xxviIntroduction:ACenturyofDieselProgressFIGUREI.16Themostpowerfulmarinedieselenginesin service (2008) were14cylinder Wartsila RT-flex96C low-speed two-stroke models developing 84420kW(HyundaiHeavyIndustries)Diesel engine pioneers MAN Diesel and Sulzer (the latter now part of theWartsila Corporation)have logged centenaries in the industry and are com-mitted with other major designers to maintaining a competitive edge deep intothis century.Valuable support will continue to flowfrom specialists in turbocharging.fuel treatment, lubrication,automation,materials,and computer-based diagnostic/monitoring systems and maintenance and spares managementprograms.Keydevelopment targets aim to improve further the abilityto burn low-grade bunkers (including perhaps coal-derived fuels and slurries) withoutcompromising reliability:reduce noxious exhaustgas emissions;extend thedurability of components and the periods between major overhauls;lowerproduction and installation costs;and simplify operation and maintenanceroutines.Low-speed engines withelectronically controlled fuel injection and exhaustvalve actuating systems are entering service in increasing numbers, paving thewayforfuture'Intelligent Engines':thosewhich can monitor their own condi-tion and adjustkey parameters for optimum performance in a selected runningmode.Traditional camshaft-controlled versions,however,arestillfavoured bysome operators.Potentialremainsforfurtherdevelopmentsinpower andefficiencyfromdiesel engines,with concepts such as steam injection and combined diesel andsteam cyclesprojected to yield an overall plant efficiency of around 60percent. The Diesel Combined Cycle calls for a drastic change in the heat balance,which can be effected by the Hot Combustion process. Piston top and cylinder
xxvi Introduction: A Century of Diesel Progress Diesel engine pioneers MAN Diesel and Sulzer (the latter now part of the Wärtsilä Corporation) have logged centenaries in the industry and are committed with other major designers to maintaining a competitive edge deep into this century. Valuable support will continue to flow from specialists in turbocharging, fuel treatment, lubrication, automation, materials, and computerbased diagnostic/monitoring systems and maintenance and spares management programs. Key development targets aim to improve further the ability to burn lowgrade bunkers (including perhaps coal-derived fuels and slurries) without compromising reliability; reduce noxious exhaust gas emissions; extend the durability of components and the periods between major overhauls; lower production and installation costs; and simplify operation and maintenance routines. Low-speed engines with electronically controlled fuel injection and exhaust valve actuating systems are entering service in increasing numbers, paving the way for future ‘Intelligent Engines’: those which can monitor their own condition and adjust key parameters for optimum performance in a selected running mode. Traditional camshaft-controlled versions, however, are still favoured by some operators. Potential remains for further developments in power and efficiency from diesel engines, with concepts such as steam injection and combined diesel and steam cycles projected to yield an overall plant efficiency of around 60 per cent. The Diesel Combined Cycle calls for a drastic change in the heat balance, which can be effected by the Hot Combustion process. Piston top and cylinder Figure I.16 The most powerful marine diesel engines in service (2008) were 14- cylinder Wärtsilä RT-flex96C low-speed two-stroke models developing 84420kW (Hyundai Heavy Industries)
Thefuturexxvii30Fourstroke2520Twostroke151050 +200019201930194019501960:19701980199020101900191020200YearFIGUREI.17 Historical and estimated future development of mean effective pressureratings for two-stroke and four-stroke diesel engines (Wartsila Corporation)head cooling is eliminated, cylinder liner cooling minimized, and the coolinglosses concentrated in the exhaust gas and recovered in a boiler feeding high-pressure steamtoaturbine (FigureI.17).Acknowledgements:ABB Turbo Systems,MAN Diesel and WartsilaCorporation
head cooling is eliminated, cylinder liner cooling minimized, and the cooling losses concentrated in the exhaust gas and recovered in a boiler feeding highpressure steam to a turbine (Figure I.17). Acknowledgements: ABB Turbo Systems, MAN Diesel and Wärtsilä Corporation. The future xxvii Four stroke Two stroke Bar 30 25 20 15 10 5 0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 Year Figure I.17 Historical and estimated future development of mean effective pressure ratings for two-stroke and four-stroke diesel engines (Wärtsilä Corporation)
ChapterloneTheory and GeneralPrinciplesTHEORETICALHEATCYCLEIn the original patent by Rudolf Diesel, the diesel engine operated on the diesel cycle in which heat was added at constant pressure.This was achieved bythe blast injection principle. Today'diesel' is universally used to describe anyreciprocating engine in which the heat induced by compressing air in the cyl-inders ignites a finely atomized spray of fuel. This means that the theoreticalcycle on which the modern diesel engine works is better represented by thedual or mixed cycle, which is diagrammatically illustrated in Figure 1.1. Thearea of thediagram,to a suitable scale,represents theworkdone on thepistonduring one cycle.Starting from point C, the air is compressed adiabatically to point D. Fuelinjection begins at D, and heat is added to the cycle partly at constant volumeas shownbyvertical lineDp,and partlyatconstantpressureas shownbyhor-izontal line PE. At point E expansion begins. This proceeds adiabatically toFAdiabaticexpansionnsAdiabaticcompressionVolumeFIGURE1.1Theoretical heatcycle of truediesel engine
C h a p t e r | o n e Theory and General Principles Theoretical heat cycle In the original patent by Rudolf Diesel, the diesel engine operated on the diesel cycle in which heat was added at constant pressure. This was achieved by the blast injection principle. Today ‘diesel’ is universally used to describe any reciprocating engine in which the heat induced by compressing air in the cylinders ignites a finely atomized spray of fuel. This means that the theoretical cycle on which the modern diesel engine works is better represented by the dual or mixed cycle, which is diagrammatically illustrated in Figure 1.1. The area of the diagram, to a suitable scale, represents the work done on the piston during one cycle. Starting from point C, the air is compressed adiabatically to point D. Fuel injection begins at D, and heat is added to the cycle partly at constant volume as shown by vertical line DP, and partly at constant pressure as shown by horizontal line PE. At point E expansion begins. This proceeds adiabatically to Pressure Adiabatic expansion Adiabatic compression F C P E Volume D Figure 1.1 Theoretical heat cycle of true diesel engine
2TheoryandGeneral Principlespoint F when the heat is rejected to exhaust at constant volume as shown byvertical line FC.The ideal efficiency of this cycle (i.e.thehypothetical indicator diagram)is about 55-60 per cent: that is to say, about 40-45 per cent of the heat sup-plied is lost to the exhaust. Since the compression and expansion strokes areassumed to be adiabatic,and friction is disregarded,there is no loss to coolantor ambient.For afour-strokeengine,the exhaust and suction strokes are shownby the horizontal line at C, and this has no effect on the cycle.PRACTICALCYCLESWhile the theoretical cycle facilitates simple calculation, it does not exactlyrepresent the true state of affairs.This is because:1. The manner in which, and the rate at which, heat is added to thecompressed air (the heat release rate)is a complexfunction of thehydraulics of the fuel injection equipment and the characteristic of itsoperatingmechanism; of thewaythesprayis atomizedand distributedin the combustion space; of the air movement at and after top dead cen-tre (ATDC)andto a degreealso of thequalities of thefuel.2.The compression and expansion strokes are not truly adiabatic.Heat islost tothecylinder wallsto an extent, which is influenced bythecoolanttemperature and by the design of the heat paths to the coolant.3.The exhaust and suction strokes on afour-stroke engine (and theappro-priate phases of a two-stroke cycle)do create pressuredifferenceswhich the crankshaft feels as'pumping work'.It is the designer's objective to minimize all of these losses without preju-dicing first cost or reliability, and also to minimize the cycle loss: that is, theheat rejected to exhaust. It is beyond the scope of this book to derive the for-mulae used in the theoretical cycle, and in practice designers have at their dis-posal sophisticated computer techniques, which are capable of representingthe actual events in the cylinder with a high degree of accuracy. But broadlyspeaking, the cycle efficiency is a function of the compression ratio (or morecorrectly the effective expansion ratio of the gas-air mixture after combustion).The theoretical cycle(Figure1.1)may be compared witha typical actualdiesel indicator diagram such as that shown in Figure 1.2. Note that in higherspeedengines, combustion events are often represented on a crank angle,ratherthan a stroke basis, in order to achieve better accuracy in portraying events atthe top dead centre (TDC)as shown in Figure 1.3.The actual indicator dia-gram is derived from it by transposition. This form of diagram is useful toowhen setting injection timing.If electronic indicators are used, it is possible tochoose either form of diagram.An approximation to a crank angle-based diagram can be madewithmechanical indicators by disconnecting the phasing and taking a card quickly.pulling it by hand: this is termed a 'draw card
Theory and General Principles point F when the heat is rejected to exhaust at constant volume as shown by vertical line FC. The ideal efficiency of this cycle (i.e. the hypothetical indicator diagram) is about 55–60 per cent: that is to say, about 40–45 per cent of the heat supplied is lost to the exhaust. Since the compression and expansion strokes are assumed to be adiabatic, and friction is disregarded, there is no loss to coolant or ambient. For a four-stroke engine, the exhaust and suction strokes are shown by the horizontal line at C, and this has no effect on the cycle. Practical cycles While the theoretical cycle facilitates simple calculation, it does not exactly represent the true state of affairs. This is because: 1. The manner in which, and the rate at which, heat is added to the compressed air (the heat release rate) is a complex function of the hydraulics of the fuel injection equipment and the characteristic of its operating mechanism; of the way the spray is atomized and distributed in the combustion space; of the air movement at and after top dead centre (ATDC) and to a degree also of the qualities of the fuel. 2. The compression and expansion strokes are not truly adiabatic. Heat is lost to the cylinder walls to an extent, which is influenced by the coolant temperature and by the design of the heat paths to the coolant. 3. The exhaust and suction strokes on a four-stroke engine (and the appropriate phases of a two-stroke cycle) do create pressure differences which the crankshaft feels as ‘pumping work’. It is the designer’s objective to minimize all of these losses without prejudicing first cost or reliability, and also to minimize the cycle loss: that is, the heat rejected to exhaust. It is beyond the scope of this book to derive the formulae used in the theoretical cycle, and in practice designers have at their disposal sophisticated computer techniques, which are capable of representing the actual events in the cylinder with a high degree of accuracy. But broadly speaking, the cycle efficiency is a function of the compression ratio (or more correctly the effective expansion ratio of the gas–air mixture after combustion). The theoretical cycle (Figure 1.1) may be compared with a typical actual diesel indicator diagram such as that shown in Figure 1.2. Note that in higher speed engines, combustion events are often represented on a crank angle, rather than a stroke basis, in order to achieve better accuracy in portraying events at the top dead centre (TDC) as shown in Figure 1.3. The actual indicator diagram is derived from it by transposition. This form of diagram is useful too when setting injection timing. If electronic indicators are used, it is possible to choose either form of diagram. An approximation to a crank angle–based diagram can be made with mechanical indicators by disconnecting the phasing and taking a card quickly, pulling it by hand: this is termed a ‘draw card’
Practicalcycles53TDCBDCVolume-FIGURE1.2Typical indicator diagram (stroke-based)ExpansionPoint ofignition14Compressionline1BDCTDCBDCCrank angleFIGURE 1.3 Typical indicator diagram (crank angle-based)
Practical cycles Pressure TDC Volume BDC Figure 1.2 Typical indicator diagram (stroke-based) Pressure Point of ignition Expansion Compression line BDC TDC Crank angle BDC Figure 1.3 Typical indicator diagram (crank angle-based)