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Reciprocating Engine

Last Update:

09/06/2016

Introduction

The reciprocating engine revolutionized the world. It is at the heart of locomotion, stationary machinery, power tools and power generation equipments. Without the invention of Engines it is doubtful that the world would be as advanced as it is today.

History

In the current context reciprocating engine is usually associated with internal combustion gas, petrol or diesel fueled engines. However, in broad terms, reciprocating means use of a piston connected through a shaft to a crankshaft that turns linear motion into rotary motion in a continuous cycle. Reciprocating engines go a long way back in time.

  • A sawmill in the age-old Roman empire used a crank and a connecting rod mechanism, a design that continued to progress. Al Jazari had developed a crankshaft and pin mechanism that converted rotary into linear motion.
  • Early inventors like Samuel Morland and Christiaan Huygens used gunpowder as fuel and Allessandro Volta used an electric spark to ignite air-hydrogen mixture to fire a gun.
  • The 18th century saw quite a few inventors patenting their processes that also included John Stevens building the first internal combustion engine in 1798 in America.
  • Nicephone Niepce developed an engine in 1807 to power a riverboat. The forerunner of internal combustion reciprocating engines can be traced back to Alphonse Beau de Rochas who, in 1861, obtained a patent for an engine design that inspired Nikolaus Otto. However, before him, Jean Joseph Etienne Lenoir, a Belgian, developed a gas fired engine in 1860 and quite a few were manufactured.
  • 1863 was a landmark year for reciprocating engines as Nikolaus Otto patented a gas engine and, along with Eugen Langen, began to manufacture it in 1864.
  • In the 18th century the steam engine was the most widely used reciprocating engine in Europe, used to power trains and machinery.

Robert Stirling, a Scot, invented a closed cycle air engine in 1816 using external combustion to heat air. A design based on his model is used in low power applications including solar based alternate energy options in recent times.

Types

Reciprocating engine is often known as a piston engine which is driven with heat and pressure, which converts the force into a rotating motion. This principle is a common feature applied in most forms of engines available today.

  • Internal combustion engines like the one used in steam vehicles uses reciprocating pistons to drive the vehicle. These steam engines were a mainstay of the Industrial Revolution era.  In this engine fuel in the form of gas, petrol or diesel is burnt inside a chamber and the resulting explosion drives the piston that translates linear motion to rotary motion. An external combustion steam engine uses heat and pressure produced by an external combustion process to drive a piston.
  • Stirling engine: This is a closed cycle engine where combustion is external and provides heated air to the engine in a closed loop.
  • Variations such as the free piston engine, swing piston engine, IRIS engine and the Bourke engine that used scotch yoke to convert linear motion to rotary motion.
  • Rotary reciprocating engines in which the cylinders move around the shaft

Compressed air, steam or hot gas operated reciprocating engine.

Main Parts

Since the internal combustion engine is the most widely used form of reciprocating engine the parts are described for this type:

  • A cylinder head with intake and exhaust valve
  • A spark plug for ignition
  • A cylinder housing the piston along with the piston rings
  • A Connecting rod
  • The Crankshaft and the Flywheel
  • The Crankcase

 External reciprocating engine parts:

  • The boiler in which water is heated to form steam at high pressure
  • Cast iron cylinder
  • Piston with connecting road
  • Crank and flywheel and linkages.
  • Valves to control in-let and exhaust of steam

 

How does a Reciprocating engine work?

  • In a four stroke reciprocating engine, the intake stroke results in the piston moving down to the BDC position, opening the valve and letting in fuel-air mixture. The piston then moves up in the compression stroke in which both valves are closed and ignition takes place next that pushes the piston down into the cylinder and opening the exhaust valve to expel burnt gases. The downward stroke results in transferring power to the crankshaft.
  • In a two stroke engine the cycle occurs in one turn of the crankshaft.
  • The simplest steam powered reciprocating engines, use steam to push the piston with one cycle happening with each rotation of the crank and the piston performing two strokes. The pressure is controlled by valves in a steam-chest next to the cylinder with valves opening and closing steam ports.

In all such reciprocating designs expansion of hot gases causes piston to move in and out of a cylinder and the piston with a connecting rod drives a crankshaft that converts linear motion to rotary motion.

Effectiveness and Challenges

  • Reciprocating engines are in wide use in marine vessels, in cars, two wheelers, farm equipments and stationary tools and machinery as well as in power generation.
  • These engines use widely available gas, petrol and diesel and have been refined to give the maximum power to weight ratio.
  • The reciprocating engine can be designed to deliver high torque or high horsepower or a combination of both keeping end purpose in mind and, therefore, it is flexible and adaptable to power anything from small tools to huge locomotives and ships.
  • The drawbacks are that the reciprocating engine does not fully burn fuel and has a limit to the power that it can deliver, which led to the use of turbine engines in aircraft and power generation.
  • There is also a limit to the compression rations that can be used in reciprocating engines.
  • Noise is another factor of concern along with the high wear and tear due to  tremendous amount of pressure within the cylinder that can damage pistons and the crankshaft over long period or rough use.

The overall challenge is to arrive at the best compromise in terms of fuel consumption to tackle stricter emission norms along with better power generation.

Maintenance

A regular reciprocating engine requires some regular check for up-keep and maintenance.

  • Checking carburetor and fuel flow lines ensure that there are no blockages or dirt clogged up in the lines.
  • Checking and setting valves for optimal clearances.
  • Oil change, cleaning of spark plugs and checking exhaust for signs of improper air-fuel mix should be done at regular intervals.
  • Wear and tear on piston rings should be checked for replacement.

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