(SEM V) THEORY EXAMINATION 2019-20 I.C.ENGINES AND COMPRESSORS

I.C. ENGINES AND COMPRESSORS (RME-051)

B.Tech (SEM-V) – AKTU

SECTION A

(Attempt all questions – 2 × 7 = 14 marks)

Q1 (a) Give the value of compression ratio for Otto cycle, Diesel cycle and Dual cycle.

The compression ratio for the Otto cycle generally lies between 6:1 to 10:1.
For the Diesel cycle, the compression ratio is higher and lies between 14:1 to 25:1.
For the Dual cycle, the compression ratio lies between 10:1 to 18:1.

Q1 (b) What do you mean by carburetion?

Carburetion is the process of mixing air and fuel in correct proportion to form a combustible mixture before it enters the engine cylinder. This process is carried out by a carburetor in spark ignition engines.

Q1 (c) Differentiate between flash point temperature, fire point temperature and self-ignition temperature.

Flash point is the lowest temperature at which fuel vapors ignite momentarily.
Fire point is the temperature at which fuel vapors burn continuously.
Self-ignition temperature is the minimum temperature at which fuel ignites without any external spark.

Q1 (d) What is the significance of Octane number and Cetane number?

Octane number indicates the anti-knocking quality of petrol used in SI engines.
Cetane number indicates the ignition quality of diesel fuel used in CI engines. Higher values result in better engine performance.

Q1 (e) Can a simple plain tube carburetor be used at higher altitude? Give reason.

No, a simple plain tube carburetor is not suitable for higher altitudes because air density decreases, causing rich air-fuel mixture which leads to poor combustion and reduced engine efficiency.

Q1 (f) Why is ignition system necessary in I.C. engine?

The ignition system is required to initiate combustion of the air-fuel mixture at the correct time. It ensures smooth engine operation, better fuel efficiency, and reduced emissions.

Q1 (g) Differentiate between two-way catalytic converter and three-way catalytic converter.

Two-way catalytic converter reduces carbon monoxide and hydrocarbons.
Three-way catalytic converter reduces carbon monoxide, hydrocarbons, and oxides of nitrogen, making it more effective in emission control.

SECTION B

(Attempt any three – 7 × 3 = 21 marks)

Q2 (a) Sketch the Diesel cycle on P-V and T-S diagram and derive efficiency expression.

The Diesel cycle consists of four processes: isentropic compression, constant pressure heat addition, isentropic expansion, and constant volume heat rejection.
The efficiency of Diesel cycle depends on compression ratio and cut-off ratio and is lower than Otto cycle for same compression ratio due to constant pressure heat addition.

Q2 (b) Describe the phenomenon of detonation or knocking in CI engine.

Detonation in CI engine occurs due to sudden ignition of accumulated fuel causing pressure rise and noise. It leads to engine damage, overheating, and reduced efficiency. Proper fuel quality and injection timing help reduce knocking.

Q2 (c) Explain different factors affecting detonation in SI engine.

Factors affecting detonation include compression ratio, inlet temperature, spark timing, fuel quality, engine speed, and combustion chamber design. Higher compression ratio and poor fuel quality increase knocking tendency.

SECTION C

(Attempt any one from each unit – 7 × 2 = 14 marks)

Q4 (a) What is the importance of ignition system in SI engine? Explain different types of ignition systems.

The ignition system provides spark at the correct time to ignite the air-fuel mixture. Types include battery ignition system and magneto ignition system. These systems ensure efficient combustion and smooth engine operation.

Q5 (b) What is supercharging? Explain the importance and types of superchargers.

Supercharging is the process of supplying compressed air to the engine to increase power output. Types include centrifugal, Roots blower, and vane type supercharg