CHAPTER -1

INTRODUCTION

Diesel engines are efficient power producing device among all the internal

combustion engines. All over the world, the diesel engines are being used in heavy

trucks, urban buses, industrial equipment and locomotives. The diesel engines are

increasingly used in passenger cars, because of their higher fuel economy and reduced

emissions. In diesel engines, unlike gasoline engines, the fuel is injected inside the

cylinder just before the end of compression stroke. This gives the fuel very less time to

vaporize and mix with the air inside the cylinder.

It is well established that in-cylinder air–fuel mixing in diesel engines is one of

the most important factors governing the combustion process, and also the resultant

engine performance and exhaust emissions. In-cylinder air motion is an important factor

in air–fuel mixing and formation of evenly distributed mixture throughout the cylinder.

Mixing enhancement can be achieved by generating swirling air flows in the

combustion chamber. Inside the cylinder the main air motions are generated by the

intake-induced swirl, the piston motion and its geometry, and the spray-induced

entrainment. Among these, intake induced swirl plays a vital role in swirl generation as

these are taken care of at the design stage itself.

The flow field and charge motion inside the cylinder are directly affected by the

intake system configuration. An optimum configuration of these components in the

intake system provides good fuel economy, better engine performance at all loading

conditions and low engine exhaust emissions. Intake port being an important component

of the engine intake system, its influence on the overall performance of the engine is of

main interest to engineers, at the design stage of a diesel engine.

1.1 Air motion inside the cylinder

The air motion inside the cylinder, due to high velocities involved, all flows into,

out of and within cylinders are turbulent and very complex flow. Characterizing

turbulent flows is always a tedious task for engineers. The main structural components

of in-cylinder engine turbulence are represented by the following three motions.

1.2 Squish

Squish is the name given to the radially inward or transverse gas motion that occurs

toward the end of the compression stroke when a portion of the piston face and cylinder

head approach each other closely. Fig 1.1 shows a bowl-in Piston diesel combustion~

chamber. The amount of squish is often defined by the Percentage squish area. Squish-

generated gas motion results from using a compact combustion chamber geometry.

Fig 1.1 Squish inside cylinder

1.3 Tumble

As the piston reaches TDC the squish motion generates a secondary flow called

tumble, where rotation occurs about a circumferential axis near the outer edge of the

cavity or piston bowl. Fig 1.2 shows the tumble motion inside the cylinder.