Laboratory-exercise-3-teofilo.docx

Laboratory Exercise 3 fnglkjglgkgtjgijgntlkjsghligkjhgtkgjhglkhdlguhtgnjklhdgkhggt Engine Parts

Name: Teofilo, Francis Erwin E.

I.

Date Submitted:___________________

Introduction

The car's engine is not a singular unit but built up from several differently sized components that perform their intended functions. The present day automobiles that derive their power from internal combustion engines operating on fossil fuels have the following principal parts: “mechanical” and “electrical." The core of the engine is the cylinder, with the piston moving up and down inside the cylinder. Single cylinder engines are typical of most lawn mowers, but usually cars have more than one cylinder. In a multi-cylinder engine, the cylinders usually are arranged in one of three ways: inline, V or flat (also known as horizontally opposed or boxer).

II.

Objectives 1. Familiarize the parts of an engine. 2. Knows the purpose and functions of the different parts of an engine.

III.

Methodology

1. Cylinder The engine cylinder is the part or space where fuel is admitted and reciprocating motion of the piston is obtained by burning it. The engine cylinder is characterized by its bore and stroke. Bore represents its inner diameter and Stroke is the effective length along which the piston reciprocates. Two terms related to stroke are top dead center (TDC) and bottom dead center (BDC). Top dead center is the uppermost point of the stroke while the Bottom Dead Center is the lowermost point of the stroke. The velocities of the piston at TDC and BDC are zero.

2. Piston The piston is the cylindrical part which moves up and down in the cylinder and enables compression and expansion of the charge during the combustion cycle. The diameter of the piston is slightly less than the bore of the cylinder to avoid direct wear of the cylindrical piston surface. Three rings known as piston rings are fitted in the circular recesses machined on the piston surface. These rings are in direct contact with the cylinder liner thus preventing piston wear. The top two rings are known as compression rings. Compression rings are chamfered on the outer periphery. They prevent the fresh charge or waste gases inside the combustion chamber from going into the crankcase, a process known as blowby. The lowermost or third ring is called the oil ring. Its purpose is to ensure proper oil distribution along the cylinder walls and also prevent the leakage of oil into the combustion chamber.

3. Crankshaft Crankshaft is a part of the engine which has projections bent and offset from the shaft axis. These projections are called crank throws or crankpins. This design converts the sliding motion obtained from the piston into rotary motion via a connecting rod. Crankshaft is placed below the cylinder block in a casing called the crankcase. In multi cylinder engines one crankpin per cylinder is provided to attach the piston by the connecting rod. The crankpin journal bearing is called the big end and has plain or sliding bearings. Crankshafts have some counterbalance weights which are either bolted to the crank body or form an integral part and are called crank balance. Crank balance is provided to counter the torsional vibrations experienced by the crankshaft due to the reciprocating unbalance of the piston which arises due to the jerks from the combustion process. Crankshafts may be manufactured in parts or as a single piece. The single piece design is preferred as it gives superior strength, better fiber flow and good stress bearing capabilities.

4. Connecting Rod The connecting rod is the link connecting the piston to the crankshaft. It converts the linear motion of the piston into rotary motion of the crank. One end of the connecting rod is attached to the piston through a piston pin/gudgeon pin/wrist pin and is called the small end while the other end is attached to the crankpin journal through bolts holding the upper and lower bearing caps and is called the big end. The bearing is in the form of two half shells which is held in place around the crank journal by the big end of the connecting rod. Both the ends of the connecting rod are not rigidly fixed but are hinged so that they can rotate through an angle. Thus both its ends are in continuous motion and under tremendous stress from the pressure from the piston. The connecting rods are the most sensitive parts and are most prone to failure and hence they are manufactured with high degree of precision.

5. Cylinder Head The cylinder head is the part which sits on top of the cylinder block and houses the valves, rocker arms and the ignition elements. It is bolted to the cylinder block with the head gasket in between. In overhead camshaft engines, the camshaft is present in the head and there is no pushrod arrangement for valve mechanism. The inlet and exhaust ports are also machined within the head to which the inlet and exhaust manifold are then attached. Cylinder heads also form part of the combustion chamber that is machined into it on the underside. Holes and channels are made for bolting and for flow of coolant. Inline engines have a single cylinder head for all the cylinders while V-type and horizontally opposed have a separate head for each bank of cylinders.

6. Camshaft Camshaft is a shaft to which cams are fitted or are machined. The function of the camshaft is to operate the valves directly by sitting over them, or indirectly through a mechanism (rocker arm, pushrod). Camshaft rotation decides the valve timing and is of critical importance. The opening and closing of valves is governed by camshaft which is coupled to the crankshaft either directly through a reduction gear or indirectly through a pulley and a timing belt. Engines in which the camshaft is coupled to the crank by a gear require a pushrod and tappet mechanism along with rocker arms. The gear on the crank has half the teeth than on the camshaft gear. This causes the camshaft to run at half the RPM of the crank. In engines where the timing belt and pulley are used, the camshaft is placed inside the head and there is no need

of a pushrod. Instead latches are used which rotate the rocker arm and operate the valves. Such a design is called overhead camshaft (OHC) design. Some engines use a single camshaft to operate both the inlet and exhaust valves and are called single overhead camshaft (SOHC) while others utilize a separate camshaft for operating the two types of valves which are arranged in two separate rows and are called double or dual overhead camshaft (DOHC) engines. OHC design reduces manufacturing cost and is less prone to failure. The lobes of the cam are tapered slightly so that the valves lifters rotate slightly with each depression and wear uniformly. There is considerable sliding friction between cam and follower surface and so they are surface hardened.

7. Valves Valves used in the IC engines are called poppet valves. They have a long thin circular rod known as the valve stem at the end of which is a flat circular disk called the valve head. The valve head has a tapered section connecting to the rod which forms the valve seat. The valve slides in a valve guide and sit in the valve seat when closed which is machined in the head. This sliding motion is enabled by the camshaft and associated linkages and the valves are kept closed or returned to their seats when not in use by valve springs. The valves are responsible for intake of fresh charge and exhaust of waste gases. The valve which admits fresh charge is called intake/inlet valve and the one which allows exhaust gases to go out is called exhaust/outlet valve.

8. Crankcase The metallic case or housing in which the crankshaft is placed is called the crankcase. The crankcase is located below the cylinder block. The crankcase also has the main bearing in which the crank rotates. The main bearing is a plain or sliding bearing with proper oil supply in it. The four cylinder inline petrol engines have three main bearings, one on each end and one in the middle while the diesel counterparts have five main bearings one on each end and one between each cylinder. The crankcase encloses the crankshaft and connecting rod assembly and protects it from dust, dirt and other foreign materials. The crankcase is filled with air and oil and is sealed off from the fuel air mixture and exhaust gases in the combustion chamber by the piston rings.

9. Fuel Pump The fuel (diesel) in a CI engine is not mixed with air unlike SI engines, but is sprayed into the combustion chamber through a nozzle for ignition. The fuel pump pressurizes the fuel to such a pressure that it atomizes and when it is sprayed in the cylinder, it gets ignited when it comes in contact with the air. The fuel pump consists of a spring loaded piston valve in a cylinder. When fuel from the fuel filter is introduced in the fuel pump, the spring loaded piston applies pressure on it. The pressure is transmitted through the pressure lines and finally to the injector which has a nozzle opening in the cylinder. Thus the fuel gets atomized and ignited.

10. Spark Plug The spark plug is an electrical device which ignites the fuel in the combustion chamber at the end of the compression stroke. The fuel gets ignited and as a result expands and pushes the piston down so as to obtain the power stroke. The spark plug is fitted into the cylinder head on the underside of the combustion chamber through threads on the plug body. The spark plug has two electrodes: one central electrode which is connected to the ignition coil or magneto through a highly insulated high tension wire; the other electrode is at the base of the plug and is

grounded. There is a small gap between the two electrodes generally between 0.9-1.8 mm. When high voltage current from the ignition coil/magneto is supplied the air between the gap gets ionized and a spark is generated which is sufficient to ignite the fuel. The electrode gap is of critical importance for proper sparking at all speeds. The spark plug requires a voltage in the range of 12,000 - 25,000 V to fire properly. The spark plug has a terminal, an insulator and its tip, metal jacket and the seals in the body structure. The terminal is connected to the ignition coil, the insulator (made of porcelain) provides insulation and mechanical support, the metal jacket conducts heat away from the plug body and to the cylinder head, and the seals properly seal the recess in the cylinder head where the spark plug is fitted.

IV.

Documentation

V.

Results and Discussion In realization of the laboratory, it is hard to assemble and disassemble an engine if you are not careful with all of its components. If you are not familiar with all the engine parts, you will end up putting the parts in the wrong place causing the engine to fail to work. Also, a missing part will surely make the engine fail. Some engine parts had been listed down in this laboratory with their functions. Some of the engine parts is like the engine cylinder where fuel is admitted and reciprocating motion of the piston is obtained by burning it, the piston which transmits the pressure forces in the combustion chamber to the rotating crankshaft, and the crankshaft which converts the rectilinear motion of the piston into rotation. Then there’s the connecting rod which transmits the power of combustion from the piston to the crankshaft, the cylinder head which houses the valves and forms a cover to the cylinder and the camshaft which used to push open valves at the proper time in the engine cycle. The valves which used for opening and closing ports and crankcase which supports the shaft. Also, there’s the fuel pump which supply fuel from the fuel tank to the engine and the spark plug which initiate combustion in an SI engine.

VI.

Summary and Conclusion During the laboratory, the engine was disassembled and then all the engine’s components were observed as shown in the images above. Then the functions of each component had been written down. The engine was assembled after the observation. I therefore conclude that we should need to know the different components of an engine in order for us to know how to assemble or disassemble one and so that we will know which part of the engine causes the engine to fail and which part is missing.