MENG422 AUTOMOTIVE ENGINEERING IENGINEERING I

SPARK & COMPRESSIONSPARK & COMPRESSIONIGNITION ENGINES

Presented by:Asst Prof Dr Hasan HacisevkiPresented by:Asst.Prof.Dr.Hasan Hacisevki

PISTON-ENGINE BASICSPISTON-ENGINE BASICS

There are two kinds of piston engines:

1. Spark-Ignition Engine

2 Compression Ignition (Diesel) Engine2. Compression-Ignition (Diesel) Engine

SPARK IGNITION ENGINE

INTRODUCTION

The actions in the spark-ignition engine can be dividedinto four parts. Each part consists of a piston stroke.p p pThis is the movement of the piston from BDC to TDC,or from TDC to BDC. The complete cycle of events inh i li d i f i k hthe engine cylinder requires four piston strokes. These

are intake, compression, power and exhaust. Thecrankshaft makes two complete revolutions to completecrankshaft makes two complete revolutions to completethe four piston strokes. This makes the engine a four-stroke-cycle engine. It is also called a four-stroke ory g ffour-cycle engine.

SPARK IGNITION ENGINE OPERATIONSPARK IGNITION ENGINE OPERATION

• Intake Stroke:

During the intake stroke of a spark-i iti i th i t i i dignition engine, the piston is moving down.The intake valve is open. Air-fuel mixturefl th h th i t k t d i t thflows through the intake port and into thecylinder. The fuel system supplies the

i t A th i t th hmixture. As the piston passes throughBDC, the intake valve closes. This seals offth d f th li dthe upper end of the cylinder.

SPARK IGNITION ENGINE OPERATION• Compression Stroke:

After the piston passes BDC, it startsmoving up. Both valves are closed. Theupward moving piston compresses the air-fuel mixture into a smaller space, betweenthe top of the piston and the cylinder head.This space is combustion chamber. Themixture is compressed 1/8 or less of itsoriginal volume. The amount that themixture is compressed is compressionratio.

SPARK IGNITION ENGINE OPERATION

• Power Stroke:

As the piston nears TDC at the end of thecompression stroke an electric spark jumps thecompression stroke, an electric spark jumps thegap at the spark plug. The heat from the sparkignites the compressed air-fuel mixture. The air-g pfuel mixture then burns rapidly. These hightemperatures cause very high pressure whichpushes down the piston. The connecting rod carriesthis force to the crankshaft, which turns to movethe drive wheelsthe drive wheels.

SPARK IGNITION ENGINE OPERATION

• Exhaust Stroke:SPARK IGNITION ENGINE OPERATION

As the piston approaches BDC on thepower stroke, the exhaust valve opens.After passing through BDC, the pistonmoves up again. The burned gases escapethrough the open exhaust port. As thepiston nears TDC, the intake valve opens.When the piston passes through TDC andstarts down again, the exhaust valvecloses.

DIESEL ENGINE

INTRODUCTION

Diesel engines are similar to sparkignition engines in construction. Both havepistons, with piston rings, moving up anddown in cylinders. Both burn fuel incombustion chambers in the upper part ofthe cylinders. The high pressure producedby the burning fuel pushes the pistonsdown. This rotates the crankshaft and therotary motion is carried through shafts andgears to the drive wheels.

Common Rail System

DIESEL ENGINE OPERATION

• Intake Stroke:

The diesel engine takes in air alone.No throttle valve impedes the airflow.In the spark-ignition engine, aIn the spark ignition engine, amixture of air and fuel enters theengine cyclinders on the intakeengine cyclinders on the intakestroke. The throttle valve controls the

t th t tamount that enters.

DIESEL ENGINE OPERATION

C i S k

DIESEL ENGINE OPERATION

• Compression Stroke:

In the diesel engine, the upward-moving piston compresses airmoving piston compresses air alone. On the other hand, in the spark ignition engine, the piston compresses the air-fuel mixture.compresses the air fuel mixture.

DIESEL ENGINE OPERATIONDIESEL ENGINE OPERATION

• Power Stroke:

In diesel engine, a light oil calledIn diesel engine, a light oil called diesel fuel is injected into the

d d h t i Th h tcompressed and hot air. The heat of compression ignites the fuel. In p gthe spark-ignition engine, a spark at the spark plug ignites theat the spark plug ignites the compressed air-fuel mixture.

DIESEL ENGINE OPERATIONDIESEL ENGINE OPERATION

Exhaust Stroke:

The exhaust stroke is the same for both engines. The exhaust valve opens and the burned gases flow p gout as the piston moves up the cyclindercyclinder.

DIFFERENCES BETWEENDIFFERENCES BETWEENSPARK & COMPRESSION

IGNITION ENGINES

The type of fuel usedThe type of fuel used.The way the fuel gets into the cyclinders.The way the fuel is ignitedThe way the fuel is ignited.Compression Ratiosp