Dobrynin WD-4K
The Dobrynin WD-4K ( Russian Добрынин ВД-4К ) was the last version of a Soviet aircraft engine from the OKB -36 in Rybinsk . It was developed and built by Vladimir Dobrynin from the late 1940s to the early 1950s and marked the high point of the Soviet development of aircraft piston engines .
It is a water-cooled 24-cylinder in-line Otto engine with four 6-cylinder stars arranged one behind the other - similar to the Junkers Jumo 222 . The WD-4K was the most powerful Soviet aircraft engine and was only used in the prototype long-range strategic bomber Tupolev Tu-85 . The power of this four-stroke engine reached 3160 kW (4300 hp). Its power-to-weight ratio was 0.51 kg / hp, which is favorable for large piston engines.
Its predecessors were the M-250, M-251TK, M-253K and WD-3TK, all of which had the same 24-cylinder design. Its closest competitor as a drive for the Tu-85 at that time was the Schwezow ASch-2K with almost the same level of performance.
technology
As the abbreviation K (“compressor”) expresses, the WD-4K was not a naturally aspirated engine, but a supercharged engine in a turbo-compound design.
A compressor (radial) integrated in the engine itself with a fixed ratio to the crankshaft was used for charging . Upstream of this was an exhaust gas turbocharger with a charge air cooler. The energy of the exhaust gases was determined by three lying between the cylinder banks turboexpander the crank drive supplied. The exhaust gases were then passed on to the turbocharger's turbine to drive it. The mixture was prepared by means of direct gasoline injection . The water cooler was arranged in a ring around the reduction gear of the 4-blade propeller . The cooling air flow was increased by a fan wheel.
The one-piece crankshaft was cranked four times - once for each of the four six-cylinder stars. The four cranks were offset by the following angles: crank I (0 °), crank II (150 °), crank III (180 °) and crank IV (330 °). The mass balance was optimal, so the engine ran virtually vibration-free. This was possible because the hexagon arrangement (6 cylinders per star with 60 ° symmetrically arranged each) achieves harmonious mass movements and free inertia forces can only be compensated by counterweights.
Furthermore, an even firing sequence was achieved every 30 ° of the crankshaft revolution, using the following ignition schemes:
| Crank I / star I. | Crank II / star II | Crank III / star III | Crank IV / star IV | |
|---|---|---|---|---|
| Cylinder bank 6 | 1 | 7th | 12 | 18th |
| Cylinder bank 1 | 3 | 21st | 14th | 8th |
| Cylinder bank 2 | 17th | 23 | 4th | 10 |
| Cylinder bank 3 | 19th | 13 | 6th | 24 |
| Cylinder bank 4 | 9 | 15th | 20th | 2 |
| Cylinder bank 5 | 11 | 5 | 22nd | 16 |
Due to the rapid development of turbo- prop engines, piston engines were soon replaced as aircraft engines, because turbo-prop engines usually achieve mass-specific performance (performance per engine mass) that is unattainable for piston engines and still have very compact dimensions. In the Soviet Union, the following bombers were often powered by the Kuznetsov NK-12s (such as the Tupolev Tu-95 ), which are still the most powerful turboprop engines ever built in the world.
There are only a few examples of other "hexagon" engines. These include the 24-cylinder Junkers Jumo 222 , the 12-cylinder Curtiss-Wright H-2120 and the 12-cylinder Curtiss H-1640 Chieftain .
Technical specifications
- Engine type: water-cooled 24-cylinder in-line Otto engine (four 6-cylinder stars)
- Stroke: 144.0 mm
- Bore: 148.0 mm
- Displacement: 59,455 cm³
- Power: 3160 kW (4300 hp ) at 2900 min -1
- specific power: 72.3 hp / liter
- Piston speed: 13.92 m / s
- Compression: 7.0: 1
- Mass: 2190 kg
- Diameter: 1.40 m
- Length: 2.50 m (with turbo system and gear)
- Power-to-weight ratio: 0.51 kg / hp
- Gasoline consumption: 0.160-0.175 kg / PS · h (in cruising mode at an altitude of 11,000 m)
- Number of items: 23