Chapter or long-stroke if its cylinders have
Chapter 2Design of EngineEngine type based on bore/stroke ratioThe diameter of the cylinder bore is divided by the length of the piston stroke to give the ratio. Under squareover squaresquareUnder square: An engine is described as under square or long-stroke if its cylinders have a smaller bore (width, diameter) than its stroke (length of piston travel) – giving a ratio value of less than 1:1.Over square: An engine is described as over square or short-stroke if its cylinders have a greater bore diameter than its stroke length, giving a bore/stroke ratio greater than 1:1.
Square: A square engine has equal bore and stroke dimensions, giving a bore/stroke value of exactly 1:1. COMBUSITION CHAMBERFor si engineThe design of combustion chamber has an important influence upon the engine performance and its knock properties. The design of combustion chamber involves the shape of the combustion chamber, the location of the sparking plug and the disposition of inlet and exhaust valves Basic requirements of a good combustion chamber high power outputHigh thermal efficiency and low specific fuel consumption Smooth engine operationReduce exhaust pollutants Different types of combustion chamberT- Head combustion chamber – It require two cam shafts (for actuating the inlet value and exhaust value separately) by two cams mounted on the two cam shaftsL- Head combustion chamber – It is a modification of the T-head type of combustion chamber. It provides the two valves on the same side of the cylinder , and the valves are operated through tappet by a single cam shaftI – Head combustion chamber – These type of combustion chamber has both inlet value and the exhaust value located in the cylinder head F- Head combustion chamber – In such a combustion chamber one value is in head and other in the block For CI engine The design of combustion chamber for CI engines must also take consideration of injection system and nozzles to be used.
Types of CI combustion chamber Open injection type- In these type the entire volume of combustion chamber is located in the main cylinder and the fuel is injected in to this volume In direct injection type – The combustion space is divided in to two parts one part in the main cylinder and other part is in cylinder head. The fuel- injection is effected usually in to the part of chamber located in the cylinder head. PISTON Piston is widely used in the diesel engine, gasoline engine and air compressor.
Engine piston structure consists of three parts, piston top, piston head and piston skirt Piston topPiston top has three different types. Flat piston top, concave top and convex top.Flat piston top. Flat piston top with an flat surface is simple and easy to produce. It is widely used in the gasoline piston and rarely used in the diesel engine piston.Concave piston top.
Concave top engine piston has an concave top surface, which is conducive to the burning of combustible mixture. The shapes of concave are double vortex shapes, ball shapes and U shapes. Concave top engine piston is commonly used in the diesel engine.
Convex piston top. Convex top engine piston is in raised ball shape, which has high strength. It can improve gas exchange process and act as the guide role. Convex top engine piston is widely used in the two-stroke gasoline engines of motorcycle. Piston headPiston head refers to the location from bottom line of piston top to the bottom line of first oil ring groove.
Piston head is mainly used for piston ring installation. piston ring groove has two to five lines. Quantity of piston ring on the gasoline piston is less than the diesel piston. Piston ring has compression ring and oil-control ring two types.
Compression ring groove uses with compression ring to seal cylinder and prevent combustible mixture from entering the crankcase. Oil-controlling ring groove uses with oil-control ring to scrape extra engine oil off cylinder.Another function of piston head is transfer the heat to cylinder wall through piston ring.TYPE OF ENGINE BORE(MM) STROKE(MM) COMPRESSION RATIOS.I(4-STROKE) 96.
8 86. 8.6S.I(4-STROKE) 84.5 88 8.5S.I(4-STROKE)TURBO CHARGED 92 80 7.5CalculationsB= BoreS= stroke lengthCc= cubic centimeterTh= thickness of piston head?b=a=radial wall thickness of ringd=nominal dia of ringh=axial width of ringS1=closed gap of ringt3=thickness of piston barrel at the top endt4=thickness of barrel at open endL1=length of piston pin Di=inner dia of piston pinCR=compression ratioPetrol engine ccCompression of petrol engine=9Ultimate tensile strength for aluminum alloy=485Factor of safety=8Cc=?/4*bore2*stroke 500= ?/4*B2*90 Bore=84 mmPiston head calculations Th = D?316*p??b=Sut/fs = 485/8 = 60.625Th=84?316*460.25 =9.34 mmCup dimensions The radius of cup=l/d?1.5 (cup required) l/d?1.5 (no cup required)radius of cup=0.7*D =0.7*84 =58.8 mmPiston ring a1=3.6 mm d1=85 mm S1=0.30+0.20Top land=Th Th=thickness of piston=9.34 mmWidth of ring groove (piston ring to piston ring gap) W=0.75*h1 =1.5 to 2 mmPiston barrel T3=0.03d1+a1+4.9 =11.05 mmT4=(0.25t3) to (0.35t3) =0.25*11 to 0.35*11.05 = 2.76 to 3.86Piston pin L1=0.45*D =0.45*84 =37.8 mmThickness of cylinder wall =0.045*D+1.6 =0.045*84+1.6 =5.38 mmThickness of dry liner =0.03*D = 0.03*84 =2.52 mmThickness of water jacket =0.032*D+1.6 =0.032*84+1.6 =4.288 mmWater space between outer cylinder wall & inner jacket wall= 0.08*D+6.5 = 0.08*84+6.5 = 13.22 mmThickness of cylinder head Th=D*?(Pmax/?c) D = 84 K=0.162 Pmax=4-5Cylinder head aluminum material Sut=210 mpaFactor safetyfs = 6?c=Sut/fs =210/6 =35 Th=92?0.162*435 = 12.51 mmComponent Material ProcessCylinder block DuctileCast iron 30c8(low carbon steel) CastingForgingAfter heat transferCylinder head Aluminium alloys CastingPiston Aluminium alloy 4625 Castingpiston rings Cast iron of fine grainHigh elastic material Pot casting methodconnecting rod Low carbon steel 30c8 ForgingAfter that heat treatmentcrank shaft 37c15 alloy steel Castingfly wheel Cast iron Castingpoppet valves Phosphorous bronzeMonel metal manifold Aluminium alloy-4600 gudgeon pin Plain carbon steel rocker arm Medium carbon steel cam shaft Plain carbon steel 10c4 GrindingCase hardening