ROLLS ROYCE MERLIN ENGINE

Introduction

Rolls Royce Merlin engine is designed to work as one of the best aircraft engine to win the world war. this engine is also called as V-12 piston powered engines. Initially it was known as P V-12 means private venture & 12 cylinders. Merlin engine was started on 15^th Oct-1933.

Type

Liquid cooled, V-12 piston powered aero engine, it was first produced in UK by Rolls Royce limited for world war.

Main components

1. Crank shaft: It converts the reciprocating motion in to rotary motion. It consists with counter weight. Crankshaft is usually made by forging process. Hardening process is also carried out in order to produce the hard outer Surface.
2. V-12 Engine: V-12 engine is main component used in Rolls Royce Merlin engine in which there are 12 cylinders arranged in V-form usually at 60 degree angle. It runs smoothly the system without any vibrations. There are 12 cylinders attached with crank-case in two rows by 6 cylinders in each row.
3. Cylinders: 12 cylinders are used over here with different heads & skirts. Inlet valves are fitted and these inlet valves are made of cast iron. Exhaust valves guides are also provided made of phosphor bronze. Piston moves in these cylinders in to and fro way.
4. Pistons: Each cylinder has separate piston that moves in cylinder and produces pressure in order to rotate the crankshaft. There are some piston rings are provided. it transfer force of expanding gases  to crankshaft with the help of piston rod or connection rod . 
5. Crankcase: Crank case is known as housing for crank-shaft, connecting rods and other parts of engine, crank case is usually made of aluminum for aircraft engines and process that used to make this is casting. In a crank case there are some arrangement to connect some key parts like crank shaft bearing, carburetor floor, space for fitting of cylinder, water jacket, Rocker arm struts.
6. Super charger: Super charger is key part of Rolls Royce engine, it increase the pressure (above atmospheric) of air entering to system. 2 stage supercharger is used in this engine, in 2 stage super charge there will be two impeller used for compressing .one impeller will be smaller than other impeller. 
7. It is driven mechanically by belt drive or chain drive with crankshaft of engine.
8. Coolant outlets- it is attached to a coolant extraction port in cooling system used in this engine.
9. Vacuum pump inlet
10. Vacuum pump return
11. De-icing connection to propeller
12. Engine mounting feet
13. Oil pressure gauge connection- To know the pressure usually measured in Psi or Kg/cm2.
14. Oil thermometer gauge connection – To know the temperature so that if temperature increases beyond the setting limit then interlocking may be used to maintain the healthiness of system
15. Coolant inlet to cylinder
16. Dowty pump drain
17. Oil inlet
18. Oil outlet
19. Coolant pump outlet
20. Starter motor terminal
21. Wheel case breather unit
22. Supercharger bearing vent 
23. Magneto earthling connection
24. Magneto Booster coil connection
25. Throttle control levers
26. Constant speed propeller governor unit
27. Slow running cut-off lever
28. Boost gauge connection
29. Cabin heater connection
30. Haywood air compressor outlet
31. Engine starting handles
32. Fire extinguishing system inlet
33. I.A.E pump delivery
34. I.A.E pump drain
35. I.A.E pump inlet
36. Fuel priming connection
37. Propeller shaft
38. Crankcase breather
39. R.A.E air compressor oil inlet
40. R.A.E air compressor air  inlet
41. R.A.E air compressor air & oil outlet
42. Engine speed indicator drive
43. R.A.E air compressor air drain
44. Boost control cut-out lever
45. Two speed supercharger control
46. Fuel priming connection to fuel pump
47. Fuel pump inlet
48. Fuel pump drain
49. Oil dilution connection
50. Fuel pressure gauge connection
51. Lockheed pump drain
52. Electric generator air cooling inlet
53. Electric generator air cooling outlet
54. Electric generator terminal
55. Exhaust manifold drain
56. Mixture control unit
57. Side rail
58. Fuel pump
59. Oil pump
60. Booster coil
61. Pressure oil strainer
62. Salt water pump
63. Distributor
64. Different sizes of hoses with high power capacity
65. Gear box- 2 stage gear box
66. Chain & chain sprocket- used to drive the supercharger by connecting with crankshaft
67. Timing chain& chain sprocket
68. Water & oil hoses
69. Booster pump

Lay out

In order to better understand I am producing a layout plan of Rolls Royce Merlin engine.

Specification of Rolls Royce Merlin engine

1. No. of cylinder = 12
2. Type = V, liquid cooled
3. Power = 1030 HP
4. Speed = 3000 rpm and increased up to produce 1520 rpm in 1943
5. Bore x stroke= 137 mm x 152 mm
6. Displacement = 27 liters
7. Weight= 600 kg
8. No. of stage of supercharger= 2
9. Oil system- dry sum with one pressure pump plus 2 scavenge pump
10. Fuel system- updraft carburetor with automatic mixture controlling unit

Details of Rolls Royce Merlin engine

Type of engine

V Engine fitted with two stages, two speed centrifugal superchargers with intercooler, pressure liquid cooling facilities.

1. No. of cylinder = 12
2. Cylinder arrangement – two row of cylinder, 6 cylinders in each row with an angle of 60 degree usually
3. Bore & stroke = 5.4 X 6 (inch x inch)
4. Swept volume = 1648 inch3
5. Cylinder numbering - 1A to 6A and 1B to 6B
6. Compression ratio= 6 to 1

Gear box type

Double stage & two speed

Propeller reduction gear type = spur gear

Direction of rotation

Propeller shaft- right hand

Crankshaft - left hand

Weight of engine -600 kg

Ignition

1. Firing order:  1A, 6B, 4A, 3B, 2A, 5B 6A, 1B, 3A, 4B, 5A, 2B
2. Magnetos:  2
3. Contact breaker gap:  0.012 plus minus 0.001 inch
4. Sparking plug gap:  0.018 inch- 0 .021 inch

Timing

Fully advanced -   Port 45⁰ before TDC , Stbd 38⁰ before TDC

Oil consumption

Consumption (at maximum cruising) =6-20 pints per hour

Minimum oil pressure = 40 psi at 2200 rpm at 90 ⁰C

Carburetion

Fuel= 100 octane

Maximum fuel consumption = 135 GPH

Pump pressure to carburetor = 9 psi

Fuel pressure to injector pump = 7 psi

Valves

Type – tulip type poppet valve

Valve timing

Inlet opens= 31 degree before TDC

Inlet close=52 degree after BDC

Exhaust opens=72 degree before BDC

Exhaust close =12 degree after TDC

Engine coolant

Type = pressure liquid

Flow= normal flow & reverse flow

Intercooler coolant

Type = pressure liquid

Starting system

Hand or electric electrical turning gear

Propeller

Rotol or De-havilland constant speed type

Rolls Royce Merlin engine- gear box

In this engine there is a gear box and its maintenance is very crucial there are some points that should be notice during maintenance of gear box

1. Decouple the gear box
2. Completely disassembled the cover of gear box
3. Drain the oil.
4. Remove internal gears from gear case.
5. Remove sludge deposits and clean thoroughly.
6. Cases, housings, etc. – we should inspect for cracks and other signs of wear.
7. Dismantle gear completely, clean and inspect all components.
8. We should Measure all "fits" and tolerances and compare with original drawing dimensions.
9. Shafts & Gearing – we should inspect and dimensionally inspected and if possible then reuse it otherwise we have to replace it by new one
10. Bearings & oil seals - inspect and dimensionally checked, for possible reuse, if oil seals are worn out replaces it by new one
11. Find if any new parts are required.
12. Shims, and gaskets will be replaced weather it is good or not for healthiness of system.
13. Bearing may be used or replaced; it depends on condition of bearing.
14. Gears and other hardware may also reuse or replaced, it depends on condition of these parts.
15. Fitting of all parts and tightening of all bolts.
16. Run it for some time to note down the performance like current reading

At starting state there was a lot of problem with Merlin engine as listed below

1. Failure of gear box
2. Failure of coolant jacket
3. Failure of cylinder head
4. Failure of crane shaft main bearing

After that a lot of development takes place in the design of Merlin engine with passes of time

1. PV-12: Generating power 740 HP at 3700 m
2. Merlin B:  Generating power 940 HP at 3400 m
3. Merlin C: Generating power 950 HP at 3400 m
4. Merlin E: Generating power 955 HP at 3400 m
5. Merlin I: this was also known as first production engine
6. Merlin II:  it was the most successful Merlin engine that produces 1030 HP power.
7. Merlin III:  it is developed after Merlin I & Merlin II and it was the most popular version of production engine.

The process was designed the way it was because

As per my opinion, it was new project at that time so there was a lot of uncertainty in selecting the suitable material, technology   , so in my point of view there were two main factors.

Knowledge

Merlin engine was designed by considering some factor of D-12 and American Curtiss. Rolls Royce used cast block engine as in D-12 it was used and D-12 was the successful and powerful engine at that time. In initial state Merlin engine has some common problem like cylinder head block cracking etc. Earlier they use evaporative cooling system but after some time they change it by ethylene liquid cooling system.

Earlier they were not use two speed supercharger, but when they use two speed superchargers, it provided the tremendous increment in power generation at higher altitudes.

Earlier there were used 100 percent glycol and compromise with engine life, but in order to rectify the reliability and efficiency of engine, they uses 70/30 coolant mixture of water and glycol, it avoid the problems of oil leakage and fire risks.

Material

In initial state as we have seen that the engine was with some problem related to crankshaft, gear box and cylinder head .the gear that was used was spur gear. Initially they were using normal metal for cylinder block and gear train and face problems with both.

They face problem of repeated failure with gear train and after they used EN material to develop gear and also use heat treatment process to make good life of gear & gearing arrangement.

Particular attributes of this artifact

They used simple gear train in gear box to reduce the speed,

In my point of view if they use planetary gear system, it can help to reduce the more speed with very little space as planetary gear system is very important in those areas where design criteria is compact space and more speed reduction .

Planetary gear system

In this gear system there will be a sun gear, 3 planet gears and one ring gear. Planet gears mesh with sun gear as well as ring gear. Ring gear has internal teeth to mesh with planet gear teeth.

Aspect of the artifact regarding sustainability

In my point of view the main aspect of this process is to produce more power at higher altitude and to maintain the reliability of engine.

Application of Merlin engine

Merlin engine was used the most successful aircraft engine in world war. It was designed for world war.

Also read

Shaft alignment techniques

Shaft alignment terminology

Basic of shaft alignment

Shaft alignment procedure

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