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Combustion engines and fuel technology

Friday 10.04.10

Team Manager Marie BysveenSINTEF Energi AS

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Piston engines

Internal combustion engine where the fuel is combusted in a cylinder and acts on a piston

The engine is driven by the fact that hot fuel (typically gasoline or diesel) is ignited, combusts within the cylinder and acts on the piston

Jet engines, most of the rocket engines and many turbines are denoted as combustion engines, but this denotion is most commonly used on gasoline and diesel engines

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History

The basis for the internal combustion engine and the theory for the two-stroke engine

Sadi Carnot, France in 1824

The american Samuel Morey patented April 1st 1826 a «Gas Or Vapor Engine».

The italians Eugenio Barsanti and Felice Matteucci

Patented the first efficient internal combustion engine in London i 1854

Jean Joseph Etienne Lenoir produced in 1860 a gasdriven combustion engine, not very different from the first steam engine by James Watts

Nikolaus Otto, who worked together with Gottlieb Daimler and Wilhelm Maybach in the 1870-årene, developed the first four-stroke engine, the so-called Otto-engine

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Use of internal combustion engines

Most commonly used in vehicles and other mobile machineries

Advantage

High power-to-weight ratio

These engines are practically used in all cars, motorcycles, boats, airplanes and locomotives

Where there is a demand for very large engines, such as in jet aircrafts and helicopters – jet engines are used instead

In very larges ships and stationary and mobile power staions – gas turbines are used

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Classification

Different ICEs exists for different use

Classified using different criteria, the most important ones being;

Two/ four stroke

Spark ignition/ compression ignition

In Norwegian we use the term «motor» both on ICEs and «electrical” engine

This may be confusing

The word «engine» (from Latin, via Old French, «ability») meant a piece of machinery

A «motor» (from Latin «motor», «movement») is a machine/engine producing power

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Number of cylinders

Between 1-12 are most common

Advantages with several cylinders in one engine

The engine may have larger volume with less reciprocating masses (meaning that the mass of each piston may be smaller), and thereby a smoother running of the engine

More cylinders/Larger engines means that more fuel may be combusted, and more power strokes per time than for engoine with less cylinders

Disadvantage with more cylinders

Higher total weight

More friction – and thereby lower efficiency

Most car engines have 4-8 cylinders

Some high-efficiency engines have 10, 12 or even 16

Some small cars and large trucks have 2 or 3

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Engine configuration

The ICE may also be classified according to its configuration

Sffects the physical size and smoother running/vibration

The most common configurations

In-line ngine (rekkemotor)

V-engine

Flat or boxer configuration

Airplane engines may also have radial configuration

Less common

"H", "U", "X", "W"

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Engine capacity

The engine capacity may be described by

Displaced or swept volume

Is normally measured in litre or cc

Engines with larger capacity

Normally more power

Larger momentum at low rotational speed

Is less fuel efficient

In addition to increasing the engine volume, there are several ways to increase the capacity of the engine:

Increase the stroke of the piston

Increase the diameter of the piston

In both cases it is important to do optimisation adjustments in order to have the best performance

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Two stroke engines

Two stroke cycle

Two stroke – one up and one down - for every power stroke

Depends on the movement in the piston bottom in the crankcase to move the fuel-air mixture

Used where small size and weight is important

Such as mopeds, outboard boat engines

Gasoline two stroke engines are normally

More noisy

Less efficient

Pollutes more

Smaller than four stroke

Large two stroke diesel engines

Do not have these problems

Used in many applications

Ex locomotives, ship engines

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Four stroke engines

Four stroke engines have one

power stroke every fourth stroke (up-down-up-down)

Used in cars, boats, light airplanes

In general less noisy and more efficient

Many variants of these cycles

Most known are the Atkinson and Miller cycles.

The Wankel engine operates with the same division of the phases as in a four stroke engine

No piston stroke

Named four-phase engine

The phases ocuur at different places in the engine

But – as for the two-stroke engine it gives onepower-stroke per rotor, giving the same spaceand weight advantage Wankel engine

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Gasoline versus diesel engines

Diesel engines generally

Heavier and more noisy than gasoline engines

More power at lower rotational speed (rpms) than gasoline engines

Diesel engines are more fuel efficient

Heavier vehicles, cars

Ships, locomotoes, some airplanes

Emissions is a problem from both gasoline and diesel engines

But different problems, fex particulate emissions (PM) and NOx

Alternative fuels

Natural gas (LPG, LNG, CNG)

Ethanol, methanol

Biodiesel

Hydrogen

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Types of gasoline engines

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Bensin, Diesel and HCCI

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HCCI

Has characteristics of the two most popular forms of combustion used in IC engines

Homogeneous charge spark ignition (gasoline engines)

Stratified charge compression ignition (diesel engines)

As in homogeneous charge spark ignition, the fuel and oxidizer are mixed together

Rather than using an electric discharge to ignite a portion of the mixture, the density and temperature of the mixture are raised by compression until the entire mixture reacts spontaneously

Stratified charge compression ignition also relies on temperature and density increase resulting from compression, but combustion occurs at the boundary of fuel-air mixing, caused by an injection event, to initiate combustion.

Much less NOx

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Engine components

The components in an engine varies depending on the engine type

For a four stroke engine this includes

Crankshaft (veivaksel)

One or more camshafts (kamaksel), valves and valve stem (ventilstang)

Both two stroke and four stroke may have

One or several cylinders, and for every cylinder a spark plug (for gasoline), injection nozzles (for diesel) and a piston

One revolution of the crankshaft, moving the piston up and down is called a stroke (takt)

When the piston is in its upper position, after the induction of the fuel (for gasoline), this is ignited by the spark

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Example - gasoline engine

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The crankshaft

The crankshaft in an ICE is found under trhe cylinder and is coupled to the pistons by connecting rods (råder)

When the pistons goes up and down, the crankshaft rotates

The crankshaft of most engines is for most engines coupled to the gear box via a clutch, and has belt pulley (reimhjul) at the other end driving the camshaft, water pump, the dynamo, fan, aircondition, comprtessor etc.

The crankshaft moves around within slide bearings (glidelagere), and depends on continous lubrication

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The camshaft

Opens and closes the valves in the engine

In order to take in air/gasoline and expell the exhaust

Normally connected to the crankshaft with a registerreim

Traditionally in a 4-stroke engine

One intake valve and one exhaust valve per cylinder

In modern engines several valves are getting more and more common

A 16V engine has an engine with two camshafts – one for the intake valves and one for the exhaust valves

For the engine to breath more easily

The valves open at the same time – the reason for double camshafts is the lackj of space for all the valve-pushers on one single

May see the camshaft by removing the top cover of the engine

The profile of the camshaft is important for the performance of the engine at high rpms

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Gasoline engine lubrication system

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Ignition of air-fuel mixture

All ICEs needs means to ignite the air-fuel charge to initiate the combustion process

Mots engines have either

Elecetrical ignition (normally gasoline engines using spark plugs) or

Compression ignition (as in diesel engines)

Electrical ignition systems

Lead battery and an induction coil delivering an electrical charge with exetremely high voltage ignition to the air-fuel charge within the engine cylinder

The battery is being recharged by the dynamo powered by the engine

Compression ignition

Diesel engines and in novel HCCI engines

Heat is produced by compressing the gasmixture within the cylinder

Fuel is then injected

When the T is high enough, the mixture self-ignites

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The combustion process - Diesel

Figur s. 5.57 (Almås) – Forstørr !

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Exhaust gas scavenging

When the available energy has been used, the hot exhaust is expelled out of the cylinder

Normally by opening a valve

The piston may then og back to its original position (Top Dead Center - TDC)

The piston may then continue to its next phase in the cycle

The heat not transferred to useful work

Waste

Removed from the engine - either by air- or water-cooling

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Pollution in short

CO – Because of incomplete combustion

NOx -Mostly because of high combustion T

Sulphur oxides – If sulphur in the fuel – Acid rain

PM – Particulate matter (Especially from diesel engines)

UHC – Unburnt hydrocarbons

Depends on

Operation of the engine

Air/fuel ratio

Type of fuel

Etc

Aftertreatment equipment

Three-way catalys

Particulate filter

Water, EGR, SCR

ETc.

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Power and mean effective pressure

Mean effective pressure (MEP)

Intensity of work generated in the cylinder

This parameter is suited for comparison of different engines of different size and type

pme =We /Vh

We = The efficient work of the engine

Vh = Total cylinder volume of the engine

Mean efficient power; Pe =i*pme *Vh *na

i= Number of cylinders

na = Rotational speed (twostroke: na =n, four stroke: na =n/2)

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Fuel consumption

Fuel mass per energy unit on the crank shaft: g/kWh

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Gasoline fuel

Gasoline consists of hydrocarbons with 4-12 C atoms

The density is typically 0,74 kg/l.

Gasoline comnpounds are typically complex hydrocarbons

Aromatics

Branched hydrocarbons

To resist self-ignition

The octane number

The ability of the gasoline to withstand self-ignition

In order for the gasoline to have needed characteristica – a additive package is needed containing different chemicals

This may typically include oxygen containing chemicals added to the gasoline to increase the octane number

This may be methanol, ethanol, MTBE (methyl tertier buthyl ether)

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Diesel fuel

The diesel fraction has a boiling point between 250°C and approx 350°C.

Diesel is generally easier and cheaper to produce than gasoline

Diesel fuel compounds are typically parafinnic compounds

Easy to self ignite by compression

Diesel has a density of about 0,84 kg/l

Heavier than gasoline because of higher C/H ratio

The ignition properties of diesel is measured in cetane number

A measure of the easiness of the diesel to

self-ignite

Poorer perfomance in cold weather

Needs additives to counteract this

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Fuel types

Gasoline needs proper treatment in a complex refinery to meet the gasoline standards

There are engiens running on fex hydrogen, metanol, etanol, LPG, LNG and biodiesel

1. gen biodiesel is an alternative for diesel engines

Replaces the glycerol in the fat with methanol

The fat may be from plants or from animals, fish etc.

Raps and rybs plants are widely used as cheap fat

Biodiesel is non-fossile

Good lubricant characteristics, aresometimes blended with the fossile diesel to improce lubrcation properties

Leess sooty than fossile fuels

Fuel-for food issue

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Modern diesel engines

Diesel

Earlier: Mechanical injection system

Now: Electronic control of the diesel injection, such as ”Common Rail”, see below. This is HUGE change, and has reduced the noise problem and emissions problem from diesel engines significantly.

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Four examples of publications from my fuel rechnology research

1

2

3

4

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