【正文】 the same cylinder has cooling 39。s light and easy to cast,while the sleeve uses another kind that is better able to stand up to wear and tear. There are three main types of sleevesdry,flanged dry,and wet. The dry sleeve can be cast in or pressed into a new block, or used to recondition badlyworn or damaged cylinders that can39。s a pressed fit in its bore in the cylinder wall is about 2mm outer surface is in contact with the block for its full top finishes flush with the top of the block and can hardly be in place,dry sleeves bee a permanent part of the cylinder block. A flanged,dry sleeve is like a normal dry sleeve,but a flange at the top fits into a recess in the surface of the engine 39。s worn. With a wet sleeve,the outer surface is part of the waterjacket around the 39。t have the same support from the block as dry sleeves so they depend on their wall thickness to stop distortion. In diesel engines,vibration caused by bustion can cause damage appears similar to corrosion and it can eventually destroy the cylinder. Grey Iron Grey iron is a form of cast are many different kinds of cast iron,depending on the particular materials they iron is a cast iron that contains carbon in the form of graphite,plus silicon,manganese and fractured surface of a cast iron with graphite appears grey,hence the is brittle and cannot absorb resists heat and corrosion,and can be cast into many different is used for many ponents. Cylinder Head The cylinder head bolts onto the top of the cylinder block where it forms the top of the bustion engines of light vehicles have just one cylinder head for all the inline engines can have two or and horizontally opposed engines have a separate cylinder head for each bank of cylinders. Just as with engine blocks,cylinders heads can be made of cast of cast iron,or aluminium head made of aluminium alloy is lighter than if it were made of cast iron. Aluminium also conducts heat away more quickly than with an aluminiumalloy head, the heat of bustion can be conducted away into the coolant more quickly . Manufacturing the head is similar to manufacturing the casting mold is cores are put in to form any hollow areas. Depending on the engine,these can be for coolant and lubricant passages,and inlet and exhaust ports. Aircooled engines have cooling fins cast into the cylinder head. The underside of the head is shaped to form the bustion chamber. Molten metal is poured in,and allowed to cool. The cores are broken out and removed,and the cylinder head cleaned of any sand. After casting es that must seal are machined are drilled and tapped for attaching blots and studs. 4 In sandcast heads, the large holes that had contained sand are machined,then fitted with soft metal plugs, called core plugs. Cylinder Head Design Cylinder heads are designed to help improve the swirl or turbulence of the airfuel mixture,and prevent fuel droplets settling on the surfaces of the bustion chamber or cylinder walls. When airfuel mixture is pressed between the piston and the flat part of the cylinder head,it produces what39。squish39。s taking in the air or airfuel mixture. Fuel starts to burn at the plug,then burning travels outward in all is called flame the plug in the middle of the hemisphere,the flame front has less distance to travel than in some other designs,which gives rapid and effective design is mon in a lot of passenger vehicles. The bathtub bustion chamber is ovalshaped,like an inverted are mounted vertically and side by side,making them simple to plug is to one side,and that creates a short flame all helps increase turbulence. The wedgeshaped bustion chamber tapers away from the plug which is at the thick end of the valves are in line and inclined from the design usually has a smaller surface area than the others,with less area where fuel droplets can fuel is left unburned after bustion ,which reduces hydrocarbon exhaust since the flame is directed toward the small end of the wedge,damage caused by detonation is reduced. Diesel Combustion Chambers Diesel bustion chambers e in 2 main and indirect are designed to promote turbulence,to help the pressed air and injected fuel mix well. Engines using direct injection have cylinder heads with a flat bustion 5 chamber is formed in the top of the , the rim of the piston provides 39。,forcing the air to the center of the bustion causes turbulence as fuel is injected into the cylinder. In indirect injection,the piston is fairly flat,or has a shallow main bustion chamber is between the cylinder head and the top of the piston,but a smaller,separate chamber is in the is injected into this smaller can have various swirl chamber is spherical,and connected to the main chamber by an angled passage .Both the injector and glow plug are screwed into the glow plug preheats the air inside to help start the pression ,the spherical shape makes the air swirl in the helps make a better mixture of the air and fuel,which improves bustion .This bustion chamber is divided into a main bustion chamber and an air cell, joined by a throat. The injector is in the throat. When injection mences,bustion pressure forces the air to flow from the air cell where it mixes with fuel from the rush of air from the air cell produces a rotary motion of gas in the main chamber which helps make bustion more prebustion chamber is screwed into the cylinder injector is mounted in the upper end. Injection occurs near the top of into the pression stroke .Only part of the fuel is burned in the prebustion because of the limited amount of air high rise in pressure forces burning fuel into the main happens very rapidly,which helps make more efficient bustion. Intake and Exhaust Passages