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marine engineering
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Indicator diagramsNATIONAL MARITIME ACADEMY
QuestionsExplain the need for taking series (set) of power cards to assess engine performanceExplain minimum information required from the power card for accurate assessment of engine performance (Hint- MIP, Pmax, Pcomp)Explain the significance of:Out of phase diagram (draw card)Light spring diagram Explain the effect on the on engine performance if it is operated with high Pmaxlow Pmax
FoundationHeat balance is done when engine is operating at its peak performanceAbout 50.5% of power from fuel is converted to shaft powerIf there is a fault, wear & tear in the engine, less power is available at the shaft
FoundationWe use diesel and dual cycle to understand the processWe use indicator cards to monitor performance
Three important ratios that affect Air Standard Efficiency and engine operation
Increase in compression ratio, Air Standard Efficiency increases-page 5Decrease in cut off ratio ASE increasesIncrease in pressure ratio ASE increases- page 3The above ratios are applicable to actual Diesel engine for the purpose of optimising performance with indicator diagrams.
Purpose of Indicator Diagrams
Power calculationMean Indicated Pressure Combustion and compression pressuresEvaluation of the combustion process Evaluation of scavenging process Calculation of air temperatures in the compression chamber.Page 7
Draw diagramcompression pressure, maximum pressure of ignition and the slope of the ignition curve. Page 7,8,9
Fault Diagnostics with Indicator Diagram
Fuel injection timingProper injection timing can be checked by an evaluation of power from indicator diagram and measurement from draw diagrams.If the Maximum Combustion Pressure (Pmax) is within limits,M.I.P is satisfactoryExhaust temperature is within limitsRack position relationship is satisfied, It should be assumed that the fuel timing is correct, if it is not correct then it can be either too late or too early
Fuel injection timing
Leakages, blow byincreased clearance volume
Light springChoked scavenge portsNormalHigh exhaust back pressure