Automotive Systems course (Module 01) - Internal Combustion Engine (ICE) basics

29 de setembro de 2016 | 1
SistemasAutomóveis
Internal Combustion Engine (ICE)
basics
Mário Alves (mjf@isep.ipp.pt)

SistemasAutomóveis
Outline
• ICE definition and operating principle
• ICE classification examples
• ICE types according to the combustion method
• Phases of the combustion cycle
• Camshaft and valve actuation
• ICE types according to the ignition principle
• Phases versus strokes (4-stroke and 2-stroke engines)
• Fuel types
• Mixture formation (direct and indirect injection)
• Cylinders configuration
• Engine cooling
• Engine lubrication

SistemasAutomóveis
ICE definition and operating principle
• An ICE is a heat engine based on the combustion of a
fuel with air
• inside a combustion chamber
• The combustion triggers an expansion of the high-
temperature and high-pressure gases
• forcing some components of the engine (e.g. pistons, turbine
blades) to move
• All this process converts chemical into mechanical
energy
• very low efficiency ( 30%) even today 

SistemasAutomóveis
ICE classification - examples
Classification
according to
Ignition
principle
Compression
Ignition (CI)
Heterogeneous
Charge (conventional)
Homogeneous Charge
(HCCI)
Spark
Ignition
Electromechanical
Distributor-less
(Direct Ignition)
http://web.iitd.ac.in/~ravimr/courses/mel345/classification.pdf

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Classification
according to
Combustion
principle
Intermittent Linear pistons with
alternating
movement
Rotary pistons
(Wankel)
Continuous Turbine engine
Jet engine

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Classification according to
Cylinders number
and configuration
Single
Multiple
In-line
Horizontally opposed
V-shaped
W-shaped
Radial

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Classification according
to the
Working Cycle
2-stroke
4-stroke
Classification according
to the
Number of valves
2 per cylinder
3 per cylinder
4 per cylinder
…

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ICE types according to how combustion is performed
• ICEs engines can be classified according to the way
combustion is performed:
• Intermittent combustion
• linear piston (alternating/reciprocating movement)
• rotary piston (Wankel)
https://www.citelighter.com/technology/technology/knowled
gecards/rotary-engine-vs-four-stroke-engine

SistemasAutomóveis
ICE types according to how combustion is performed
• ICEs engines can be classified according to the way
combustion is performed (cont.):
• Continuous combustion
• Turbine engine (e.g. jet engine)
http://www.navyaircrew.com/blog/2009/07/18/suck-squeeze-bang-
and-blow/

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ICE main components (linear pistons)
• Piston
• transmits movement to the rod
• Connecting Rod
• transmits the movement to the crankshaft
• Crankshaft
• transforms reciprocating into circular movement
http://direns.mines-paristech.fr/Sites/Thopt/en/co/maci.html

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Phases of the combustion cycle (strokes)
• In ICEs, combustion is composed of four phases:
• Admission (or Intake, or Induction) Stroke
• Air (direct injection) or air/fuel mixture (indirect injection) is
admitted into the combustion chamber, by opening the admission
valves
• Air comes from the intake manifold: atmosphere  air filter 
(throttle body)  (turbo-compressor)  admission pipes
• Compression Stroke
• the air/fuel mixture is compressed
• the piston moves upwards from the Bottom Dead Center (BDC) to
the Top Dead Center (TDC)
http://www.chevelle.fr/chevelle.fr/articles.php?lng=fr&pg=423

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Phases of the combustion cycle (strokes)
• In ICEs, combustion is composed of four phases (cont.):
• Power (or Expansion) Stroke
• Air/fuel mixture ignites, triggering the combustion
• The piston is forced to move downwards
• Exhaust Stroke
• burned gases are expel from the combustion chamber
• Air goes out through the exhaust valves  exhaust pipes turbo-
compressor  …
http://www.chevelle.fr/chevelle.fr/articles.php?lng=fr&pg=423

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Camshaft and valve actuation
• Objective
• Open/close intake and exhaust valves
• Operation
• synchronization (aka timing) belt (or chain) drives camshaft
• camshaft lobes (called cams) push (intake and/or exhaust) valves to
open/close as the camshaft rotates
• springs return valves to closed position
• Valve (open/close) timings can be
• fixed (conventional)
• variable, to optimize ICE operation
https://xorl.wordpress.com/2011/03/27/valve-timing-and-variable-valve-timing/

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Camshaft and valve actuation
• The most common camshaft arrangements are:
• OHV (Over-Head Valve) – left
• SOHC (Single Over-Head Cam) – middle
• DOHC (Double Over-Head Cam) – right
http://www.samarins.com/glossary/dohc.html

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ICE types according to ignition principle
• The ignition of the fuel mixture is either
• natural/gradual (Diesel)
• requires high pressure&temp.  Compression Ignition (CI)
• Homogeneous Charge technology (HCCI) requires lower
temperatures and results in lower NOx emissions
• forced/artificial (gasoline, LPG, alcohol, natural gas, hydrogen)
• requires an ignition system  Spark Ignition (SI)
http://www.ni.com/white-paper/13516/en/

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ICE phases versus piston movements
• The four phases of the ICE cycle can be performed in 2
or 4 piston movements
• 2 stroke engines
• 2 phases per piston movement
• 4-stroke engines
• 1 phase per piston movement

SistemasAutomóveis
• Phases
• Admission (Intake)
• Compression
• Power (Expansion)
• Exhaust
4-stroke CI engine (Diesel cycle)
Rudolf Diesel (1858 - 1913)
https://www.uclm.es/profesorado/porrasysoriano/

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4-stroke CI engine
• Admission (Intake) stroke
• the piston starts moving down, from the Top
Dead Center (TDC) downwards
• the intake valve opens (forced by the
camshaft), letting fresh air enter the
combustion chamber
• the piston moves down and reaches the
Bottom Dead Center (BDC)
• the combustion chamber is now full of air,
ready to be compressed (next stroke)
http://beamerguide.blogspot.pt/2010/10/how-diesel-engine-work.html

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• Compression
• the intake valve closes (forced by the
camshaft)
• the piston starts moving up, from the BDC
upwards, to the TDC
• the piston moves up, compressing the air, until
reaching the TDC
• at TDC, air temperature and pressure are
maximized, enabling optimized ignition (upon
fuel injection)
4-stroke CI engine

SistemasAutomóveis
4-stroke CI engine
• Power (Expansion)
• Fuel is injected into the combustion chamber
(at very high pressure)
• air-fuel mixture inflames (ignites) and
combustion is spread all over the combustion
chamber
• combustion triggers volume expansion,
pushing the piston downwards

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• Exhaust
• at the end of expansion, once the piston hits
the BDC, the exhaust valve opens
• piston moves upwards (forced by the
mechanical inertial movement)
• the burned gases are gradually expel from the
cylinder, through the exhaust valve and pipes
4-stroke CI engine

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• 4 stroke Otto cycle
• Compression
• Ignition + Expansion
• Exhaust
4-stroke SI engine (Otto cycle)
Nicolaus Otto (1852 - 1891)

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• the piston starts moving down, from the Top
Dead Center (TDC) downwards
• the intake valve opens (forced by the intake
camshaft), letting fresh air enter the
combustion chamber
• (in Indirect Injection fuel is already mixed with air
outside the cylinder)
• the piston moves down and reaches the
bottom dead center (BDC)
• the combustion chamber is now full of air,
ready to be compressed (next stroke)
4-stroke SI engine
http://www.indycarz.com/threads/tech-basics-part-2-the-four-stroke-cycle.141585/

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• Compression
• the intake valve closes (forced by the
camshaft)
• the piston starts moving up, from the BDC
upwards, to the TDC
• (in Direct Injection, fuel is injected into
the combustion chamber during
Compression)
• the piston reaches TDC, where air
temperature and pressure are maximized,
enabling optimized combustion
4-stroke SI engine

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• Power (Ignition + Expansion)
• when the piston reaches the TDC
(actually a few miliseconds before), the
spark plug ignites the air-fuel mixture
• air-fuel mixture inflames (ignites) and
combustion is spread all over the
combustion chamber
• combustion triggers volume expansion,
pushing the piston downwards
4-stroke SI engine

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• Exhaust
• at the end of expansion, once the
piston hits the BDC, the exhaust
valve opens (forced by the exhaust
camshaft)
• piston moves upwards (forced by the
mechanical inertial movement)
• the burned gases are gradually expel
from the cylinder, through the
exhaust valve and pipes
4-stroke SI engine

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2 stroke gasoline engine
2-stroke SI engine
• 2 stroke SI cycle:
• Compression stroke
• Combustion stroke

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2-stroke SI engine
• Sparks fire
• the fuel-air-oil mixture has been fully compressed
and the spark plug fires, igniting the mixture in the
combustion chamber (red area at the top)
• the piston is driven downwards, compressing the
air-fuel-oil mixture in the crankcase (blue area at
the bottom)
• when reaching the BDC, the exhaust port is left
opened
• the pressure in the cylinder drives most of the
exhaust gases out of it

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2-stroke SI engine
• Fuel intake
• when the piston reaches the BDC, the intake port is
left opened (pipe/port on the lefthand of the
combustion chamber)
• The piston's downwards movement has pressurized
the mixture in the crankcase, so when the intake
port is opened, the air-fuel-oil mixture rushes into
the combustion chamber, expelling the remaining
exhaust gases

SistemasAutomóveis
2-stroke SI engine
• Compression Stroke
• The momentum in the crankshaft starts driving the
piston upwards (compression stroke)
• as the air-fuel-oil mixture in the piston is
compressed, vacuum is created in the crankcase;
this vacuum forces the reed valve to open and lets
the air-fuel-oil mixture enter the cylinder
• once the piston gets to the TDC, the spark plug fires
again…

SistemasAutomóveis
2-stroke CI engine
• Intake + Compression
• As the piston reaches BDC, it uncovers the air intake ports, filling the
combustion chamber of fresh air and forcing out the remaining exhaust gases
• the exhaust valves close
• the piston starts moving upwards, covering the intake ports and compressing
the air inside the combustion chamber
http://railmotorsociety.org.au/images/diesel_page_00.gif

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2-stroke CI engine
• Injection + Expansion
• when the piston gets to the TDC, the combustion chamber contains a charge
of highly compressed air.
• Diesel fuel is sprayed into the cylinder by the injector and immediately
ignites due to the heat and pressure inside the cylinder
• The pressure created by the combustion of the air-fuel mixture drives the
piston downward

SistemasAutomóveis
2-stroke CI engine
• Exhaust
• as the piston moves downwards (towards BDC),
the exhaust valves open and exhaust gases rush
out of the cylinder, relieving the pressure

SistemasAutomóveis
• 4-stroke Wankel engine:
• Intake
• Compression
• Combustion
• Exhaust
4 stroke Wankel engine
4-stroke Wankel engine
http://auto.howstuffworks.com/rotary-engine4.htm

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• Intake
• intake starts when the tip of the rotor passes the
intake port (clockwise movement)
• the intake port is exposed to the chamber, when the
volume of the chamber is close to its minimum
• as the rotor moves past the intake port, the volume
of the chamber expands, drawing air/fuel mixture
into the chamber
Intake

SistemasAutomóveis
• Compression
• as the rotor continues its motion around the
housing, the volume of the chamber gets smaller
and the air/fuel mixture gets compressed
• when it reaches the spark plugs, the volume of the
chamber is close to its minimum (maximum
compression)
• this is when sparks ignite the air-fuel mixture and
combustion starts
Compression

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• Combustion
• most rotary engines have two spark plugs; as the
combustion chamber is very long, the flame would
propagate too slowly if there was just one plug
• when the spark plugs ignite the air/fuel mixture,
pressure quickly builds, forcing the rotor to move
(clockwise)
Combustion

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• Exhaust
• once the peak of the rotor passes the exhaust port,
the high-pressure combustion gases are free to flow
out, through the exhaust port
• as the rotor continues to move (clockwise), the
chamber shrinks, forcing the remaining exhaust
gases out
Exhaust

SistemasAutomóveis
Fuel types
• ICEs can run on several types of fuels:
• Gasoline*
• Diesel*
• Liquefied petroleum gas (LPG)*
• Alcohol
• Natural gas*
• Hydrogen
• Biodiesel**
* Most common in Europe
** Commonly mixed with Diesel, in a low percentage

SistemasAutomóveis
Fuel types – gasoline vs. Diesel
• Advantages of Diesel engines:
• Higher energy efficiency  lower fuel consumption
• No spark ignition system (no spark plugs, no igniters, …)
• Longer lifetime (several hundreds of thousands km)
• Advantages of gasoline engines:
• Less acoustic noise and mechanical vibrations
• More elasticity (allows higher RPM)
• Lighter/smaller engine (less CC) for the same power
• No combustion chamber pre-heating system (no glow plugs, no
relays,…)

SistemasAutomóveis
Mixture formation
• ICEs can be distinguished according to where the air/fuel
mixture is formed
• Indirect Injection (IDI) aka external injection
• Inside the combustion chamber
• Direct Injection (DI) aka Internal Injection
• Outside the combustion chamber
• This applies to both Compression Ignition (CI) and Spark
Ignition (SI) Engines

SistemasAutomóveis
Mixture formation – CI engine
• In Compression Ignition engines
• Indirect Injection
• Injector sprays into a pre-chamber (aka swirl chamber)
• Glow-plug heats pre-chamber
• Direct Injection
• Injector sprays directly into combustion chamber
• Glow-plug heats combustion chamber
http://www.jensales.com/blog/indirect-injection-vs-
direct-injection-diesels/

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Mixture formation – SI engine
• In Spark Ignition engines
• Indirect Injection
• Injector sprays into the intake pipe (before intake valve)
• Before Throttle  Single-Point Injection – Figure a)
• After Throttle  Multi-Point Injection – Figure b)
• Direct Injection
• Injector sprays into the combustion chamber – Figure c)
http://www.intechopen.com/books/advances-in-internal-combustion-engines-and-fuel-
technologies/combustion-process-in-the-spark-ignition-engine-with-dual-injection-system

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Mixture formation
• Direct versus indirect injection
Direct Injection Indirect Injection
Losses Lower thermal losses
High thermal losses
(between chambers)
Performance Higher Lower
Speed Lower engine speed Higher engine speed
Fuel type
Demands higher quality
fuels
Works with lower quality
fuels
Injection
Multi-jet
(higher injection pressure)
Single-jet
(lower injection pressures)
Efficiency
More efficient
(lower fuel consumption)
Less efficient
(higher fuel consumption)
Emissions Less pollutant More Pollutant

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Cylinders configuration
• ICEs can be classified by their cylinders configuration
In-line V-shape
W-shape Radial
Opposed Horizontal
Wankel
http://auto.howstuffworks.com/

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• In-line configuration
• most used, simple and inexpensive
• single engine block where cylinders are aligned
• main disadvantage (against other configurations) is requiring a
longer crankshaft

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• V-shape configuration
• cylinders are disposed in two blocks, in a V shape
• the two blocks share a common crankshaft
• main advantage is having a shorter crankshaft for the same
number of cylinders (comparing to the in-line configuration)
• most used when the number of cylinders is ≥ 6

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• W-shape configuration
• similar to V-shape but has 3 blocks of cylinders
• This allows to have more cylinders with the same space
(comparing to other configurations), i.e. shorter crankshaft
• mostly used for 12-cylinder engines

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• Opposed-Horizontal configuration (aka boxer or flat)
• more balanced, because the movement of one piston is
compensated by the movement of the other moving in the
opposite direction
• allows a lower center of gravity for, improving driveability
• pistons movement is not affected by gravity (like in other
configurations)

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• Radial configuration
• pistons arranged in circle (around the crankshaft)
• typically 3-9 cylinders
• mostly used in airplanes

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• Wankel configuration
• Piston rotates (instead of linear movement, as in traditional
ICEs)
• Rarely used, due to inherent technical limitations (e.g. cooling,
lubricating)

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Cylinders volume vs number
• Two approaches (for the same volume – CC):
• More cylinders of smaller capacity
• Less cylinders of larger capacity
• Pros of having more cylinders
• Better thermal efficiency
• Larger specific power (relation between the engine capacity and
power) augmenting the engine´s maximum regime
• Greater uniformity of engine torque
• Better balance of mass in motion, which results in lower engine
vibrations
• Cons of having more cylinders
• Larger crankshaft length, resulting in torsional vibration problems
• Increase in engine volume and weight
• Decrease in mechanical efficiency and thus in engine power

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Cooling System
• Objectives
• Guarantee a suitable engine operating temperature
• cooling it down (after reaching a stationary regime)
• helping to warm it up (keep fluid inside engine, while cold)
• keep the physical and chemical proprieties of the lubricating oil
• can deteriorate upon overheating
• supply heat to acclimatize the interior of the vehicle
• Facts
• Most of the heat is dissipated through the exhaust
• leading to wasted energy, thus low energy efficiency
• Some heat is dissipated via lubricating oil (and oil cooler)
• fixed engine parts (e.g. block, head) are cooled by the main
cooling system
• moving parts (e.g. pistons, crankshaft, rods) are mostly cooled
by the lubricating oil

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Cooling System
• Liquid-cooled engine
• dedicated cooling circuit (pump, thermostat, radiator, fan,…)
https://tyeschenbach.files.wordpress.com/2013/06/cooling.jpg

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Cooling System
• Air-cooled engine
• air circulates over hot parts; extended cylinders radiation area
http://www.vdubxs.com/vintage-speed-vw-split-screen-rear-end-
transformation/air_cooled_engine/#sthash.k3hPi7nw.dpbs

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Lubricating System
• Objective
• Mitigate friction and overheating of moving parts
http://www.britannica.com/technology/lubrication

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Glossary (English  Portuguese)

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Bibliography
[1] Ricardo Marques (1030379), André Soares (1021069), class project under the
SIAUT course, ISEP, 2011.

Automotive Systems course (Module 01) - Internal Combustion Engine (ICE) basics

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