MT 313 IC ENGINES LECTURE NO: 04 (24 Feb, 2014) Khurram Yahoo Group Address: ICE14

Air Standard Cycle

Important Formulas

Ideal cycles are simplified

Otto Cycle, ideal for spark ignition engines

OTTO CYCLE 1 2 V2V2 V1V1 P2P2 P1P1 pV γ = c

OTTO CYCLE Process No 1-2 – Reversible Adiabatic or Isentropic Expansion T – S diagram No Heat is added or rejected Q 1-2 = S 1, S 2 T2T2 T1T1

OTTO CYCLE Process No 2-3 – Constant volume cooling process p– V diagram Heat is rejected by air getting cooled from T 2 to T V2V2 P2P2 P3P3

OTTO CYCLE Process No 2-3 – Constant volume cooling process T – S diagram Heat is rejected by air getting cooled from T 2 to T 3 2 S 1, S 2 T2T2 S 3, S 4 T3T3

OTTO CYCLE 4 3 V3V3 V4V4 P3P3 P4P4 pV γ = c

OTTO CYCLE Process No 3-4 – Reversible Adiabatic or Isentropic Expansion T – S diagram No Heat is added or rejected Q 3-4 = 0 S 3, S 4 T3T3 T4T4 3 4

OTTO CYCLE Process No 4-1 – Constant volume heating process p– V diagram Heat is absorbed by air getting heated from T 4 to T V2V2 P1P1 P4P4

OTTO CYCLE Process No 4-1 – Constant volume heating process T – S diagram Heat is absorbed by air getting heated from T 4 to T S 1, S 2 T4T4 T1T1 S 3, S 4

OTTO Cycle

OTTO CYCLE 1 2 V2V2 V1V1 P2P2 P1P1 pV γ = c

OTTO Cycle

Problem 1 Calculate the air standard efficiency of a four stock Otto cycle engine with the following data Piston diameter (bore)= 13.7 cm Length of stock= 13.0 cm Clearance volume= 14.6 % Diagram

Solution

Problem 2 In an Otto cycle the compression ratio is 6. The initial pressure and temperature of the air are 1 bar and 100˚C. the maximum pressure in the cycle is 35 bar. Calculate the parameter at the salient points of the cycle. What is the ratio of heat supplied to heat rejected How does air standard efficiency of the cycle compares with that of a Carnot cycle working within the same extreme temperature limits? Explain the difference between the two values

Problem 2 If the engine has a relative efficiency of 50 % determine the fuel consumption per kWh. Assume the fuel used has a calorific value of 42,000 kJ/kg

Problem 3 An Otto cycle working on air has a compression ratio of 6 and starting condition are 40˚C and 1 bar. The peak pressure is 50 bar. Draw the cycle on p-v and T-S coordinates if compression and expansion follow the law pV 1.25 = C. Calculate mean effective pressure and heat added per kg of air.

Problem 4 An Otto cycle has compression ratio of 8 and initial conditions are 1 bar and 15˚C. Heat added during constant volume process is 1045 kJ/kg. Find : Maximum cycle temperature Air standard efficiency Work done per kg of air Heat rejected Take c v = kJ/kg-K and γ = 1.4

Problem 5 Find out the compression ratio in an Otto for maximum work output An Otto cycle engine has the following data. Calculate compression ratio, air standard efficiency and specific fuel consumption. Piston diameter =13.7 Length of stock=13 cm Clearance volume= 280 cm 3 Relative efficiency=60 % Lower calorific volume of petrol =41900kJ/kg