IC Engine Cycles MCQ Quiz in తెలుగు - Objective Question with Answer for IC Engine Cycles - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

Explanation:

Concept:

Q₂₃ = m × C_v × (T₃ – T₂)

T = temperature (K)

V = volume (m³)

Q₂₃ = specific heat added by combustion

C_v = specific heat at constant volume (kJ/kg.K)

Calculation:

Given:

P₁ = 100 kPa

T₁ = 10°C = 10 + 273 = 283 K

Process 1 – 2 → isentropic compression

T₂ = 283 × (9)^{1.4 – 1} = 681.52 K

Process 2 – 3 → heat addition at constant volume

Q₂₃ = m × C_v × (T₃ – T₂)

C_v = 718 J/kg.K

Q₂₃ = 718 (2500 – 681.52)

Q₂₃ = 1.305 × 10⁶ J/kg

Q₂₃ = 1.305 MJ/kg

Concept:

Brake Thermal efficiency:

It is defined as the ratio of brake power to the fuel energy per unit time.

where m_f = mass flow rate of fuel, BP = Brake Power, CV = Calorific Value.

Indicated power:

The energy of the fuel that is converted to power is called the indicated power (I.P).

Friction power:

The energy applied to the piston passes through the connecting rod to the crankshaft. In the transmission, there are energy losses due to friction, pumping, etc. The sum of all there losses converted to power is termed as friction power(F.P).

Brake power:

Brake power(B.P) = Indicated power (I.P) - Friction Power (F.P)

Volumetric efficiency (η):

Volumetric efficiency is defined as the ratio of actual volume flow rate of air into the system to the rate at which the volume is displaced by the system.

Mechanical efficiency:

Concept:

Heat addition in the diesel cycle is a constant pressure process.

Heat added (Q) = C_p × (T­₃ – T₂) kJ/kg

C_p = Heat capacity at the constant process.

T₂ = Temperature at the end of the heat addition process

T₂ = Temperature at the beginning of the heat addition process

Calculation:

Given:

C_p = 1 kJ/kgk, T₃ = 1723 K, T₂ = 1473 K

Q = 1 × (1723 - 1473) = 250 kJ/kg

Explanation:

The thermal efficiency of the Otto Cycle:

Compression ratio: r = v₁/v₂

Conclusion:

From the above equation, it can be observed that the efficiency of the Otto cycle is mainly the function of compression ratio for the given ratio of Cp and Cv i.e. ratio of specific heats.

The thermal efficiency of the theoretical Otto cycle increases with an increase in compression ratio and specific heat ratio but is independent of the heat added (independent of load).

The efficiency of the Otto cycle is given by

As  and Hence .

Option (b), (c) and (d) are the knock parameters.

Explanation:

Otto cycle:

The air-standard-Otto cycle is the idealized cycle for the spark-ignition internal combustion engines.

Otto cycle is the one which has two constant volume heat transfer processes and two adiabatic work transfer processes.

The Otto cycle 1-2-3-4 consists of the following four processes:

• Process 1-2: Reversible adiabatic compression of air
• Process 2-3: Heat addition at constant volume
• Process 3-4: Reversible adiabatic expansion of air
• Process 4-1: Heat rejection at constant volume
   

• During constant volume process heat addition and heat, rejection takes place and no work transfer.
• During the adiabatic processes [compressions/expansion] only work transfer taken place but no heat transfer occurs.

Important Points

Concept:

For the Diesel cycle:

Processes involved in compression engine (diesel cycle) are:

1-2: Reversible adiabatic compression

2-3: Constant pressure heat addition

3-4: Reversible adiabatic expansion

4-1: Constant volume of heat rejection

Now 

The compression ratio is given by

The cut-off ratio is given by

The expansion ratio is given by 

⇒ r_c × r_e =  =  = r   (From diagram V₄ = V₁)

Explanation

Volume Ratio:

• The ratio of larger volume to lesser volume during any process is known as the volume ratio of that process.
• The volume ratio during the compression process is known as the compression ratio and the volume ratio during the expansion process is known as the expansion ratio.
• Thus compression ratio is given by the ratio of volume before compression to volume after compression.

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• The compression ratio of the petrol engine is approximately 6 to 10. As the compression ratio is low the petrol engine is lighter and cheaper.
• A diesel engine has a compression ratio of approximately 15 to 20. As the compression ratio is high diesel engine is heavier and costlier.

Concept:

P-V and T-S diagram of Otto cycle is shown in the figure.

Compression Ratio (r) is the ratio of the total cylinder volume when the piston is at the bottom bead centre, VT, to the clearance volume VC.

Calculation:

Given:

η = 60%, γ = 1.5

Concept:

• A dual cycle or limited pressure cycle is a thermodynamic cycle for high-speed diesel and hot spot ignition engines.
• Whether heat is added at constant pressure or constant volume in actual applications, depends upon the rate of heat added and the rate at which pressure decreases due to movement of the piston.
• In an ideal cycle, the piston is assumed stationary during heat addition at constant volume, but in practice, this does not happen.
• As the speed of the engine increases, the rate of decrease of pressure due to the movement of the piston increases, and heat addition cannot be assumed at either constant volume or constant pressure.
• In such a case, a better approach for modeling the situation will be to assume heat addition initially at constant volume and then at constant pressure. That is why a dual combustion cycle is used.

• All diesel engines except slow-speed engines use mixed dual cycles.
• This is because in mixed dual cycles the heat input occurs partially at constant volume and partially at constant pressure.