CHAPER 9 GAS POWER CYCLES PAR MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR INRODUCION What is IC Engine? An internal combustion engine is a thermal system (power plant) that conerts heat obtained from chemical energy sources (gasoline, natural gas) into mechanical wor. Where are IC Engines Used? IC engines are used as the propulsion systems for land transport ehicles such as automobiles (cars, etc.), marine ehicles (boats, etc.) and small airplanes. IC engines are also used in portable electrical generators and as prime moer in grass cutting machine, etc. MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR INRODUCION Main Components of IC Engines Main Components of IC Engines Inlet ale (air) Exhaust ale (gas) Cylinder, piston, inlet ale, exhaust ale and spar plug Piston moes from the top dead center (DC) to the bottom dead center (BDC). Clearance olume, V c is a spacing between the top of the piston and the ale s heads when the piston is at the end of the deliery troe. DC BDC bore piston V c Stroe (V swept ) Connecting Rod MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR INRODUCION MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR ENGINE CLASSIFICAION Reciprocating internal combustion (IC) engines are classified into two general categories, depending on how the combustion process in the cylinder is initiated, i.e.: a) Spar-ignition (SI) engines; b) Compression-ignition (CI) engines. MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR ENGINE CLASSIFICAION Description of SI Engines Fuel : gasoline or petrol, which is mixed with air. he air-fuel mixture enters the cylinder and is compressed to a highest pressure and temperature. A spar from a spar-plug ignites the combustible air- fuel mixture. he high pressure gases pushes the piston downwards, producing a power stroe of the piston. he cranshaft transforms the reciprocating motion into rotational motion (rpm) MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR ENGINE CLASSIFICAION Description of CI Engines Run on liquid diesel fuel he fresh air enters the cylinder and is compressed to about / of its original olume, causing its temperature to raise to about 50 o C (000 o F) or higher. Diesel is then injected into the compressed air causes the diesel to burn. he combustion gases pushes the piston downward during the power stroe.piston. he cranshaft transforms the reciprocating motion into rotational motion (rpm) MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR ENGINE CLASSIFICAION IN BOH SI AND CI ENGINES, HE COMBUSION GASES ARE EVENUALLY EXHAUSED OU OF HE CYLINDER SO HA FRESH-AIR MIXURE CAN BE INDUCED INO HE CYLINDER O CONINUE HE HERMODYNAMICS CYCLES therefore woring on an open cycle is the characteristics of all internal combustion engines since the woring fluid does not undergo a complete thermodynamic cycle. MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR ENGINE CLASSIFICAION BY CYCLES Reciprocating internal combustion engines operate either on two-stroe or four-stroe cycle Four-stroe Cycle Most automotie engines operate on a -stroe cycle. Eery fourth piston stroe is the power stroe. he cranshaft maes two reolutions to complete the cycle. wo-stroe Cycle Commonly used in small and medium motorcycles and lawn moers he cranshaft maes one reolutions to complete the cycle. Less efficient than -stroe because incomplete expulsion of exhaust gases Simple and inexpensie Hae high power to weight ratio MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR ENGINE CLASSIFICAION BY CYCLES FOUR SROKE CYCLE Intae stroe: he intae ale opened. he piston moing downward (from DC to BDC), allowing the air-fuel mixture to enter the cylinder Compression stroe: he intae ale closed. he piston is moing upward (BDC to DC), compressing the mixture. MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR FOUR SROKE CYCLE Power stroe: he ignition system deliers a spar to the spar plug to ignite the compressed mixture. As the mixture burns, it creates high pressure that pushes the piston down. Exhaust stroe: he exhaust ale opened. he piston moes upward as the burned gases escape from the cylinder. ENGINE CLASSIFICAION BY CYCLES MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR FOUR CYLINDER, FOUR SROKE ENGINE he ignition occurs before the compression process end. P sys > P atm during the exhaust stroe. P sys < P atm during the intae stroe. ENGINE CLASSIFICAION BY CYCLES MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR ENGINE CLASSIFICAION BY CYCLES FOUR SROKE IN-LINE CYLINDERS ARRANGEMEN he cylinders are arranged in a line in a single ban. i.e inline-, inline-, inline-5, inline-6 MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR ENGINE CLASSIFICAION BY CYCLES FOUR SROKE V CYLINDERS ARRANGEMEN V8 V6 he cylinders are arranged in bans set at an angle to one another i.e. V6, V8, V0, V V0 MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR ENGINE CLASSIFICAION BY CYCLES FOUR SROKE HORIZONAL OPPOSED CYLINDERS ARRANGEMEN he cylinders are arranged in bans on opposite sides of the engine MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR ENGINE CLASSIFICAION BY CYCLES FOUR SROKE W CYLINDERS ARRANGEMEN he cylinders are arranged in / bans set at an angle to one another i.e. W, W8 W9 W8 W MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR WO SROKE CYCLE Only two stroes power stroe and compression stroe. One reolution per cycle. he exhaust gases exits from the cylinder during the end of the power stroe, while the mixture of fuel/air enters the cylinder. his cycle is simple and cheap Suitable for low power consumption machine such as motorbie, etc. ENGINE CLASSIFICAION BY CYCLES MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR ENGINE CLASSIFICAION BY CYCLES WO SROKE CYCLE MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR ENGINE ECHNOLOGIES VV (VEC, MIVEC, VVi, DVV, CPS), DOHC/SOHC VV - Variable Vale iming System SOHC Single Oerhead Cam Shaft DOHC -Double Oerhead Cam Shaft HONDA FA SOHC VEC 50 HP HONDA HA DOHC VEC 0 HP HONDA ENGINES B6A (.6L) DOHC VEC 70 HP B8C (.8) DOHC VEC 0 HP HA (.L) DOHC VEC 00 HP F0C (.0L) DOHC VEC 0 HP K0A (L) DOHC ivec 5 HP MOS POWERFUL ENGINE BUGAI VEYRON 8L W8 QUAD URBO - 00 HP MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR PERFORMANCE CRIERIA Compression Ratio, r Compression ratio Maximum olume Minimum olume VBDC Vc + Vs V V DC Note: compression ratio is olume ratio and it is not a pressure ratio c MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR PERFORMANCE CRIERIA Mean Effectie Pressure, MEP It is defined as the height of a rectangle on a pressure-olume (P-) diagram. his pressure gies the same total net wor as actual pressure. For the same engines size, MEP can be used as a criteria or parameter to compare the engines performance. Wor Force x Distance PAL W net MEP MEP MEP V max ( V V ) Wnet V x Swept max min min Volume PV MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR CARNO CYCLE Recall -he Carnot Cycle Is the most efficient cycle that can be executed between a heat source, H and a heat sin, L. Operate on a totally reersible cycle. he Carnot cycle is composed of totally reersible processes: - : isothermal heat addition at H : isentropic expansion, temp drops from H to L : isothermal heat rejection at L : isentropic compression, temp increases from L to H Carnot efficiency, η th,carnot W Q net sup ply L H MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR CARNO CYCLE Why we cannot use the Carnot cycle as the model cycle for all heat engines? Hard-ware related. Reersible isothermal heat transfer is ery difficult to achiee in reality since it would require ery large heat exchanger and it would tae a ery long time. MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR EXAMPLE 9-9 Show that the thermal efficiency of a Carnot Cycle operating between the temperature limits of H and L is solely a function of these two temperatures and is gien Analysis : qin H and q out ( s s ) L ( s s ) ( s s ) L η th w q net in q q out in L H L H ( s s ) ( s s ) s s and s s MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR IDEAL CYCLES Actual cycles are difficult to analyze because of the present of complicating effects such as friction and non-equilibrium conditions. Ideal cycle is used to simplify the analysis. Ideal cycle is a cycle that resemble the actual cycle with less complexities than actual cycles All processes inole are assume totally reersible o mae an analytical study of a cycle practicable, the complexities are ept at a manageable leel and utilize some idealizations. Models deeloped from these idealizations are simple and able to study the effects of major parameters towards actual engines performance, since they still retain the general characteristics of the actual engines they represent. MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR AIR SANDARD ASSUMPIONS he actual gas power cycles are complex, thus approximations, nown as air standard assumptions is used. he woring fluid is air, continuously circulates in a closed loop and always behae as an ideal gas All the processes that mae up the cycle are internally reersible. he combustion process is replaced by a heataddition process from an external source. he exhaust gas is replaced by a heat-rejection process that restores the woring fluid to its initial state Air has constant specific heats MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR OO CYCLE he ideal cycle for spar ignition reciprocating engines Named after Niolaus A.Otta, who built a four stroe engine in 876 in Germany MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR OO CYCLE MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR OO CYCLE Otto cycle consists of four internally reersible processes: - Isentropic compression - Constant-olume heat addition - Isentropic expansion - Constant-olume heat rejection Note: In the Otto cycle, the woring fluid is alternately expanded and compressed in a piston-cylinder deice, therefore, equations pertaining to closed systems are used in the analysis. MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR he Analysis OO CYCLE From st Law of hermodynamics for ( q q ) + ( w w ) Δu in and out q q in out u u in u u out c c ( ) ( ) Closed System, η th,otto w q net in q q out in c c ( ) ( ) ( ) ( ) MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai OO CYCLE he Analysis thus, and and are isentropic - and ocess - Pr ( ) ( ) - th,otto r - η min max r OPIC : GAS POWER CYCLES - PAR
OPIC : GAS POWER CYCLES - PAR Under the cold-air standard assumptions, the relations between state and of isentropic expansion process or isentropic compression process can be related by the following equations. P P where, c c p p p OO CYCLE Some Formulas to recall and c p c and R ( ) for standard air can be taen as. Note : he aboe equation is only alid for the ideal Otto cycle under the cold airstandard assumptions he aboe equation shows that the thermal efficiency of Otto cycle depends on the compression ratio and the specific heat ratio of the woring fluid. MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR Summary OO CYCLE η η η otto otto otto W Q net in r L basic L function of L function of temperatures compression ratio and index MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR Example 9-9 An ideal Otto cycle has a compression ratio of 8. At the beginning of the compression process, air is at 00 Pa and 7 o C and 800 J/g of heat is transferred to air during the constant-olume heat addition process. Assuming the specific heats of air are constant, determine, determine a) he maximum temperature and pressure that occur during the cycle b) he net wor output c) he thermal efficiency d) he mean effectie pressure for the cycle he maximum temperature and P max P ( ) ( ) qin qin c ( ) + c 0. ( 90)( 8) 666. K 800 + 666. 780. K 0.78 MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai Example 9 Example 9- () Pa 9.5 666. 780. 87.8 P P P P ( ) Pa 87.8 8 90 666. 00 P P P P b) q out c ( ) 775.0 K 8 780. ( ) J/g 8. 90 775.0 0.78 q out 5.8 J/g 8. 800 q q q w out in net net 5.0% or 0.50 800 5.8 q w c ) in net th η ( ) 56.5% or 0.565 8 r r. th η OPIC : GAS POWER CYCLES - PAR
OPIC : GAS POWER CYCLES - PAR Example 9-9 d ) MEP w net w net / r w net ( r ) R P ( 0.87 )( 90) 00 0.8 m / g MEP w net 5.8 ( r ) 0.8( 8) 57. Pa MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR Example 9-9 Reconsider the ideal Otto cycle in Problem 9-. Assuming that the specific heats ary with temperature, determine: a) the pressure & temperature at the end of heat addition process, b) the net wor output, c) the thermal efficiency, and d) the mean effectie pressure for the cycle. MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR Problem 9-5 Pg 57 he compression ratio of an air-standard Otto cycle is 9.5. Prior to the isentropic compression process, the air is at 00 Pa, 5 o C and 600 cm. he temperature at the end of the isentropic expansion process is 800 K. Using specific heat alues at room temperature, determine, a) the highest temperature and pressure in the cycle b) the amount of heat transferred in c) the thermal efficiency, and d) the mean effectie pressure for the cycle. MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR ASSIGNMEN Problem 9-9 Pg 57 A -cylinder, -stroe,.6 L gasoline engine operates on the Otto cycle with a compression ratio of. he air is at 00 Pa and 7 o C at the beginning of the compression process, and the maximum pressure in the cycle is 8 MPa. he compression and expansion processes may be modeled as polytropic with a polytropic constant of.. he air-fuel ratio is 6. Using constant specific heats at 850 K, determine, a)he temperature at the end of the expansion process b)he net wor output c)he thermal efficiency d)he mean effectie pressure; e)he engine speed for a net power output of 50 Kw f)he specific fuel consumption (g/wh). MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR DIESEL CYCLE Diesel cycle is the ideal airstandard cycle for compression ignition (CI) reciprocating engines. First proposed by Rudolph Diesel in 890 MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR DIESEL CYCLE Diesel cycle consists of four internally reersible processes are, - Isentropic compression - Constant pressure heat addition - Isentropic expansion - Constant olume heat rejection Note : p p and MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR Heat added to the engine q q c in HE ANALYSIS he Diesel Cycle Analysis under the cold air-standard assumptions Heat rejected from the engine q q c out he thermal η th,diesel q q p efficiency, out in c - c - ( ) ( ) ( ) ( ) ( ) ( ) p DIESEL CYCLE MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai r c c r isobaric process ratio for off - cut r L DIESEL CYCLE DIESEL CYCLE HE ANALYSIS c r r x Also, c c c c r r r r r r r ( ) ( ) [ ] ( ) [ ] r r r - c c th,diesel Diesel η η OPIC : GAS POWER CYCLES - PAR
OPIC : GAS POWER CYCLES - PAR DIESEL CYCLE For the same compression ratio, thermal efficiency of Otto cycle is greater than that of the Diesel cycle As the cutoff ratio decreases, the thermal efficiency of the Diesel cycle increases. When r c, the efficiencies of the Otto and Diesel cycles are identical. hermal efficiencies of large diesel engines range from about 5 to 0 percent. Higher efficiency and lower fuel costs mae diesel engines attractie in applications such as in locomotie engines, emergency power generation units, large ships, and heay trucs. MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR EXAMPLE 9- An ideal Diesel cycle with air as the woring fluid has a compression ratio of 8 and cutoff ratio of. At the beginning of the compression process, the woring fluid is at 00 Pa, 7 o C and 97 cm. Utilizing the cold-air standard assumptions, determine a) he temperature and pressure of air at the end of each process b) he net wor output and the thermal efficiency c) he mean effectie pressure Assumptions : R 0.87 J/gK, c p.005 J/gK,. a) he temperature and pressure at end each process V V V V r r c V V 97 8 97 06.5 cm ( )( 06.5) cm cm MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR EXAMPLE 9- Process - : isentropic compression process P V V V P V ( 00)( 8). 95 K. ( 00)( 8) 570 Pa Process - : constant pressure expansion P PV P 570 PV Pa V V Process - : isentropic expansion P P V V V V ( 960) 97 97. ( 95)( ) 960 K. 79 K ( 570) 6 Pa MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR EXAMPLE 9- b) he net wor is equialent to the net heat transfer m Q Q W η in out th net P V R W Q 6 ( 00)( 97 x0 ) ( 0.87 )( 00) mc mc Q net in p in 0.00 g ( ) ( 0.00)(.005 )( 906 95) ( ) ( 0.00)( 0.78)( 79 00) Q out.6 J 0.786 J.6 0.786.5 J.5 0.6 or 6.%.6 Wnet Wnet.5 c ) MEP 6 V V V V x0 max min ( 97 06.5) 76 Pa MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR EXAMPLE 5 est Sept 005 he engine operating on the air standard Diesel cycle has a compression ratio of 7/ and the maximum and minimum cycle temperatures are 57 o C and 5 o C respectiely. If the maximum cycle pressure is 500 N/m calculate, a) the olume ratio of the combustion; b) the temperature and pressure at the end of the expansion stroe; c) the thermal efficiency of the cycle; d) the mean effectie pressure. For air assume R 0.87 J/gK;.; c p.005 J/gK and c 0.78 J/gK. MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR ASSIGNMEN Problem 9-60 Pg 58 A six-cylinder, four-stroe,.-l compression-ignition engine operates on the ideal Diesel cycle with a compression ratio of 9. he air is at 95 Pa and 67 C at the beginning of the compression process and the engine speed is 750 rpm. he engine uses light diesel fuel with a heating alue of,500 J/g, an air fuel ratio of 8, and a combustion efficiency of 98 percent. Using constant specific heats at 850 K, determine: a) the maximum temperature in the cycle and the cutoff ratio, b) the net wor output per cycle and the thermal efficiency, c) the mean effectie pressure, d ) the net power output, and e) the specific fuel consumption, in g/wh. MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai
OPIC : GAS POWER CYCLES - PAR Dual Cycle: Realistic Ideal Cycle for CI Engines Approximating the combustion process as a constant-olume or a constant-pressure heataddition process is oerly simplistic and not quite realistic. A better approach would be to model the combustion process in both SI and CI engines as a combination of two heat-transfer processes, one at constant olume and the other at constant pressure. he ideal cycle based on this concept is called the dual cycle. Note: Both the Otto and the Diesel cycles can be obtained as special cases of the dual cycle. MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai 50
OPIC : GAS POWER CYCLES - PAR HE END MOHD KAMAL ARIFFIN, Faculty of Mechanical Engineering, UM, Sudai