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1999 | Buch | 3. Auflage

Introduction to Internal Combustion Engines

verfasst von: Richard Stone

Verlag: Macmillan Education UK

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SUCHEN

Inhaltsverzeichnis

Frontmatter
Chapter 1. Introduction
Abstract
The reciprocating internal combustion engine must be by far the most common form of engine or prime mover. As with most engines, the usual aim is to achieve a high work output with a high efficiency; the means to these ends are developed throughout this book. The term ‘internal combustion engine’ should also include open circuit gas turbine plant where fuel is burnt in a combustion chamber. However, it is normal practice to omit the prefix ‘reciprocating’; none the less this is the key principle that applies to both engines of different types and those utilising different operating principles. The divisions between engine types and between operating principles can be explained more clearly if stratified charge and Wankel-type engines are ignored initially; hence these are not discussed until section 1.4.
Richard Stone
Chapter 2. Thermodynamic principles
Abstract
This chapter provides criteria by which to judge the performance of internal combustion engines. Most important are the thermodynamic cycles based on ideal gases undergoing ideal processes. However, internal combustion engines follow a mechanical cycle, not a thermodynamic cycle. The start and end points are mechanically the same in the cycle for an internal combustion engine, whether it is a two-stroke or four-stroke mechanical cycle.
Richard Stone
Chapter 3. Combustion and fuels
Abstract
The fundamental difference between spark ignition (SI) and compression ignition (CI) engines lies in the type of combustion that occurs, and not in whether the process is idealised as an Otto cycle or a Diesel cycle. The combustion process occurs at neither constant volume (Otto cycle), nor constant pressure (Diesel cycle). The difference between the two combustion processes is that spark ignition engines usually have pre-mixed flames while compression ignition engines have diffusion flames. With pre-mixed combustion the fuel/air mixture must always be close to stoichiometric (chemically correct) for reliable ignition and combustion. To control the power output a spark ignition engine is throttled, thus reducing the mass of fuel and air in the combustion chamber; this reduces the cycle efficiency. In contrast, for compression ignition engines with fuel injection the mixture is close to stoichiometric only at the flame front. The output of compression ignition engines can thus be varied by controlling the amount of fuel injected; this accounts for their superior part load fuel economy.
Richard Stone
Chapter 4. Spark ignition engines
Abstract
This chapter considers how the combustion process is initiated and constrained in spark ignition engines. The air/fuel mixture has to be close to stoichiometric (chemically correct) for satisfactory spark ignition and flame propagation. The equivalence ratio or mixture strength of the air/fuel mixture also affects pollutant emissions, as discussed in chapter 3, and influences the susceptibility to spontaneous self-ignition (which can lead to knock). A lean air/fuel mixture (equivalence ratio less than unity) will burn more slowly and will have a lower maximum temperature than a less lean mixture. Slower combustion will lead to lower peak pressures, and both this and the lower peak temperature will reduce the tendency for knock to occur. The air/fuel mixture also affects the engine efficiency and power output. At constant engine speed with fixed throttle, it can be seen how the brake specific fuel consumption (inverse of efficiency) and power output vary. This is shown in figure 4.1 for a typical spark ignition engine at full or wide open throttle (WOT). As this is a constant-speed test, power output is proportional to torque output, and this is most conveniently expressed as bmep, since bmep is independent of engine size. Figure 4.2 is an alternative way of expressing the same data (because of their shape, the plots are often referred to as ‘fish-hook’ curves); additional part throttle data have also been included. At full throttle, the maximum for power output is fairly flat, so beyond a certain point a richer mixture significantly reduces efficiency without substantially increasing power output.
Richard Stone
Chapter 5. Compression ignition engines
Abstract
Satisfactory operation of compression ignition engines depends on proper control of the air motion and fuel injection. The ideal combustion system should have a high output (bmep), high efficiency, rapid combustion, a clean exhaust and be silent. To some extent these are conflicting requirements; for instance, engine output is directly limited by smoke levels. There are two main classes of combustion chamber: those with direct injection (DI) into the main chamber, (figure 5.1) and those with indirect injection (ID) into some form of divided chamber (figure 5.5). The fuel injection system cannot be designed in isolation since satisfactory combustion depends on adequate mixing of the fuel and air. Direct injection engines have inherently less air motion than indirect injection engines and, to compensate, high injection pressures (up to 1500 bar and higher) are used with multiple-hole nozzles. Even so, the speed range is more restricted than for indirect injection engines. Injection requirements for indirect injection engines are less demanding; single-hole injectors with pressures of about 300 bar can be used.
Richard Stone
Chapter 6. Induction and exhaust processes
Abstract
In reciprocating internal combustion engines the induction and exhaust processes are non-steady flow processes. For purposes such as some combustion modelling, the flows can be assumed to be steady. However, there are many cases for which the flow has to be treated as non-steady, and it is necessary to understand the properties of pulsed flows and how these can interact.
Richard Stone
Chapter 7. Two-stroke engines
Abstract
The absence of the separate induction and exhaust strokes in the two-stroke engine is the fundamental difference from four-stroke engines. In two-stroke engines, the gas exchange or scavenging process can have the induction and exhaust processes occurring simultaneously. Consequently, the gas exchange processes in two-stroke engines are much more complex than in four-stroke engines, and the gas exchange process is probably the most important factor controlling the efficiency and performance of two-stroke engines.
Richard Stone
Chapter 8. In-cylinder motion and turbulent combustion
Abstract
The induction of air or an air/fuel mixture into the engine cylinder leads to a complex fluid motion. There can be an ordered air motion such as swirl, but always present is turbulence. The bulk air motion which approximates to a forced vortex about the cylinder axis is known as axial swirl, and it is normally associated with direct injection diesel engines. When the air motion rotates about an axis normal to the cylinder axis (this is usually parallel to the cylinder axis), the motion is known as barrel swirl or tumble. Such a motion can be found in spark ignition engines (normally those with two inlet valves per cylinder). Barrel swirl assists the rapid and complete combustion of highly diluted mixtures, for instance those found in lean-burn engines, or engines operating with stoichiometric mixtures but high levels of exhaust gas recirculation (EGR).
Richard Stone
Chapter 9. Turbocharging
Abstract
Turbocharging is a particular form of supercharging in which a compressor is driven by an exhaust gas turbine. The concept of supercharging, supplying pressurised air to an engine, dates back to the beginning of the century. By pressurising the air at inlet to the engine the mass flow rate of air increases, and there can be a corresponding increase in the fuel flow rate. This leads to an increase in power output and usually an improvement in efficiency since mechanical losses in the engine are not solely dependent on the power output. Whether or not there is an improvement in efficiency ultimately depends on the efficiency and matching of the turbocharger or supercharger. Turbocharging does not necessarily have a significant effect on exhaust emissions.
Richard Stone
Chapter 10. Engine modelling
Abstract
The aim with modelling internal combustion engines is twofold:
1
To predict engine performance without having to conduct tests.
 
2
To deduce the performance of parameters that can be difficult to measure in tests, for example, the trapped mass of air in a two-stroke engine or a turbocharged engine.
 
Richard Stone
Chapter 11. Mechanical design considerations
Abstract
Once the type and size of engine have been determined, the number and disposition of the cylinders have to be decided. Very often the decision will be influenced by marketing and packaging considerations, as well as whether or not the engine needs to be manufactured with existing machinery.
Richard Stone
Chapter 12. Heat transfer in internal combustion engines
Abstract
There are two aspects to heat transfer within internal combustion engines. Firstly there is heat transfer from within the combustion chamber to its boundaries (discussed in chapter 10, section 10.2.4), and secondly there is heat transfer from the combustion chamber to its cooling media — this aspect is discussed here.
Richard Stone
Chapter 13. Experimental facilities
Abstract
The testing of internal combustion engines is an important part of research, development and teaching of the subject. Engine test facilities vary widely. The facilities used for research can have very comprehensive instrumentation, with computer control of the test and computer data acquisition. On the other hand, a more traditional test cell with the engine controlled manually, and the data recorded by the operator, can be better for educational purposes. This second type of test cell is covered in some detail by Greene and Lucas (1969), and is dealt with first in this chapter. A more recent treatment of engine testing by Plint and Martyr (1995) also includes substantial coverage of the building and infrastructure requirements for engine testing.
Richard Stone
Chapter 14. Case studies
Abstract
The three engines that have been chosen as case studies are the Rover K Series spark ignition engine, the Chrysler 2.2 litre spark ignition engine, and the Ford (high-speed) 2.5 litre DI diesel engine. Each engine has been chosen because of its topicality, and characteristics that are likely to be seen also in subsequent engines. The Rover engine uses a pent-roof combustion chamber; this permits the use of a high compression ratio and the combustion of lean mixtures, both of which lead to economical operation. The Chrysler 2.2 litre spark ignition engine is typical of current practice in the USA and thus has low emissions of carbon monoxide, unburnt hydrocarbons and oxides of nitrogen.
Richard Stone
Backmatter
Metadaten
Titel
Introduction to Internal Combustion Engines
verfasst von
Richard Stone
Copyright-Jahr
1999
Verlag
Macmillan Education UK
Electronic ISBN
978-1-349-14916-2
Print ISBN
978-0-333-74013-2
DOI
https://doi.org/10.1007/978-1-349-14916-2