

, condenser, and feed pump along with steam engine. Steam generated in boiler is sent to steam engine where it is expanded upto certain pressure. Steam leaving engine are fed to condenser where steam gets converted into condensate (water) which is sent back to boiler through feed pump.

CLASSIFICATION OF STEAM ENGINES

Steam engines can be classified in the following ways. Selection of particular steam engine depends upon the requirements and constraints of an application and features of the engine

Based on axis of engine:

i. Horizontal steam engine

ii. Vertical steam engine

Engine having vertical axis cylinder is called vertical steam engine and engine having horizontal axis cylinder is called horizontal steam engine.

Based on speed of engine

i. High speed engine—having speed of 250 rpm and above.

ii. Medium speed engine— having speed lying between 100 to 250 rpm.

iii. Slow speed engine— having speed less than 100 rpm.

Based on type of steam action

i. Double acting steam engine.

ii. Single acting steam engine.

Depending upon whether the steam acts on both sides of piston or only on one side of piston the engine. In case of single acting engine out of two piston strokes i.e. forward stroke and backward stroke, only one stroke is used for work output. While in double acting engine both the forward and backward strokes of piston are used for work output alternatively i.e. expansion of steam occurs from both sides of piston alternatively. Power developed from double acting engine will be nearly double of power developed from single acting steam engine.

Based on expansive or non-expansive type of working

Steam engines can be of non-expansive type in which steam is injected throughout the piston stroke i.e. piston movement is caused due to high pressure steam forcing piston from one end to other end throughout and not due to expansion of steam.

Expansive type steam engine has steam injection for only a part of piston stroke and the expansion occurs in remaining part of stroke.

The cut off ratio in case of non-expansive engine is unity while for expansive engine it is less than unity

Based on type of exhaust from engine

Exhaust from steam engine may either go to atmosphere or to condenser. In certain applications where expansion in steam engine is extended up to sub atmospheric pressure then the exhaust steam from engine is sent to condenser. Such type of engine whose exhaust goes to condenser are termed as ‘Condensing engine’. The steam engines whose exhaust steam is delivered to atmosphere is called ‘non-condensing engine’.

Based on number of stages

Depending upon the number of stages of expansion in steam engine, it may be termed as single stage, two stage, three stage, four stage engine etc.

Based on number of cylinders

Steam engine may have steam expanding in single cylinder and engine is called “simple steam engine”. Steam engine may have the expansion of steam occurring in more than one cylinder such as expansion occurring in high pressure cylinder and low pressure cylinder etc. Such steam engine having expansion in more than one cylinders sequentially are termed as “Compound steam engine”.

Based on type of governing

Steam engine may have different types of governing as throttle governing and cut-off governing.
Engine may be called as throttle governed engine or cutoff governed engine.

Based on type of application

Steam engine may be of following types depending upon applications as;

i. Stationary engine

ii. Marine engine

iii. Locomotive engine