MARINE PROPULSION DIESEL ENGINE

MARINE PROPULSION DIESEL ENGINES LMD 23203 ..\\..\\..\\syllabus\\5.LMD 10403 Diesel ..\\..\\..\\Lesson Plan\\Marine Propulsion Jan 09 SEM.doc Diesel Engine rev1.doc Lecturer: Fauzuddin Ayob B. Sc Marine Eng; M. Eng Materials Sc & Eng

Section 1- Theory and General Principles of Engine FAA Lesson Plan 1: (week 1) Working Cycles and Timing of Diesel Engine A diesel engine may be designed to work on the two-stroke or on the four-stroke cycle. ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2. ppt

MES ENGINE CYCLES The terms ‘cycle’ refers to one complete sequence of operations required to produce power in an engine. This cycle of operation is continuously repeated while the engine is running. For a diesel engine it consists of four operations within the cylinder: 1. Compression of a charge of air 2. Injection of fuel which then ignites 3. Expansion of the hot gases formed during combustion 4. Expulsion of the used gas to exhaust. The cylinder is then recharged with air and the cycle is repeated. ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2.ppt

ENGINE CYCLES – continued MES Diesel engines can be designed to complete this cycle once during each revolution and this is termed the two-stroke cycle , or alternatively to take two engine revolutions to complete – the four-stroke cycle. Engine stroke is measured as the full distance through which the piston moves between each end of its travel. It can be seen that it must move through two complete strokes (one up and one down) during each revolution of the engine. ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2.ppt

MES Two-stroke Cycle Practically all large, slow speed, direct drive marine diesel engines operate on two-stroke cycle . As its name implies a two-stroke cycle takes place in two consecutive strokes of the engine piston, or one revolution of the crankshaft. Thus each operation in the cycle is repeated during every revolution of the engine. The two strokes of the cycle may be termed : Compression stroke and Power or expansion stroke. ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2. ppt

MES Four-stroke Cycle The majority of medium and high speed diesel engines for main or auxiliary drive operate on the four-stroke cycle, which takes place during four consecutives strokes, or two complete revolutions, of the engine. The four strokes may be termed: Compression stroke, Power or expansion stroke, Exhaust stroke, and Aspirating or air induction stroke. ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2. ppt

ENGINE TIMING MES Engine timing refers to the relative time or position of the crank, at which each operation during the cycle is commenced and is completed. It is measured as the angle through which the crank has been rotated from a datum position such as top or bottom centre. TIMING DIAGRAM ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2.ppt Operations or events of the two-stroke and four-stroke cycle take place in a fixed order and must occur when the piston reaches a corresponding position in its stroke. It is convenient to express them in terms of angles of crank position measured from top dead centre (TDC) or bottom dead centre (BDC) and they may be shown as a circle on a timing diagram.

Four-Stroke Cycle ➢ The four-stroke cycle is completed in four strokes of the piston, or two revolutions of the crankshaft. ➢ In order to operate this cycle the engine requires a mechanism to open and close the inlet and exhaust valves. ➢ Consider the piston at the top of its stroke, a position known as top dead centre (TDC). ➢ The inlet valve opens and fresh air is drawn in as the piston moves down (Figure 2.1 (a)) this is known as suction stroke .At the bottom of the stroke, i.e. bottom dead centre (BDC), the inlet valve closes and the air in the cylinder is compressed (and consequently raised in temperature) this is known as

➢ Compression stroke.As the piston rises (Figure 2.1(b)). Fuel is injected as the piston reaches top dead centre and combustion takes place, producing very high pressure in the gases (Figure 2. l(c)). ➢ The piston is now forced down by these gases and at bottom dead centre the exhaust valve opens- this is known as power stroke. ➢ The final stroke is the exhausting of the burnt gases as the piston rises to top dead centre to complete the cycle (Figure 2.1(d)). The four distinct strokes are known as 'inlet' (or suction), 'compression', 'power' (or working stroke) and 'exhaust'. This is known as exhaust stroke. ➢ These events are shown diagrammatically on a timing diagram (Figure 2.2).

4-stroke cycle: (a) suction stroke, (b) compression stroke, Figure 2.1

(c) power stroke and (d) exhaust stroke Figure 2.1



The angle of the crank at which each operation takes place is shown as well as the period of the operation in degrees. This diagram is more correctly representative of the actual cycle than the simplified explanation given in describing the four- stroke cycle. For different engine designs the different angles will VARY, but the diagram is typical.

2-stroke cycle ➢ The two-stroke cycle is completed in two strokes of the piston OR one revolution of the crankshaft. ➢ In order to operate this cycle where each event is accomplished in a very short time. ➢ The engine requires a number of special arrangements that first, the fresh air must be forced in under pressure. ➢ The incoming air is used to clean out or scavenge the exhaust gases and fill or charge the space with fresh air. Instead of using exhaust, the valve is known as 'ports', are used which are opened and closed by the sides of the piston as it moves.

➢ Consider the piston at the top of its stroke (TDC) where fuel injection and combustion have just taken place (Figure 2.3(a)). ➢ The piston is forced down on its working stroke until it uncovers the exhaust port (Figure2.3(b)). ➢ The burnt gases then begin to exhaust and the piston continues down until it opens the inlet or scavenge port (Figure 2.3(c)). ➢ Pressurized air then enters and drives out the remaining exhaust gas to atmosphere. ➢ The piston, on its return stroke, closes the inlet and exhaust ports. ➢ ➢ The air is then compressed as the piston moves to the top of its stroke to complete the cycle (Figure 2.3(d)). ➢ A timing diagram for a two-stroke engine is shown in Figure 2.4.





MES

The Four-stroke Cycle Timing Diagram MES 2 stroke&4 stroke operation.ppt 4 and 9 are TDC positions. 1 and 7 are BDC positions. Numbers have been added for reference. ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2. ppt

MES 1-2 Completing of scavenge. Air is entering the cylinder, expelling exhaust gas and recharging it for the next combustion. Scavenge and exhaust are open. 2-3 Post-scavenge. Scavenge ports have closed and some air within the cylinder may leak to exhaust. In some engine 2 and 3 are made to coincide to eliminate leakage of air. 3-4 Compression. Exhaust has now closed and the air trapped within the cylinder is compressed by the upstroke of the piston to raise its temperature sufficiently to ignite the fuel. 4-5-6 Fuel injection takes place and combustion occurs causing a rapid rise in pressure. The period for which this continues depend upon the fuel pump setting and power to be produced. 6-7 Expansion. Combustion completed, the hot gases expand forcing the piston downwards and converting the heat energy from combustion into wok on the piston. 7-8 Exhaust blowdown. Exhaust has opened allowing gas to pass to exhaust manifold, and pressure drops rapidly in cylinder. 8-1 Scavenge. Scavenge ports have opened and air enters to expel the remaining exhaust gas. 1- etc. Scavenging then continues for the next cycle. Position 1 represents bottom of stroke (BDC). Position 5 represents top of stroke (TDC)

The Two-stroke Cycle Timing Diagram CCP Figure above shows the sequence of events in a typical two-stroke cycle, which, as the name implies, is accomplished in one complete revolution of the crank. Source: Pounder’s Marine Diesel Engines and Gas Turbines Eighth edition

The Two-stroke Cycle Timing Diagram MES 2 stroke&4 stroke operation.ppt Numbers have been added for reference. Position 1 represent bottom of stroke (BDC). Position 5 ..\\..\\..\\..\\..\\July 2008\\Intro to represents top of stroke (TDC) ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2. ppt

MES 1-2 Completion of aspiration. 2-3 Compression. Air inlet valve has closed, air in cylinder is now compressed to raise its temperature for combustion of fuel. 3-4-5 Fuel injection. Combustion takes place with corresponding rise in pressure. Period controlled by fuel pump setting. 5-6 Expansion. Combustion completed, gas pressure does work on piston during downward stroke. 6-7-8 Exhaust. Exhaust valve opened, piston expels exhaust gas on upward stroke. 8-9-10 Overlap. Air inlet valve opened while exhaust remains open. The length of this is increased in supercharged or high speed engines. 10-1 Aspiration. Exhaust valve closed, piston draws air into the cylinder during downward stroke. 1- etc. Aspiration continue for next cycle. 4 and 9 are TDC positions. 1 and 7 are BDC positions.

The Four-stroke Cycle Timing Diagram CCP Figure above shows diagrammatically the sequence of events throughout the typical four-stroke cycle of two revolutions. Source: Pounder’s Marine Diesel Engines and Gas Turbines Eighth edition

MEK Typical 2-stroke Crank Timing Diagram

MEK Typical 4-stroke Crank Timing Diagram

Lesson Plan 2: (week 2) Theoretical Heat Cycle Thermodynamic cycle of Reciprocating-Internal-Combustion Engines: – Otto, Diesel and Dual or mixed cycles

INTRODUCTION- Thermodynamics First Law Of Thermodynamics: Energy can be neither created nor destroyed but only transformed • Solar energy----> photosynthesis---plant/animals--->fossil--->fuel—heat engine---> heat energy---->mechanical energy----> • Heat Engine- is a device that converts heat energy to mechanical energy continuously The Second Law Of Thermodynamics: All energy received as heat by a heat engine cycle cannot be converted into work (This means that no cycle can have a thermal efficiency of 100%)

Otto cycle – spark ignition engine THERMO This practical cycle is applied to the petrol or S.I. engine which is perhaps the most common heat engine in popular use. The cycle was originally proposed in 1862 but was made practicable by the German scientist Nikolaus Otto 1876. The Otto cycle is an ideal air standard cycle which closely represent the actual cycle, and is shown on a p-V diagram below. P3 Isentropic expansion Heat addition 2 4 Isentropic Heat compression rejection 1 TDC BDC V Clearance Swept volume volume Otto cycle

Otto cycle – spark ignition engine THERMO Air standard Otto cycle on a p-V diagram The cycle consist of four non-flow process. At state 1 the cylinder is assumed to be full of air at approximately atmospheric pressure and temperature. The piston is at the bottom dead centre (BDC) position. Process 1-2 is isentropic ( adiabatic and reversible) compression of the air. The piston moves to TDC compressing the air into the clearance volume and so raising its pressure and temperature. Process 2-3 is heat addition at constant volume. The piston remains at TDC whilst the heat is supplied from the surrounding and the pressure and temperature are raised to their maximum values in the cycle. Process 3-4 is isentropic expansion. The hot high-pressure air forces the piston down the cylinder to BDC. Work energy is released to the surrounding at the expense of the internal energy of the air. Process 4-1 is heat rejection at constant volume. The piston remains at BDC whilst the heat is transferred to the surrounding and the air returns to its original state 1.

Diesel cycle – compression ignition engine THERMO Thermodynamic analysis of an internal combustion engine could be simplified by applying the air standard cycles. Below is the air standard cycle for a diesel engine on a p-V diagram P Heat addition 23 Isentropic expansion Isentropic 4 compression Heat Diesel Cycle rejection 1 V The cycle was invented around 1892 by the French-born German engineer Rudolf Diesel

Diesel cycle – compression ignition engine THERMO Air standard diesel cycle on a p-V diagram The cycle consists of four non-flow processes. At state 1 the cylinder is assumed to be full of air at approximately atmospheric pressure and temperature, and the piston is at the bottom dead centre (BDC) position. Process 1-2 is isentropic (adiabatic and reversible) compression of the air. The piston moves to TDC, compressing the air into the clearance volume and so raising its pressure and temperature. Process 2-3 is heat addition at constant pressure. Heat is supplied to the air from the surroundings resulting in a further increase in air temperature to its maximum at 3. This produces an increase in volume, and the pressure remains constant until the heat supply is cut off at 3. Process 3-4 is isentropic expansion of the air during the remainder of the stroke until the piston reaches BDC at 4. Process 4-1 is heat rejection at constant volume. The piston remains at BDC whilst the heat is transferred to the surroundings and the air returns to its original state at 1.

CCP Dual /mixed cycle – modern diesel engine In the original patent by Rudolf Diesel the diesel engine operated on the diesel cycle in which the heat was added at constant pressure. This was achieved by the blast injection principle. Today the term 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. p-V diagram Theoretical heat cycle of true/ modern diesel engine ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentati on Materials\\For Pedagogy presentation\\P resentation2.p pt

CCP p-V diagram Theoretical heat cycle of true/ modern diesel engine

Dual /mixed cycle – modern diesel engine CCP Air standard dual cycle on a p-V diagram Starting from point C, the air is compressed adiabatically to a 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 the point E expansion begins. This proceeds adiabatically to point F when the heat is rejected to exhaust at constant volume as shown by vertical line FC. 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.

Lesson Plan 3: (week 2) CCP Practical / Actual Cycle And Indicator Diagram p-V diagram Combustion The actual cycle is Expansion also known as indicator diagram as it is obtained using a device known as engine indicator Compression Exhaust Release ..\\..\\..\\..\\..\\July 2008\\Intro to Aspiration ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2. ppt Typical indicator diagram (stroke based) of two-stroke Diesel Engine

THERMO PRACTICAL / ACTUAL CYCLES- continued ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2. ppt Typical indicator diagram (stroke based) of four-stroke Diesel Engine

CCP PRACTICAL/ ACTUAL CYCLE- continued The actual cycle also known as an indicator diagram as it is obtained using a device known as engine indicator (Comparison of the theoretical – Dual/mixed cycle of a modern diesel engine and the actual cycle:) The corners of the diagrams are rounded due to valve throttling and because combustion process does not occur at truly constant volume or constant pressure. The compression and expansion processes are not adiabatic as assumed in the theoretical cycle since cooling of the cylinder walls is essential to avoid failure of the engine materials. ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2. ppt

CCP PRACTICAL/ ACTUAL CYCLE- continued (Comparison of the theoretical – Dual/mixed cycle and the actual cycle:) 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 (TDC); 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’.

CCP PRACTICAL/ ACTUAL CYCLE- continued 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 in figure below. ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2. ppt This crank angle based diagram is obtained by an electronic indictor or by a mechanical indicator- draw card or out-of-phase diagram Typical indicator diagram (crank angle based) of a Diesel Engine

THERMO Lesson Plan 4: (week 2) Heat transfer/balance analysis and thermal efficiencies The energy input in the engine must balance the energy outputs from the engine. Energy input- For a diesel engine combustion of fuel is the source of heat energy and the energy is considered as 100% heat supply to the engine in the cylinder. Energy output- The energy output from the engine are in the form of work or output power and energy dissipated (heat lost) Energy distribution- From the 100% of the fuel (heat) energy introduced to the cylinder, the main and common losses are to the exhaust gases, to coolant, lub oil and radiation. The remaining energy are the one being converted into useful work. ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2.ppt

THERMO Energy Losses- from internal combustion engine i.e. diesel engine 1. Energy in the exhaust gas- It is not practical to utilize all of the energy of combustion and a significant amount is lost in the exhaust gas. 2. Heat flow to the cooling system- Due to the temperature limitations of metal components, cooling is necessary, and this usually in the form of water cooling. Some of the heat generated by friction is also transferred to the cooling water. 3. Heat flow to surrounding- Heat generated by friction, or occurring from heat transfer through the cylinder are also dissipate through the lubrication system and from the hot parts of the engine, and then to the atmosphere by conduction, convection and radiation. A small energy loss also occurs as a result of vibration, sound, and air resistance with the external moving parts. A typical diagram (usually known as a Sankey diagram), representing the various energy flows through a modern diesel engine.

CCP Typical Sankey diagrams of a naturally aspirated engines Out of 100% heat released from the fuel in the cylinder, only 35% is converted to useful work. The balance 37% of the heat lost to the exhaust, 15% coolant, 5% lube oil and 8% lost to radiation.

CCP Typical Sankey diagrams of a turbocharged engines Heat rejected from the cylinder to exhaust is not necessarily totally lost, as practically all modern engines use up to 25 per cent of that heat to drive a turbocharger. The heat released from the fuel in the cylinder is augmented by the heat value of the work done by the turbocharger in compressing the intake air. This is apart from the turbocharger’s function in introducing the extra air needed to burn an augmented/increased quantity of fuel in a given cylinder, compared with what the naturally aspirated system could achieve.

CCP THERMAL EFFICIENCY Thermal efficiency (Thη) is the overall measure of performance. In absolute terms it is equal to: heat converted into useful work total heat supplied Heat converted into work per hour = N kWh = 3600 N kJ where N = the power output in kW Heat supplied = M x K where M = mass of fuel used per hour in kg and K = calorific value of the fuel in kJ/kg therefore Thη = 3600N MxK Details are in section 2

Rudolf Diesel's patent 1893

MARINE PROPULSION DIESEL ENGINES LMD 23203 ..\\..\\..\\syllabus\\5.LMD 10403 Diesel ..\\..\\..\\Lesson Plan\\Marine Propulsion Jan 09 SEM.doc Diesel Engine rev1.doc Lecturer: Fauzuddin Ayob B. Sc Marine Eng; M. Eng Materials Sc & Eng

Section 1- Theory and General Principles of Engine FAA Lesson Plan 1: (week 1) Working Cycles and Timing of Diesel Engine A diesel engine may be designed to work on the two-stroke or on the four-stroke cycle. ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2. ppt

MES ENGINE CYCLES The terms ‘cycle’ refers to one complete sequence of operations required to produce power in an engine. This cycle of operation is continuously repeated while the engine is running. For a diesel engine it consists of four operations within the cylinder: 1. Compression of a charge of air 2. Injection of fuel which then ignites 3. Expansion of the hot gases formed during combustion 4. Expulsion of the used gas to exhaust. The cylinder is then recharged with air and the cycle is repeated. ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2.ppt

ENGINE CYCLES – continued MES Diesel engines can be designed to complete this cycle once during each revolution and this is termed the two-stroke cycle , or alternatively to take two engine revolutions to complete – the four-stroke cycle. Engine stroke is measured as the full distance through which the piston moves between each end of its travel. It can be seen that it must move through two complete strokes (one up and one down) during each revolution of the engine. ..\\..\\..\\..\\..\\July 2008\\Intro to ME\\Presentation Materials\\For Pedagogy presentation\\Presentation2.ppt