Turbojet, turbofan, turboprop: one core, different jobs
All three engine types share the same thermodynamic core: air is compressed, mixed with fuel and burned, and the resulting high-energy gas expands through a turbine that drives the compressor. What differs is how the remaining energy becomes thrust. A turbojet turns all of it into a high-velocity exhaust jet — effective at high speed, but inefficient and loud at low speed. A turbofan uses most of that energy to drive a fan, pushing a far larger mass of air around the core at a lower velocity. A turboprop takes the same idea further with a propeller. The physics is unchanged: producing a given thrust by accelerating a larger mass of air less is always more efficient.
Why efficiency gains keep getting harder
The thermal efficiency of a gas turbine is set largely by turbine inlet temperature and compressor pressure ratio. Raising either improves efficiency, but turbine inlet temperature runs into the limits of material strength, and pressure ratio into the limits of compressor aerodynamics and engine weight. Film cooling of turbine blades pushes that boundary a little further, yet the cooling air is bled from the cycle and therefore carries an efficiency penalty of its own. Today’s engines have already optimised most of these trade-offs, so the remaining margin has narrowed and every additional percentage point costs more. This is exactly where exergy-based assessment methods become useful in deciding where improvement is worth pursuing.
Mission profile, not design point
Engines are certified at a single design point but spend their working lives across take-off, climb, cruise and descent. Understanding real performance requires evaluating them along the mission profile. Prof. Dr. Yasin Şöhret’s work includes a thermo-environmental evaluation of a cargo aircraft engine during flight, a thermodynamic assessment of a new-generation turbojet used in unmanned aerial vehicles, and an environmental and enviroeconomic assessment of a turboprop engine.
Unmanned aircraft are a different design problem
Propulsion systems for unmanned aerial vehicles are designed under quite different constraints from airliners: endurance, altitude profile, weight budget and cost balance all differ. Performance metrics developed for commercial aviation therefore cannot be applied directly. Şöhret’s research in this area includes a comprehensive classification of unmanned aerial vehicles with a proposal for military use, and thermodynamic assessments of the turbojet engines used in them.
Combustion and emission prediction
Engine performance and emission formation are two sides of the same process: temperature, pressure and mixing conditions in the combustor determine both the power produced and the formation of nitrogen oxides and particulates. Emissions therefore cannot sensibly be treated as an after-the-fact correction; they have to be computed within the combustion model itself. Şöhret’s work includes developing a model to predict the combustion performance and emissions of a turboprop engine, and predicting emission characteristics using artificial neural networks.
