ES ID: 0 ESE- 09 (Prelims) - Offline est Series est 5 MECHANICAL ENGINEERING IC ENGINES, REFRIGERAION and AIR CONDIIONING + POWER PLAN ENGINEERING SOLUIONS 0. Ans: (c) otal heat loss area = Heat loss from cylinder surface + Heat loss from cylinder head + Heat loss through piston = DL D D 9 9 7 9 0. Ans: (c) When SHF = (sensible cooling) c i e e c BPF c i 0 e c = 0 e = c Room dew point temperature will be equal to the coil dew point temperature. 0. Ans: (c) 0. Ans: (a) Pulse jet engine can be idealised to follow Lenoir cycle. it consists of constant olume Disadantages of gas turbine power plant in utility system are : heat addition, reersible adiabatic expansion and constant pressure heat rejection. Low cycle efficiency, due to large exhaust loss, large compressor work and inefficiencies. Large compressor work input, since power required to drie the compressor is considerably higher. Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata
: : Mechanical Engg._ est 5 _ Solutions Large exhaust loss, since exhaust gas temperature is quite high. Machine inefficiencies, since with decreases in compressor efficiency take work input to compressor increases and with decreases in turbine efficiency work output from turbine decreases. Gas turbine plants respond quickly to load changes. 05. Ans: (d) he ultimate analysis gies the chemical elements that comprise coal substance together with ash and moisture. It is used to determine percentage of carbon, hydrogen, oxygen, sulphur, nitrogen, moisture and ash on mass basis. Some types of coal during and after release of olatile matter become soft and pasty and form agglomerate. hese are called caking coal. Swelling index is a property used to determine the extent of caking of coal. 06. Ans: (a) E = 7C = 80 K G = 87C = 60 K O = 7C = 0 K COP E G G O O E 80 87 7 60 7 7 8050.9 600 07. Ans: (c) Due to shortcomings of distribution and limited intermixing of fuel CI engine are operated at high air fuel ratios than stoichiometric requirements. -methyl naphthalene is a hydrocarbon with poor ignition quality. It is assigned zero centene number. 08. Ans: (c) For a constant elocity of flow, if the duct diameter is increased he flow through duct will increase he friction pressure drop in the duct will decrease 09. Ans: (b) In CI engine detonation occurs at the beginning of combustion. 0. Ans: (c) Reheating and intercooling decreases turbine efficiency. Regeneration improes thermal efficiency of gas turbine by increasing mean temperature of heat addition. Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata Ahmedabad
: : ESE - 09 (Prelims) Offline est Series. Ans: (a) Crank case dilution and eaporation loss are effected by tail end olatility. Engine warm up is effected by mid range olatility.. Ans: (b) Increase in injection adance increases delay period, because pressure and temperature are lower when injection begins. Increase in jacket water temperature increases compressed air temperature and hence delay period is reduced.. Ans: (d) COP of heat pump = 00 7 7 W net 0 W net 0 0 00 H H kw L Q W From first law of thermodynamics Q L + W net = Q H Q L 0 56 8.67 kw H net. Ans: (c) Air has 79 % Nitrogen by olume, Nitrogen does not participate in chemical reaction. 5. Ans: (b) COP 6. Ans: (b) Re frigerating eff W net.5 N.75 kw W = (h h ) = 90 900 kj/kg = 00 kj/kg Pump work = kj/kg W net = 00 = 000 kj/kg Specific steam consumption 7. Ans: (d).5 N COP (as R =.5 kw) 600 = kg / kw hr 000 =.6 kg/kw-hr Degree of saturation () = s s Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata Ahmedabad
work capacity capacity : : Mechanical Engg._ est 5 _ Solutions 8. Ans: (b) Due to reheating of steam in steam turbine power plant Efficiency improes marginally Specific work output increases Blade erosion reduces 9. Ans: (b) Regeneratie feed water heating increases the mean temperature of heat addition. Hence, cycle efficiency increases. 0. Ans: (b) Economiser heats the feed water to the saturated temperature corresponding to the boiler pressure. 00 P = 9.76 P P =.97 kpa P Relatie humidity () = P.97 = 0.6566 = 65.66 %. Ans: (a) Approach of cooling tower is difference between cold water outlet temperature and wet bulb temperature.. Ans: (b) c =0C i =0C e =5C s. Ans: (b) W c max p max min = 5 00 = 5 0 = 5 kj/kg Contact factor BPF 5 0 0 0 5 0.75 0. Ans: (a) Specific humidity () = m m a 0.6 P P P t 5. Ans: (c) 0.5 0.6 P 0 00 P.88 P 0.5 00 P (r p ) opt (r p) max r p Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata Ahmedabad
: 5 : ESE - 09 (Prelims) Offline est Series If pressure ratio increases, the work capacity of Brayton cycle first increases, becomes maximum and then decreases. Work capacity is zero when r p is unity ; becomes maximum when (r p ) opt = r p max min max max min, and again becomes zero when as shown in the figure below. At maximum pressure ratio the efficiency of Brayton cycle becomes equal to Carnot efficiency and work output become zero. 6. Ans: (d) hermostatic expansion ale maintains a constant degree of super heat. 7. Ans: (a) he air fuel ratio in gas turbine is kept ery high. It aries from 60 / to 0 /. Because of high air fuel ratio used, gases entering HP turbine contain high percentage of oxygen and therefore if reheating is performed, the additional fuel can be burnt in the HP turbine. Reheating in gas turbine increases turbine work. Intercooling and reheating in gas turbine decreases thermal efficiency. 8. Ans: (b) Risers installed all around the furnace walls act as cooling tubes or a water wall and carry away heat from furnace at the same rate at which heat is released in it by the burning of fuel. If circulation is inadequate the rate at which heat is carried away will be less than heat released. he difference will be stored in riser tubes leading to their oerheating and rupturing. Riser located in the corners of furnace are relatiely cooler. So these will hae more circulation ratio than other riser tubes. Circulation ratio = = flow of saturated waterin downcomer flow of steam released from drum m = m g 9. Ans: (c) m g m m g Use of condenser increases the work output and efficiency of steam power plant. Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata Ahmedabad
: 6 : Mechanical Engg._ est 5 _ Solutions 0. Ans: (c) he following are the reasons for the pressure drop :. Friction, due to fluid elocity, resulting in frictional pressure drop.. Acceleration, due to the flashing off the liquid refrigerant into apour, resulting in momentum pressure drop.. Ans: (c) Benson boiler is a drumless once through boiler. his boiler can operate at super critical pressure.. Ans: (d) Proximate analysis indicate behaiour of coal when it is heated. It is used to determine percentage of fixed carbon, ash, olatile matter and moisture.. Ans: (c) Function of high steam and low water safety ale is two fold :. It blows out if the steam pressure is higher than the working pressure.. It blows out steam when water leel in the boiler is low.. Ans: (b) During cooling and dehumidification process, relatie humidity may increases, decreases or remain constant. Chemical dehumidification process 5. Ans: (c) (DP) < (DP) Bomb calorimeter is used to determine higher calorific alue of fuels by olume. Orsat apparatus is used to determine products of only dry constituents of combustion by olume. 6. Ans: (b) DB (DP) (DP) (DP) (DP) DB Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata Ahmedabad
: 7 : ESE - 09 (Prelims) Offline est Series During adiabatic saturation process : DP Process is cooling and humidification WB = constant Enthalpy = constant 7. Ans: (c) 9 t = sec 6N 6 00 = 0.005 sec sprayed into the steam mixes directly with cold water and gets condensed. Jet condenser, spray condenser and barometric condenser are direct contact type condenser.. Ans: (a) Absorption system is not a reersible refrigerating machine. Because of the mixing process of refrigerant and absorbent, a degree of irreersibility is inoled. 8. Ans: (a) Compressed gas enters the tube tangentially not normally. 9. Ans: (d) he component which is used to recoer heat of exhaust gases before boiler furnace is air preheater. 0. Ans: (b) In shell tube surface condenser for conenience of cleaning and maintenance cooling water flows through tubes and steam condenses outside the tube. Spray condenser is a direct contact type condenser in which cooling water is. Ans: (c) Efficiency of Otto cycle is gien by r where r is compression ratio Adiabatic index, for Helium is.67, Air is. and CO is.. otto (Helium) > otto (Air) > otto (Carbon dioxide). Ans: (b) For maximum power the fuel-air mixture should be 0% rich.. Ans: (a) he third fluid remains mainly in the eaporator thus reducing the partial pressure of the refrigerant to enable it to eaporate at low pressure and hence low temperature. Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata Ahmedabad
: 8 : Mechanical Engg._ est 5 _ Solutions Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata Ahmedabad
: 9 : ESE - 09 (Prelims) Offline est Series 5. Ans: (b) For maximum work output in two stage expansion turbine with perfect reheating, the intermediate pressure is 6. Ans: (a) p p p. he octane number in a single cylinder CFR diesel engine, the engine speed and jacket water temperature are 900 rpm and 00C respectiely. 7. Ans: (c) From the energy balance : M W = Q + S 8. Ans: (a) As engine speed increases in terms of crank angle hence ignition delay increases. Because of retarding due to increased heat loss ignition delay increases. Due to ignition adance, as pressure and temperature are low ignition delay increases. Due to engine size increases, ignition delay decreases in terms of crank angle. i d s 50. Ans: (a) If the inlet pressure is low temperature at the end of compression is low, temperature at the end of heat supply is low, low peak pressure and temperatures, reduce knocking. Hence, statement is wrong. 5. Ans: (b) Vapour pressure Effectie temperature is the temperature saturated air (00 % RH) at which the subject would experience the same feeling of comfort as experienced in the actual unsaturated enironment. Vapour pressure corresponding to effectie temperature is more than that of actual comfort condition. 00 % RH 50 % RH 9. Ans: (b) he delay period decreases with cetane number of the fuel because it reduces the self ignition temperature of the fuel. E 5C where, E = effectie temperature emperature Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata Ahmedabad
: 0 : Mechanical Engg._ est 5 _ Solutions 5. Ans: (d) Fuel is injected on to the hot piston. Slow rate of pressure rise takes place resulting in less noise. Cold starting is difficult as the piston is cold. 5. Ans: (a) EGR displaces some incoming air and also heats the air, lowering its density. he olumetric efficiency is thus reduced by EGR. 57. Ans: (b) COP of the Bell-Coleman cycle = when r p COP where, r p = pressure ratio c r p = ratio of specific heats c 58. Ans: (a) Knocking tendency in SI engine is reduced by decreasing the compression ratio. p 5. Ans: (c) Due to the expansion of the refrigerant, temperature of the refrigerant decreases in the capillary tube. For cooling process : Joule-homson coefficient () > 0 55. Ans: (a) he main objectie of supercharging is to obtain more power by burning the large amount of fuel or to reduce the weight and the size of the engine for a gien power output. 56. Ans: (d) A method usually employed for starting the engine from the cold is to shut off most of the main air supply to the main jets and thus produce rich mixture necessary for cold starting. 59. Ans: (c) Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata Ahmedabad Actual gas refrigeration cycle : Actual cycle Ideal cycle Pressure, P > P P > P entry to compressor exit from compressor entry to turbine exit from turbine S
: : ESE - 09 (Prelims) Offline est Series 60. Ans: (b) Volumetric efficiency of four stroke engine is higher than two stroke engine due to greater time of induction. In two stroke engine cycle is completed in two stroke of piston cylinder in one reolution of crankshaft. hus, more uniform turning moment than four stroke engine. 6. Ans: (b) For better starting 0% of the fuel should eaporate at low temperatures. In winter, as atmospheric temperature are low, olatility cure should be lower. 6. Ans: (c) Constant specific olume line WB line 6. Ans: (a) hermal efficiency of combined cycle plant is higher than indiidual cycles. hus, higher conersion efficiency from fuel to electricity can be achieed. 6. Ans: (b) In SI engines supercharging increases the tendency to detonate and pre-ignite whereas in CI engines supercharging tend to preent knocking. 65. Ans: (b) When the body temperature is less than the air temperature. Heat will not be transfer from the body by conection, conduction and radiation. he heat will be transferred by eaporatie cooling. 66. Ans: (d) As the number of cylinders increases, the dwell angle decreases as the firings are more for eery two reolutions. DB For constant specific olume line, specific humidity changes. (i.e., moisture content changes). Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata Ahmedabad
: : Mechanical Engg._ est 5 _ Solutions Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata Ahmedabad
: : ESE - 09 (Prelims) Offline est Series 67. Ans: (a) Joule -homson coefficient for an ideal gas () = 0 d dp h 0 d = 0 If we use throttling ale, there will not be change in the temperature. 68. Ans: (a) Net work is practically unity W W W p W W P Pump work is ery small compared to turbine work because pump compresses the saturated liquid which has small specific olume. 69. Ans: (a) Fuel leel in the compensating well decreases with the increase in air flow rate. For compensating jet or double jet engine, the compensating jet supplies leaner mixture and the main jet makes richer mixture and both together maintain constant air fuel ratio at all speeds. 70. Ans: (b) V-C cycle : x x S New peak temperaure of the cycle 7. Ans: (b) Octane rating of gasoline is based on isooctane and normal-heptane. etraethyl lead is added to gasoline to increase octane number. 7. Ans: (a) In diesel engine, cut off ratio depends on load. Hence, unlike Otto cycle the air standard efficiency of diesel cycle depends on load and increase as the load is increased. 7. Ans: (d) x < x S Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata Ahmedabad
Per cent of full load efficiency Specific fuel consumption kg/kwh consumption h Where x = quality of the mixture. As condenser temperature decrease, refrigerating effect increases and power input decreases. Because of this COP will increases. 7. Ans: (b) 6 5 0 00 90 80 70 60 50 0 0 0 0 0 50% 75% 00% Regeneration effectieness 00% 75% 5% 50% 5% No generation 0 6 8 0 6 8 0 Pressure ratio, r p (a) Fig. (a) shows, ariation of specific fuel consumption with pressure ratio with different degree of regeneration. It is clear that there is a optimum pressure ratio for each degree of regeneration. semi-closed cycle Open cycle with regenerator intercooler & reheater Simple open cycle 0 0 0 0 0 50 60 70 80 90 00 Per cent Load (b) Closed cycle with regenerator intercooler & reheater : : Mechanical Engg._ est 5 _ Solutions Fig. (b) shows the ariation of percentage of fuel load efficiency with part load. It is clear that for semi-closed cycle the part load efficiency is the best. 75. Ans: (b) At high engine speed acuum at the throat is high and we get too rich mixtures. In multicylinder engines, the mixture passing through the intake many fold generally contains a certain amount of petrol in the droplet form. hese droplets hae greater inertia then gaseous mixture and, hence, wheneer the direction of flow is changed abruptly, the droplets tend to continue in their original direction of moement. As a result, there is a ariation in the A/F ratio between cylinders, the outer cylinders getting richer mixture than the inner cylinders, the outer cylinders getting richer mixture than the inner cylinders. Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata Ahmedabad
: 5 : ESE - 09 (Prelims) Offline est Series Hyderabad Delhi Bhopal Pune Bhubaneswar Lucknow Patna Bengaluru Chennai Vijayawada Vizag irupati Kukatpally Kolkata Ahmedabad