4262: Rockets and Mission Analysis

4261: Air-Breathing Engines Name: ______

Exam #1 October 21, 2008

Exam has 100 points

Show as much work as possible and qualify any assumptions you make.

Question 1 (10 Points):

Given the picture below, answer the following questions:

Position

1) Draw an arrow in the direction that air comes into this engine, and label it, ‘IN’

2) What type of an airplane would such an engine be most likely found on?

3) Using the left ordinate axis, labeled P, roughly sketch the axial pressure distribution through this engine. Label this curve ‘P’.

4) Using the right ordinate axis, labeled T, roughly sketch the axial temperature distribution through this engine. Label this curve ‘T’.

Question 2 (20 Points):

Below is a schematic of a turbine within a turbojet engine. Parameters describing the flow into and out of the turbine are given. The changes in flow properties across the turbine result in a force that is carried by the casing around the blades and main shaft.

What is the magnitude and direction of this force?

Question 3 (20 Points):

A ramjet is to propel an aircraft at Mach 3 at high altitude where the ambient pressure is 8.5 kPa and the ambient temperature is 220 K. The temperature at the end of the combustion process is 2,500 K. Using any set of assumptions that you feel are justifiable, estimate the 3 primary efficiencies of the ramjet:

The thermal efficiency
The propulsive efficiency
The overall efficiency

Question 4 (20 Points):

An ideal bypass turbofan has a bypass ratio of 8 and a maximum allowable turbine inlet temperature of 1,000 °C. The bypass nozzle exhaust and core engine nozzle exhaust velocities are identical. For these conditions, and using any assumptions that you feel are justifiable, estimate the compressor pressure ratio that will maximize take-off thrust?

Question 5 (30 Points):

Compare the specific fuel consumption of a turbojet and a ramjet that are being considered for a new airplane to fly at M0=1.5 and at 50,000 ft altitude (ambient pressure is 11.6 kPa and ambient temperature is 205 K).

· The turbojet compressor pressure ratio is 12 and the maximum allowable temperature is 1,400 K.

· For the ramjet, the maximum temperature is 2,500 K.

Ignore aerodynamic losses in both engines, and assume the engine uses conventional hydrocarbon fuel, with a heating value of 42.8 MJ/kg.

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