Four Stroke Four Cylinder Petrol Engine

Four Stroke Four Cylinder Petrol Engine ABSTRACT Since last 150 years different type of engine used in different vehicles so one should know how the engine works and different parameters related to it. This project contains preparation of experimental setup to determine the various performance parameter of four stroke four cylinder petrol engine in first stage of project. In this stage of project, the Morse test setup with Rope brake dynamometer will be prepared for the measurement of engine performance parameters such as Break power, Indicated power, Friction power, Mass flow rate, Brake thermal efficiency, etc. In the second stage study of existing engine and scuderi split engine to be done and effort will be done to develop scuderi split engine. Since last 150 years no modification has been done for basic engine design. This scuderi split engine completely change the design structure of engine. CHAPTER 1 INTRODUCTION Project on EXPERIMENTAL SETUP FOR PERFORMANCE MEASUREMENT OF FOUR STROKE FOUR CYLINDER PETROL ENGINE DEVELOPEMENT OF SCUDERI SPLIT ENGINE consist of two stages. In first stage of the project, experimental setup for 4-cylinder petrol engine (Morse test) will be developed to determine the various engine performance parameters such as Break power, Indicated power, Friction power, Mass flow rate, Brake thermal efficiency, etc. The basic task in the design and development of engines is to reduce the cost of production and improve the efficiency and power output. In order to achieve the above task, the development engineer has to compare the engine developed with other engines in terms of its output and efficiency. Towards this end he has to test the engine and make measurements of relevant parameters that reflect the performance of the engine. For this the various test perform on engine are as follow: Willans line method Morse test Motoring test From the measurement of indicated and brake power Retardation test From this set-up of Morse test is simple and comparatively easy to conduct. Here, Rope brake dynamometer is used to measure power output. In second stage of project, the study of the scuderi split engine will be done comparison of it with conventional engine (4-S 4 Cylinder Petrol engine of Fiat Make). In conventional 4 Stroke engine, four strokes such as intake, compression, power exhaust performed in the single cylinder. While in scuderi split engine above Strokes performed in two cylinder which are connected using cross-over passage, in which pressure remains constant, in which two stroke intake compression take place in First cylinder, remaining stroke power exhaust take place in Second cylinder. CHAPTER 2 LITERATURE SURVEY 2.1 Introduction: The internal combustion engine is an engine in which combustion of fuel and an oxidizer (typically air) occurs in a confined space called a combustion chamber. This exothermic reaction creates gases at high temperature and pressure which are permitted to expand. The defining feature of an internal combustion engine is that useful work is performed by the expanding hot gases acting directly to cause movement of solid parts of the engine, by acting on pistons, rotors, or even by pressing on and moving the entire engine itself. The first internal combustion engines did not have compression, but run on air/fuel mixture sucked or blown in during the first part of the intake stroke. The most significant difference between modern internal combustion engines and the early designs was the use of compression and in particular of in-cylinder compression. 1876: Nikolaus Otto working with Gottlieb Daimler and Wilhelm Maybach had developed a practical four-stroke cycle (Otto cycle) engine. 2.2. Application of I.C. engine:- Internal combustion engines are most commonly used for mobile propulsion in automobiles, equipment, and other portable machinery. In mobile equipment internal combustion is advantageous, since it can provide high power to weight ratios together with excellent fuel energy-density. These engines have appeared in transport in almost all automobiles, trucks, motorcycles, boats, and in a wide variety of aircraft and locomotives, generally using petroleum (called All-Petroleum Internal Combustion Engine Vehicles or APICEVs) . Where very high power is required, such as jet aircraft, helicopters and large ships, they appear mostly in the form of turbines. 2.3. Classification of I.C. Engine:- The internal combustion engine may be classified in many ways, but following are the subject point of view: 1) According to the type of fuel used (a)Petrol engine (b)Diesel engine (c)Gas engine 2) According to the method of igniting the fuel (a)Spark ignition engine (b)Compression ignition engine (c)Hot spot ignition engine 3) According to the number of stroke per cycle (a)Four stroke cycle engine (b)Two stroke cycle engine 4) According to the cycle of operation (a)Otto cycle (b)Diesel cycle (c)Dual cycle 5) According to the speed of the engine (a)Slow speed engine (b)Medium speed engine (c)High speed engine 6) According to the cooling system (a)Air cooled engine (b)Water cooled engine (c)Evaporative cooling engines 7) According to method of fuel injection (a)Carburettor engine (b)Air injection engines (c)Airless or solid injection engines 8) According to number of cylinder (a)Single cylinder engines (b)Multi cylinder engines 9) According to arrangement of cylinder (a)Vertical cylinder engines (b)Horizontal cylinder engines (c)Radial engines (d)In-line multi cylinder engines (e)V-type multi-cylinder engines (f)Opposite-cylinder engines (g)Apposite piston engines 10) According to the valve mechanism (a)Overhead valve engines (b)Side valve engines 11) According to the method of governing (a)Hit and miss governed engines (b)Quantitatively governed engines (c)Qualitatively governed engines 2.4 Basic Engine Parts:- 2.4.1 Cylinder block:- The cylinder block is the main supporting structure for the various components. The cylinders of multi-cylinder engine are cast as single unit, called cylinder block. The cylinder head mounted on the cylinder block .The cylinder head and cylinder block are provided with water jacket for cooling. 2.4.2 Cylinder:- As the name implies it is a cylindrical vessel or space in which the piston makes a reciprocating motion. The varying volume created in the cylinder during the operation of the engine is filled with the working fluid and subjected to different thermodynamics processes such as suction, compression, combustion, expansion and exhaust .The cylinder is supported in cylinder block. 2.4.3 Combustion chamber:- The space enclosed in the upper part of the cylinder, by the cylinder head and the piston top during the combustion process, is called the combustion chamber. 2.4.4. Piston: Piston is the heart of the engine. The functions of the piston are to compress the charge during the compression stroke and to transmit the gas force to the connecting rod and then to the crank during power stroke. The piston is a disc which reciprocates within cylinder. It is either moved by the fluid or it moves the fluid which enters the cylinder. The main function of the piston of an internal combustion engine is to receive the impulse from the expanding gas and to transmit the energy to the crankshaft through the connecting rod. The piston of internal combustion engines are usually of trunk type. This type of piston consists of different parts such as Head or Crown, Piston rings, Skirt, Piston pin etc. 2.4.5. Piston Ring: Piston rings provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder. The rings serve two purposes: 1. They prevent the fuel/air mixture and exhaust in the combustion chamber from leaking into the sump during compression and combustion. 2. They keep oil in the sump from leaking into the combustion area, where it would be burned and lost. A piston ring is an open-ended ring that fits into a groove on the outer diameter of a piston in an internal combustion engine. The gap in the piston ring compresses to a few thousandths of an inch when inside the cylinder bore. 2.4.6 Inlet manifold:- The pipe which connects the intake system to the inlet valve of the engine and through which air or air-fuel mixture is drawn in to the cylinder is called inlet manifold. 2.4.7 Exhaust manifold:- The pipe which connects the exhaust system to the exhaust valve of the engine and through which the product of combustion escape in to the atmosphere is called the exhaust manifold. 2.4.8 Inlet and exhaust valve:- Valves are commonly mushroom shaped poppet type. They are provided either on the cylinder head or on the side of the cylinder for regulating the charge coming in to the cylinder (inlet valve) and for discharging the products of combustion from the cylinder (exhaust valve). 2.4.9. Connecting Rod: The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its angle can change as the piston moves and the crankshaft rotates. The small end attaches to the piston pin, gudgeon pin (the usual British term) or wrist pin, which is currently most often press fit into the con rod but can swivel in the piston, a floating wrist pin design. The big end connects to the bearing journal on the crank throw, running on replaceable bearing shells accessible via the con rod bolts which hold the bearing cap onto the big end; typically there is a pinhole bored through the bearing and the big end of the con rod so that pressurized lubricating motor oil squirts out onto the thrust side of the cylinder wall to lubricate the travel of the pistons and piston rings. 2.4.10. Spark Plug: The spark plug supplies the spark that ignites the air/fuel mixture so that combustion can occur. The spark must happen at just the right moment for things to work properly. 2.4.11. Crank shaft: The crankshaft turns the pistons up and down motion into circular motion just like a crank on a jack-in-the-box does. The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation. It typically connects to a flywheel, to reduce the pulsation characteristic of the four-stroke cycle, and sometimes a torsional or vibrational damper at the opposite end, to reduce the torsion vibrations often caused along the length of the crankshaft by the cylinders farthest from the output end acting on the torsional elasticity of the metal. 2.4.12. Cam shaft:- The camshaft and its associated parts control the opening and closing of the two valves. The associated parts are push rods, rocker arms, valve springs and tappets. This shaft also provides the drive to the ignition system. 2.4.13. Gudgeon pin: It forms the link between the small end of the connecting rod and the piston. 2.4.14. Cam:- These are made as integral parts of the camshaft and are designed in such way to open the valves at the correct timing and to keep them open for necessary duration. 2.4.15. Fly wheel: The net torque imparted to crankshaft during one complete cycle of operation of the engine fluctuates causing a change in the angular velocity of the shaft. In order to achieve a uniform torque an inertia mass in the form of a wheel attached to the output shaft and this wheel is called the flywheel. 2.4.16. Sump:- The sump surrounds the crankshaft. It contains some amount of oil, which collects in the bottom of the sump (the oil pan). 2.5. DIFFERENT TYPES OF MATERIAL USE FOR ENGINE PARTS:- 2.5.1. Cylinder liner: The cylinder liners are made in two types: wet liner dry liner. In case of wet liner, water in jacket is in direct contact with the outer wall of the liner; where as the dry liner is pressed into the cylinder proper. In engines over about 13cm bore; usually the wet type of liner is used. Liner materials: The liner material should be strong hard corrosion resistance. The following materials are used. 1. A good grade grey cast iron with homogenous and close grained structure i.e. prelatic and similar cast iron. 2. Nickel cast iron and nickel chromium cast iron 3. Nickel chromium cast steel with molybdenum in some case. 2.5.2. Material of cylinder head:- The cylinder head are usually made of close grained cast iron or alloy cast iron containing nickel, chromium and molybdenum, for small sized engine, while for large engine, the material is low Cast-steel. 2.5.3. Material used for piston piston ring:- Commonly used materials for piston of I.C. engine are cast iron, cast aluminum, cast steel forged steel. Generally cast steel is used for piston head. The material for the piston ring is cast iron alloy cast iron due to their good wearing qualities also they retain the spring characteristics even at high temperature. The material used for piston ring is nitrogen hardened or case hardened steel alloy containing nickel, chromium, molybdenum or vanadium. 2.5.4. Material used for connecting road:- The connecting rods of I.C.engine are mostly manufactured by drop forging. The material for connecting rod ranges from mild or medium carbon steel to alloy steels. In industrial engine, carbon steel with ultimate tensile strength ranging from 550-670Mpa is used. 2.5.5. Material used for crankshaft: The cylinder head are usually made of close grained cast iron or alloy cast iron containing nickel, chromium and molybdenum, for small sized engine, while for large engine, the material is low C-steel. Heavy duty cast iron, cast steel, nickel chromium steel is mainly used for manufacturing of crank shaft. 2.5.6. Material used for valves: Inlet valve run cooler than exhaust valves. So, the material for the inlet valves may be carbon steel, nickel steel, chrome nickel steel chrome molybdenum alloy, which may be hardened to withstand the repeated high stresses. Material for exhaust valves must be able to maintain their strength at high temperature. Therefore the material used for it is standard chrome nickel steel, cobalt nickel steel, high speed steel stainless steels. 2.6 NOMENCLATURE:- 2.6.1 Cylinder bore (d): The nominal inner diameter of the working cylinder is called the cylinder bore. It is expressed in millimeter (mm). 2.6.2 Piston area: The area of the circle of diameter equal to the cylinder bore is called the piston area. It is expressed by square centimeter (cm ²). 2.6.3 Stroke (L): The nominal distance through which a working piston moves between two successive reversals of its direction of motion is called the stroke is expressed in millimeter (mm). 2.6.4 Stroke to bore ratio: L/d ratio is an important parameter in classifying the size of the engine. If d If d=L, it is called square engine. If d>L, it is called over -square engine. An over square engine can operate at higher speeds because of large bore shorter stroke. 2.6.5 Dead center: The position of the working piston the moving parts which are mechanically connected to it, at the moment when the direction of the piston motion is reversed at either end of the stroke is called the dead center. There are two dead centers in the engine: Top dead center (TDC): It is the dead centers when the piston is farthest from the crankshaft. It is designated TDC for vertical engines inner dead center (IDC) for horizontal engines. Bottom dead center (BTC): It is the dead center when the piston is nearest to the crankshaft. It is designated as BDC for the vertical engines outer dead center (ODC) for horizontal engines. 2.6.6 Displacement or Swept volume: The nominal volume swept by the working piston when traveling from one dead center to other is called the displacement volume. It is expressed in terms of cubic centimeter (cc) given by VS = à Ã¢â€š ¬d ²L/4 2.6.7 Cubic Capacity of Engine Capacity: The displacement volume of a cylinder multiplied by number of cylinders in an engine capacity. For example, if there are K cylinders in an engine, then Cubic capacity = Vs x K 2.6.8 Clearance Volume (Vc): The nominal volume of the combustion chamber above the piston when it is at the top dead centre is the clearance volume. It is designated as Vc and expressed in cubic centimeter (cc). 2.6.9 Compression Ratio (r): it is the ratio of the total cylinder volume when the piston is at the bottom dead centre, Vt, to the clearance volume, Vc. It is designed by the letter r. r = Vt/Vc = (Vc + Vs)/Vc = 1 + Vs/Vc CHAPTER 3 WORKING OF AN I.C. ENGINE I.C. engine is a device which develops the work continuously taking the working fluid through cyclic process. The combination of piston and cylinder is suitable device for developing the work. In an arrangement of piston and cylinder of an ideal engine, following for process constitute the cycle: The air is compressed in the engine. Heat is added to the compressed air by external source. High pressure and high temperature air expands performing the work. The air after expansion returns to the original condition by rejecting heat to external sink. 3.1 The working principle of four-stroke spark ignition engine:- If an engine is to work successfully then it has to follow a cycle of operation in sequential manner. The sequence is quite rigid and can not be changed. In the following sections the working principle of both SI and CI engines is described. Even though both engines have much in common there are certain fundamental differences. The cycle of operation for an ideal four-stroke SI engine consist of the following four-stroke:- 1. Intake or suction stroke 2. Compression stroke 3. Power or expansion stroke 4. Exhaust stroke Intake or suction stroke :- Suction stroke starts when the piston is at the top dead centre and about to move downwards. The inlet valve is open at this time and exhaust valve is closed. Due to the suction created by the motion of the piston towards the bottom dead centre, the charge consisting of fuel-air mixture is drawn in to the cylinder. When the piston reaches the bottom dead centre the suction stroke ends and the inlet valve closes. compression stroke :- The charge taken in to the cylinder during the suction stroke is compressed by the return stroke of the piston. During this stroke both inlet and exhaust valves are in closed position. The mixture which fills the entire cylinder volume is now compressed in to the clearance volume. At the end of the compression stoke the mixture is ignited with the help of a spark plug located on the cylinder head. During the burning process the chemical energy of the fuel is converted in to heat energy producing temperature rise of about 2000 °C.The pressure at the end of the combustion process is considerably increased due to the heat release from the fuel. Expansion or power stroke :- The high pressure of the burnt gases forces the piston towards BDC. Both, the valves are in closed position .Of the four stroke only during this stroke power is produced. Both pressure and temperature decrease during expansion. Exhaust stroke :- At the end of the expansion stroke exhaust valve opens and inlet valve remains closed. The pressure falls to atmospheric level a part of the burnt gases escape. The piston starts moving from the bottom dead centre to top dead centre and sweeps the burnt gases out from the cylinder almost at atmospheric pressure. The exhaust valve closes when the piston reaches TDC .At the end of the exhaust stroke and some residual gases trapped in the clearance volume remain in the cylinder. CHAPTER 4 ACTUAL CYCLE FOR I.C.ENGINE DIFFERENCE BETWEEN ACTUAL CYCLE THERMODYNAMIC CYCLE:- The working substance is not air but a mixture of fuel and air during suction and compression and many gases during expansion and exhaust. Combustion of fuel not only adds the heat but changes the chemical composition also. The specific heat of gases changes with respect to temp. The residual gases change the composition, temp. and amount of fresh charge. The constant volume combustion is not possible. Compression and expansion are not isentropic. There is always some heat loss-due to heat transfer from the hot gases to cylinder walls. There is exhaust blow down loss due to early opening of exhaust valve. 4.2 VALVE TIMING DIAGRAM FOR 4-STROKE PETROL ENGINE:- (1) Inlet valve:- The intake valve should open, theoretically, at TDC; almost all SI engines an intake valve opening of a few degrees before TDC on the exhaust stroke. This is to ensure that the valve will be fully open and the fresh charge starts to flow into cylinder as soon as the piston reaches TDC. In figure ( ), the intake valve starts to open 10 o before TDC. As the piston descends on the intake stroke, the fresh charge is drawn in through the intake port and valve. It may be noted from figure ( ), that for a low speed engine, the intake valve closes 10o after BDC, and for a high speed engine, 60o after BDC. If the inlet valve is allowed to close at BDC, the cylinder would receive less charge than its capacity and the pressure of the charge at the end of the suction stroke will be below atmosphere. When the piston reaches BDC and start to ascend on the compression stroke, the inertia of the fresh charge tends to cause it to continue to move into the cylinder. At low engine speeds, the charge is moving into the cylinder relatively slowly, and its inertia is relatively low. If the intake valve were to remain open much beyond BDC, the up moving piston on the compression would tends to force some of the charge, already in the cylinder back into the intake manifold, with consequent reduction in volumetric efficiency. Hence, the intake valve is closed relatively early after BDC for a slow speed engine. For High Speed Engine, Inlet Valve closing is delayed after BDC to take above advantage. (2) Exhaust valve:- The exhaust valve usually opens before the piston reaches BDC on the expansion stroke. This reduces the work done by the expanding gases during power stroke, but decreases the work necessary to expel the burned products during exhaust stroke, and the result in an overall gain in output. During the exhaust stroke, the piston forces the burned gases out at high velocity. If the closing of the exhaust valve is delayed beyond TDC, the inertia of the exhaust gases tends to scavenge the cylinder better by carrying out greater mass of the gas left in the clearance volume, and result in increased volumetric efficiency. Consequently, the exhaust valve is often set to close a few degrees after TDC on the exhaust stroke, as indicated in figure ( ), it should be noted that it is quit possible for both the intake and exhaust valves to remain open, or partially open, at the same time. This is termed the valve overlap. (3) Ignition:- It would be proper to produce spark at the end of compression if the charge could burn instantaneously. How ever, there is always a time lag between the spark and ignition of the charge. The ignition starts some time after giving the spark, it is necessary to produce the spark before piston reaches the TDC to obtain proper combustion without losses. The angle through which the spark is given earlier is known as Ignition advance or Angle of advance 4.3 SOURCES OF LOSSES:- The difference between I.P. B.P. is known as total friction loss. This includes direct mechanical friction throttling losses through valves, pumping loss, blow down losses many others. 4.3.1. Direct frictional losses:- It includes bearing losses, as main bearing, camshaft bearing, and piston cylinder friction loss in many moving parts. The frictional losses are comparatively higher in reciprocating I.C. Engine. 4.3.2. Pumping losses:- The difference of work done in expelling the exhaust gases and the work done by fresh charge during the suction stroke is called the pumping work. In other words loss due to the gas exchange process (Pumping Loss) is due to pumping gas from lower inlet pressure to higher exhaust pressure. The pumping loss increases at part throttle because throttling reduces the suction pressure. Pumping loss increases with speed. The gas exchange processes affect the volumetric efficiency of the engine. 4.3.3. Blow by losses:- This loss because of leakage of combustion products past the piston forms the cylinder into the crank case. This loss depends upon inlet pressure and compression ratio .This loss increase directly with compression ratio but reduced with an increase in the engine speed. 4.3.4. Valve throttling losses:- The standard practice for sizing the exhaust valve is to produce smaller exhaust area than inlet valve area. This increases the pumping loss as smaller area resists more for the flow of exhaust gasses. This increase in speed of the engine rapidly if the valve size, valve timing and valve flow coefficients are not designed properly as shown in fig. by dotted line . The inlet throttling occurs due to the restrictions imposed by air cleaner, carburettor, and venture, throttle valve, inlet manifold and inlet valve. All these add in pressure loss .Similarly some pressure loss occurs during exhausting the burned gases. 4.3.5. Combustion chamber pump losses:- This loss occurs with pre-combustion chamber. This loss occurs due to the pumping work required to push the air into pre-combustion chamber through small orifice. This depends upon orifice size, and speed. It also increases with increasing the engine speed. 4.3.6. Power loss to drive the auxiliaries:- Some power is required to drive the auxiliaries such as water pump, fuel pump, cooling fan generator. This is also considered as loss as part of engine power developed is used for these purposes. 4.3.7. Heat loss factor:- During the combustion process and expansion the heat flows through the cylinder head. Some heat enters the piston and flows through the piston rings into the cylinder wall or is carried away by the engine lubricating oil which splashes on the underside of the piston. The heat loss along with other losses is shown on p-v diagram (Figure ( )). Heat loss during combustion has maximum effect on cycle efficiency while heat loss just before the end of expansion stroke has very little effect because of the contribution of useful work is very little. The heat lost during the combustion doesnt represent the complete loss only about 15% of total heat is lost during combustion expansion. If all the heat loss is recovered only 20% of if may appear as useful work. The effect of loss of heat during combustion is to reduce the maximum temperature and therefore, the specific heats are lower. Heat loss factor contributes around 12% to all their losses 4.3.8. Time loss factor:- In a thermodynamic cycle heat addition is assumed to be instantaneous process where as in actual cycle it is over a definite period of time .the time required for combustion is such that under all circumstances some change in volume takes place while it is in progress. The consequence of finite time of combustion is that peak pressure will not occur when volume is minimum i.e. when the piston at TDC but it will occur sometime after TDC. 4.3.9. Exhaust blow down:- The cylinder pressure at the end of exhaust stroke is about 7 bar depending on the compressor ratio. If the exhaust valve is opened at bottom dead centre the piston has to do work against high cylinder pressure during the part of the exhaust stroke. If the exhaust valve is opened too early, a part of the expansion stroke is lost. The best compromise is to open the exhaust valve 40 to 700 before BDC. Thereby, reducing the cylinder pressure to halfway to atmospheric before the exhaust stroke begins. 4.3.10. Knocking in SI- Engine:- Knocking is due to the auto-ignition of the end portion of the unburned charge in the combustion chamber. As the normal flame front proceeds across the chamber, the pressure the temp of the unburned charge increase due to compression by the burned portion of the charge. This unburned compressed charge may auto ignite under certain temp. Conditions release the energy at a very rapid rate compared to normal combustion process in the cylinder. This rapid release of energy during auto-ignition causes a high pressure differential in the c.c. and a high pressure wave is released from auto-ignition region. The motion of high pressure compression waves inside the cylinder causes vibration of the engine parts and pinking noise and it is known as knocking or detonation. Effect of knocking:- Mechanical damage:- Knocking creates very high pressure wave (200bar) of large amplitude. This increases the rate of wear almost of all mechanical parts like piston, cylinder head, valves. The frequency of this wave is as large as 5000 CPS. (2) Noise:- When the intensity of knock is high, a loud pulsating noise is created because of high intensity pressure wave vibrates back and forth across the cylinder. This noise is like as bell noise. (3) Increase in heat transfer rate:- When the engine is knocking, more heat is lost to the coolant as the dissipating rate increases. The major reason of increases in heat transfer rate during knocking is, the boundary layer of the gas near the wall is removed because of high vibration of gas molecules. (4) Power output:- It is also observed that slightly rated spark develops more power under knocking condition. This may be due to rapid burning of the last part of the charge and retard spark may be optimum under knocking. (5) Pre ignition:- It defined as an ignition of the charge as it comes in contact with hot surface, in the absence of spark. Auto ignition may overheat the spark plug and exhaust valve and it remains so hot that its temp. is sufficient to ignite the charge in the next cycle during the compression stroke before the spark occurs an this causes the pre ignition of the charge. The temperature required for pre i