Junkers Jumo 222

A.I.2.(g) Report No. 2309

Junkers Jumo 24-Cylinder Aero-Engine

The Jumo 222, an engine of original and strikingly compact design, was first reported on by Intelligence sources as far back as 1941. It has since been mentioned at frequent intervals.

Information recently obtained from captured German documents and P/W [prisoner of war] sources indicates that this engine, after prolonged and serious development troubles, is now in production, and may shortly appear in service. Sub-types A-l, A-2, B-1 and B-2 have already been identified.

General Description

24-cylinder, liquid-cooled "parallel radial", consisting of six blocks of four cylinders arranged equidistantly around the crankcase. Two inlet and one exhaust valve per cylinder operated by single overhand camshafts through the normal Junkers-type rocker gear. Single-stage, two-speed centrifugal supercharger. Two magnetos. Pressure cooling (max. coolant temp. 120°C). Fuel B4 (87 octane) or C3 (100 octane) in emergency.

The valve seats are treated with a deposit of 75% nickel, 20% chromium and 1.8% boron (similar to British “Brightray”).

Reported weight as complete power-egg: 1,830 kg (4,030 lb)

Take-off power (unspecified sub-type): 2,500 hp at 3,100 rpm at 1.62 ata boost (8.3 lb)

It is believed that a version exists wit the compression ratio raised to 7.3:1, fitted with a turbo-supercharger and operating normally on C3 (100 octane) fuel.

Application to Aircraft

The Jumo 222 was to have been installed in one version of the Ju 288, and Fw 191 bombers and in a version of the He 177. A P/W has recently stated that it will be used to power the Do 435, a development of the Do 335.

All the above installations would probably utilise frontal radiators. In some cases the GM-1 power boosting system might be used to increase performance at altitude.

Owing to the comparatively small diameter of the engine it has obvious possibilities for installation in single-seat fighters, such as the Ta 152.

Signed by M. Lambert, Squadron Leader, for Wing Commander, A.I.2.(g), D. of I. (R), 17 February, 1945

A.I.2.(g) Report No. 2333

Junkers Jumo 222 24-Cylinder Aero-Engine

1. A Jumo 222 engine was recently found at an assembly plant near Frankfurt-on-Main and has been flown to England. The existence of this design has been known for nearly five years and the more recent intelligence reports have correctly described its layout, but this is the first occasion on which it has been possible to inspect one of these engines. As the specimen recovered is new and undamaged—it has not even been bench-tested—it is hoped that it may eventually be possible to run it and so determine performance. For this reason only a superficial examination, involving a minimum of dismantling, has so far been made. The findings are incorporated in this preliminary report.

2. The Jumo 222 has been mentioned in connection with the Ju 288 and Fw 191, twin-engined bombers, a version of the He 177, and the Do 435, but so far as is known it has not yet been installed in an operational aircraft.

3. The unit examined is obviously a prototype. There is no plate to indicate the sub-type designation but there is evidence of experimental, rather than series, production. The supercharger, too, is very small for an engine of this size, as might be expected during the early stages of development.

4. Considerable interest attaches to the Jumo 222 because it is the latest and most powerful German engine to approach the production stage, and because it is the first high-powered enemy power plant to depart from the conventional inverted-vee or 2-row radial layout.

General Layout

5. As will be seen from Figures 1 and 3, the engine is a combination of radial and in-line designs. The twenty-four cylinders are arranged in six banks of four, equally spaced at 60° around the crankcase. The engine may therefore be properly described as a 4-row 24-cylinder liquid-cooled radial. It is designed for mounting with a "vee” uppermost and an opposed pair of cylinder heads in the horizontal axial plane.

6. The four mounting points are arranged two on each side between the upper and the horizontal heads, as seen in Figure 2; the spaces between these heads are, for this reason, left unencumbered except for the exhaust pipes (not fitted). The crankcase is split as asymmetrically, the two bottom banks of cylinders being carried by what would normally be regarded as the sump of an in-line engine.

7. Deep ribs are formed around the long reduction gear housing, which may have bean deliberately extended to facilitate installation and cowling. The propeller shaft, which is co-axial with the crankshaft, terminates in a large, deeply-serrated flange (Fig. 3). The reduction gearing, which is presumed to be epicyclic, is reported to have a ratio of 2.714:1, but this has not been checked because of the risk of damage in turning a dry engine.

8. At the rear of the engine there is a compact circular wheelcase to the outer end of which is bolted the supercharger casing (Fig. 4).

9. The crankshaft and connecting rod arrangement have not yet been determined and will be described in a later report.

Dimensions

Length overall : 89.25"

Maximum diameter: 46.00"

Cylinders

11. The cylinder bore is 150 mm. This is the same as that of the Jumo 213. The stroke, and consequently the capacity, could not be obtained, but the capacity is obviously considerably greater than the 46.5 liters previously reported.

12. The six banks of cylinders are numbered clockwise from the front, No. 1 being the horizontal block on the left (Fig. 3). Propeller rotation is clockwise.

13. There are no separate cylinder blocks, the wet liner being mounted in the crankcase, which is ducted to permit circulation of the coolant. The cylinder head of each bank is detachable and forms the upper part of the liner coolant jacket. A rubber “necklace” makes a liquid-tight joint between the cylinder head and crankcase (Fig. 6). The lower end of each cylinder liner has a flange into which four waisted studs are screwed; these project through the cylinder head and serve to pull up the liner against a conical seating round the combustion chamber. An aluminium sealing ring interposed between the liner and the head makes a gas- and liquid-tight joint. The liner studs are sealed by small rubber rings and chamfered steel washers fitted between the nuts and the cylinder head.

14. Each light-alloy cylinder head has an overhead camshaft driven from the rear of the crankshaft by a train of spur gears running on plain bearings. The camshaft runs in nine split bearings; the large rear bearing is adjacent to the driving gear and the smaller bearings are arranged in four groups of two, giving maximum support near the cams (Fig. 7).

15. There are two inlet valves, 55.3mm in diameter, and one sodium-cooled 63.5mm diameter exhaust valve per cylinder. Each valve has two large-diameter springs retained by conventional split taper-collets.

16. The valves are operated by light-alloy rocker arms mounted above the camshaft and pivoted centrally on small lay shafts (Fig. 7). The adjustable tappets have small self-aligning hardened steel tips that engage the valve stem pads. The rocker arms have hardened steel rollers running on the quick-lift cams.

17. Small serrated extensions at the front of the camshafts are utilised on the two lower heads to drive auxiliary oil scavenge pumps. Various auxiliaries are driven from the camshaft-operated gears of the different banks.

18. Each combustion chamber is of wide-angle asymmetrical pent-house shape and has the fuel injector mounted between the two inlet valves. The two phosphor-bronze sparking-plug inserts are diametrically opposed and are screwed and doweled into the casting (Fig. 6). The plugs are shrouded by aluminum tubes that push into the head and protrude through the camshaft cover, an oil-tight seal being formed by a rubber ring in the top of each tube.

19. The tapered induction trunks are of cast aluminium-bronze. There are three delivery trunks from the supercharger volute casing, each of which branches into two pipes and feeds two cylinder blocks. A balance pipe is fitted between the induction manifolds of numbers 1 and 6, 2 and 3, and 4 and 5 (Figs. 1 and 4). A rubber ring and quick-release clips provides a pressure-tight joint between each manifold and the induction trunk.

20. The coolant is circulated by a centrifugal impeller pump mounted below the crankcase at the forward end. Three delivery pipes lead the coolant to elbow joints bolted to the front of the crankcase between numbers 1 ad 2, 3 and 4, and 5 and 6 cylinder heads. A coolant outlet is provided at the front of each cylinder head (Fig. 3).

21. The camshaft and rocker arm mechanism is lubricated by oil fed under pressure to the top four banks of cylinders by pipes at the front of the heads. The oil from the two horizontal heads (Nos. 1 and 4) drains into the two lower heads (Nos. 5 and 6) through flexible pipes (Fig. 3) and lubricates the camshaft and rocker mechanism of these heads. Scavenge oil from the two upper heads drains via the rear train of gears into the crankcase. Auxiliary scavenge pumps mounted at the front of heads Nos. 5 and 6 returns the excess oil to the crankcase.

Supercharger

22. The 2-speed supercharger is driven by plain spur gears off the rear end of the crankshaft. The automatic change-over control is seen at the side of the wheel case in Figure 4. Two rectangular air intakes (Figs. 2 and 4) with “eyelid” type throttles lead the air through variable-pitch guide vanes into the eye of the impeller. A single aluminum-bronze casting forms the rear impeller bearing housing and air intake. The “Komandogurat” is mounted above this casting (Fig. 4).

23. Each of the three induction elbows has a priming connection for starting.

Fuel Injection System

24. There are three separate fuel injection pumps, one being mounted between numbers 2 and 3, one between 4 and 5 and one between 6 and 1 heads. Each pump feeds two banks of cylinders.

25. The fuel supply pump is driven off the rear of number 4 camshaft and supplies fuel under pressure to a unit mounted between numbers 2 and 3 heads, presumably a pressure-reducing valve; from this unit fuel is distributed to the three injection pumps.

Ignition

26. Two “duplex” magnetos are fitted. One is driven from the crankshaft driving gears of number 2 bank and serves Nos. 1, 2 and 6 cylinder banks; the second is driven off the camshaft gears of number 3 bank and serves the remaining banks. The magnetos and harness are fully screened. Each magneto has four contact breakers operated by a single 6-lobe cam of laminated plastic; these are readily accessible on removal of the end plates (Fig. 5). The cam followers are looped spring-steel strips.

Main Lubrication System

27. The pressure pump is mounted below, and driven from, the wheelcase. A self-cleaning metal disc oil filter is mounted in the rear of the oil pump housing, which also incorporates an adjustable pressure-relief valve. The main scavenge pump is apparently incorporated in the same housing as the pressure pump, and there is an auxiliary supply scavenge pump co-axial with the coolant pimp for draining the reduction gear housing.

Hydraulic Pump

28. This unit is driven from the rear of No. 5 camshaft.

Starter and Generator

29. The starter is mounted in an accessible position above the reduction gear housing (Fig.1), and turns-the crankshaft though a train of gears. Engagement of the starter is by a solenoid-operated mechanical linkage.

30. The generator is mounted between numbers 2 and 3 banks and is driven off the same train of gears.

Tachometer Drive

31. The revolution counter is driven from a small gear-case mounted on the main wheelcase adjacent to the rear of number 1 cylinder bank.

Power Output

32. The power output of the Jumo 222 has been reported by P's/W [sic; prisoners of war] as between 2,400 and 3,000 hp for take-off and 1,800 ~ 2,400 hp at a rated altitude of about 18,000 ft.

In view of the increased cubic capacity, however, these figures may have been exceeded.

Signed by G.E.F Proctor, Wing Commander, A.I.2.(g), D. of I.(R), 18 April, 1945

	Fig. 1
Fig. 2	Fig. 3	Fig. 4
Fig. 5	Fig. 6	Fig. 7

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