Dossier Rafale :The enginesThe requirements for a multirole and powerful engine were met with the M88
-2. This completely new engine has been designed specifically for the Rafale.
The main characteristic of an engine for low altitude is a low specific fuel consumption. The new engine, a two spool turbofan achieves this with a high compression rate (24.5) and high efficiency components.
However, an engine for high alitude requires a strong specific thrust, and a low by-pass ratio. This is why a bypass of 0.3 was chosen, and the TIT (Turbine Inlet Temperature) is as high as 1577°C (1800 K). Afterburner acts on both flow.
Such performance were achieved due to the following new technologies : single-piece bladed compressor disks (blisks), on-polluting combustion chamber, single crystal high-pressure turbine blades, powder disks, ceramic coatings, composite materials, etc
The engine is digitally controled by two calculators, a FADEC programmed with 160 laws. This makes the piloting easy, optimal, and restriction-less in all the flight envelope. For example, both engines are started in less than two minutes, and they accelerate from iddle to full afterburner in only three seconds. This regulation plays a great role in the pilot workload reduction, but also for the technician because it also takes care of itself as much as possible and identify and locate its defaults, calculate performances, check the aging, the vibrations, etc... in real time !
The engines are started with the APU (Auxiliary Power Unit), which also handle the cockpit conditioning when the aircraft is on the ground.
It's interesting to notice that, in terms of evolution, that the M88 is an engine whose weight (897kg) and lenght (3.53m) are diminished by 45 per cent compared the 9K50 (Mirage F1). However, its thrust-to-weight ratio has improved by 88 per cent, to reach 9.
But the M88-2 is also a discreet engine : it uses the latest technological breakthroughs so as to reduce its RCS and mostly its IR signature. In most situation, the M88-2 doesn't even compromise the IR signature of the Rafale !
Yet, the engine is one of the first components whose evolution is planed from the begining, and the M88 is designed as the father of a family.
Though research for the 90kN M88-3 and the 115kN M88-4 were unsuccessful up to now, they are used for the programme ECO.
ECO consists in two prototypes, one demonstrating the feasibility of a 90kN engine (with increased air flow, and re-dimensioned air intake) and the other so as to increase by 50% the lfe time. The developed technologies are about blisks, new regulators, increased TIT (2100 K) etc
Sources : Air & Cosmos, Snecma, Air Fan, Flight Global, etc
http://tmor.rafale.free.fr/quatre.html
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