lesson 13 internal combustion engine the diesel part a

Lesson 13 Lesson 13 Internal Combustion Engine Internal Combustion Engine The DieselThe DieselPart APart A

ContentsContents

• Working Principle of a Diesel Engine • Operation of systems

• Two stroke engines• Four stroke engines

• Comparison between the Two-Stroke Engine and the Four-Stroke Engine

• Gas Exchange Process• Other Supporting Systems

Working Principle of a Diesel EngineWorking Principle of a Diesel Engine

• The diesel engine is a type of internal combustion engine that ignites the fuel by injecting it into hot, high-pressure air in a combustion chamber.


• In common with all internal combustion engines the diesel engine operates with a fixed sequence of events, which may be achieved either in four strokes or two, a stroke being the travel of the piston between its extreme points.

• Each stroke is accomplished in half a revolution of the crankshaft.

Working Principle of a Diesel Working Principle of a Diesel EngineEngine

• Increased pressure of combustion gases acts on piston -> converted to rotary motion

• Can be 2 or 4 stroke engines• 2-stroke: 1 power stroke per 1 crankshaft

rev.• 4-stroke: 1 power stroke per 2 crankshaft

rev.

OperationOperation• Engine stroke

• A stroke is a single traverse of the cylinder by the piston (from TDC to BDC)

• 1 revolution of crankshaft = 2 strokes of piston


TDC

BDC

V comp

Vs

S

Vs+Vc V1

e = ----------- = ------Vc V2

p x D2

Vc= ----------- x S

4

pk = p1 x en

n = polytrope exponent 1.35p1 = pressure at the beginning

of the compressionabsolute pressure

tk = T1 x en-1 -273

T1= temp at the beginning of the

compression in Kelvin degree( rec. temp. +273 )

Four-Stroke Diesel EngineFour-Stroke Diesel Engine

• The four-stroke cycle is completed in four strokes of the piston, or two revolutions of the crankshaft.

• In order to operate this cycle the engine requires a mechanism to open and close the inlet and exhaust valves.


• Intake stroke• Intake valve open, exhaust valve shut• Piston travels from TDC to BDC• Air drawn in

• Compression stroke• Intake and exhaust valves shut• Piston travels from BDC to TDC• Temperature and pressure of air increase


• Power stroke• Intake and exhaust valves shut• Fuel injected into cylinder and ignites• Piston forced from TDC to BDC

• Exhaust stroke• Intake valve shut, exhaust valve open• Piston moves from BDC to TDC• Combustion gases expelled

Two-Stroke Diesel EngineTwo-Stroke Diesel Engine

• The two-stroke cycle is completed in two strokes of the piston or one revolution of the crankshaft.

• In order to operate this cycle where each event is accomplished in a very short time, the engine requires a number of special arrangements.


• First, the fresh air must be forced in under pressure.

• The incoming air is used to clean out or scavenge the exhaust gases and then to fill or charge the space with fresh air.

• Instead of valves, holes, known as ‘ports’, are used which are opened and closed by the sides of the piston as it moves.


• One power stroke every crankshaft revolution

• Uses pressurized air to simultaneously supply new air and expel combustion gases

• Scavenging• Exhaust valve open, inlet port exposed• Pressurized air enters, expels combustion gases• Piston near BDC


• Compression• Intake and exhaust valves shut• Piston travels from BDC to TDC• Temperature and pressure of air increase

• Power stroke• Intake and exhaust valves shut• Fuel injected into cylinder and ignites• Piston forced from TDC to BDC

Two-Stroke Diesel EngineTwo-Stroke Diesel EngineFuel injectionends

Fuel injectionbegins

Scavengeportsclose

Scavengeportsopen

Exhaustportsopen

Exhaustportsclose

Scavenging

Exhaust

Rotation

1st Stroke (Compression)

Piston at BDC

Scavenge Ports and Exhaust Valve Open

Scavenge air flows into the cylinder and presses the exhaust gases through the exhaust valve to the turbocharger.

Piston Moves Upwards:

Scavenge ports are being closed

Exhaust valve shuts, compression begins

Two-Stroke Diesel EngineTwo-Stroke Diesel EngineFuel injectionends

Fuel injectionbegins

Scavengeportsclose

Scavengeportsopen

Exhaustportsopen

Exhaustportsclose

Scavenging

Exhaust

Rotation

2nd Stroke (Ignition – Combustion – Expansion – Exhaustion – Scavenging)

Just Before TDC

Fuel is injected into the cylinder, Fuel Ignites in the compressed and heated air = ignition, with ignition combustion begins

Gases Expands and Press Piston Downwards (working stroke)

The exhaust valve opens, exhaust gases flow out if the cylinder to the turbo.

Scavenge ports are being uncovered by the downward moving piston, scavenge air flows into the cylinder and presses the exhaust gases out through the exhaust valve to the the turbocharger.

ComparisonComparison

• Two-stroke advantages• Higher power to weight ratio• Less complicated valve train

• Four-stroke advantages• More efficient burning process• As size increases, power-to-weight ratio

improves

Gas Exchange ProcessGas Exchange Process


Uniflow Scavenging


Cross Flow Loop Flow

Mean Effective Pressure

MEP is the value referring to the constant pressure which would have to exist in a cylinder during power stroke to produce the same power at the flywheel.

Diesel Fuel SystemDiesel Fuel System

• Fuel System• Fuel Supply System 燃油供给系统• Fuel Injection System 燃油喷射系统

• Injection Nozzles• Injection Pump• Filters• Transfer Pump• Fuel Tank

Diesel Fuel SystemDiesel Fuel SystemDensity: 密度

Viscosity: 粘度Flash point: 闪点

measure the delivery quantity by weight

adjust centrifuges

temperatures for treatment & injection

for safety

Combustion:

Combustion product:

Maintenance:

viscosity 粘度cetane number 十六烷值calorific value 发热值

sulphur 硫carbon residue 残碳ash 灰分

flash point 闪点 setting point 凝点viscosity 粘度 specific gravity 比重water content 水分mechanical impurities 机械杂质

Fuel Injection SystemFuel Injection System

• the amount of fuel • 定量• at the right moment• 定时• in a suitable condition• 定质

a metered amount of fuel according to the load on the engine

timing mechanism

to atomize the fuel

Fuel Injection SystemFuel Injection System

Cooling Water SystemCooling Water System

• Fresh Water Cooling System• 淡水冷却系统• Sea Water Cooling System• 海水冷却系统


• Fresh Water Cooling System

To cool: cylinder jackets and covers

exhaust valves

water cooled turbochargers


• Fresh Water Cooling System

Cooling water pumps:

冷却水泵

Fresh water cooler:

淡水冷却器

Corrosion prevention:

防腐蚀

independently driven & controlledin duplicate (one as standby)with pressure relief valves & alarms

cooled with sea waterpressure of fresh water higher

corrosion inhibitors 抑蚀剂alkaline agents 碱剂chemical additives 化学添加剂


• Sea Water Cooling SystemUsual arrangement

Central cooling system

individual coolers for lubricating oil, jacket water, and piston cooling

one large sea water circulated cooler

individual coolers circulated by fresh water

☆Advantage ： Corrosion problems are greatly reduced.

Words & ExpressionsWords & Expressions

• internal a. 内在的• ignite v. 发火、点火 • mechanism n. 机械装置、机构

• scavenge v. 扫气• timing n. 定时• cylinder n. 汽缸• combustion n. 燃烧• exhaust vi. 排气• cycle 周期 , 循环• inlet 进口 , 入口

AssignmentsAssignments

• What is a diesel engine?• What is the four-stroke cycle?• What is the two-stroke cycle?• What special arrangements does the two-

stroke cycle require?• Describe the operation between two fuel

injections.

lesson 13 internal combustion engine the diesel part a

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