2 ObjectivesTo become familiar with the operation of a compression-ignition (diesel) engineTo determine the effect of load variation at constant speed onMechanical efficiencyThe primary characteristics of in-cylinder pressure developmentTo perform an energy balance on the engine
3 cylinder volume greatest. Engine NomenclatureFuel InjectorValvesCylinderPistonConnecting RodCrankshaftPiston at bottomdead center (BDC),cylinder volume greatest.Piston at topdead center (TDC),cylinder volume leastSwept Volume = Volume A – Volume BCompression Ratio = Volume A / Volume B
4 Operation of a 4 stroke compression ignition engine Cylinder VolumeCylinderPressureTDCBDCMaximum cylinder pressureCombustion commencesFuel injection commencesPhysical & chemicalignition delayExhaustB- IntakeStrokeP-V Diagram of the compression ignition cycleA to C is Intake strokePiston starts with minimum volume at A when it is at TDCIntake valve opensPiston moves downPressure stays at near atmospheric pressureCA
5 Operation of a 4 stroke compression ignition engine Cylinder VolumeCylinderPressureTDCBDCMaximum cylinder pressureCombustion commencesFuel injection commencesPhysical & chemicalignition delayExhaustInductionP-V diagram of the beginning of the compression strokeBoth valves are closedPiston begins to move upwards from C to DThe air in the cylinder is compressedPressure and temperature riseDC
6 Operation of a 4 stroke compression ignition engine C to E is called the Compression StrokeCylinder VolumeCylinderPressureTDCBDCMaximum cylinder pressureCombustion commencesFuel injection commencesPhysical & chemicalignition delayExhaustInductionEP-V diagram of the entire compression stroke (From C to E)Fuel injection begins at D before the piston has reached TDCCombustion commences a short time laterDelay is due to the fact that the chemical reaction of combustion takes a finite timeNo ignition source like a spark plugFuel air mixture ignites due to the high air temperatureSharp rise in pressure as the products of combustion expandDC
7 Operation of a 4 stroke compression ignition engine E to G is called the Power StrokeCylinder VolumeCylinderPressureTDCBDCMaximum cylinder pressureCombustion commencesFuel injection commencesPhysical & chemicalignition delayExhaustInductionF – Power StrokeEP-V diagram of power stroke (From E to G)Expanding gasses in the cylinder force the piston downThis is when the usable power is producedG
8 Operation of a 4 stroke compression ignition engine Cylinder VolumeCylinderPressureTDCBDCMaximum cylinder pressureCombustion commencesFuel injection commencesPhysical & chemicalignition delayH- ExhaustStrokeInductionOnce piston reaches BDC the exhaust valve opensBack at atmospheric pressurePiston moves up to expel the exhaust and the cycle begins againIt is called a 4 stroke cycle engine because the piston makes four strokes to complete one engine cycleGA
10 Injector Needle Lift and Fuel Line Pressure Fuel Injection Pump RackDisplacementTransducerPfuelFuelSupplyFuelSpill PortInjector NeedleRotate Shaft to AdjustCam at ½Engine Speed
11 Petter Diesel Engine Injector Pump PLUNGERFUEL SPILL PORTFUEL SUPPLY PORTHELIX (The position of the helix to the fuel spill portmeters the amount of fuel delivered to the injector bychanging the effective stroke of the pluger.)In this experiment we will vary the injector pump setting to allow more or less fuel to enter the engineWorks by adjusting the control rack which turns the helix on plunger.The fuel can spill to both sides of the plungerIntake the plunger moves down to allow fuel in the inlet portAs it moves up the pressure increases until it is sufficient to overcome the spring and fuel flows to the injectorOnce the helix passes the bypass port, fuel is allowed to flow out the fuel spill
12 In Lab Procedure Collect data at four operating points. Constant RPM (N=1050 RPM)Increase fuel injection and obtain N=1050 by increasing loadAt each operating pointAwait steady state (exhaust gas temp.)Fill out data sheetsCapture Pcyl and V vs time waveform on oscilloscopeAt intermediate operating point (3rd operating point)4 Pcyl and V vs. time for single cyclesInjector needle lift, Pfuel, Pcyl , vs time
13 Calculations and Discussion Brake PowerIndicated PowerNeed to plot P-V diagrams for each loadSpecific Fuel ConsumptionVolumetric EfficiencyAir/Fuel RatioMechanical EfficiencyBrake Thermal EfficiencyMass flow rate of Exhaust“Willans Line” TestEnergy BalancePlot a Pcyl and V vs. t diagram for a cycle at the 3rd load conditionPcyl vs. t for 4 cycles at 3rd test conditionV vs. t for 4 cycles at 3rd test conditionPlot injector needle lift, fuel line pressure, and Pcyl vs. timePlot the first derivative of Pcyl on a Pcyl vs. t diagramPreliminary DiscussionOperation of fuel injector pumpTiming of fuel pressure, injector needle lift, pcylDiscuss Signals on the scopePredictions of how performance measures will change between operating pointsHow does the data differ from the idealized Diesel cycle (what assumptions are not valid in a real engine)
14 1. Brake Power Rotational speed of engine [rev/s] Brake load [N] Power measured at the output shaftBrake load [N]Load arm radius [m]
15 3. Specific Fuel Consumption Fuel consumption (kg/h)Brake Power
16 4. Volumetric Efficiency Orifice coefficientOrifice areaAmbientDifferential pressure acrossOrifice (Pa)Free air delivery is the volumetric rate that air is actually delivered to the cylinderSwept volume rate is the rate at which the cylinder volume actually changesMeasures if the valve cannot incorporate air fast enough during intake
18 6. Mechanical Efficiency Brake PowerIndicated Power
19 7. Brake Thermal Efficiency Mass flow rate of fuelLower heating value for fuel
20 8. Mass Flow Rate of Exhaust Conservation of Mass
21 11. Pcyl and V vs. tLabel the four strokes on a Pcyl and V vs. t diagram for one of the four cycles observed at the 3rd test condition.PV
22 14. Injector Needle Lift, Fuel Line Pressure, and Pcyl vs. t Plot injector needle lift, fuel line pressure, and Pcyl vs. time on a single plot.Comment on the relationship between these three. (Focus on the order and timing of when things occur).
23 15.Calculate the first derivative of in-cylinder pressure for ONE cycle taken at the 3rd load condition.Plot it on the corresponding Pcyl vs. time diagram and comment on the relationship of this graph to the operation of the engine.
24 What do we want in our logbook: Explain a summary of experiment Explain about general operation of injector pump.Thermodynamic cycle and changes in pressure and volumeWhat is the relation between of fuel injection, combustion and rate of change in pressure in cylinder.Fill data sheet completely.
25 2. Indicated Power: Proportional to the area within the power and compression strokes minus the area within the intake and exhaust strokes.Only 2 of 4 strokes consideredArea within intake and exhaust strokes is very small and can be neglected!Cylinder VolumeCylinderPressureTDCBDCMaximum cylinder pressureCombustion commencesFuel injection commencesPhysical & chemicalignition delayExhaustInductionArea under P-VIndicated power is calculated by the area inside the P-V diagramThe Intake and exhaust strokes are negligible compared to the comperession and power strokesCan neglect themN/2 because only 2 of the four strokes are considered
26 Step 1: Plot P-V Diagram P-V Data will look something like this Noisy Goes below the origin
30 P-V Diagram after Offsets and Filtering We only do this to make the data easier to work with.It would work without because we are just finding the area inside the P-V diagram
31 Indicated PowerMean effective pressure basically transforms the integral of the P-V diagram into a rectangleFind area inside the P-V diagramPower generated - Power used in compression stroke.Use the same area can find a constant pressure
32 Indicated PowerIndicated Mean Effective PressureWhy N/2 ?