SCHOOL OF COMPUTING, ENGINEERING AND MATHEMATICS SEMESTER 2 EXAMINATIONS 2014/2015 ME340. Power Train Engineering

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1 s SCHOOL OF COMPUTING, ENGINEERING AND MATHEMATICS SEMESTER 2 EXAMINATIONS 2014/2015 ME340 Power Train Engineering Time allowed: TWO hours Answer: Any FOUR questions only Items permitted: This is a losed-book examination Items supplied: Nomenlature Chart (on page 8 and 9) Marks for whole and part questions are indiated in brakets ( ) ME340_SEM2_2014/2015 Page 1 of 9 Printing date:23/09/2015

2 Question 1 A four stroke spark ignition gasoline engine with a swept volume of 1.3 litres and a ompression ratio of 12.5:1 is operated at a part load ondition with an engine speed of 2000 rev/min. The engine output is ontrolled by throttling the inlet with the inlet manifold pressure being redued to 60 kpa. (i) (ii) (iii) Draw a sketh of the pressure-volume diagram for the yle. (3 marks) Find the net indiated power of the yle learly stating any assumptions that you make. (11 marks) Determine the fuel onversion effiieny. (1 marks) The engine is onverted to diret injetion (DI) and will operate with a wide open throttle at the same load and speed as the engine desribed in part. (i) (ii) (iii) Draw a sketh of the pressure-volume diagram for the DI engine yle, marking learly any differenes between the throttled engine from part. (2 marks) Find the in-ylinder air fuel ratio (AFR) of the diret injetion engine. State any assumptions you make. Disuss what NOx aftertreament systems ould be required for both the throttled and DI engines. (3 marks) Ambient onditions: Tamb = 300 K, pamb = 100 kpa Properties of air R = kj/kg K, γ = 1.4 Properties of fuel qlhv = 44,000 kj/kg, stoihiometri AFR = 14.7 kg/kg The Otto yle effiieny is given by 1 1 r otto ME340_SEM2_2014/2015 Page 2 of 9 Printing date:23/09/2015

3 Question 2 A single ylinder Diesel researh engine uses an external loop to enable exhaust gas reirulation, ooled using a shell and tube type of heat exhanger. The engine is operated at the following ondition: air to fuel ratio, AFR = 20 kg/kg mass onentration of exhaust gas entering the engine, EGR = 25% fuel onsumption, m f 3 kg h What are the mass flow rates of fresh air and reirulated exhaust gas entering the engine? Exhaust gas leaves the engine at a temperature of 540 C and is ooled to 120 C. The ooling water is supplied at a rate of 15 litre/min and a temperature of 85 C. Assume the Cp of water is 4,200 J/kgK (i) Evaluate whether the heat exhanger should be operated in ounter flow or parallel flow? (6 marks) (ii) Determine the logarithmi mean temperature differene for the seleted arrangement. (3 marks) (iii) What is the effetiveness, ε, of the heat exhanger? (1 marks) After a period of operation, the ooler outlet temperature is observed to inrease from 120 C to 160 C due to the deposition of soot in the heat exhanger. Assume that the flow rates are unhanged from part b. (i) (ii) Calulate the perentage loss in heat transfer performane of the heat exhanger. State learly any assumptions you make. (7 marks) Suggest two possible hanges to the test bed to maintain the EGR outlet temperature at the original value and state any measures that will not be effetive. (3 marks) Question 2 ontinued on the next page ME340_SEM2_2014/2015 Page 3 of 9 Printing date:23/09/2015

4 Question 2 ontinued Type of Heat Exhanger f N TU Double Pipe parallel flow Double Pipe ounter flow All types when C C min 0 C max N 1 e TU 1 C 1 e N TU 1C N 1C 1 Ce TU 1C N TU f 1 1 N TU ln 1 C 1 1 C 1 1 N TU ln C 1 C 1 1 e N TU N TU ln1 Table Q2 Question 3 List the five fluids that enter and / or leave an automotive diret injetion Diesel engine ylinder head assembly. A 2 litre, four ylinder, four stroke, diret injetion Diesel engine operating at 4000 rev/min has a measured brake torque of Nm, a gross indiated mean effetive pressure of 1200 kpa, and a net indiated mean effetive pressure of 1150 kpa. Determine the following: (i) brake power (2 marks) (ii) total frition power (2 marks) (iii) total frition indiated mean effetive pressure (2 marks) (iv) pumping indiated mean effetive pressure (2 marks) Disuss how and why the pumping indiated mean effetive pressure and frition indiated mean effetive pressure will differ for a naturally aspirated multi-point injetion, throttled gasoline engine (MPI), diret injetion gasoline engine (DI-G), and turboharged diret injetion Diesel engine (TC-DI). (12 marks) ME340_SEM2_2014/2015 Page 4 of 9 Printing date:23/09/2015

5 Question 4 Draw a sketh showing how the emissions of unburned hydroarbons, arbon monoxide and oxides of nitrogen vary with equivalene ratio for a spark-ignition engine. For eah pollutant, desribe the fators that influene the level of emissions as the equivalene ratio is varied. (10 marks) Making referene to the in ylinder proesses, explain why the NOx emissions of a Diesel engine are generally higher whereas the HC and CO emissions are lower that a spark-ignition engine operating at stoihiometri air fuel ratio (AFR). A new vehile with a gasoline engine must ahieve the emissions limits desribed below. Given a mean drive yle load of 7.2 kw, fuel onsumption of 334 g/kwh, a total yle time of 19 minutes and a journey length of 11 km, alulate the minimum light-off time for the atalyst to ahieve the target HC emissions levels. State learly any assumptions you make. (10 marks) Measured emissions Target emissions HC 455 ppm 0.1 g/km Table Question 4 100% 80% NOx Catalyst Effiieny 60% 40% HC CO 20% 0% Equivalene Ratio ME340_SEM2_2014/2015 Page 5 of 9 Printing date:23/09/2015

6 Effetiveness Capaity Rate Ratio Question 5 Figure Q4 Draw a sketh of the operating map for a radial ompressor as used in an automotive turboharger. Using the sketh from part indiate the ideal loation on the ompressor map for the maximum torque operating ondition and give two reasons why you seleted this loation. A 120 kw 1.4 litre turboharged gasoline engine operates at stoihiometri air fuel ration (AFR) at rated power (4000 rpm). The fuel onsumption is 290 g/kwhr. (i) (ii) (iii) Calulate the required harge air flow and boost pressure, assuming the harge air an be ooled to 60 C. (6 marks) Calulate the turboharger outlet onditions assuming an isentropi effiieny of 68%. (4 marks) Calulate the minimum frontal area of the harge air ooler, assuming a single pass of air from the front of the vehile at a vehile speed of 50 kph. Ambient onditions: Tamb = 300 K, pamb = 100 kpa Properties of air R = kj/kg K, γ = 1.4 Properties of fuel qlhv = kj/kg, stoihiometri AFR = 14.7 kg/kg Cross flow heat exhanger with both flows umixed Number of Thermal Units ME340_SEM2_2014/2015 Page 6 of 9 Printing date:23/09/2015

7 Question 6 Graph for Question 5 Draw a sketh of the onfiguration of a parallel and a series hybrid vehile powertrain. (6 marks) Disuss the advantages and disadvantages of the two hybrid onfigurations in part with a onventional IC engine powertrain. (8 marks) A series gasoline hybrid vehile has a plug in faility and an be reharged from the grid. On a typial 20 minute, 12 km journey the vehile operates at a mean load of 5 kw at a mean fuel onsumption of 6l/100km. Calulate the operating ost and arbon emissions from ompleting the journey with only the IC engine or the battery harged from the grid. Clearly state any assumptions you make. (11 marks) Cost Carbon emissions Petrol 110 p/l 270 gco2/kwhr Eletriity 13 p/kwhr 397 gco2/kwhr ME340_SEM2_2014/2015 Page 7 of 9 Printing date:23/09/2015

8 Nomenlature Chart Symbol Quantity Units A Area m 2 AFR Air to fuel ratio m kg/kg a AFR m For Diesel burnt in air AFR = 14.5 kg/kg For gasoline burnt in air AFR = 14.7 kg/kg b Cylinder bore m Engine operating yle For a 4 stroke engine 4 - p Speifi heat apaity at onstant For air p = 1005 J/kg K J/kg K pressure v Speifi heat apaity at onstant For air v = J/kg K J/kg K volume Capaity rate m p W/K D Diameter m EGR Exhaust gas reirulation m kg/kg egr EGR m m g Aeleration due to gravity g = 9.81 m/s 2 m/s 2 h Convetion heat transfer oeffiient W/m 2 K k Thermal ondutivity W/m K m Mass flow rate m V kg/s mep Mean effetive pressure W Pa mep 2 Vd N J/m 3 N Rotational speed rev/s NTU Number of Thermal Units UA - qlhv Calorifi value (lower heating value) For Diesel qlhv = 42.5 MJ/kg For regular gasoline qlhv = 42.7 MJ/kg r Compression ratio Vd V r V min f egr a J/kg m 3 /m 3 R Gas onstant R p v J/kg K For air R = J/kg K s Cylinder stroke m sf Speifi fuel onsumption m kg/j f sf W or kg 9 g/kw h T Temperature C or K U Overall heat transfer oeffiient W/m 2 K V Clearane volume m 3 J g kwh ME340_SEM2_2014/2015 Page 8 of 9 Printing date:23/09/2015

9 Symbol Quantity Units Vd Displaed volume For 1 ylinder V d 2 b s 4 m 3 W Power W 2N W Volume expansion oeffiient K -1 Heat exhanger effetiveness q - Ratio of speifi heats For air = 1.4 Dynami visosity kg/m s v Kinemati visosity m 2 /s otto Otto yle effiieny 1 otto 1 r - vol Volumetri effiieny m - a vol 2 avd N Density For an ideal gas kg/m 3 p RT For Diesel = 845 kg/m 3 b Brake torque b q max p v b For gasoline = 775 kg/m 3 W 2N Nm Gr Grashoff number 3 gtd - 2 Nu Nusselt number hd - k Pr Prandtl number p - k Ra Raleigh number GrPr - Fourier s Law of Condution dt q k dx q is the heat flux at the wall Newton s Law of Cooling b b k is the thermal ondutivity of the wall ~ Q A h T T Ai is the ombustion hamber area ~ h is the heat transfer oeffiien t T T m w i m w is the mean gas temperature is the mean temperature of thewall - ME340_SEM2_2014/2015 Page 9 of 9 Printing date:23/09/2015

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