198257221 Otto Diesel Dual Ideal Cycle ppt Compatibility Mode PDF

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Download 198257221 Otto Diesel Dual Ideal Cycle ppt Compatibility Mode PDF

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carnot, otto, diesel & dual Cycle

Topics       

Air Standard Cycle Air Standard Carnot cycle Reciprocating Engines Air Standard Otto Cycle (Sp Air Standard Diesel Cycle ( Air Standard Duel Cycle (H Air Standard Brayton (Gas T

carnot, otto, diesel & dual Cycle

Air Standard Assump 1. 2. 3.

4.

Working fluid is AIR and i All PROCESSES are inte The combustion process HEAT TRANSFER from e The ‘discharge and intake replaced by a HEAT REJ restores the working fluid

carnot, otto, diesel & dual Cycle

Example 1.1 Show that the thermal eff cycle operating between the temperatu TH is solely a function of these two tem

Solution Wnet Q  1 L QH QH 2  Q  and S2  S1     1  T  rev for rev. Isothermal process, T  const. 1 2 Q then S 2  S1   Q  1 2 rev T T 1   or ( ) T S 2 S1 1 Q2 Therefore , Q H  T H (S 2  S 1 ), and Q L  T L (S 3  But S1  S4, and S2  S3 Q T (S  S 4) T  th  1  L  1  L 3  1 L QH TH ( S 2  S1 ) TH from

 th 

carnot, otto, diesel & dual Cycle

1.5. An air-standard cycle is executed in a and is composed of the following four proc 1-2 v = constant heat addition from 10 amount of 701.5 kJ /kg 2-2 P = constant heat addition to 2000 3-4 Isentropic expansion to 100 kPa 4-1 P = constant heat rejection to initi (a) Show the cycle on P-v and T-s diagram (b) Calculate the total heat input per unit m (c) Determine the thermal efficiency. Account for the variation of specific heats 1.6. Repeat Prob. 5 using constant specifi

carnot, otto, diesel & dual Cycle

Over View on Reciprocating Engines Top Dead Center (TDC Bottom Dead Center (B

Exhaust valve

Intake valve

Stroke : Length of piston TDC Stroke Bore

Bore : Diameter of the cy Clearance Volume (Vc) Displacement Volume (V

BDC

Compression Ratio (rv ) Mean Effective Pressur Wnet = (MEP) x Reciprocating Engine is INTERNAL COMBUSTIO into 2 types: 1. Spark Ignition: Gasoline Engine, Mixing air by a spark plug 2. Compression Ignition: Diesel engine, fuel self ignited as a result of compression.

carnot, otto, diesel & dual Cycle

Four Stroke Engine Intake

Com

1. Intake Stroke drawing in 2. Compression TDC, com 3. Power Stroke the air-fue very fast t TDC. Afte 4. Exhaust Strok pushes the

carnot, otto, diesel & dual Cycle

Air Standard Otto Cycle Ideal cycle of spark ignition engine, compris Process 1-2 Isentropic Compression (piston move Process 2-3 v = constant, heat added (piston stay Process 3-4 Isentropic expansion (piston moves fro Process 4-1 v = constant, heat rejection (piston and INTAKE stroke) P

There are o

T

3

wout 2

4

w in

1

v 2=v3

v1=v4

TDC

BDC

v

What is the different of Otto cycle from Carnot Draw the T-s and P-v diagrams by y

carnot, otto, diesel & dual Cycle

Otto Thermal efficiency q th  1 4 1 2 q3 q  C v(T4  T1 ) 4 1 2 q 3  C v(T3  T2 ) C (T T ) th  1 v 4 1 C v(T 3  T 2 ) (T T ) 1  4 1 (T3  T2 ) T (T / T  1) 1  1 4 1 T2(T3 / T2 1) T1  v 2     T 2  v1  th, Otto  1  rv 

V max Vmin

k 1

v    3  v 4

1

rvk 1 V v  1  1 V2 v2

1. The higher 2. The higher engine 3. Higher Oc the self 4. Typical r v 5. Thermal e ignitio

k 1



T4 T3

carnot, otto, diesel & dual Cycle

Example 2.1 An ideal Otto cycle has a compressio begining of the compression process, the air is at 1 800 kJ/kg of heat is transfered to air during the he Accounting for the variation of specific heats of ai determine, (a) the maximum temperature and pres the cycle, (b) the net work out put, (c) the thermal mean effective pressure of the cycle Given: rv = 8.0 P 1= 100 kPa and

T1=17 oC q H = 800 kJ/kg

P

3

wout 2

4

variation of specific heats

Determine: a) Tmax b) w net c)  th d) MEP

win v 2=v 3

1 v 1=v4

carnot, otto, diesel & dual Cycle

(b) wnet = qH – q L , similar to q23 ; -qL 3-4 Isentropic proc. v r4/vr3 = v4/v 3 , v4 /v3 = rv = 8,  vr4 = vr3r v Table A-17 : at vr4 = 48.864  T 2 = 795 4-1 Constant volume heat rejected, 1 st law q 41 = w 41 + u 1 –u4 ; w41 = 0 q 41 = u1 –u4 = 206.91 - 588.74 q L = -q41 = 381.83 kJ/kg wnet = q H – q L = 800 – 381.83 = 4 (c) th = w net /qH = 418.83/800 = 0.523 or (d) MEP = w net /(v1-v2 ) ; P1v 1 = RT 1  v1 = 0.832 m3 /kg , v2 = v1 /8, MEP = 574.4 kPa answer

carnot, otto, diesel & dual Cycle

Otto Cycle 2-8 What four processes make the ideal OT 2-9 How is the rpm (revolutions per minute) gasoline engine related to the number of th What would your answer be for a two-stroke 2-10 Are the processes which make up the closed-system or steady-flow processes? W 2-11 How does the thermal efficiency of an with the compression ratio of the engine an the working fluid? 2-12 Why are high compression ratios not u engines? 2-13 An ideal Otto cycle with a specified co executed using (a) air, (b) argon, and (c) eth For which case will the thermal efficiency be 2-14 What is the difference between fuel-inj and diesel engines?

carnot, otto, diesel & dual Cycle

Reciprocating Eng

Exhaust valve

Intake valve

TDC Stroke Bore BDC

Top Dead Center (TDC Bottom Dead Center (B Stroke : Length of piston Bore : Diameter of the cy Clearance Volume (Vc ) Displacement Volume (V Compression Ratio (r v) Mean Effective Pressur Wnet = (MEP) x

Diesel engine, Compression Ignition

•

Only air is drawn into the cylinder during intake stroke fuel is injected into the cylinder after the air is compre and the piston reaches TDC And continue injecting until reaches “Cut Off Volume,

•

Cut off ratio rc = V3 /V2 = v3 /v2

• •

Fuel is self ignited as a result of compression. Therefore, the Compression Ratio, r v , must be high eno Typical rv ~12 – 24 During the combustion PRESSURE remains constant . Others processes are the same as Otto Cycle Thermal efficiency of actual Diesel engine ~ 30-40%

• •

• • •

carnot, otto, diesel & dual Cycle

Analysis of Air Standard Diesel C Review of equations used: Constant pressure heat trans fer 1st law : closed system 2 q3  u3  u 2  2 w 3 P  const . 2 w 3  P( v3  v 2 ) or 2q 3  h 3  h 2 Ideal gas : Pv  RT, dh  C p dT 2 q3  C p (T3  T2 ) v cutoff ratio, r c  3 v2 Isentropic Process of Ideal gases k k Pv k  P1v 1  P2v 2  constant k

and

k

V  P2  v 1       1  P1  v 2  V 2  ( k 1) / k v T2  P2    1    T1  P1   v2

.......... ...(6.18)   

k 1

.....(6.19 )

carnot, otto, diesel & dual Cycle

Example 3.1 An air standard Diesel cycle has a compression the compression process, the air is at 100 kPa and 15 oC, and transferred to air during the heat addition proceed determin (a) the temperature and pressure at each point in the cycle, (b) the net work and the thermal efficiency, and (c) the mean effective pressure of the cycle Assume constant specific heat. (Van Wylen) Given: rv = 18.0 P1= 100 kPa and T1=15 o C

qH = 1,800 kJ/kg

Determine: a) T, P b) wnet and  th c) MEP

Analysis: step by step calculation: property relation for each process definition, parameter of the Diesel engine 1 st law: Closed system Answer: (a) State T(K) P(MPa) v (m3/kg) 1 0.827 2 915.8 5.72 0.04595 3 2710 = P2 0.13598 4 1316 = v1 (b) Wnet = 1063.4 kJ/kg, th = 59.1 % (c) MEP = 1362 kPa

carnot, otto, diesel & dual Cycle

1 c D t t

Thermal efficiency comparison: P

Diesel 2

Otto

Diesel 1

v 2/

v2

v1

v

2 h c th m b th g

carnot, otto, diesel & dual Cycle

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3-8 An ideal diesel engine has a compression rati fluid. The state of air at the beginning of the com 20°C. If the maximum temperature in the cycle is (a) the thermal efficiency and (b) the mean effect specific heats for air at room temperature. Answe 3-9 Repeat Prob. 3-8, but replace the is en tropic expansion process with the polytropic exponent n 3-10 A four-cylinder 4.5-L diesel engine that ope compression ratio of 17 and a cutoff ratio of 2.2. beginning of the compression process. Using the determine how much power the engine will deliv 3-11 Repeat Prob. 3-10 using nitrogen as the wor 3-12 The compression ratio of an ideal dual cycle at the beginning of the compression process and addition process. Heat transfer to air takes place at constant pressure, and it amounts to 1520.4 kJ heats for air, determine (a) the fraction of heat tra the thermal efficiency of the cycle....