Compressors, Gas Turbines And Jet Engines MCQ Questions & Answers | Mechanical Engineering

In open cycle turbojet engines used in military aircraft, reheating the exhaust gas from the turbine by burning, more fuel is used to increase the Thrust and range of aircraft

The efficiency of the vane blower is $$\frac{{{{\text{W}}_2}}}{{{{\text{W}}_1} + {{\text{W}}_2}}}$$
Where,
W₁ = Work done due to compression
W₂ = Work done due to back flow

At high altitudes, the air density decreases, which means that there is less oxygen available for combustion in engines and compressors.

To compensate for this reduction in air density, a compressor must work harder to intake and compress the air to achieve the desired pressure levels. As a result, the compressor will require more power to maintain its performance and efficiency under these conditions.

This increased power demand is necessary to overcome the challenges posed by the thinner atmosphere, ensuring that the system operates effectively even at elevated altitudes.

In a jet propulsion unit, the products of combustion after passing through the gas turbine are discharged into discharge nozzle

In jet engines the products of combustion after passing through the gas turbine are discharged into Discharge nozzle

Gas turbine is a self starting unit

The closed cycle in gas turbines Provides greater flexibility

The efficiency of a gas turbine can be increased by several methods, and one of the most effective approaches is to use a combination of these methods. Here are the options:

Option A: Reheating: Reheating involves dividing the turbine into multiple stages and adding heat to the gas between these stages. This process helps to maintain a high temperature and pressure of the working fluid, improving the overall efficiency of the gas turbine. Reheating reduces the work done per stage, which reduces the overall thermal losses.

Option B: Intercooling: Intercooling is the process of cooling the air between the compression stages of the gas turbine. By reducing the temperature of the air before it enters the combustion chamber, intercooling helps to improve the overall efficiency of the gas turbine. Cooler air is denser, allowing for higher power output.

Option C: Adding a Regenerator: A regenerator, also known as a heat exchanger, is used to recover heat from the hot exhaust gases and transfer it to the incoming air. This preheating of the air before it enters the combustion chamber reduces the amount of fuel needed to achieve the desired temperature, thereby increasing the efficiency of the gas turbine.

Option D: All of the above: All three methods mentioned above (reheating, intercooling, and adding a regenerator) contribute to increasing the efficiency of a gas turbine. Combining these methods can lead to significant improvements in the overall performance of the gas turbine.

So, the correct option is: Option D: All of the above

The pressure ratio for an open cycle gas turbine compared to closed cycle gas turbine of same h.p. is low

Air-fuel ratio in a jet engine will be of the order of 60 : 1