Internal Int ernal Combustion Combustion Engines TUTORIAL
Ker erba bala la Univ Univer ersi sity ty College of Engineering Mechanical Engineering Department Academic Year
2012 - 2013
Class
3rd Year Class
Subject
Internal Combustion Engines
Lecturer
Dr. Raoof M. Radhi
Kerbala University I C Engine Engineering College Sheet No. 01 Mech. Eng. Dept. 2012 – 2013 -----------------------------------------------------------------------------------------------------------
Thermodynamics review 1 - Explain the Pv diagram , defining all lines of significance , an d state it’s use in dealing with problems in internal combustion engines . 2 – Define the following thermodynamic processes and terms : adiabatic - isentropic – isothermal – isobaric – polytropic , specific heat ratio , ambient conditions , perfect gas . 3 – Define each of the followings, and state the differences between them A – nozzle – diffuser – throttle B – pump – compressor – fan – turbine 4 – Explain briefly the four laws of thermodynamics 5 – convert the following units : lbm to kg - Btu to Joule - calorie to Joule - feet to meter - ft/s to m/s inch to centimeter - psi to atm - Btu/lbm to kJ/kg - Btu/hr to kw - cu.ft to liter – 6 – relate each of the following temperature units to each others : Deg. C - deg. F - deg. K - deg. R
Kerbala University Engineering College rd Mech. Eng. Dept. – 3 year
I C Engine Sheet No.02 2012 – 2013
1a – list the important parts of I. C. Engine. 1b – what are the engine emission and how they can be controlled. 2a – classify IC engines. 2b – give 6 examples of classified engine by using different classifying terms. 3a – explain the 2-stroke engine operation. 3b – explain what does this statement means "discovery of crud oil resulted in the development of reliable fuel appropriate for ICE use". 4a – explain the 4-stroke engine operation. 4b – "manufacturing pneumatic rubber tire made the automobile more practical, desirable, comfortable, thus generate a large market demand". Is this true, give your reasons. 5a – compare 2-stroke and 4-stroke engines. 5b - explain the opposed piston engine operation. 6a – compare SI and CI engines. 6b – what are the thermodynamic cycles applicable to both SI and CI engines.
Kerbala University I C Engine Engineering College Sheet No.03 rd Mech. Eng. Dept. – 3 year 2012 – 2013 ----------------------------------------------------------------------------------------------------------STUDY THE DIAGRAMS OF EACH QUESTION BELOW , then answer the followings : i / identify what you see in the diagram. ii/ explain the process shown.
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Kerbala University I C Engine Engineering College Sheet No.04 rd Mech. Eng. Dept. – 3 year 2012 – 2013 ----------------------------------------------------------------------------------------------------------STUDY THE DIAGRAMS OF EACH QUESTION BELOW , then answer the followings : i / identify what you see in the diagram. ii/ explain the process shown. ================================================================== Q.1/
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Kerbala University I C Engine Engineering College Sheet No. 05 Mech. Eng. Dept. 2012 – 2013 ----------------------------------------------------------------------------------------------------------1 – A four cylinder , 4 – stroke , SI engine has a bore of (80 mm) and stroke of (80 mm). The compression ratio is (8) . Calculate : i – engine cubic capacity . ii – cylinder clearance volume . iii – state what type of engine is this . 3 3 ( anws : 1608.4 cm , 57.4 cm , ….. ) 2 – A six cylinder , 4 – stroke , SI engine operates at (3600 rpm) . Calculate : i – the rate of spark plug firing in the entire engine . ii – how many power stroke per minutes each cylinder produce . iii – the number of induction strokes that takes place in (5 sec.) ( anws : 10800 , 1800 , 150 ) 3 – An engine of (0.2 m) bore , has piston stroke and clearance volume expressed as follows : B = 90 % of the piston stroke . V c = 10 % of engine cylinder volume . Find : i – the piston displacement in (lit) ii – compression ratio . ( anws : 7 lit , 10 ) 4 – A twin cam , 32 valve , 4-stroke , 8 – cylinder SI engine operates at (4000 rpm) , find : i – the rate a cam pushes a valve in the entire engine . ii – how many valve openings take place in (15 secs) . iii – ratio of spark plug firing to number of valve opening per cycle . ( anws : 64000 , 16000 , 0.25 ) 5 – Solve Q.4 by considering CI engine to be used instead of SI engine . 6 – Solve Q.2 by considering 2-stroke CI engine instead of 4-stroke SI engine .
Kerbala University I C Engine Engineering College Sheet No. 06 Mech. Eng. Dept. 2012 – 2013 ----------------------------------------------------------------------------------------------------------2
A – A square engine having piston face area of (58 cm ), engine speed of (3600 rpm) , and a volume at the end of the compression stroke (10 %) of the total volume . If the con rod is perpendicular with the crankshaft off-set and their ratio is (3.86) . Calculate :
1–B,S,r. 2–r,a,x. 3–θ,φ ,ω. 4 – Vd , Vc , V t 5 - Vθ , Vφ , Vc / Vθ 6 – ATS , U p , a p . B - If the angle between (r) and (a) is decreased by (8 %) , repeat your calculation in above Q.A :
1 – ATS , Up , a p 2 – Vθ , Vφ , Vc / Vθ 3 – Vd , Vc , V t 4–B,S,r. 5-θ,φ ,ω. 6–r,a,x. C - Several engine geometry parameters are related to the piston position inside the cylinder at a given instance . Discuss when the following parameters would reach a maximum value and calculate each one accordingly .
1–s,r 2–x,S 3 – Up , U p 4 – ap , ω 5 – ATS , Acs 6 – Vθ , V φ
Kerbala University I C Engine Engineering College Sheet No.07 rd Mech. Eng. Dept. – 3 year 2012 – 2013 -----------------------------------------------------------------------------------------------------------
A two stroke gas engine has piston diameter of 150 mm, length of stroke 400 mm and indicated mean effective pressure 5-5 bar. The engine makes 120 explosions per minute. Determine the mechanical efficiency of the engine, if its BHPis 5 kW. [ans.: 64.2 %] 1-
2 - A S.I. engine uses a fuel-air mixture consisting of 1 part fuel and 13-5 part air by mass. Calorific value of fuel is 44000 kJ/kg. The brake thermal efficiency of the engine is 25%. Find its (a) brake output for a fuel consumption of 1 k g/Hr (b) brake specific fuel consumption (c) air consumption/kW Hr. [ans.; 3.06 kw, 0.327 kg/kw.hr, 4.41 kg] A 4 cylinder four stroke petrol engine develops indicated power of 14-7 kW at 1000 rpm. The mean effective pressure is 5-5 bar. Calculate the bore and stroke of engine if the length of stroke is 1-5 times of the bore. [ans.: 87.9 mm, 131.8 mm] 3-
An engine uses 8 kg of oil per hour of calorific value 42000 kJ/kg. If the brake power of the engine is 40 kW and mechanical efficiency is 85%. Calculate: (a) Indicated thermal efficiency (b) Brake thermal efficiency (c) Specific fuel consumption in kg/BP/Hr. [ans: 50.42%, 42.86%, 0.17 kg/ip.h, 0.2 kg/bp.hr] 4-
A single cylinder, 4-stroke diesel engine running at 1800 rpm has a bore of 85 mm and a stroke of 110 mm. It takes 0-56 kg of air per minute and develops a brake power output of 6 kW while the air fuel ratio is 20 : 1. The calorific value of the fuel used is 42550 kJ/kg and the ambient 3 air density is 118 kg/m . Calculate: (a) The volumetric efficiency and (b) Brake specific fuel consumption. [ ans.:84.5%, 0.28 kg/bp.hr] 5-
A four cylinder, 4-stroke petrol engine is designed to develop 35 kW indicated power at a speed of 3000 rpm. The compression ratio used is 5. The pressure and temperature at the beginning of compression stroke are 1 bar and 27°C respectively. The maximum pressure of the cycle is limited to 30 bar. Calculate the diameter and stroke of each cylinder, assuming all cylinder have equal dimensions. Take L/D = 1-5. Assume γ = 1-4. [ans.:78.76 mm, 118.12 mm] 6-
Kerbala University I C Engine Engineering College Sheet No.8/ quiz rd Mech. Eng. Dept. – 3 year 2012 – 2013 ----------------------------------------------------------------------------------------------------------Q.1// – A (3-liter) SI-V6 square engine operates on a 4-stroke cycle at (3600) rpm with AF of (15), and a fuel of (44000 kJ/kg) heating value is combusted at (97%) efficiency. The engine is connected to a dynamometer which gives a brake output torque reading of (205)N.m. At this speed consider the followings : 1. Combustion ends at (20° aTDC). 2. Inlet cylinder pressure is (85 kPa). 3. Air inlet temperature is (60 °C). 4. Engine mechanical efficiency is (85%). Do a complete engine performance analysis by calculating the followings: 1. Cylinder bore and stroke (cm) 2. Clearance volume (cm³) 3. Piston average speed (m/s) 4. Find at the end of combustion: i – piston speed (m/s) ii – distance the piston has traveled from TDC (cm) iii – volume in the combustion chamber (m³) 5. The engine power in (kW) as: i – indicated. ii – brake iii – friction 6. The engine mean effective pressure in (kPa) as: i – indicated ii – brake iii – friction 7. Brake power per unit mass of gas in the cylinder (kJ/kg) 8. Brake specific power (kW/cm²) 9. Brake output per displacement (kW/liter) 10. Engine specific volume (liter/kW). 11. Rate of fuel flow into engine (kg/s) 12. Brake specific fuel consumption (gm/kW.hr) 13. The engine emission in terms: i – rate of unburned hydrocarbon (HC) fuel that is expelled into exhaust system (kg/hr) ii – specific emission of HC (gm/kW.hr) iii – emission index of HC 14. Engine efficiencies as: i – brake thermal eff. ii – indicated thermal eff. iii – volumetric eff.
Kerbala University I C Engine Engineering College Sheet No. 09 rd Mech. Eng. Dept. – 3 year 2012 – 2013 ----------------------------------------------------------------------------------------------------------1 – A full load test on a 2-stroke single engine yielded the following results: Engine speed 180 rpm Bore - B 200 mm imep 450000 N/m² Stroke - S 250 mm Fuel rate 7 kg/hr Fuel CV 43500 kJ/kg Calculate : I – the indicated power II – the indicated thermal efficiency. [ans – 10.59 kW , 12.5 % ] 2 – A 6 cylinder petrol engine operates on the 4-stroke cycle (Otto cycle), cylinder bore (70 mm), and piston stroke (100 mm). The clearance volume per cylinder is (67 cm³ ). At a speed of (3960 rpm) the fuel consumption is (19.5 kg/hr) and the torque developed is ((140 Nm). Calculate: i – brake power ii – bmep iii – brake thermal eff. iv – relative eff. On brake power basis [ans: 58 kW , 7.61x10**5, 24.4%, 45.7%] 3 – A 4 cylinder 4-stroke S.I square engine has a compression ratio of (8), and bore (100 mm). The volumetric efficiency of each cylinder is (75%). The engine operates at a speed of (4800 rpm) with air to fuel ratio of (15).given the calorific value of fuel is (42 MJ/kg), atmospheric air density is (1.12 kg/m³), mean pressure in the cylinder (10 bar) and mechanical eff (80%). Determine indicated thermal eff and brake power. [ans: 42.5% , 4 – The following results refer to a test on a petrol engine Indicated power 30 kw Calculate Brake power 26 kw a Indicated thermal eff. Engine speed 1000 rpm b Brake thermal eff. Fuel/brake power.hr 0.35 kg Mechanical eff. c Fuel CV 43900kJ/kg [ans: 0.27 , 0.234, 0.866]
5 – Compute the mean piston speed, bmep, torque, and power per piston area for the following engines: engine Bore (mm) Stroke (mm) cylinders Engine speed Brake power marine 136 127 12 2600 rpm 1118 kw construction 108 95 8 6400 447 racing 86 57 8 10500 522 6 – The brake power of a single cylinder engine is defined by the relation BP = 9.75 (N/1000)³ Where (N) is the engine speed in (rpm), the bore and stroke are (80 , 130) mm respectively. If the engine speed is (1200) rpm, and the mechanical efficiency is (80%), (3.2) kg of fuel of CV (43500 kJ/kg) is consumed during (30 min) Calculate: i- Brake power ii- Brake thermal eff. iii- imep iv- [ans: 16.84 kw , 21.77%, 0.038 bar]
Kerbala University I C Engine Engineering College Sheet No. 10 rd Mech. Eng. Dept. – 3 year 2012 – 2013 -----------------------------------------------------------------------------------------------------------
1 - The efficiency of otto cycle for petrol engine is 50% and the adiabatic constant is 1.4.Calculate the compression ratio? [ans.: 5.7] Calculate the thermal efficiency and compression ratio for an automobile working on Otto cycle. If the energy generated per cycle is thrice that of rejected during the exhaust. Consider working fluid as an ideal gas with Π = 1.4. [ans.: 66.6%, 15.59] 2-
3 - An
engine of 250 mm bore and 375 mm stroke works on Otto cycle. The clearance volume is 3 o 0.00263 m . The initial pressure and temperature are 1 bar and 50 C. If the maximum pressure is limited to 25 bar. Find i-The air standard efficiency of the cycle ii- The mean effective pressure for the cycle. [ANS.:56.57%, 1.87 bar] o
In an Otto cycle, the air at the beginning of isentropic compression is at 1 bar and 15 c, The ratio of compression is 8. If the h eat is added during the constant volume process is 1000 kJ/kg. Take C p = 0.718 kJ/kg K, and Π = 1.4 . Determine: (a)The maximum temperature in the cycle (b)The air standard efficiency (c)The work done per kg of air, (d)The heat rejected. [ans.:2056K, 56.5%, 565 kj/kg, 435 kj/kg] 4-
The minimum pressure and temperature in an Otto cycle are 100 kPa and 27oC. The amount of heat added to the air p er cycle is 1500 kJ/kg. Determine the pressure an d temperatures at all salient points of the air standard Otto cycle. Also, calculate the specific work and the thermal efficiency of the cycle for a co mpression ratio of 8 : 1. [Take C p /C v = 1.4 and C v = 0.72 kJ/kg K] [ans.: temperatures(1-5) {300, 689.22, 2772.55, 1206.83} K pressures (1-5) {100, 1837.92, 7393.48, 402.28} kPa {sp. Work (272.68 kj/kg)}, { thr. Eff. (54.08%)}, {mep (1.79 bar)} 5-
In a petrol engine the pressure in the cylinders at 30% and 70% of the compression strokes 1.33 are 1.30 bar and 2.60 bar respectively. Assuming that the compression follows the law PV = constant. Find the compression ratio. [ans.: 4.51] 6-
Kerbala University I C Engine Engineering College Sheet No.11 Mech. Eng. Dept. – 3rd year 2012 – 2013 ----------------------------------------------------------------------------------------------------------1 - A
4-stroke diesel engine has L/D ratio of 1-25 The mean effective pressure is found with the help of an indicator equal to 0-85 MPa. The engine produces indicated power of 35 HP while it is running at 2500 rpm. Find the dimensions of the engine. [ans.: An ideal Diesel engine has a diameter of 15 cm and stroke 20 cm. The clearance volume is 10 percent of swept volume. Determine the compression ratio and the air standard efficiently of engine if the cut off takes pla ce at 6 percent of the stroke. [ans.: 11, 57.53%] 2-
3 - A
o
diesel engine receives air at 0.1 MPa and 300 K in the beginning of compression stroke. The compression ratio is 16. Heat added per kg of air is 1506 kJ/kg. Determine fuel cut off ratio and cycle thermal efficiency. [ ans.:2.65, 58.39%] 4 - An
engine working on ideal diesel cycle operates on 1 kg of standard air with an initial pressure of 0.98 bar a temperature of 35oC. The pressure at the end of compression is 33 bar and the cut off is 6% of the stroke. Determine the heat supplied during the cycle and mean effective pressure. Assume Cp = 1.0 kJ/kg K, ∏ = 1.4 [ans.:heat supplied = 573 kj/kg, heat rejected =2 38.5 kj/kg, kep = 4.05 bar]
5 - An engine operates on the air-standard diesel cycle with a compression ratio o f 18. The air pressure and temperature at the beginning of the compression are 0.12 MPa and 43°C. If the maximum temperature is 1992 K and the heat addition is 1274 kJ/kg, find the maximum pressure for which the cylinder must be d esigned. Also find T2 . [ans.: 6.86 MPa, 1007 K] 6 - The combustion process in an air-standard diesel cycle adds 800 kJ/kg to the medium. The minimum temperature and pressure are 20°C an d 0.1 MPa while the maximum temperature is 1000°C. Find the thermal efficiency. [ans.:22.37%]
Kerbala University I C Engine Engineering College Sheet No.12 Mech. Eng. Dept. – 3rd year 2012 – 2013 ---------------------------------------------------------------------------------------------------------- A dual cycle operates with ideal air between inlet conditions of 1 bar, 300 K and a maximum temperature in the cycle of 2000 K. If equal amounts of heat are supplied in the constant volume and constant pressure processes. Determine the total heat supplied if the compression ratio is 15: 1. [Take C v = 0.718 kJ/kg K and C p = 1.005 kJ/kg K ] [ans.:932.54 kj/kg] 1-
2 – An air standard dual cycle has (Cr=10), the pressure and temperature at start of compression stroke are (1 bar and 27 deg.C). The max pressure reached is (42 bar), and max temperature is (1500 deg.C). Let Cv = 0.717 and Cp = 1.004 kJ/kg.K. Determine : i- Temperature at end of constant volume heat addition ii- Cut off ratio iii- Work done per kg air Cycle efficiency.
[ans.: 1260K, 1.407, 513.3 kj, 58.42%] 3 – In an engine working on dual cycle, The (T,P) at the beginning of compression are (100 C & 1 bar) respectively. The (Cr=10), max pressure is limited to (70 bar), and (1700 kJ) heat added per kg air. Determine the temperatures at salient points of the c ycle and air standard eff. of the engine. [ans.: (373, 937, 2611, 3139,1347)K, 59.6%] 4 – For an engine working on dual cycle, the (Cr=10), and max pressure is limited to (70 bar). If the heat supplied is (1680 kJ/kg). Find the (p & T) at the salient points of the cycle and the cycle efficiency. The (P & T) of air at the commencement of compression are (1 bar and 1 00 C) respectively. [ans.: {pressures : (1, 25.12, 70, 70, 3.53) bar }, { Temperatures : (373, 936.9, 2611, 3088.8, 1314.4)K, (eff. = 59.8%) ] 3
5 – The swept volume of a diesel engine working on dual cycle is (0.0053 m ) and clearance 3 volume is (0.00035 m . The max pressure is (65 bar). Fuel injection ends at (5%) of the stroke. The (T & P ) at start of compression are (80 C and 0.9 bar). Determine the cycle air standard efficiency. [ans.: ( Cr=11, γ=1.4, β=1.5, λ=2.51) sub. To find eff.] 6 – An IC engine operating on the dual cycle,( T1=27 C), the ratio of the max and min pressures is (70), and compression ratio is (15), the amount of heat added at constant volume and at constant pressure are equal. Compute the air standard thermal efficiency of the cycle. [ans.: 65.3 % ]
Kerbala University I C Engine Engineering College Sheet No. 13 rd Mech. Eng. Dept. – 3 year 2012 – 2013 ----------------------------------------------------------------------------------------------------------1 - Gasoline having an average chemical formula (C8 H 17 ) is burned in an engine at a fuel air ration of (0.08). i- write the chemical reaction equation. ii-calculate the fraction of (C) burned to (CO). iii-write the final balanced chemical reaction equation. [ans.: 1/3] 2 – Light diesel oil of average chemical formula (C 12 H 26 ) burns in a diesel engine with air Coefficient ( α = 4.5 ) during idling and ( α = 1.35 ) at full load. Calculate : i- the ( FA ) of the mixture used in each case. ii-write the reaction equation for both mixture. iii-the percentage by weight of the products for the full load mixture. [ans.; FA = 0.0148, 0.0493] 3 – Ethyl alcohol [ C2 H 5 (OH) ] is used in a carburetor engine. The carburetor is adjusted to give ( AF ) of ( 9 ) . If (60 %) of fuel must be evaporated before entering the engine cylinder making combustible for smooth starting and operation. Write : i- the stoichiometric chemical reaction equation. ii- the actual and balanced final chemical reaction equation. 4 - A fuel oil containing (86 %) carbon and (14 %) hydrogen by mass is burned with (10 %) excess air. If supplied is dry and combustion is complete. Determine : i-the chemical formula of the fuel. ii-the balanced chemical reaction equation. iii-the composition of the products by mass. 5 - Iso-octane (C8 H 18 ) is burned with chemically corrected amount of air. i-write the reaction equation. ii-calculate the percentage by weight of the products. iii-calculate the percentage by volume of the products. 6 – Methyl alcohol ( CH3 OH ) is burned in an engine at (FA = 0.14). i-write the reaction equation. ii-what is the (FA) for chemically corrected mixture. iii- find the equivalence ratio. [ans.: FA = 0.155 , φ = 0.903]
Kerbala University I C Engine Engineering College Sheet No.14 rd Mech. Eng. Dept. – 3 year 2012 – 2013 ----------------------------------------------------------------------------------------------------------1 – what do you understand by : i / ON = 85 ii / CN = 75 iii / from the above find the { CN in (i) and ON in (ii) } iv/ comments on your results as related to the statement ""good diesel engine fuel is bad gasoline engine fuel"" . [ans : 6.9 , (-102.25)]
2 - “AKI , FS , PN , MON , RON “ are gasoline related terms : i– identify each one ii – express (AKI) in terms of (FS) iii – properly insert (CN) into expression(ii), and discuss the out-coming correlation. 3
3 - A fuel blend has a density of (720 kg/m ), if ( 50 % ) of such fuel evaporates at (91° C) . Calculate the Cetane index ( CI ) using the following correlation : 2 2 2 CI = - 420.34 + 0.016 G + 0.192 G { log Tmp } + 65.01 { log T mp } - 0.0001809 T mp [ans : P
P
P
P
R
R
R
R
P
P
P
P
R
R
4 – If an engine using pure iso-octane fuel works 100% efficient, find the engine efficiency if an equivalent fuel of (CN = 11) is to be used instead. Comments on your results. [ans. 73.75%] 5 – If you are given a bad type of fuel to be used in your SI engine. What are the fuel characteristic would you ask the fuel supply company to adjust in order to make the use, in this case, of such fuel acceptable. 6 – If you are given a bad type of fuel to be used in your CI engine. What are the fuel characteristic would you ask the fuel supply company to adjust in order to make the use, in this case, of such fuel acceptable.
Kerbala University I C Engine Engineering College Sheet No.15 rd Mech. Eng. Dept. – 3 year 2012 – 2013 ----------------------------------------------------------------------------------------------------------1 – The venturi of a simple carburettor has a thraot diameter of (20 mm) and discharge coefficient of (0.8). the fuel caoilary tube has diameter of (1.14 mm) and discharge coefficient of (0.65). the gasoline surface is (5 mm) below the throat. Assume the density 3 3 of air and fuel to be (1.2 kg/m and 750 kg/m ) respectively, and the pressure across the system is (0.08 bar). Calculate : i – the air/fuel ratio under incompressible state. ii – the air/fuel ratio under sonic state conditions iii – discuss your results under the two conditions. 2 – A four cylinders 4-stroke square engine running at (40 rev/s) has a carburettor venturi with (3 cm) throat diameter. Assuming the bore to be (10 cm), volumetric efficiency of 3 (75%), the air density to be (1.15 kg/m ), and coefficient of discharge is (0.75). calculate the pressure drop at the throat. (ans. : 0.045 bar ) 3 – A simple carburettor is required to suppl (5 kg) of air & (0.5 kg) of fuel per minute. The fuel specific gravity is (0.75). the air is initially at (1 bar & 300 K). iCalculate the throat diameter at which pressure is (0.912) and discharge ceofficient (0.8). iiCalculate the fuel orifice diameter when ceofficient of discharge is (0.6). (ans. : 3.12 cm , 2.34 mm ) 4 – The diameter of venturi throat and fuel nozzle of a carburettor are (8cm & 5 mm) respectively. The coefficients of discharge for air anf fuel are (0.9 & 0.7) respectively. 3 The air and fuel densities are (1.3 & 700) kg/m respectively. The fuel level in the float chamber is (5 mm) below the fuel capilary tube tip at the throat, and the pressure at the throat is (96%) of the ambient pressure. Neglecting the effect of air compressibility, calculate : i – air mass rate ii – fuel mass rate iii – air/fuel ratio [ ans. : 5 – The volumetric efficiency of a four cylinder 4-stroke engine is (0.8) when running at (3000)rpm. The venturi pressure drop at this speed is (150 cm) water. Determine the venturi diameter and fuel jet diameter if the AF ratio of the mixture supplied to the engine by the carburettor is (12). The atmospheric conditions are (1.027) bar and 3 (15.5 °C). Take (Cdt = 0.84), (Cdc = 0.7), (ρf = 700 kg/m ), and for rengine cylinder take (B = 8.25 cm), (S = 11.5 cm). Neglecting compressibility of air. [ ans. : Dt=2.2 cm , Dc=1.43 mm ]
6 – A petrol engine consumes (6.8 kg/hr) of fuel. The throat diameter of the engine 3 carburettor is (2 cm). the density of the fuel is (700 kg/m ). The AF ratio of the mixture supplied by the carburettor is (15). Determine the carburettor jet diameter if ( h = 5 mm). take ambient conditions as (1 bar & 32 °C). assume value of (Cdt = 0.9), (Cdc = 0.7), and ( R = 287 J/kg.K). [ ans. : 1.19 mm]
Kerbala University I C Engine Engineering College Sheet No. 16 rd Mech. Eng. Dept. – 3 year 2012 – 2013 ----------------------------------------------------------------------------------------------------------1 - In a trial on a SI engine at full speed, full power (i.e full open throttle) the spark occurred at (25 bTDC), and the delay ended at (3 bTDC). Estimate the optimum spark timing for maximum power under: I – under full throttle condition when the engine is operated at half the maximum speed . II – when the engine operated at conditions of half the maximum speed and the thr ottle is half open. Assume that the combustion period should finish (12 aTDC) for maximum power and that the effect of half closing the throttle at constant speed is to increase the delay perio by (15%) of the value at full throttle. °
°
°
°
°
[ans. : 14 bTDC , 15.65 bTDC]
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2 - In a SI engine at full speed full power, the spark occurred at (26 bTDC) and delay ends at (4 bTDC). Assuming that the combustion period should finish (13 aTDC) for maximum power and that the effect of half closing the throttle at constant speed is to increase the delay period by (14%) of the value at full throttle. Estimate the optimum spark timing for maximum power under the following cond itions : I – under full throttle conditions when the engine speed is operated at half the maximum speed. II – when the engine is operated at conditions of half the maximum speed and the throttle half open. °
°
[ans. : 15° bTDC , 16.54° bTDC ]
3 - A SI engine operating at (1200)rpm, has a (10.2 cm) bore with spark plug offset by (6 mm) from the centre. The spark plug is fired at (20° bTDC). It takes (6.5°) of engine rotation for combustion to develop and get into flame propagation mode, where the average flame speed is (15.8 m/s). Calculate : I – time of one combustion process in (sec), i.e the time for the flame front to reach the farthest cylinder wall. II – crank angle position at the end of combustion [ ans. :
, 12.48° aTDC]
4 - Two CI engines [(10cm-1500rpm) A & (40cm-375rpm) B ] bore & speed respectively, are geometrically similar in design. The injection of fuel is at a constant rate and occupies (30) degrees of crank travel in each engine. The pressure rise upto the end of rapid combustion phase to the fraction of total fuel injected upto that point is equal for both engines. . The 2 pressure of compressed charge when actual ignition start in both engines is (3.42 MN/m ). The fuel has ignition lag of (0.0012 sec), and the rapid combustion phase occupies (4.5) degrees of crank travel in each engine. If the pressure at the end of rapid combustion phase in engine (A) 2 is (7.05 MN/m ). Calculate : I - the pressure at the end of rapid combustion phase in engine (B). II- the ignition lag in degrees of crank travel for each engine III-fraction of total fuel injected upto the point of rapid c ombustion ends. IV-the pressure at the end of rapid combustion phase in engine (B) V-the ignition lag in degrees of crank travel for each engine [ans. :
5 - The spark plug is fired at (18° bTDC) in an engine running at (1800 rpm). It takes (8°) of engine rotation to start combustion and get into flame propagation mode. Flam termination stage start at (12° aTDC). Cylinder bore is (8.5 cm) a nd spark plug offset is (8mm) from cylinder centerline. Calculate effective flame front speed during flame propagation stage. [ans. :
]
6 - The piston of a 4-stroke, 1800 rpm, S.I. engine travel a distant of ( 2 % ) of the power stroke at the instant of flame termination. A ( 0.7 ms ) delay period ends at ( 10º bTDC ). Determine: i– crank angles where combustion process starts and ends . ii – combustion process crank angle span . iii – combustion process time duration . [ans. : 17.56 bTDC combustion starts , , The span 31.96 of crank rotation , ] °
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