Engine Performance : Turbofan, Turboprop and Turboshaft Engines

Introduction

The purview of aerospace engineering falls under two separate branches. One is aeronautical engineering which focuses on path and practice of flight of aircraft within the atmosphere of the earth. Another is aerospace engineering which focuses on flight of spacecraft outside the atmosphere of earth. The engine performance is based on the application of Newton’s third law of motion. Here air is displaced at the rear of aircraft, which acts opposite to the airflow current. The thrust developed through this measure propels the aircraft to move forward.Engines are developed keeping intact this working property of atmospheric air which is used as principal fluid in motion of aircraft.  

 Discussion

Turbofan Engine

It is referred to as a bypass engine or fanjet at times; this variant of jet engine uses a combination of bypass air and jet core efflux to achieve desired thrust for propelling aircraft motion. A ducted is used to achieve desired acceleration for aircraft’s purpose. The “bypass ratio”, is achieved by dividing the mass of air that bypasses the core of the engine, by, a mass of air that goes through the engine. A paradigm of variance may be stated here where an engine that achieves its thrust from “core efflux” is stated as a low bypass engine. A high bypass engine refers to that property where thrust is developed from thrust of the fan. The presence of a low bypass engine is found in military applications. This is because a low bypass engine may later be fitted with an afterburner mechanism.

The presence of a high bypass engine is prevalent in commercial aviation jet engines. A turbofan engine is based on a two-spool design base. Here the core consists of multistage compressors and a section of combustors. The “multistage turbine unit” which drives low-speed spools is more robust in its structural design. It may also be said that conventional turbofan engines have a low-pressure compressor for the same speed whereas in the course of geared turbofan low-pressure compressor does not find its place. The property of generating a nearly equal thrust for the fuel burned by its core is applicable here. 

 Turboprop Engine 

The engine of a turboprop uses the same principles as that of a turboprop engine to produce energy for propelling aircraft. Within the gas generator in the gearbox of the engine has the presence of a combustor, turbine and compressor. Incorporated in the design of a turboprop engine are the additional gearbox, power shaft and reduction gearbox which is the primary difference from that of a turbojet engine. The design lets the turbine extract almost all the energy that is created by the propelling system. The “reverse airflow mechanism” in the turboprop engine lets it intake a large scoop of air at a time and then reversing the release pattern for extra thrust makes it more fuel-efficient. 

The Core Engine and the propeller are the two main parts of the propulsion system for turboprops. “Axial flow” is the first stage of compression where air passes through a direction parallel to the shaft of the engine. The engine property of a turboprop and turbo-shaft engine is quite similar. The primary difference is the design base as per its usage. The turboprop version needs to be designed in such a way that it supports the load of the attached propeller. While the design of turboprop the load of the propeller is supported by the design of the aircraft. 

 Turbo-shaft Engine 

The variant of jet engine property here is optimised shaft power which would drive the machinery and does not depend wholly on the production of thrust. This application of the turbo shaft engine is most commonly used by the “auxiliary power units”. This property is generally used in powerlifting propulsions. Therefore it may be iterated that increasing the efficiency of a turbo shaft engine would not only involve reducing fuel consumption but also improving the overall capacity of the heavy weight lifting propulsions systems.  The rotational speed in the “free power turbine” is governed with the help of FADEC, that is, “Full Authority Digital Engine Control: system which helps in optimising the fuel efficiency of the lifting systems. 

The most likely reason for choosing the property of consistent rotational speed for a turbo-shaft engine is to decrease the engine load. Decreasing the engine load would grant better and more variant variations in speed. Even though the gear systems of the shaft are complex and preferably may be broken down. The “power-to-weight” ratio of the piston engine grants it higher capacity in lifting off. Optimising the free power turbine helps in minimising the specific fuel consumption in the offshoot design of the turbo shaft engine. This makes it possible for the state-of-the-art turbo-shaft designs to accommodate more varying speed rotors within the system.

Conclusion

The paradigm of aerospace engineering covers within itself the paradigm of an advanced stage of design and utilisation of engine improvement. In this assignment, three basic engines used in aeronautical engineering have been discussed. It may be iterated here that even though the design structures are same yet the difference in potentiality of the system structure varies as per usage. The property of turbofan application is used in jet and commercial aircraft. While turboprop engines are used for aircraft which require small runway structures, turbo-shaft engine is used in heavy-lift-off air vehicle structures like helicopters.

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