Combustion Engineering

I

Introduction

Combustion Engineering, application of the science of combustion to industrial fuel burning. Combustion engineering is necessary in applications ranging from home furnaces and automobile engines to the massive fossil fuel-run generating plants that supply the major part of the world's electrical energy. Combustion engineering is closely connected with the chemistry of burning fuels, the engineering laws of fluid flow and heat transfer, and the principles of mechanical design.

Combustion engineers are concerned with the general problem of burning a given fuel or fuel mixture in a given combustion space. This combustion space might be an industrial furnace, the cylinder of an automobile engine, or the chamber of a rocket motor. Factors that the combustion engineer must take into account include furnace and burner design and specification, including pumps, blowers, fans, and stacks; high-temperature materials problems, automatic controls, and protective devices; fuel properties, storage, preparation, and distribution; flame characteristics and heat release; air quantity; fuel, air, and furnace pressures; furnace and gas temperatures; and maintenance of efficiency.

II

Design

The combustion engineer designs furnaces, boilers, burners, heat exchangers, and pollution control devices. In addition to mechanical design, the engineer must also be familiar with structures and materials.

III

Combustion Chambers

Many types of combustion chambers are important in industrial applications. Open-hearth furnaces, for example, produce extensive hot flames to melt steel in large crucibles. Kilns may be used to condition materials with or without direct flame contact and are important in the production of items such as glass, bricks, and ceramics. Boiler furnaces burn solid, liquid, or gaseous fuels to heat steam boilers for purposes ranging from space heating to generating electric power. Combustion chambers in gas turbine engines, like the aircraft turbojet, add heat directly to the working fluid of the engine. This process also occurs in rocket motors, where the hot combustion gases are expelled from a nozzle to produce thrust.

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The transfer of heat energy in combustion devices occurs through radiation, conduction, and convection. In order to be useful, this heat must be transferred efficiently while avoiding temperature buildups that might damage burners, chamber walls, and boiler tubes.

IV

Fuels

Solid fuels, such as coal, may be burned in lump form on grates, or they may be pulverized to a fine powder before combustion, depending on the application. For lump burning, coal may be partially oxidized to produce combustible gases that are then burned after mixing with secondary air. Pulverized coal, on the other hand, may be fed to a furnace after having been premixed with enough air for efficient combustion.

Fuel oil and natural gas are important fuels for industrial furnaces. Fuel oil and other liquid fuels are normally atomized by pressurization when being fed to a combustion chamber. This is the case, for example, in a diesel engine. Gaseous fuels may be premixed with air before entering a combustion chamber, or they may undergo mixing after injection, depending on the type of flame desired.