1. Brainware group of Institutions Barasat IC Engines & Gas Turbine ME 601 (Module 1-13) Dr. Shyamal Goswami Jan – july 2016

2. Module 1 Classification and working of basic Engine types : 2 stroke, 4 stroke. CI, SI etc.

3. Classification and working of basic engine Engine : device which transforms one form of energy into another form ( energy of conversion plays a role) Heat Engines : convert thermal energy into mechanical work ( conversion of chemical energy of fuel into thermal energy) Classified into : Internal combustion engines & External combustion engines Engines can be : Rotary or Reciprocating Advantage : absence of Heat Exchangers (Boiler and Condensers ) in IC engines makes it considerable mechanically simple with improved power plant efficiency as against EC engines.

4. Working Principals Four Stroke SI Engine : cycle of operations completed in four strokes of piston / two revolutions of the crankshaft. Four strokes / Five events : suction, compression, combustion, expansion and exhaust.

5. Internal Combustion Engine an engine in which the combustion of a fuel (normally a fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber (within the engine itself and hence its name).enginecombustionfuelfossil fuel combustion chamber the expansion of the high-temperature and high - pressure gases produced by combustion apply direct force to some component of the engine. This force is applied typically to pistons, gas turbine blades, or a nozzle. This force moves the component over a distance, transforming chemical energy into useful mechanical energytemperature pressure forcepistonsturbine blades nozzle energy Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years (coal, oil, natural gas)fuelsanaerobic decomposition organisms

6. Internal and External Engine internal combustion engine usually refers to an engine in which combustion is intermittent internal combustion engine different from external combustion engines, such as steam engines(steam turbine where steam is introduced to the turbine after having been raised externally in a boiler ), in which the energy is delivered to a working fluid not consisting of, mixed with, or contaminated by combustion products. Working fluids can be air, hot water, pressurized water or even liquid sodium, heated in some kind of boilerexternal combustion enginessteamenginespressurized waterboiler

7. Internal and External Engine Cycle The thermodynamic cycles like Carnot cycle, Stirling cycle, Brayton cycle are closed cycles as the working fluid keeps on circulating inside the cycle. In these cycles the addition of heat takes places externally, hence they also called external combustion engines. The most commonly used practical engines used in our day-to-day life are internal combustion engines for our vehicles, motorcycles, construction machineries etc.These run on Air standard cycle.Carnot cycleStirling cycleinternal combustion

8. Application of IC Engines mobile propulsion in vehicles and portable machinery.vehicles advantageous in mobile application - provide high power-to-weight ratios together with excellent fuel energy density. Generally using fossil fuel (mainly petroleum), these engines have appeared in transport in almost all vehicles (automobiles, trucks, motorcycles, boats, and in a wide variety of aircraft and locomotives)energy densityfossil fuelpetroleumautomobilestrucksmotorcyclesboatsaircraftlocomotives For high power-to-weight ratios - internal combustion engines appear in the form of gas turbines – e.g jet aircraft, helicopters, large ships and electric generators.gas turbinesjet aircrafthelicopterselectric generators

9. Classification cycle used layout of the engine source of energy use of the engine cooling system employed.

10. Classification based on engine configuartion Reciprocating : Two-stroke engine Four-stroke engine Six-stroke engine Diesel engine Atkinson cycle Petrol Engine Rotary: Wankel engine Continuous combustion: Gas turbine Jet engine (including turbojet, turbofan, Rocket, etc.) Jet engineturbojetturbofanRocket

11. IC Engine In IC engine – gases inducted and exhausted through ports Opening and closing are related to piston positions In two stroke ports can be closed or closed by piston itself In four stroke done by separate shaft called cam shaft which operates poppet valves. Timing of the valves and point of ignition are fundamental to engine performance. Beginning and end of each process does not coincide with TDC and BDC position Timing of valve indicated by timing diagram in terms of crankshaft angle

12. Four / Two stroke engine four-stroke internal combustion engine : four basic steps that repeat with every two revolutions of the engine : Two – stroke internal combustion engine : completes the process cycle in one revolution of the crankshaft (an up stroke and a down stroke of the pistonpiston accomplished by using the end of the combustion stroke and the beginning of the compression stroke to perform simultaneously the intake and exhaust (or scavenging) functions. In this way, two-stroke engines often provide high specific power, at least in a narrow range of rotational speeds. ( otto cycle animation – start yr engine, diesel cycle )scavengingspecific power

13. Four stroke Operation 1. Intake stroke (suction stroke ) : piston moves to the maximum volume position (downward direction TDC to BDC, pressure reduced to atm pressure in the cylinder ). inlet valve opens - the vaporized fuel mixture enters the combustion chamber. The inlet valve closes at the end of this stroke. 2. Compression stroke: both valves closed - piston starts its movement to the minimum volume position (upward direction )- compresses the fuel mixture (at TDC, charge occupies the volume above the piston called clearance volume), the spark is timed to occur at a point (S) before TDC - pressure, temperature and the density of the fuel mixture increases.

14. Four stroke Operation 3. Power stroke: spark plug ignites the fuel mixture at minimum volume position and burns. The fuel produces power that is transmitted to the crank shaft mechanism. to assist in exhausting the gaseous products the exhaust valve opens before BDC somewhere at (E). The pressure falls from E to nearly atm pressure at 4 4. Exhaust stroke: In the end of the power stroke, the exhaust valve opens - piston starts its movement in the minimum volume position. The open exhaust valve allows the exhaust gases to escape the cylinder.Some exhausted gases equivalent to clearance volume cannot be exhausted and mixes with the fresh charge of the next cycle. At the end of this stroke, the exhaust valve closes, the inlet valve opens, and the sequence repeats in the next cycle.

15. Ideal Otto Cycle

16. Otto Cycle 0-1: Intake stroke 1-2: Isentropic compression work done on the air by the piston 2-3: Heat supplied at constant volume 3-4 : Isentropic expansion work done by the air 4-1 : Heat rejected at constant volume 1-0 : Exhaust stroke

17. Four stroke Operation Exhaust and Inlet Valve Overlap : Exhaust and inlet valve overlap is the transition between the exhaust and inlet strokes and is a practical necessity for the efficient running of any internal combustion engine. Given the constraints imposed by the operation of mechanical valves and the inertia of the air in the inlet manifold, it is necessary to begin opening the inlet valve before the piston reaches Top Dead Centre (TDC) on the exhaust stroke. Likewise, in order to effectively remove all of the combustion gases, the exhaust valve remains open until after TDC. Thus, there is a point in each full cycle when both exhaust and inlet valves are open. The number of degrees over which this occurs and the proportional split across TDC is very much dependent on the engine design and the speed at which it operates.

18. Exhaust and Inlet Valve Overlap :

19. Two stroke cycle As piston ascends on the compression stroke, the next charge is drawn into the crankcase C, through the spring loaded automatic valve S. Ignition occurs before TDC and at TDC the working stroke begins. As the piston descends through about 80% of the working stroke, the exhaust port E is uncovered by the piston and exhaust begins. The transfer port T is uncovered later in the stroke due to the shape of the piston or the position of the port in relation to the port E and the charge in the crankcase C which has been compressed by the descending piston, enters the cylinder through the port T.

20. Two Stroke cycle

22. Two stroke cycle The piston can be shaped to deflect the fresh gas across the cylinder to assist the scavenging of the cylinder,; this is called cross flow scavenge. As the piston rises, the transfer port T is closed slightly before the exhaust port E and after E is closed compression of the charge in the cylinder begins. Instead of the spring loaded valve S, a design with the third port so called induction port controlled by the piston may be used. In case of CI engine spark plug is replaced by an injector and air is only compressed Scavenging : scavenging is the process of pushing exhausted gas-charge out of the cylinder and drawing in a fresh draught of air or fuel/air mixture for the next cycle. cylinder This process is essential in having a smooth-running internal combustion engine. If scavenging is incomplete, the following stroke will begin with a mix of exhaust fumes rather than clean air. This may be inadequate for proper combustion, leading to poor running conditions such as four-stroking.internal combustion enginefour-stroking Scavenging is equally important for both two- and four-stroke engines. However it is more difficult to achieve in two-stroke engines, owing to the proximity, or even overlap, of their induction and exhaust strokes. Scavenging is also equally important to both petrol and diesel engines.two-four-strokepetroldiesel engines

23. Advantages and disadvatage of two stroke engines Advantage : for every two strokes of the piston inside the cylinder, one power stroke is produced. In four-stroke engines, power is produced once during four strokes of the piston. For the same size engine, the power produced by the two-stroke engine is more that the four-stroke engine. Ideally the power produced by the two-stroke engine is double that of the four-stroke engine, but in actual practice it is only about 30% more than four- stroke engine. since the power produced by the two-stroke engine is higher, these engines are small and compact in size. Since there are no valves in the two-stroke engine and only ports, they are cheaper and require less maintenance. the torque produced on the crankshaft is more uniform because the power is produced during every alternate stroke of the piston. Disadvantage : When the inlet valve of the engine is opened for intake of the air-fuel mixture, the exhaust valve is also open. Although there is deflector between the inlet and exhaust areas of the engine, some fresh air-fuel mixture always escapes through the exhaust area. Thus part of the fuel that would have produced power goes wasted. This increases the fuel consumption and reduces the engine's overall efficiency. The two-stroke engine does not operate with the same efficiency at different speeds. When the carburetor's throttle valve is partly opened, the air-fuel mixture taken inside the cylinder is not sufficient to drive out all the exhaust gases, leaving some of the exhaust gases inside the cylinder even during the combustion stroke. This causes non-uniform burning of the fuel and inconsistent efficiency at different speeds. One disadvantage that applies to both diesel and petrol two-stroke engines is the extensive cooling and lubricating requirements of the two-stroke engines. Since in two-stroke engines power stroke is produced after every stroke, a large amount of heat is generated within them. To reduce the temperature of the engine and keep the moving parts well-lubricated, good lubrication and cooling systems for the engine are required.

24. Petrol Engine

25. 4-cylinder Petrol Engine

26. Criteria of Performance Engine selected to suit a particular application Main consideration – power/speed characteristics Brake horse Power : Brake horsepower (bhp) is the measure of an engine's horsepower before the loss in power caused by the gearbox, alternator, differential, water pump, and other auxiliary components such as power steering pump, muffled exhaust system, etc. (measured output of the engine). Brake or dynamometer which is loaded in such a way that torque exerted by the engine is measured. T (torque) = W (net load) x R (radius from axis of rotation) Brake power (bp) = 2 ∏ N T

27. Criteria of Performance Indicated power (ip) : rate of work done on the piston as evaluated from an indicator diagram obtained from the engine. Indicated mean effective pressure pi is given by: pi = (net area of diagram /length of diagram ) x constant ( constant depends on the scales of the recorder) for one engine cylinder : Work done per cycle = pi x A (area of piston) x L ( length of stroke) Power output / unit time = work done per cycle x cycles per minute or ip = pi A L x ( cycles / unit time ) The number of cycles per unit time depends on the type of engine, for four stroke engines the number of cycles per unit time is N/2 and for two strokes the number of cycles per unit time is N, where N is the engine speed. Indicated power ip for four stroke engines therefore is : ip = pi ALNn /2

28. Criteria of Performance Friction Power (fp) : difference between ip and bp and is that power required to overcome the frictional resistance of the engine parts fp = ip – bp nearly constant at a given engine speed Mechanical efficiency ƞ M : defined as bp / ip ( lies between 80 -90 % ) Depends on bp and ip - found by evaluating these experimentally. Brake effective pressure (bmep) : bp of an engine can be obtained accurately and conveniently using a dynamometer : bp = ƞ M x ip = ƞ M x pi A L Nn /2 Since ƞ M and pi difficult to obtain, they may be combined and replaced by a brake mean effective pressure p b b p = p b A L Nn /2 The bmep may be thought of as that mean effective pressure acting on the pistons which would give the measured bp if the engine were frictionless. Useful criterion for comparing engine performance.

29. Criteria of Performance Putting two equations together : pb A L Nn /2 = 2 ∏ N T Therefore pb = K x T ( k is a constant ) – directly proportional to the engine torque and is independent of the engine speed. The power output of the engine is obtained from the chemical energy of the fuel supplied. The overall efficiency of the engine is given by the brake thermal efficiency : ƞ BT = brake work / energy supplied = bp /( f x Q net.v ) (mass of fuel consumed, net calorific value ) The specific fuel consumption ( sfc) is the mass flow rate of fuel consumed per unit power output and is criterion of economical power production i.e sfc = f / bp The indicated thermal efficiency : ƞ IT = ip / ( f x Q net.v ) Therefore : ƞ BT / : ƞ IT = bp / ip = ƞ M

30. Diesel Engine (also known as a compression-ignition engine) uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber. This is in contrast to spark-ignition engines such as a petrol engine (gasoline engine) or gas engine (using a gaseous fuel as opposed to gasoline), which uses a spark plug to ignite an air-fuel mixture.heat of compressionignition fuelcombustion chamber petrol enginegas engine spark plug has the highest thermal efficiency of any regular internal or external combustion engine due to its very high compression ratio. Low-speed Diesel engines (as used in ships and other applications where overall engine weight is relatively unimportant) the largest of which can have a thermal efficiency that exceeds 50 percent.thermal efficiency internalexternal combustioncompression ratio

31. Diesel Engine Diesel engines have several advantages over other internal combustion engines: burn less fuel than a petrol engine performing the same work, due to the engine's higher temperature of combustion and greater expansion ratio. Gasoline engines are typically 30 percent efficient while diesel engines can convert over 45 percent of the fuel energy into mechanical energy have no high voltage electrical ignition system, resulting in high reliability and easy adaptation to damp environments. The absence of coils, spark plug wires, etc., also eliminates a source of radio frequency emissions which can interfere with navigation and communication equipment, which is especially important in marine and aircraft applications. The life of a diesel engine is generally about twice as long as that of a petrol engine due to the increased strength of parts used. Diesel fuel has better lubrication properties than petrol as well.

32. Diesel Cycle The Diesel cycle is the cycle used in the Diesel (compression-ignition) engine. In this cycle the heat is transferred to the working fluid at constant pressure. The process corresponds to the injection and burning of the fuel in the actual engine. The cycle in an internal combustion engine consists of induction, compression, power and exhaust strokes

33. Diesel Cycle Induction Stroke : The induction stroke in a Diesel engine is used to draw in a new volume of charge air into the cylinder. As the power generated in an engine is dependent on the quantity of fuel burnt during combustion and that in turn is determined by the volume of air (oxygen) present, most diesel engines use turbochargers to force air into the cylinder during the induction stroke. From a theoretical perspective, each of the strokes in the cycle complete at Top Dead Centre (TDC) or Bottom Dead Centre (BDC), but in practicality, in order to overcome mechanical valve delays and the inertia of the new charge air, and to take advantage of the momentum of the exhaust gases, each of the strokes invariably begin and end outside the 0, 180, 360, 540 and 720 (0) degree crank positions ( valve timing chart).valve timing chart

34. Diesel Cycle Compression Stroke : The compression stroke begins as the inlet valve closes and the piston is driven upwards in the cylinder bore by the momentum of the crankshaft and flywheel. The purpose of the compression stroke in a Diesel engine is to raise the temperature of the charge air to the point where fuel injected into the cylinder spontaneously ignites. In this cycle, the separation of fuel from the charge air eliminates problems with auto-ignition and therefore allows Diesel engines to operate at much higher compression ratios than those currently in production with the Otto Cycle.

35. Diesel Cycle Compression Ignition : Compression ignition takes place when the fuel from the high pressure fuel injector spontaneously ignites in the cylinder. In the theoretical cycle, fuel is injected at TDC, but as there is a finite time for the fuel to ignite (ignition lag) in practical engines, fuel is injected into the cylinder before the piston reaches TDC to ensure that maximum power can be achieved. This is synonymous with automatic spark ignition advance used in Otto cycle engines.

36. Diesel Cycle Power Stroke : The power stroke begins as the injected fuel spontaneously ignites with the air in the cylinder. As the rapidly burning mixture attempts to expand within the cylinder walls, it generates a high pressure which forces the piston down the cylinder bore. The linear motion of the piston is converted into rotary motion through the crankshaft. The rotational energy is imparted as momentum to the flywheel which not only provides power for the end use, but also overcomes the work of compression and mechanical losses incurred in the cycle (valve opening and closing, alternator, fuel injector pump, water pump, etc.).

37. Diesel Cycle Exhaust Stroke : The exhaust stroke is as critical to the smooth and efficient operation of the engine as that of induction. As the name suggests, it's the stroke during which the gases formed during combustion are ejected from the cylinder. This needs to be as complete a process as possible, as any remaining gases displace an equivalent volume of the new charge air and leads to a reduction in the maximum possible power.

38. Diesel Cycle Exhaust and Inlet Valve Overlap: Exhaust and inlet valve overlap is the transition between the exhaust and inlet strokes and is a practical necessity for the efficient running of any internal combustion engine. Given the constraints imposed by the operation of mechanical valves and the inertia of the air in the inlet manifold, it is necessary to begin opening the inlet valve before the piston reaches Top Dead Centre (TDC) on the exhaust stroke. Likewise, in order to effectively remove all of the combustion gases, the exhaust valve remains open until after TDC. Thus, there is a point in each full cycle when both exhaust and inlet valves are open. The number of degrees over which this occurs and the proportional split across TDC is very much dependent on the engine design and the speed at which it operates.

39. Diesel Cycle

41. Diesel Engine

42. Ideal Diesel Cycle

43. Diesel cycle