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[技术] 美国密歇根州威廉姆斯研究所制造的WR24-7-2型发动机

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发表于 2018-1-5 20:59:19 | 显示全部楼层 |阅读模式
威廉斯研究WR24-7-2
我再次有机会获得美国密歇根州威廉姆斯研究所制造的WR24-7-2型发动机

发动机

发动机

诺斯罗普公司选择了发动机来驱动他们的MQM-74C Chukar II型空中目标无人机(即他们唯一的目的是为了在......艰难的生活中被射击);-)。 然而,这个电厂也被用于其他制造商生产的侦察机的测试,即使它后来还没有实现。 我得到的引擎起源于后面的应用程序之一。
WR24-7-2的主要特点是:

美国密歇根州威廉姆斯研究所制造的WR24-7-2型发动机

美国密歇根州威廉姆斯研究所制造的WR24-7-2型发动机



 楼主| 发表于 2018-1-5 21:01:04 | 显示全部楼层
原文:
The engine was chosen by Northrop to power their MQM-74C Chukar II aerial target drone (i.e. their only purpose was for being shot at...hard life ;-). Yet, this power plant was also used for testing of reconnaissance drones produced by other manufacturers, even if it later didn’t come to fruition. The engine that I got originated from one of the latter applications.

The leading particulars of the WR24-7-2 are:
   
                                Type of engine:
                                Turbojet
                           
                                Layout:
                           
                                Single shaft, 1 axial and 1 radial compressor, annular combustor with centrifugal injection, 1 axial turbine, convergent thrust nozzle
                           
                                Rated thrust (ISA conditions):
                           
                                800N (180lbs) minimum
                           
                                Rated RPM:
                           
                                60900+-250 / min
                           
                                “Idle” RPM:
                           
                                50000+-500 / min
                           
                                Steady state EGT:
                           
                                765°C maximum
                           
                                Specific fuel consumption:
                           
                                no more than 0.123 kg/Nh
                           
                                Lubrication system:
                           
                                Compressor-bleed operated oil mist system, total loss
                           
                                Oil consumption:
                           
                                125 g/h maximum
                           
                                Oil type:
                           
                                MPDS-3.26.020 (whatever that is)
                           
                                Engine control system:
                           
                                Electronically controlled fuel metering system using RPM as the only input signal
                           
                                Ignition system:
                           
                                High energy system, mounted remotely of engine
                           
                                Fuel System:
                           
                                Bleed air pressurized fuel cell, proportional valve integral to the electronic fuel control unit
                           
                                Recommended fuel:
                           
                                JP-5, Jet A-1
                           
                                Accessories:
                           
                                Integrated switched reluctance alternator on main shaft, 40-70VAC, 20A, doubles as RPM pickup


Calculations show that the engine will have a pressure ratio of around 5:1 and an air mass flow of 1.4 to 1.5kg/s. The gas temperature at the turbine stage entry will be around 980°C. Here’s a link to a short lineup of the WR24’s turbomachinery particulars.
 楼主| 发表于 2018-1-5 21:02:34 | 显示全部楼层
This sketch shows the basic layout of the engine (click the image for a higher resolution TIFF version). The engineers at Williams Research found some very clever solutions for details to keep the engine as simple as possible while it requires minimum maintenance and can still be manufactured at reasonable expenses. There are three peculiarities that distinguish this engine from most other small turbojets.
   Firstly, there’s the rotating atomizer that was introduced by Turbomeca of France but had been pioneered for very small engines by Williams with the WR2. The advantage of this fuel injection pinciple is that only a very low fuel pressure is required and that the atomisation over a wide RPM range stays close to perfect. The most serious disadvantage is that no shaft tunnel can be used for the bearing arrangement and hence the engine casing becomes a structural member of the rotor suspension, requiring high precision on that component.
   Secondly, and closely related to the fuel injection system, is the way the fuel is delivered to the engine. The Williams engineers used compressor bleed air to slightly pressurize the fuel cell in order to feed the fuel to the engine-mounted fuel control unit. This completely eliminates the need for a pump.
   And finally, the lubrication system is configured as a total loss system, running on a finely atomized oil mist. A small oil tank is attached to the engine, containing round about 0.4 liters, and compressor bleed air is used in some kind of venturi arrangement to atomize the oil. The oil flow is very low (specified to be less than 125 gramms per hour), and many “big” engines have higher losses through their labyrinths, even though they feature a return oil system.

The engine is specified to be recoverable after salt water immersion (of course only after shut- and cooldown...) and is only supposed to be flushed and cleaned with different liquids and then test run to dry out the cleaning agents. For such a simple motor, that’s a great advantage since it’s not automatically a write-off if the drone has to go down over the sea (i.e. it runs out of fuel while operating as a target over water).
   On the particular engine that I got, this cleaning procedure probably has not been carried out completely or in a timely manner, the result was some minor corrosion on the aluminium parts, major corrosion on the magnesium alloy (probably...) axial compressor rotor and salty-oily deposits everywhere in the engine. Otherwise, the engine was in a very nice condition, yet I had to tear it down completely to clean everything. And I won’t do a job like this without my camera, so now some photos of the components are show (from intake to the exhaust...)..

发动机

发动机


The intake with the fuel inlet and purge air fittings

发动机

发动机


 楼主| 发表于 2018-1-5 21:03:55 | 显示全部楼层
The area that shrouds the axial compressor is internally lined with a (brownish) polymer, thus permitting an interference fit with the axial impeller for very small tip clearance.

发动机

发动机

The center cone houses the carbon (graphite) seal that slides on a polished insert in the rotor shaft. Fuel enters through the annular orifice between the capillary tube and the graphite disc while the scavenge air is introduced through the tube. The engine manual didn’t mention it but I guess the air is required to scavenge all fuel from the shaft upon engine shutdown and thus preventing the four injection nozzles from coking when the heat soaks from the hot engine components to the shaft.

发动机

发动机

The components of the rotating assembly from top left to lower right: The shaft nut, the axial compressor impeller, the alternator rotor, a spacer, the compressor bearing, the radial compressor impeller (with another spacer more or less permanently attached to the rear of its hub), and finally the turbine wheel/shaft assembly with the roller bearing inner race riding on the short shaft end.

发动机

发动机

Here a close-up of the spare axial compressor impeller that shows minor traces of corrosion but is generally still in acceptable shape. It’s incredible how light-weight this component is, hence I assume it’s made of either magnesium alloy or even aluminium-lithium.

 楼主| 发表于 2018-1-5 21:05:08 | 显示全部楼层

发动机

发动机

The alternator’s stator is located inside the axial compressor stator. The stator itself consists of a set of iron laminations that contain AlNiCo magnets to provide the bias field. the rotor only consists of laminations that close and interrupt the magnetic flow, thus producing an oscillating field that induces the voltage in the coils. This type of alternator is called “switched reluctance machine”. Since the AlNiCo magnets are susceptible to demagnetization if a too strong counter-field is applied, inside the stator a “magnetic keeper” has to be installed during disassembly.

发动机

发动机


The wires of the alternator run through one of the three struts of the radial compressor cover. The other strut extracts first stage compressor bleed air (here in the 12 o’clock position) to cool the turbine bearing, the third one (in the 4 o’clock position) feeds the oil mist to the compressor bearing.

发动机

发动机

The rear of the compressor cover. There’s slight surface corrosion present but it’s nothing to worry about. Also the starting air nozzle is visible that directs compressed air into the radial section of the second stage compressor to spin up the engine to ignition speed (air impingement starter).

 楼主| 发表于 2018-1-5 21:06:00 | 显示全部楼层
The compressor bearing seat contains two O-rings that prevent the outer race of the front bearing from rotating. Moreover, they act as vibration dampers. The labyrinth area is lined with a polymer coating to permit minimum clearance.

发动机

发动机

This is the starting air port that contains a check valve. To the right, some of the starting air is diverted to pressurize the oil mist generator and the fuel cell. Top left is the oil mist inlet for front bearing lubrication.

发动机

发动机

This sketch shows the starting air scheme and how it is diverted to supply the oilmist generator and to pressurize the fuel cell.

发动机

发动机

The front bearing is of the four-point contact type and is of the highest precision.

 楼主| 发表于 2018-1-5 21:07:03 | 显示全部楼层
The split inner race has to be assembled in a certain orinetation. For this purpose, an arrow (V) has been etched over the two halves of the race to indicate the direction of the axial force. Upon assembly, the “V” has to be matched.

发动机

发动机

A total of 34 blades are a lot for a radial compressor of that size (just short of 150mm).

发动机

发动机

In contrary to the previous engine(s) - WR2-6 -, the hub of the compressor is MUCH stronger.

发动机

发动机

The radial compressor placed inside the diffuser housing.

 楼主| 发表于 2018-1-5 21:07:53 | 显示全部楼层

发动机

发动机

The radial compressor diffuser housing without the compressor. Once again, there’s slight surface corrosion present in this area, but ist’s basically just surface discoloration. No material loss can be found.

发动机

发动机

A close-up of the radial diffuser vanes. Due to the shallow angle it’s hard to tell the shape of the vanes, but using a soft wire to “feel” the shape lets me assume that the vanes are of the wedge type, but I’m not 100% sure of this.

发动机

发动机

Here the axial diffuser/flow straightener vanes are visible from the rear of the diffuser housing.

 楼主| 发表于 2018-1-5 21:08:53 | 显示全部楼层

发动机

发动机

That’s the central labyrinth seal that is placed between the radial compressor rotor and the combustion chamber. It also ducts compressor air to the cooling channels inside the rotor shaft.

发动机

发动机

The front of the combustor with the heat shield. It’s amazing how small the clearance is for the inrushing primary combustion air.

发动机

发动机

The combustor front viewed from the compressor side.

 楼主| 发表于 2018-1-5 21:10:00 | 显示全部楼层

WR24-7-2型发动机

WR24-7-2型发动机

And here the “flame side” of the combustor is shown. This part is of rather simple construction, just a pressed sheet metal part/welded cosntruction with the primary air slots stamped/pressed into. Yet I guess, this “simple” part was the result of many hours of testing and experimenting.

WR24-7-2型发动机

WR24-7-2型发动机

This photo is a close-up of the fuel injector section of the turbine shaft. The tangetial bores duct cooling air from the central labyrinth seal into the hollow shaft and to the aft combustor labyrinth seal.

WR24-7-2型发动机

WR24-7-2型发动机

This sketch displays how the fuel is ducted through the hollow shaft and into the combustor.

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