chapter1 introduction icengines

8/17/2019 Chapter1 Introduction ICEngines

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1

Internal Combustion Engine

The internal combustion (IC) engine is a heat engine that convertschemical energy in a fuel into mechanical energy, usually made

available on a rotating output shaft.

History of IC engines:

1700s - Steam engines (external combustion engines)

1860 - Lenoir engine (h = 5%)

1867 - Otto-Langen engine (h = 11%, 90 RPM max.)

1876 - Otto four stroke “spark ignition” engine (h = 14%, 160 RPM max.)

1880s - Two stroke engine1892 - Diesel four stroke “compression ignition” engine

1957 - Wenkel “rotary” engine



2

Atmospheric Engine

Process 1-2: Fuel air mixture introduced into cylinder at

atmospheric pressureProcess 2-3: Constant pressure combustion (cylinder open

to atmosphere)

Process 3-4: Constant volume cooling (produces vacuum)

Process 4-5: Isentropic compression (atmosphere pushes piston)

Process 5-1: Exhaust process

31

2Po

4

5

P

V

VALVEPatm



3

Historical IC Engines

FLYWHEEL



4

Two-stroke Lenoir Engine


atmospheric pressure

Process 2-3: At half-stroke inlet valve closed and combustion

initiated constant volume due to heavy piston

producing high pressure products

Process 3-4: Products expand producing work

Process 4-5: At the end of the first stroke exhaust valve opens and

blowdown occursProcess 5-1: Exhaust stroke

3

1 2Po

4

5

P

V



5

Two-stroke Otto-Langen Engine


atmospheric pressure

Process 2-3: Early in the stroke inlet valve closed and combustion

initiated constant volume due to heavy piston

producing high pressure products

Process 3-4: Products expand accelerating a free piston

momentum generates a vacuum in the tube

Process 4-5: Atmospheric pressure pushes piston back, pistonrack engaged through clutch to output shaft

Process 5-1: Valve opens gas exhausted

Disengagedoutput shaft

Engaged

output shaft



6

Four stroke Spark Ignition (SI) Engine

Stroke 1: Fuel-air mixture introduced into cylinder through intake

valveStroke 2: Fuel-air mixture compressed

Stroke 3: Combustion (roughly constant volume) occurs and

product gases expand doing work

Stroke 4: Product gases pushed out of the cylinder through the

exhaust valve

Compression

Stroke

Power

StrokeExhaust

Stroke

A

I

R

Combustion

Products

Ignition

Intake

Stroke

FUEL

Fuel/Air

Mixture



7

Crank shaft

90o

180o

BC

TC

0o

270o

q

Engine Operating Cycle

Spark plug for SI engineFuel injector for CI engine

Top

Center

(TC)

Bottom

Center

(BC)

Valves

Clearance

volume

Cylinderwall

Piston

Stroke

CA

rev

rev

sCA

360

1

speedcrank

anglescranktime



8

Pressure-Volume Graph 4-stroke SI engine

One power stroke for every two crank shaft revolutions

1 atm

Spark

TC

Cylinder volume

BC

Pressure

Exhaust valve

opens

Intake valve

closes

Exhaust

valve

closes

Intake

valve

opens



9

IVO - intake valve opens, IVC – intake valve closes

EVO – exhaust valve opens, EVC – exhaust valve opens

Xb – burned gas mole fraction

Motored Four-Stroke Engine

10

Pressure (bar)

100

Intake Exhaust

TC

BC



10

IVO - intake valve opens, IVC – intake valve closes

EVO – exhaust valve opens, EVC – exhaust valve opens

Xb – burned gas mole fraction

Four-Stroke SI Engine

Valve overlap

Exhaust gas

residual

10

Pressure (bar)

100

Intake Exhaust



11

Compression

Stroke

Power

Stroke

Exhaust

Stroke

A

I

R

Combustion

Products

Intake

Stroke

Air

Fuel Injector

Four stroke Compression Ignition (CI) Engine

Stroke 1: Air is introduced into cylinder through intake valveStroke 2: Air is compressed

Stroke 3: Combustion (roughly constant pressure) occurs and

product gases expand doing work

Stroke 4: Product gases pushed out of the cylinder through the

exhaust valve



12

SOI – start of injection

EOI – end of injection

SOC – start of combustionEOC – end of combustion

Four-Stroke CI Engine

Fuel mass

flow rate

Fuel mass

burn rate

Cylinder

volume

Cylinder

pressure



13

Camshaft

Intake valve

Rocker arm

Piston

Connecting rod

Crankshaft

Oil pump

Exhaust valve

Carburetor

Crank sprocket Oil pickup

Timing belt

Cam sprocket

Air cleaner

Timing belt

tensor

Engine Anatomy



14

Poppet Valve Actuation with Overhead Camshaft

Camshaft

Spring

Air manifold

Stem

Guide

Valve head

Valve seat

Piston

Sparkplug



15

Cylinder Head Design

Honda VTEC (variable intake valve timing)



16

Modern Two-Stroke Spark Ignition Engine

Stroke 1: Fuel-air mixture is introduced into the cylinder andis then compressed, combustion initiated at the end of

the stroke

Stroke 2: Combustion products expand doing work and then

exhausted

* Power delivered to the crankshaft on every revolution



17

Two Stroke Spark Ignition Engine

Intake (“Scavenging”)

Compression Ignition

ExhaustExpansion

Fuel-air-oil

mixture

Fuel-air-oil

mixture

Crank

shaft

Reed

valve

Exhaust

Port*

Transfer

Port*

*No valves andthus no camshaft



18

EPO – exhaust port openEPC – exhaust port closed

IPO – intake port open

IPC – intake port closed

Two-Stroke CI Engine

scavenging

Ai

Ae

Intake area (Ai)

Exhaust area (Ae)

P i

P e

Exhaust Press (Pe)

Intake Press (Pi)

Cylinder Press (P)

110 CA



19

Cross Loop Uniflow

Scavenging in Two-Stroke Engine



20

Advantages of the two stroke engine:

• Power to weight ratio is higher than the four stroke engine since thereis one power stroke per crank shaft revolution.

• No valves or camshaft, just ports

Most often used for low cost, small engine applications such as lawn

mowers, marine outboard engines, motorcycles….

Disadvantages of the two-stroke engine:

• Incomplete scavenging or to much scavenging

• Burns oil mixed in with the fuel



21

Single Cylinder Engine

Single-cylinder engine gives one power stroke per crank revolution

(360 CA) for 2 stroke, or every two revolutions for 4 stroke.

The torque pulses on the crank shaft are widely spaced, and engine

vibration and smoothness are significant problems.

Used in small engine applications where engine size is more important

180 CA0 CA(TC)

720 CA(TC)

540 CA360 CA(TC)

180 CA

4-stroke

2-stroke



22

Multi-cylinder Engines

Multi-cylinder engines spread out the displacement volume amongst

multiple smaller cylinders. Increased frequency of power strokes

produces smoother torque characteristics.

Most common cylinder arrangements are in-line 4 and V-6:

Engine balance (inertia forces associated with accelerating and

decelerating piston) better for in-line versus V configuration.



23

V-6 Engine

Air intake

manifold

Inlet

runner



24

• In spark ignition engines the air and fuel are usually mixed prior to entry

into the cylinder.

• Initially a purely mechanical device known as a carburetor was used to

mix the fuel and the air

• Most modern cars use electronic fuel-injection systems:

- 1980s single injector used to spray fuel continuously into the air manifold

- 1990s one injector per cylinder used to spray fuel intermittently into the

intake port

Fuel-Air Mixing



25

Gasoline Direct Injection (GDI) Engine

• Fuel is injected directly into the cylinder during the intake stroke or the

compression stroke

• High pressure injector required, 5-10 MPa

• Need bowl in piston design to direct the fuel spray towards the spark plug



26

Direct-Injection Stratified-Charge Engines

• Create easily ignitable fuel-air mixture at the spark plug and a leaner

fuel-air mixture in the rest of the cylinder.

• Lean burn results in lower emissions and higher energy efficiency

Example:

Mitsubishi GDI engine achieves complete combustion with an air-fuel

ratio of 40:1 compared to 15:1 for conventional engines

This results in a 20% improvement in overall fuel efficiency and CO2

production, and reduces NOx emissions by 95% with special catalyst



27

Stratified Charge Engine

During intake stroke air enters the cylinder

Near the end of the compression stroke fuel is injected and directed

by the piston head bowl towards the spark plug

The mixture at the spark plug is “rich” in fuel thus easy to ignite but

the amount of fuel injected results in an overall “lean” fuel-air mixture

Lowers heat transfer to the walls but increases thermal cyclic load on

the spark plug, and standard catalytic converter doesn’t work

chapter1 introduction icengines

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