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Combustion Engines

Last Update:

09/06/2016

Introduction

The combustion engine came into existence about two centuries ago and has undergone constant refinements since then. Despite lacking quite a bit in efficiency and with inherent pollution problems, combustion engines are here to stay due to their adaptability and lack of a cost effective alternative. There is no denying the fact that combustion engines changed lives of man-kind as it evolved over time.

History

  • Combustion engine in one form or the other has been in use since the 18th century. Experimenters used ingenuity and materials available at that time to provide power that could be translated to work.
  • Chrustiaan Huygens used gunpowder powered engines in the 17th century to drive water pumps in the Versailles Palace gardens.
  • Around 1807, a Hydrogen and Oxygen mix was used as fuel in an internal combustion engine built by Francois Isaac de Rivaaz, a Swiss engineer.
  • Most engines developed during the 18th and 19th century were compression-less types and the first engine with in-cylinder compression was probably designed by William Barnett in 1838 followed by Eugenio Barsanti and Felice Matteucci.
  • While some designs remained on paper and as patents, Pietro Benini, an Italian engineer built a combustion engine delivering 5 HP in 1856 that were used in place of steam engines.
  • Nikolaus Otto built a compressionless engine based on the design of Jean Joseph Etienne Lenoir’s gas fired combustion engine, manufacturing such engines in partnership with Eugen Langen in 1864.
  • While Otto, along with Daimler and Mayback developed engines that were used in cars, it was Dugald Clerk who came up with a two stroke engine in 1878. However, automobiles that were manufactured on production level were vehicles powered by Karl Benz engines.
  • Karl Benz designed a four stroke engine in 1885 and patented them in 1886, Edward Butler was probably the first to build a genuine petrol combustion engine in 1884, which used spark plug and electrical ignition system along with a carburetor.
  • Another path-breaking development was Rudolf Diesel’s compression ignition based engine in 1893.
  • Equally interesting is the development of the rotary combustion engine in which the cylinders and crankcase rotate around a stationary crankshaft. These engines found wide use in aircrafts around WWI. Hanns Dieter Paschke developed a KKM rotary combustion engine that became the forerunner of the Wankel.
  • The history of external combustion engines is equally interesting, with most work being focused on using steam. Thomas Savery developed a steam engine of 1 HP in 1698 used as a water pump in mines.
  • Thomas Newcomen came up with a piston steam engine that developed 5 HP and it was used for water pumping in mines.
  • James Watt introduced a steam engine in 1781 that could produce 10 HP using steam at pressure to drive a piston. It is believed his invention of high pressure steam based engines gave an impetus to the industrial revolution.
  • His work was further refined by Oliver Evans and Richard Trevithick, who, around 1800-1801 developed higher pressure steam engines that were used in locomotives. Corliss developed it still further with a four valve design.

 

Types of Combustion Engine

Combustion engines may be broadly classified into two types:

  • Internal combustion engines

The internal combustion engine can be further classified into various types based on fuel, strokes per cycle, cycle type, number of cylinders, ignition, lubrication type, cooling, valve arrangement, cylinder positioning and pressure boost type to name only a few.

  • External combustion engines

Steam engines were the earliest type of external combustion engine. Other engines that used more or less the same principle, i.e. external heating of fluid, are the rankine cycle engine, Stirling engine, trochilic engine, naphtha engine and nuclear power stations.

Parts of Combustion Engines

  • The main parts of an internal combustion piston-cylinder type engine are the piston, cylinder, connecting rod, cylinder head with valves and spark plug, crankshaft, crankcase, flywheel, timing belt and overhead camshaft.
  • A rotary wankel engine includes a flattened oval chamber for combustion that has inbuilt inlet and exhaust ports, a triangular rotor with seals and eccentric gear riding on a drive shaft
  • External steam engines employ a separate burning chamber to burn fuel that heats water in a boiler at high pressure. The steam is used to drive pistons in a cylinder. The piston is connected in a way that converts the linear motion into rotary motion.

How a combustion engine works

Two Stroke Combustion Engine

  • In a two stroke combustion engine, as the piston descends to 75% of the bottom position the exhaust valve opens
  • Simultaneously a fresh fuel-air mix enters the cylinder.
  • As the piston starts moving up the exhaust port closes and then the upward travel also causes intake port to close.
  • The upward movement of the piston results in compression and when the piston is at TDC, the sparkplug fires.

Four Stroke Combustion Engine

  • In a four stroke engine the intake happens when the piston moves down and camshaft pushes the intake valve open.
  • Next is the compression stroke in which both valves are closed and piston is at TDC when the sparkplug ignites.
  • The resulting explosion and expansion of gases forces the piston downward and at the bottom position the exhaust valve opens.
  • The piston moves up and forces burnt gases out of the exhaust manifold.

External Combustion Engine

  • An external combustion steam engine may operate in the closed loop or open loop operating just one cylinder-piston or multiple expansion array with steam from one chamber passing to the other.
  • In the simplest type, the steam enters the cylinder from an inlet valve, pushes the piston and is exhausted into the atmosphere, losing temperature and energy in the process.

Diesel Engine

  • The diesel engine uses high pressure and compression to cause ignition.
  • As the piston moves up, air is drawn in.
  • The air is further compressed and the fuel is sprayed through a fuel injector at the top dead center, creating high temperature and pressure levels, which results in ignition.

Effectiveness and Challenges

Internal combustion engine has overtaken external combustion steam engines for use in ships and heavy locomotives as well as cars, motorcycles and power tools as well as equipments.

  • Today’s combustion engines are technologically advanced and give the best performance as regards power to weight, fuel efficiency, durability and maintenance.
  • It is easy to configure an engine according to the load.
  • Still, however, combustion engines are not without issues.
  • Combustion results in emission of pollutants in the atmosphere responsible for greenhouse effect.

Though advanced, today’s combustion engines have a conversion efficiency of only 30% with the rest of the energy being lost as heat and as an unburnt fuel.

Maintenance

  • A combustion engine requires regular maintenance such as checking for blocked fuel lines.
  • Ensure the spark plugs are clean and that there is no wear on the piston and rings which would cause reduced power output and higher amount of fuel and oil in exhaust.

 

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