Performance and Operating Characteristics of IC Engine1Geometric parameter of reciprocating engine The performance oftheinternal combustion engine ischaracterized with several geometric andthermodynamic parameters The following geometric parameters are of particular interest :bore(B), connecting rodlength (l),crank radius (a),stroke (S)andcrank angle (ө) For any single cylinder, the cranks shaft, connecting rod,piston, andhead assembly canbe represented bythe mechanism shown totheleft 2Geometric parameter of reciprocating engine Thetopdead center TDCofanengine refers to thecrankshaft being inaposition suchthatө=00. Thevolume atTDCisminimum andisoften called theclearance volume Vc Thebottom dead center (BDC) refers tothe crankshaft being atө=1800,thevolume atBDC ismaximum andoften denoted byVT Thedifference between theVTand Vcisthe displacement volume Vd 3Geometric parameter of reciprocating engine Engine Capacity (Ve) Where n-is number of cylinders Vd-cylinder swept volume Displacement RateStroke VS BoreVS VS VSTDC BDC ()   =×=42BnSnV Vd eπ For 4-Stroke EngineGeometrical Properties of Reciprocating Engines Compression ratio r, or = 8 to 12 for SI engines and or = 12 to 24 for CI engines; Ratio of Cylinder bore to piston Stroke: B/S=0.8to1.2forsmall-andmedium-size engines, about 0.5forlarge slow-speed CIengines ; 5Geometrical Properties of Reciprocating Engines Ratio of Connecting rod length to crank radius: R = 3 to 4 for small -and medium -size engines, increasing to 5 to 9 for large slow -speed CI engines. Thestroke andcrank radius arerelated by alR= 6The cylinder volume V at any crank position Thevolume ofthecylinder canbedetermined as function ofcrank angle (),from thecompression ratio,thestroke ,boreandconnecting rodlength . AtTDC thecrank shaft isatcrank angle of0o. (Clearance volume, Vc) AtBDC thecrank angle isat180o.(Maximum cylinder volume, VT)θ 7The cylinder volume V at any crank position Displacement volume = (Maximum - minimum) cylinder volume The displacement volume can also be represented asafunction ofthebore and stroke Atagiven crank angle thevolume isgiven by: )(42 θπxBVVC+=θ 8