This project gives a brief description of the cylinder head and its functions in an engine. Then it involves various experiments on the Flow Bench Machine FS300 to measure the air flow through the intake and exhaust ports. For these experiments K-Series cylinder head has been selected. The main objective of this project is to study the various aspects which affect the air flow, on which the power of the engine depends.
Description of Engine
Engine is the deriving body of a vehicle that converts the chemical energy from a fuel into thermal energy then to mechanical energy hence causing the vehicle to move. The engine consists of many parts moving as well as stationary which includes spark plugs, cam shafts, cylinder head etc.
Cylinder head is a single casting which makes a important part of the internall combustion engine, the location of the cylinder head in on top of the cylinder( as its name suggests). In the figure below the red square identifies the cylinder head. It holds the parts which allow the flow of gasses through the engine and burning of the fuel eg the vavles, injectors and spark plugs. It has also got an water jackets inside it which helps it in keeping the temperature of the cylinder head down. the cylinder head is connected with the rest of the engine with the help of studs and bolts which hold it in place and the gap btween them is covered with a cylinder gaskit which prevetns the gasses excaping from the gap. Cylinder head consits of a really simple structure which is the main reason of its success in the automation industry.
The internal structre of the cylinder head consists of different passages for the gas and air mixture as well as the lubricant oil. Gas exchange valves are also mounted in the cylinder head also called its valve ports. In which the intake manifold is used for the inlet valves and the exhaust manifold for the release of the exhaust gasses . it also has the cooling passages for the anti-freeze to cool the head and engine.
The design of the engine block determines the shape of the cylinder head. Most engines have one cylinder head like in normal car eingine where as some have 2 or even more depending on the shear size of the engine.
The cylinder head is an important key to the performance of the internal combustion engine, as the inlet passages and ports as wel as the shape of the combustion chamber determines a major portion of the volumetric efficiency and compression ratio of the engine.
Types of cylinder head
There are different types of cylinder heads depending on the valve position whose usage depends on which type of engine they will be used in. Following are the types used.
* “L” Head
* “I” Head
* “F” Head
* “T” Head
The “L” Head
Pict0018in the L type cylinder head the inlet and the exhaust ports are on the same side of the cylinder block and operated by a single cam shaft
The “I”Head type
Pict0019In this type of cylinder head the inlet and exhaust valves are located on one side of the cylinder head. These valves are also operated by a single camshaft through the tappet, pushrod and rocker arm mechanism.
The “F” Head type
Pict0020In this type of cylinder head the inlet valves are located on one side of the cylinder head and the exhaust valves are located on the other side of the cylinder block. They are also operated by a single camshaft. The inlet valves are operated by the tappet, pushrod and rocker arm mechanism and the exhaust valves are operated by the tappet directly
Pict0021In ‘T' heads, the inlet valves are located on one side of the cylinder block and exhaust valves are located on the other side of the cylinder block. Two camshafts are used to operate the valves, one for inlet and one for exhaust. In this mechanism the valves are operated by the tappet directly.
Manufacturing of the cylinder head
Cylinder head is made of grey iron which is a form of cast iron cast iron. There are different types of cast iron available depending on which materials have been used along with the iron which usually makes 90% of the whole material. In grey iron the additional materials used are graphite, silicon, manganese and phosphorus along with the iron. The grey surface apprerence of the component gives it the name grey iron. It is brittle and does not sustain too much shocks, on the other side it resists corrosion, absorbs heat and can be cast into many shapes by the moulding process of sand casting. Cast iron cylinder heads are used in diesel engines.
Aluminium is also used in manufacturing cylinder heads, it is commonly used in petrol engines, it is dearer as compared to cast iron because its properties like lighter weight with great stregth to weight ratio and conducts away heat quicker than cast iron so with the aluminium alloy head the heat of the combustion can be conducted away into the coolent more quickly
Aluminum cylinder head is also made in the same ways as the iron cylinder head i.e. sand casting using a sand mould which is filled with the molten metal then allowed to cool down. Sand moulding is broken down to recover the mould. The whole process of sand casting is explained in a form of a diagram below.
Components of the cylinder head
The cylinder head comprises of the following parts
* The valves
* Valve guide
* Valve spring
* Valve stem seal
* Spark plugs
* Water jacket
* Cylinderhead gasket
* Intake manifold
* Exhaust manifold
Now day's modern engines are using poppet valves. They can be opened by applying a force against the stem and can be closed by the pressure of the spring. The valve consists of following parts.
* The large diameter end of the valve is known as head.
* The angled outer edge of the head is called the face.
* The relative smaller diameter long end is called the stem.
* The area between the valve face and valve head is called the margin.
* Valve seat is the point at which the seal is made by the valve face. 70% of the heat produces during the engine operation is dissipated through these valve seats. Other 30% is removes through the stem.
* The fillet is the curved area between the stem and the head.
Valve guide provides the sliding surface and location for the valve stem as it moves up and down in the cylinder head. The guide is made of cast iron and is precision machined so that when the valve closes, its face makes full contact wit the valve seat in the cylinder head. Valve guides are machined to fit a few thousandths of an inch clearance with the valve stem. This close clearance is very important because it keeps lubricating oil from getting sucked into the combustion chamber past the intake valve stem during the intake stroke. It also keeps the valve face in perfect alignment with the valve seat. Valve guides are constructed in two ways, either they are cast integrally with the head or they may be removable.
The head of the intake valve is larger than the exhaust valve because exhaust valves are forced out of the chamber through the upward movement of the piston. So exhaust valves have fewer restrictions and are able to work in small size. While the intake valves drawn in the air/fuel mixture and their large size increases the efficiency. And also there is very limited area in the combustion chamber, so if the intake valve is in larger size than the other should be of smaller size.
Usually the valve face is cut at an angle so that it caused the seal to wedge tighter when the valve is closed and allow free flow of air/fuel mixture when valve is open. Normally this angle is either of 30o or 45o.
If careful attention is paid to the port size, valve throat shape and size and to the valve guide bosses together with careful reshaping of the back/seat of the valves and the seat inserts, the resulting increase in volumetric efficiency is quite marked.
The purpose of the valve springs are to return the valves to their seats, keeping them close until they are opened again by the cam lobe. The most common device used to hold the valve and spring in position is the retainer and collets. The retainer is shaped to fit over the valve stem and sit on top of the valve spring. The hole in the centre of the retainer is tapered to take the two collets. On assembly of the valve and spring, the collets are wedged against the valve stem by the action of the taper in the retainer locking the components in position so they move as one unit.
http://howautowork.com/part_1/ch_1/cylinder_head_11.html (visited 28 jan 10)
http://www.5min.com/Video/Cylinder-head-designs-30592630 (visited 28 jan 10)