Lecture 3 10/03/2012

Diesel engine applications

To derive mobile power generator (up to 10 kW/cylinder)

Cars and light commercial vehicles ( up to 50 kW/cylinder)

Construction industry and agricultural machinery (up to 50 kW/cylinder)

Heavy trucks and tractor vehicles (up to 80 kW/cylinder)

Fixed installations such as emergency power generator (up to 160 kW/cylinder)

Railway locomotives and ships (up to 1000 kW/cylinder)

Diesel History

The Diesel Engine

“.... an internal combustion engine in

which air is compressed to a temperature

sufficiently high to ignite fuel injected

into the cylinder where the combustion

actuates a piston.”

Typical DI Chambers

Heavy duty - 4-valve,

central injector, low swirl,

wide shallow bowl Light duty - 4-valves, central

vertical injector, high swirl,

deep narrow bowl

Spray Outline

Diesel Combustion

Fuel sprayed in cylinder near TDC

Atomization, vaporization & mixing delay ignition

Ignition occurs wherever conditions right (1000 F)

Combustion rate controlled by injection

characteristics (injection rate, spray angle,

injection pressure, nozzle size and shape),

chamber shape, mixture motion, & turbulence

Glow plug may be used to aid cold starting

Power output controlled only by amount of fuel

injected

MAXIMUM SPECIFIC POWER & BMEP

COMPARISONGASOLINE vs DIESEL

0

5

10

15

20

25

30

35

40

45

50

0 1000 2000 3000 4000 5000 6000 7000

SPEED, r/min

PO

WE

R,

kW

/L &

BM

EP

, b

ar

BMEP-GAS

POWER-GAS

POWER-DIESEL

BMEP-DIESEL

COMPARISON OF FUEL CONSUMPTIONDIESEL & GASOLINE @ 2500 r/min

BSFC vs BMEP

150

200

250

300

350

400

450

500

550

600

0 2 4 6 8 10 12 14 16

BMEP, bar

BS

FC

, g

/kW

h

Gasoline

DI-Diesel

Compression Ratio

The diesel engine compresses at a very high ration of 14:1 to 25:1.

The higher the compression ratio, the more power is generated.

The main limiting factor to compression ratio is based on the knock limits of the fuel.

Knock is the term used to describe the auto ignition that occurs when a fuel ignites because the pressure in the cylinder is such that combustion occurs.

The knock limit of the fuel is determined by the point at which the engine begins to shake.

The higher the knock limit, the higher the compression ratio, the more power is generated

Dr. Walid Abdelghaffar

DIESEL ENGINES


A typical injector-pump-type automotive diesel fuel injection system

DIESEL ENGINES

A typical injector-pump-type automotive diesel fuel injection system.

Basic Parts Of A Diesel Fuel System

Injection nozzles

Injection pump

Filters

Transfer pump

Fuel tank


HOW AN ENGINE WORKS:


DIESEL ENGINES

The diesel engine requires compression ratios of 14:1 and higher.

Incoming air is compressed until its temperature reaches about 1,000°F (540°C).

This is called heat of compression.

As the piston reaches the top of its compression stroke, fuel is injected into the cylinder, where it is ignited by the hot air

Diesel combustion occurs when fuel is

injected into the hot, highly compressed

air in the cylinder.

DIESEL ENGINES Indirect and Direct Injection

In an indirect injection

(IDI) diesel engine, fuel is

injected into a small pre-

chamber, which is

connected to the cylinder by

a narrow opening.

The initial combustion takes

place in this pre chamber.

This has the effect of

slowing the rate of

combustion, which tends to

reduce noise.


An indirect injection diesel engine uses

a pre chamber and a glow plug.

DIESEL ENGINES Indirect and Direct Injection


direct injection diesel

engine injects the fuel

directly into the combustion

chamber. Many designs do

not use a glow plug.

ENGINE-DRIVEN VACUUM PUMP

Because a diesel engine is un throttled, it creates

very little vacuum in the intake manifold.

Several engine and vehicle components operate

using vacuum, such as the exhaust gas

recirculation (EGR) valve and the heating and

ventilation blend and air doors.

Most diesels used in cars and light trucks are

equipped with an engine-driven vacuum pump to

supply the vacuum for these components.


Durability

Diesel engines are also capable of running high miles

without major engine work.

Truck diesel engines can run 250,000 or even 500,000

miles without major engine work.

In 1978, Mercedes-Benz launched a “Great Diesel

Search” to find the highest mileage diesel in the United

States.

Robert O’Reilly drove his 1957 Mercedes-Benz 180D

1,184,000 miles, 750,000 on its original engine.

Another owner drove his 1968 Mercedes-Benz 220 D

912,000 miles, 902,000 miles on its original engine.

Efficiency One positive aspect of the diesel engine is that

they are thermally efficient.

The improved efficiency is caused by the

relatively high compression ratios

The diesel engine is 54% thermally efficient,

while gasoline engines are only 34%.

As a result of diesel engines thermally efficiency,

they are able to achieve better gas mileage

because they produce greater horsepower

output for fuel intake.

Main Differences of Gasoline and Diesel

The main difference between a gasoline engine and a diesel engine is that in a diesel engine, there is no spark plug to ignite the fuel.

Diesel fuel is injected into the cylinder, and it ignites spontaneously as the heat and pressure of the compression stroke cause the temperature inside the cylinder to increase.

The other major difference between the two types of engines is in the gas mileage.

As a result of diesel fuel having a higher energy density than gasoline, diesel engines get higher gas mileage.


Fuel supply system (low pressure stage)

Fuel Supply system (low-pressure stage)

The job of the fuel supply is to store the fuel required, to filter it and to supply it to the fuel-injection installation at a specific supply pressure under all operating conditions. For some applications, the fuel return is also cooled

1. Fuel tank

2. Preliminary filter

3. Control unit cooler

4. Pre-supply pump with non-return

valve

5. Fuel filter

6. Main pre-supply pump

7. Pressure control valve

8. Fuel distributor line

9. Fuel cooler

FUEL TANK AND LIFT PUMP

A fuel tank used on a vehicle equipped with a diesel engine differs from the one used with a gasoline engine in several ways, including:

A larger filler neck for diesel fuel.

No evaporative emission control devices or charcoal (carbon) canister.

The diesel fuel is drawn from the fuel tank by a lift pump and delivers the fuel to the injection pump.

Between the fuel tank and the lift pump is a water-fuel separator.

Water is heavier than diesel fuel and sinks to the bottom of the separator.

Fitted far the engine for no ignition in accidents

Should be corrosion resistance and leak-proof to a pressure equivalent to double the system pressure and at least 30 kPa

Should have Pressure relief vents or valves


DIESEL INJECTOR NOZZLES

Diesel injector nozzles are spring-loaded closed valves

that spray fuel directly into the combustion chamber or

pre combustion chamber.

Injector nozzles are threaded into the cylinder head, one

for each cylinder, and are replaceable as an assembly.

The top of the injector nozzle has many holes to deliver

an atomized spray of diesel fuel into the cylinder.

Parts of a diesel injector nozzle include:

Heat shield.

Injector body.

Diesel injector needle valve.

Injector pressure chamber.


DIESEL INJECTOR NOZZLE OPERATION

The electric solenoid

attached to the injector

nozzle is computer

controlled and opens to

allow fuel to flow into

the injector pressure

chamber


Typical computer-controlled diesel engine

fuel injectors

GLOW PLUGS

Glow plugs are always used in diesel engines

equipped with a pre-combustion chamber and may

be used in direct injection diesel engines to aid

starting.

A glow plug is a heating element that uses 12

volts from the battery and aids in the starting of a

cold engine.

As the temperature of the glow plug increases, the

resistance of the heating element inside increases,

thereby reducing the current in amperes needed

by the glow plugs.


Can be metal line or flexible

Fire resistant lines

Avoid contact with the moving parts

Leakage fuel should not collect or ignite

Far from the heating source

Should not gravity fed

Must not be routed through the passenger compartment

Fuel lines

Diesel fuel filter The job is to reduce the

contamination of the fuel by suspended particles

Must capable of accumulating a quantity of particles

Preliminary filter is a strainer type filter (300 m)

Main filter: easy-change, two in parallel

Water separator: water removed by a discrete separator after collection in an accumulation chamber.

Fuel preheating: using electrical heater, engine coolant, or recirculation fuel, to prevent clogging of the filter

Should give adequate supply of fuel to the high

pressure components:

1. Irrespective of operating state

2. With a minimum of noise

3. At the necessary pressure

4. Throughout the vehicle’s complete service life

Manual priming pumps

Prime and vent the system after changing the filter

Fuel pre-supply pump

Fuel-supply pump types

Electrical

fuel pump

Gear fuel

pump

Vane

type

pump

Tandem

pump

Distributor tube: in Unit injector system to ensure the same quantity to each injector.

Low-pressure control valve: installed in the fuel return of the UIS and UPS to ensure adequate operating pressure in the low pressure stages so that the pumps are always filled with fuel.

ECU Cooler:

In commercial vehicles for the ECU of the UIS and UPS. Fuel is used as a cooler and passed through cooling channels

Fuel cooler: fuel return from the high pressure pump should be cooled to avoid damage to the fuel tank and level sensor. Connection to the engine cooling system should not affect the fuel cooling.

How Is Engine Speed Controlled In A Diesel Engine?


The throttle control regulates only the amount of

fuel injected into the cylinder

The throttle control in a gasoline engine regulates

the amount of air/fuel mixture allowed into the

cylinder

How Are Diesel Engines Stopped?


By shutting off the fuel to the cylinders

by a manual control or solenoid switch

Gasoline engines are stopped by

cutting off the spark from the spark

plugs to the cylinders

High Pressure Systems 1. In-line fuel-

injection pumps

2. Distributor injection pumps

3. Common-rail (CR) system

4. Discrete cylinder systems

Unit injector system

Unit pump system

Lecture 3 10/03/2012

Documents

Transcript of Lecture 3 10/03/2012