Question

Motors are treated in the thermodynamics as a [Select] system

a) warm

b) cold

c) closed

(d) open

The combustion of the fuel is replaced by [Select 1] and the exhaust gases [Select 2]

[Select 1]

(a) cold air

b) compression

c) expansion

d) heat supply

[Select 2]

(a) hot air

b) compression

c) expansion

d) heat supply

In an ideal Otto Cycle, expansion work is done [Select 1] but for a Stirling cycle it does [Select 2].

[Select 1]

a) isothermal

b) isobaric

c) isenthalpic

(d) isokort

c) isentropic

[Select 2]

a) isothermal

b) isobaric

c) isenthalpic

(d) isokort

c) isentropic

For a long time, Brayton cycles were mainly improved by raising [Select 1] at the inlet to the turbine, however, in recent times, the improvement work has mainly revolved around lowering [Select 2] and implementing [Select 3] in the cycle.

[Select 1]

a) the pressure

b) the flow

c) entropy

(d) the temperature

[Select 2]

a) the pressure increase

b) the flow losses

c) the entropy generation

d) the enthalpy generation

Answer 1

1. Thermodynamics basically deals with 2 systems, i.e. open and closed system.

Open system is that system in which matter interacts with surroundings.

In Closed system matter does not interacts with surroundings. System remains isolated from the environment.

Warm System: The system which delivers warm air to surroundings.

Cold System: which keeps system and surroundings colder.

Motors are treated as Closed System in the thermodynamics.

Important point to notice: If a system is 100% closed, it is in danger of exploding.

2. The Combustion of fuel needs three requirements:

(i) Fuel to burn

(ii) Air to supply oxygen

(iii) Heat to start the combustion process

Thus the combustion of fuel is replaced by heat supply.

Exhaust gases- waste gases expelled from engine.

When gases expands from a system, it is expelled from the system.

Exhaust gases are replaced by expansion.

3. Otto cycle follows compression and expansion at constant entropy. In stirling cycle, during expansion more and more heat is added to keep temperature constant.

In an ideal Otto engine, expansion work is done isentropically and for a Stirling cycle, it is done as isothermally.

4. Brayton Cycles were improved mainly by raising the pressure at the inlet to turbines.