Internal combustion engine and hybrid powertrains

Internal combustion engines & hybrid powertrains

Università della Calabria Dipartimento di Ing. Meccanica, Energetica e Gestionale

Course notes of Internal combustion engines & hybrid powertrains

Piofrancesco Barone

Theory lessons: Mr Sergio Bova Ingegneria Energetica

Exercises: Ing. Diego Perrone A.A. 2020/2021

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5th October 2020 (Mr Bova)

Lunedì 5 ottobre 2020 11:30

Prof. Sergio Bova

Office: Cube 44C, 5th floor

Telephone: 0984494828

Email: sergio.bova@unical.i

Contents and course organization

The course provides students with (=fornisce agli studenti) the tools to evaluate the influence of properties of working fluids, of mass exchange and combustion processes, of heat (=calore) and friction (=attrito) losses on power, efficiency and emissions of Internal Combustion Engines.

The operating characteristics of different types of internal combustion engines (=motori a combustione interna) (spark ignition (=accensione per scintilla), Diesel, GDI (=gasoline direct injection), 2 or 4 stroke) will be described in detail and critically compared. The different architectures, functions, operating modes and sizing criteria (=criteri di dimensionamento) of the hybrid propulsion systems will be also described.

Numerical simulations and laboratory experience will complete the learning experience.

We will talk about internal combustion engines from a thermodynamic and fluidodynamic point of view (not from the material resistance one). Gasoline engine = motori a benzina.

Exams

Only oral exam. We will be asked to make a report of some calculations we will do in the classroom. At the beginning of the exam, there will be a discussion about the report, then the real exam starts.

Textbooks and further references

J.B. Haywood, “Internal Combustion Engine Fundamentals”, Second Edition, Mc Graw-Hill, New-York, 2018.

Copies of the slides used during the lectures are available at: http://icampus.dimeg.unical.it

• Further textbook (in Italian): Giancarlo Ferrari, “Motori a Combustione Interna”, Ed. E sculaccio, Bologna, 2016

Introduction to the internal combustion engines

“Engine” means that our machine keeps (=genera) chemical energy and provides (=fornisce) mechanical work. Sono macchine motrici (o generatrici).

“Internal combustion” means that the combustion takes place into the fluid. So the fluid which goes into the machine is the same that burns.

The differences with external combustion are in the place where combustion occurs (such as in a steam plant (=impianto a vapore)).

Of course, from this definition, also the gas turbine are internal combustion engines, but the convention is that if we talk about “internal combustion engines”, we mean those we can use in cars and other vehicles.

Actually, these engines can be volumetric or dynamic, but we don’t say “volumetric”.

Reciprocating engines are characterized by a piston that goes up and down.

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Hysterical prospective: three main topics

1. Engine

Important dates:

• 1854: Barsanti – Matteucci patent (=brevetto). È stato il primo brevetto di motore.
• 1861: Otto-Langen Atmospheric Engine
• 1876: Otto 4-Stroke Engine
• 1892: Diesel patent

Where was the engine invented? This is not commonly accepted by the different experts in the world.

Nowadays we are moving towards electrical cars (or hybrid ones). As a comparison, the important dates of the electrical machine are:

• 1799: Alessandro Volta invented the electrochemical battery
• 1821: Michael Faraday creates two experiments of electromagnetic rotation
• 1832: William Sturgeon invented the first commutator DC electric motor
• 1864: Antonio Pacinotti first described the ring armature

From these dates we can understand that the electrical machines are a little bit older than ICE. In fact, when the Otto and Diesel engine were born, the electrical machines were already developed.

First developments of ‘atmospheric’ internal combustion engines.

The Barsanti – Matteucci engine (1854), draft (=schizzo) to the left, and the Otto-Langen (1861) engine, to the right.

Operating principles (=principi operativi): in the chamber, some mixture of air and fuel is introduced at atmospheric pressure. Then a spark is given to fuel to fire the mixture. The increase of pressure pushes up the piston. When the piston comes again down, we have the connection with the wheel (=ruota) and some work. La corsa di potenza meccanica è data dalla discesa del pistone. The weight, approximately, was 4000 lb (= circa 2000 kg, si divide per 2,205); the power was very low: only 2 horsepower.

Fifteen years later, Otto had the idea to compress the mixture of air and fuel before the combustion: that marked the birth of 4-stroke engine.

The weight was about 1250 lb (=570 kg), for a power of 2 horsepower. In that case, the overall efficiency is a little bit higher than the Otto-Langen engine (14% vs 11%).

Internal combustion engine vs electric vehicles

At the end of two centuries ago, they were both available in the world. What was the hurdle of ICE?

First of all, the start-up engine (=avviamento del motore): it was necessary to crank (=avviare con una manovella) the engine with the arm until it starts. It was also difficult to change the gear (=marcia). The distance that a car could travels was very small (about 5-10 km).

So, at the end of the 18th century, the electric car was more developed than the ICE-ones. Cranking wheel = ruota di bloccaggio.

In 1911 there was a new invention: an electric motor (electrical starter) to start an ICE, introduced by Cadillac. That was the key to develop ICE: from that moment, the cars with ICE were more sold (in a much bigger number) than the electric ones.

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2. Fuels

Important dates:

• 1860-1913: Gas and lighter fraction of crude (=grezzo) oil (=petrolio)
• 1913: Thermal cracking
• 1923: Tetraethyl lead (piombo tetraetilico)
• Late ‘30: activated catalyst
• ‘70: first energy crisis ....

One of the problems at the very beginning was that when in the first project the mixture was compressed, it auto-ignited.

It was not possible to compress so much the mixture: otherwise, we had an auto-uncontrolled combustion.

Prima della scintilla, la miscela andava incontro ad autocombustione, e ciò non faceva lavorare bene i motori.

The tetraethyl lead (=piombo tetraetile) combined with gasoline solved the problem, but this substance is toxic, so it isn’t good to use it. This tetraethyl lead was not used anymore.

The price goes up when a war is in course.

Il petrolio oggi costa pochissimo: alcuni giacimenti non vengono sfruttati perché non è conveniente.

3. Exhaust emissions

Important dates:

• 1940: air-pollution problem became apparent in L.A. basin
• ‘60: emission standards introduced in California and USA nationwide
• ‘70: first emission standards in EU
• ‘91: Euro1 .... Sett 2018 Euro 6d
• 2015: limit of 130 gCO2/km ... 2020: limit of 95 gCO2/km

When pollution was “discovered”, an high number of limitations on engine emissions were introduced. The word “smog” is the connection between “smoke” and “fog”. The smog was produced by the ICE.

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Gli Nox sono dei composti gassosi, che si formano con l’azoto ogni volta che l’aria viene riscaldata al di sopra dei 1400°C.

Non sono un inquinante. Se combinati con la benzina producono ozono, che è un inquinante secondario.

Tutte le emissioni, per legge, devono diminuire.

But this is still not today the main problem: we also have to reduce CO2. CO2 is not a pollutant (=agente inquinante): it isn’t toxic.

CO2 is dangerous for the climate’s health.

Today in Europe the limit of CO2 is about 95 gCO2/km. If we buy a car with a lower Co2 emission, we will that car a little bit less.

Today, much of the cars have Diesel or gasoline engine. The electrical and hybrid cars are in lower number. This number will increase through the years, and the prevision is that in 2030 the cars will be electric for 30%. The remaining 70% will be a mix of hybrid and gasoline or Diesel engine. For this reason, studying ICE is important also for the new future car that will be developed: also is an hybrid vehicle there is an internal combustion engine.

Gli inquinanti sono quelle sostanze davvero dannose per l’uomo, che possono portare anche alla morte se inalate per troppo tempo.

La CO2 non dipende dalle emissioni tossiche, ma solo dal consumo.

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Internal combustion engines

We can use many different classifications for ICE, but the most useful and fundamental one is to divide the engines between spark-ignition engines (SI) (=motori ad accensione comandata o accensione per scintilla) and compression-ignition engines (CI) (=motori ad accensione per compressione o diesel). Both of these two families can operate with a four-stroke operating cycle or a two-stroke operating cycle. We will talk about reciprocating engines (with a piston that goes up and down cyclically).

Four-stroke operating cycle

The piston moves into the cylinder from an upper position, which we called top center (=punto morto superiore), to a lower position, which we called bottom center (=punto morto inferiore), cyclically.

In the first stroke, the piston moves from TC to BC. During this stroke, the inlet valve is open: the gas is induced by the outside into the cylinder. This gas can be only air or a mixture of air and fuel. We have described the intake stroke.

Then we have the compression stroke: the valve is closed. The piston comes up and compresses the gas.

If we have a spark-ignition engine, we will have a spark plug (=candela d’accensione) that ignites the compressed mixture a little bit before the end of the compression stroke.

If the ICE is a Diesel one, we will have an injector that injects Diesel fuel (=gasolio) into the compressed air, which has an high temperature. The Diesel fuel will burn automatically =. After gas combustion, we have the expansion stroke: the high pressure pushes the piston down. This is the only stroke where we have an active power given from the engine to the crankshaft (=albero motore).

In the fourth and “last” stroke, the piston goes up again while the exhaust valve is open: the exhausted gasses are forced to live the cylinder.

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Two-stroke operating cycle

Compression and expansion strokes are the same of the four-stroke operating cycle ones.

The difference between the two operating cycles is in the gas exchange.

At the end of the expansion stroke, the piston opens first an exhaust port (=luce).

After a little bit, the piston goes down and opens the transfer port, through which the fresh charge can pass. In order to make this fresh charge entering into the cylinder, it must be slightly compressed. There are also big two-stroke operating cycle-engines with exhaust valves and inlet ports.

Crankcase (=carter) scavenged engine (=motore da motocicletta)

Engine components

Engine applications

If we want much power, we have to use more cylinder.

• Transportation (Car, Truck, Marine, Rail ...) Compression rings (=anelli di tenuta o fasce elastiche)
• Military avoid the loss of the gasses from the combustion
• Stationary power generation chamber to the crankcase. The piston is connected
• Service appliances with the crankshaft through the connecting rod (=Biella).

Dimensions: 1 cm ÷ 1 m

Power: 10 W ÷ 10 MW

The piston moves up and down and so the crankshaft rotates. In the upper part of the engine there is the engine head (=testata), that has the valves which control the flow of the fluid inside and outside the cylinder.

Then, the device to control these valves is a camshaft (=albero a camme).

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Diesel engine

Each cylinder is made as a single piece of metal. Intake = immissione

The most efficient cylinder dimension is about half a liter.

Arrangement of cylinders

Radial engine

V

Two in line cylinders with the two heads that make an angle of 72° or 90°.

If this angle is equal to 180°, we have two special cases:

• Boxer engine
• Opposed-piston engine

Opposed-piston engine (=motore ad accensione comandata: due motori a due tempi messi assieme, eliminando le testate)

In line

The axis of these cylinders are parallel and they stay on the same plane

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6th October 2020 (Mr Bova)

Martedì 6 ottobre 2020 14:30

Spark-ignition engine

Spark-ignition engine operation

Air and Fuel are pre-mixed at the time of ignition, when the combustion starts. In some engines, air and fuel are already premixed during the intake; in direct injection engines, during intake we have only air and we have the fuel injected during the final stage of intake or initial stage of compression. Anyway, fuel and air are already premixed in SI engines at the top center (=when the combustion starts or is going to start).

A/F≈15: mass air-fuel ratio. This air fuel ratio, for the commonly used fuels (gasoline or diesel fuel), is about 15. In every working condition, we have this value for the air/fuel ratio.

How do we control the torque we want from the engine (=the output of the engine)? (=push acceleration pedal a little bit or more; if we push up to the end, we have full load operation; if we only push a little bit the acceleration pedal, we have part load operation).

The Engine output (load = carico) is controlled by means of a throttling valve (valvola a farfalla o valvola di strozzamento) or Variable Valve Timing

We control the amount of mixture which enters into the cylinders.

If we run full output, for example, we let enter 1 g of mixture. If we want only 10% of the all, we will let enter 0.1 g of the mixture, at the same air fuel ratio.

Se noi vogliamo tutta la potenza del motore, schiacciamo l’acceleratore fino in fondo (=in condizioni di salita, sorpasso ecc). Volendo poca potenza, alzeremo quanto basta il pedale dell’acceleratore. All’interno del motore c’è una valvola di strozzamento che si chiude parzialmente se alziamo il pedale dell’acceleratore: in questa maniera entra meno carica (=meno gas o meno massa) altrimenti è completamente aperta quando il pedale è pienamente schiacciato. Tutto ciò vale a parità di rapporto aria combustibile. Il motore ad accensione comandata funziona sempre a rapporto aria combustibile stechiometrico o circa stechiometrico, che per benzina e gasolio è circa 15.

We said that both SI and CI engines can work with a 2-stroke or a 4-stroke cycle. Actually, in the spark ignition engine, 2-stroke is only used for very small engines.

Recently all the new engines are down-sized (=smaller) and turbocharged (subturbocharged or supercharged).

As an example: fifteen years ago, medium cars had 2 liters engine with 100kW power. Today we obtain the same power of those big engines but with smaller engines (1.3 liters). But, In order to get the same power, we must compressed the mixture before the intake, so we use a turbocharged engine.

How can an engine achieve this stoichiometric mixture? Historically (up to 1990, when Euro1 was born) we had the carburator:

The carburator is a Venturi (= particolare condotto). In the throat of the venturi we have an increase of the velocity and a decrease of the pressure. Il carburatore ha all’interno una gola di venturi.

In corrispondenza della stessa, la velocità aumenta e la pressione scende.

As the pressure decreases, some gasoline will be sucked from a very little tank. It’s not the car tank, it’s smaller. Then the gasoline mixes with the air.

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Today, we don’t use the carburator anymore, because it’s not very adapt to control the air fuel ratio very precisely. Today, in order to control the exhaust emission, we must control very precisely the air fuel ratio.

Per controllare le emissioni oggi si usa la marmitta catalitica. Quest’ultima richiede una miscela rigorosamente stechiometrica.

In order to obtain a stoichiometric mixture, we must work under closed loop conditions.

The carburator is a mechanical device: the technique moved toward an electronic-injector.

If we control the time the current flows into the winding (avvolgimento, bobina), we control the quantity of fuel which exits from these injector.

Per il carburatore, aprendo la valvola, entra più aria e aumenta quindi la velocità perché aumenta la portata.

Aumentando la velocità diminuisce la pressione e quindi succhia più combustibile. Aumenta l’aria, aumenta il combustibile, e di conseguenza il rapporto aria combustibile si mantiene costante ma non così costante come nel sistema moderno (con la marmitta catalitica) richiede.

Today we have mainly 3 different injection systems.

The first one was the carburator. The second one is the injector, placed just behind the intake valve.

The newer system is the direct injection system: the injector is not outside the cylinder, but inside, like a Diesel engine, but the pressure is completely different from a Diesel engine.

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Let’s see what happens within the cylinder. The internal combustion engine is a volumetric machine, so we want to know the volume and the pressure, in order to get the pressure volume diagram.

Per le macchine volumetriche servono il volume e la pressione, cosicché possiamo calcolare il lavoro (integrale di pdV)

Il motore a combustione interna è un motore alternativo.

The first thing we have to observe is that in the abscissa we don’t have the time, but the crank position and angle. In ascisse non abbiamo il tempo, ma l’angolo di manovella. The volume has a shape which is almost a sinusoidal function. The volume has the minimum value at the top center (when the piston is up) and the maximum value at bottom center (when the piston is down).

Let’s analyze the pressure within the cylinder graph:

During the intake, when the piston comes down, the intake valve is open, so the pressure within the cylinder is the atmospheric pressure, if the throttling valve is completely open. If the thr