Worldwide growth in air traffic has been on a continuous upward curve for decades. And it will continue to climb, with experts estimating an annual growth rate of between four and six percent. Another curve has a similar shape, the one showing how the bypass ratio (BPR) of engines has developed over time. The bypass ratio indicates how much air inside the nacelle flows past the combustor and how much passes through it. As a rule: the higher the ratio, the more efficient the engine. And more efficient engines mean lower fuel consumption and emissions.
Higher BPRs are therefore one of the most effective tools for engineers striving to make aviation more environmentally friendly. The BPR curve is an impressive record of the industry's success. Since the 1960s, the ratios have climbed from an initial value of 2:1, reaching 6:1 for the classic V2500 engine in the 1980s, before the Geared Turbofan™ (GTF) achieved the current record of 12:1. Dr. Edgar Merkl from MTU Aero Engines in Munich is now ensuring that the BPR curve continues to rise for the engines of tomorrow in his capacity as coordinator of the EU's ENOVAL project, which started four years ago.