Misplaced Pages

#610389

125-449: The Rolls-Royce Crecy was a British experimental two-stroke , 90-degree, V12 , liquid-cooled aero-engine of 1,593.4 cu.in (26.11 L ) capacity , featuring sleeve valves and direct petrol injection . Initially intended for a high-speed "sprint" interceptor fighter, the Crecy was later seen as an economical high-altitude long-range powerplant. Developed between 1941 and 1946, it was among

250-534: A North American P-51 Mustang for engine installation trials. This prompted a series of studies for a Crecy version and the Mustang turned out a more suitable mount than the Spitfire. However these studies were not taken further. As the possibility of a flight-worthy engine approached, on 28 March 1943 Hawker Henley L3385 was delivered to Hucknall for fitting with a Crecy. However the engine never became available and

375-415: A power-valve system . The valves are normally in or around the exhaust ports. They work in one of two ways; either they alter the exhaust port by closing off the top part of the port, which alters port timing, such as Rotax R.A.V.E, Yamaha YPVS, Honda RC-Valve, Kawasaki K.I.P.S., Cagiva C.T.S., or Suzuki AETC systems, or by altering the volume of the exhaust, which changes the resonant frequency of

500-421: A rotary valve is that it enables the two-stroke engine's intake timing to be asymmetrical, which is not possible with piston-port type engines. The piston-port type engine's intake timing opens and closes before and after top dead center at the same crank angle, making it symmetrical, whereas the rotary valve allows the opening to begin and close earlier. Rotary valve engines can be tailored to deliver power over

625-476: A "universal" propeller shaft, allowing either de Havilland or Rotol manufactured propellers to be used. The first major version to incorporate changes brought about through experience in operational service was the XX, which was designed to run on 100- octane fuel. This fuel allowed higher manifold pressures , which were achieved by increasing the boost from the centrifugal supercharger . The Merlin XX also utilised

750-475: A Crecy engine and compared this to a Griffon 61 -powered variant. The report stated that the Crecy's maximum power output would be too much for the Spitfire airframe but that a derated version would have considerable performance gains over the Griffon-powered fighter. Studies on the de Havilland Mosquito also showed it to raise complex problems with Crecy installation. In 1942 Rolls-Royce Hucknall received

875-421: A DKW design that proved reasonably successful employing loop charging. The original SAAB 92 had a two-cylinder engine of comparatively low efficiency. At cruising speed, reflected-wave, exhaust-port blocking occurred at too low a frequency. Using the asymmetrical three-port exhaust manifold employed in the identical DKW engine improved fuel economy. The 750-cc standard engine produced 36 to 42 hp, depending on

1000-934: A Merlin X with a two-speed supercharger in high gear generated 1,150 hp (860 kW) at 15,400 feet (4,700 m) and 1,160 hp (870 kW) at 16,730 feet (5,100 m). From late 1939, 100-octane fuel became available from the U.S., West Indies , Persia , and, in smaller quantities, domestically, consequently, "... in the first half of 1940 the RAF transferred all Hurricane and Spitfire squadrons to 100 octane fuel." Small modifications were made to Merlin II and III series engines, allowing an increased (emergency) boost pressure of +12 pounds per square inch (183 kPa; 1.85 atm). At this power setting these engines were able to produce 1,310 hp (980 kW) at 9,000 ft (2,700 m) while running at 3,000 revolutions per minute. Increased boost could be used indefinitely as there

1125-613: A build-up of lead in the combustion chambers, causing excessive fouling of the spark plugs . Better results were achieved by adding 2.5% mono methyl aniline (M.M.A.) to 100-octane fuel. The new fuel allowed the five-minute boost rating of the Merlin 66 to be raised to +25 pounds per square inch (272 kPa; 2.7 atm). With this boost rating the Merlin 66 generated 2,000 hp (1,500 kW) at sea level and 1,860 hp (1,390 kW) at 10,500 ft (3,200 m). Starting in March 1944,

1250-448: A crossflow engine) is always best and support is good. In some engines, the small end is offset to reduce thrust in the intended rotational direction and the forward face of the piston has been made thinner and lighter to compensate, but when running backward, this weaker forward face suffers increased mechanical stress it was not designed to resist. This can be avoided by the use of crossheads and also using thrust bearings to isolate

1375-630: A higher power-to-weight ratio than a four-stroke engine, since their power stroke occurs twice as often. Two-stroke engines can also have fewer moving parts , and thus be cheaper to manufacture and weigh less. In countries and regions with stringent emissions regulation, two-stroke engines have been phased out in automotive and motorcycle uses. In regions where regulations are less stringent, small displacement two-stroke engines remain popular in mopeds and motorcycles. They are also used in power tools such as chainsaws and leaf blowers . The first commercial two-stroke engine involving cylinder compression

SECTION 10

#1732852077611

1500-457: A higher altitude of over 19,000 ft (5,800 m); and also improved the design of both the impeller, and the diffuser which controlled the airflow to it. These modifications led to the development of the single-stage Merlin XX and 45 series. A significant advance in supercharger design was the incorporation in 1938 of a two-speed drive (designed by the French company Farman ) to the impeller of

1625-516: A new 1,100 hp (820 kW)-class design known as the PV-12, with PV standing for Private Venture, 12-cylinder , as the company received no government funding for work on the project. The PV-12 was first run on 15 October 1933 and first flew in a Hawker Hart biplane ( serial number K3036 ) on 21 February 1935. The engine was originally designed to use the evaporative cooling system then in vogue. This proved unreliable and when ethylene glycol from

1750-465: A patent in 1880 in Germany. The first truly practical two-stroke engine is attributed to Yorkshireman Alfred Angas Scott , who started producing twin-cylinder water-cooled motorcycles in 1908. Two-stroke gasoline engines with electrical spark ignition are particularly useful in lightweight or portable applications such as chainsaws and motorcycles. However, when weight and size are not an issue,

1875-493: A problem after some months due to the physical and mental effects of wartime conditions such as the frequent occupation of air-raid shelters . It was agreed to cut the punishing working hours slightly to 82 hours a week, with one half-Sunday per month awarded as holiday. Record production is reported to have been 100 engines in one day. Immediately after the war the site repaired and overhauled Merlin and Griffon engines, and continued to manufacture spare parts. Finally, following

2000-449: A scavenging function. The units run in pairs, with the lower half of one piston charging an adjacent combustion chamber. The upper section of the piston still relies on total-loss lubrication, but the other engine parts are sump lubricated with cleanliness and reliability benefits. The mass of the piston is only about 20% more than a loop-scavenged engine's piston because skirt thicknesses can be less. Many modern two-stroke engines employ

2125-658: A similar system. Traditional flywheel magnetos (using contact-breaker points, but no external coil) worked equally well in reverse because the cam controlling the points is symmetrical, breaking contact before top dead center equally well whether running forward or backward. Reed-valve engines run backward just as well as piston-controlled porting, though rotary valve engines have asymmetrical inlet timing and do not run very well. Serious disadvantages exist for running many engines backward under load for any length of time, and some of these reasons are general, applying equally to both two-stroke and four-stroke engines. This disadvantage

2250-518: A turbocharger. Crankcase-compression two-stroke engines, such as common small gasoline-powered engines, are lubricated by a petroil mixture in a total-loss system . Oil is mixed in with their petrol fuel beforehand, in a fuel-to-oil ratio of around 32:1. This oil then forms emissions, either by being burned in the engine or as droplets in the exhaust, historically resulting in more exhaust emissions, particularly hydrocarbons, than four-stroke engines of comparable power output. The combined opening time of

2375-400: A wider speed range or higher power over a narrower speed range than either a piston-port or reed-valve engine. Where a portion of the rotary valve is a portion of the crankcase itself, of particular importance, no wear should be allowed to take place. In a cross-flow engine, the transfer and exhaust ports are on opposite sides of the cylinder, and a deflector on the top of the piston directs

2500-413: Is accepted in most cases where cost, weight, and size are major considerations. The problem comes about because in "forward" running, the major thrust face of the piston is on the back face of the cylinder, which in a two-stroke particularly, is the coolest and best-lubricated part. The forward face of the piston in a trunk engine is less well-suited to be the major thrust face, since it covers and uncovers

2625-422: Is attributed to Scottish engineer Dugald Clerk , who patented his design in 1881. However, unlike most later two-stroke engines, his had a separate charging cylinder. The crankcase -scavenged engine, employing the area below the piston as a charging pump, is generally credited to Englishman Joseph Day . On 31 December 1879, German inventor Karl Benz produced a two-stroke gas engine, for which he received

SECTION 20

#1732852077611

2750-590: Is being phased out. Honda , for instance, ceased selling two-stroke off-road motorcycles in the United States in 2007, after abandoning road-going models considerably earlier. Due to their high power-to-weight ratio and ability to be used in any orientation, two-stroke engines are common in handheld outdoor power tools including leaf blowers , chainsaws , and string trimmers . Two-stroke diesel engines are found mostly in large industrial and marine applications, as well as some trucks and heavy machinery. Although

2875-565: Is common in on-road, off-road, and stationary two-stroke engines ( Detroit Diesel ), certain small marine two-stroke engines ( Gray Marine Motor Company , which adapted the Detroit Diesel Series 71 for marine use ), certain railroad two-stroke diesel locomotives ( Electro-Motive Diesel ) and large marine two-stroke main propulsion engines ( Wärtsilä ). Ported types are represented by the opposed piston design in which two pistons are in each cylinder, working in opposite directions such as

3000-495: Is not the case because the output of the engine depends solely on the mass of air it can be made to consume efficiently, and in this respect the supercharger plays the most important role ... the engine has to be capable of dealing with the greater mass flows with respect to cooling, freedom from detonation and capable of withstanding high gas and inertia loads ... During the course of research and development on superchargers it became apparent to us that any further increase in

3125-432: Is that the two-stroke's crankcase is sealed and forms part of the induction process in gasoline and hot-bulb engines . Diesel two-strokes often add a Roots blower or piston pump for scavenging . The reed valve is a simple but highly effective form of check valve commonly fitted in the intake tract of the piston-controlled port. It allows asymmetric intake of the fuel charge, improving power and economy, while widening

3250-409: Is under every circumstance more efficient than cross-flow scavenging. In a uniflow engine, the mixture, or "charge air" in the case of a diesel, enters at one end of the cylinder controlled by the piston and the exhaust exits at the other end controlled by an exhaust valve or piston. The scavenging gas-flow is, therefore, in one direction only, hence the name uniflow. The design using exhaust valve(s)

3375-619: The Aeronautical Research Committee (ARC), was a proponent of a high-powered "sprint" engine for fighter aircraft and had foreseen the need for such a powerplant as early as 1935 with the threat of German air power looming. It has been suggested that Tizard influenced his personal friend Harry Ricardo to develop what eventually became the Crecy. The idea was officially discussed for the first time at an engine sub-committee meeting in December 1935. "The Chairman remarked that if it

3500-656: The Air Ministry had provided a total of £1,927,000 by December 1939. Having a workforce that consisted mainly of design engineers and highly skilled men, the Derby factory carried out the majority of development work on the Merlin, with flight testing carried out at nearby RAF Hucknall . All the Merlin-engined aircraft taking part in the Battle of Britain had their engines assembled in the Derby factory. Total Merlin production at Derby

3625-452: The Air Ministry , the Ministry of Aircraft Production and local authority officials. Hives was an advocate of shadow factories , and, sensing the imminent outbreak of war, pressed ahead with plans to produce the Merlin in sufficient numbers for the rapidly expanding Royal Air Force. Despite the importance of uninterrupted production, several factories were affected by industrial action . By

3750-466: The Battle of Britain Memorial Flight , and power many restored aircraft in private ownership worldwide. In the early 1930s, Rolls-Royce started planning its future aero-engine development programme and realised there was a need for an engine larger than their 21-litre (1,296 cu in) Kestrel , which was being used with great success in a number of 1930s aircraft. Consequently, work was started on

3875-458: The Junkers Jumo 205 and Napier Deltic . The once-popular split-single design falls into this class, being effectively a folded uniflow. With advanced-angle exhaust timing, uniflow engines can be supercharged with a crankshaft-driven blower, either piston or Roots-type. The piston of this engine is "top-hat"-shaped; the upper section forms the regular cylinder, and the lower section performs

Rolls-Royce Crecy - Misplaced Pages Continue

4000-616: The PV-12 , it was later called Merlin following the company convention of naming its four-stroke piston aero engines after birds of prey . The engine benefitted from the racing experiences of precursor engines in the 1930s. After several modifications, the first production variants of the PV-12 were completed in 1936. The first operational aircraft to enter service using the Merlin were the Fairey Battle , Hawker Hurricane and Supermarine Spitfire . The Merlin remains most closely associated with

4125-587: The Second Tactical Air Force (2TAF) also began using 100/150 grade fuel. This fuel was also offered to the USAAF where it was designated "PPF 44-1" and informally known as "Pep". Production of the Rolls-Royce Merlin was driven by the forethought and determination of Ernest Hives , who at times was enraged by the apparent complacency and lack of urgency encountered in his frequent correspondence with

4250-579: The Supermarine Spitfire and the Hawker Hurricane ; the latter designed in response to another specification, F36/34. Both were designed around the PV-12 instead of the Kestrel, and were the only contemporary British fighters to have been so developed. Production contracts for both aircraft were placed in 1936, and development of the PV-12 was given top priority as well as government funding. Following

4375-479: The crankshaft . The Crecy sleeve valves were of similar construction but differed in their operation compared to the rotary sleeve valve design that was pioneered by Roy Fedden , and used successfully for the first time in an aircraft engine, the Bristol Perseus , in 1932. Supercharging was used to force the charge into the cylinder, rather than crankcase compression, as on most two-stroke engines. This allowed

4500-506: The expansion chamber , such as the Suzuki SAEC and Honda V-TACS system. The result is an engine with better low-speed power without sacrificing high-speed power. However, as power valves are in the hot gas flow, they need regular maintenance to perform well. Direct injection has considerable advantages in two-stroke engines. In carburetted two-strokes, a major problem is a portion of the fuel/air mixture going directly out, unburned, through

4625-473: The oil reservoir does not depend on gravity. A number of mainstream automobile manufacturers have used two-stroke engines in the past, including the Swedish Saab , German manufacturers DKW , Auto-Union , VEB Sachsenring Automobilwerke Zwickau , VEB Automobilwerk Eisenach , and VEB Fahrzeug- und Jagdwaffenwerk , and Polish manufacturers FSO and FSM . The Japanese manufacturers Suzuki and Subaru did

4750-494: The time between overhauls (TBO) was typically 650–800 hours depending on use. By then single-stage engines had accumulated 2,615,000 engine hours in civil operation, and two-stage engines 1,169,000. In addition, an exhaust system to reduce noise levels to below those from ejector exhausts was devised for the North Star/Argonaut. This "cross-over" system took the exhaust flow from the inboard bank of cylinders up-and-over

4875-514: The 1,700 hp (1,300 kW) 42-litre (2,560 cu in) Rolls-Royce Vulture used four Kestrel-sized cylinder blocks fitted to a single crankcase and driving a common crankshaft, forming an X-24 layout. This was to be used in larger aircraft such as the Avro Manchester . Although the Peregrine appeared to be a satisfactory design, it was never allowed to mature since Rolls-Royce's priority

5000-528: The 1960s due in no small way to the increased power afforded by loop scavenging. An additional benefit of loop scavenging was the piston could be made nearly flat or slightly domed, which allowed the piston to be appreciably lighter and stronger, and consequently to tolerate higher engine speeds. The "flat top" piston also has better thermal properties and is less prone to uneven heating, expansion, piston seizures, dimensional changes, and compression losses. SAAB built 750- and 850-cc three-cylinder engines based on

5125-407: The 1960s, especially for motorcycles, but for smaller or slower engines using direct injection, the deflector piston can still be an acceptable approach. This method of scavenging uses carefully shaped and positioned transfer ports to direct the flow of fresh mixture toward the combustion chamber as it enters the cylinder. The fuel/air mixture strikes the cylinder head , then follows the curvature of

Rolls-Royce Crecy - Misplaced Pages Continue

5250-560: The Bentley marque and the factory. Today it is known as Bentley Crewe. Hives further recommended that a factory be built near Glasgow to take advantage of the abundant local work force and the supply of steel and forgings from Scottish manufacturers. In September 1939, the Air Ministry allocated £4,500,000 for a new Shadow factory. This government -funded and -operated factory was built at Hillington starting in June 1939 with workers moving into

5375-478: The Chief Designer. Bore was 5.1 in (129.5 mm), stroke 6.5 in (165.1 mm), compression ratio 7:1 and weight 1,900 lb (862 kg). The firing angle was 30 degrees BTDC , and 15 lbf/in² (100 kPa ) supercharger boost was typical. In bench-testing it produced 1,400 horsepower (1,000 kW), but there were problems with vibration and the cooling of the pistons and sleeves. The thrust produced by

5500-458: The Crecy itself, in conjunction with the Ricardo company , the decision had been taken by the Air Ministry to revert to a more conventional spark-ignition layout, although still retaining fuel injection. The Crecy has been described as one of the most advanced two-stroke aero engines ever built. The first complete V12 engine was built in 1941, designed by a team led by Harry Wood with Eddie Gass as

5625-448: The German inventor of an early form in the mid-1920s, it became widely adopted in Germany country during the 1930s and spread further afield after World War II . Loop scavenging is the most common type of fuel/air mixture transfer used on modern two-stroke engines. Suzuki was one of the first manufacturers outside of Europe to adopt loop-scavenged, two-stroke engines. This operational feature

5750-421: The Merlin 130/131 versions specifically designed for the de Havilland Hornet . Ultimately, during tests conducted by Rolls-Royce at Derby , an RM.17.SM (the high altitude version of the Merlin 100-Series) achieved 2,640 hp (1,970 kW) at 36 lb boost (103"Hg) on 150-octane fuel with water injection. With the end of the war, work on improving Merlin power output was halted and the development effort

5875-462: The Merlin 60 series gained 300 hp (220 kW) at 30,000 ft (9,100 m) over the Merlin 45 series, at which altitude a Spitfire IX was nearly 70 mph (110 km/h) faster than a Spitfire V. The two-stage Merlin family was extended in 1943 with the Merlin 66, which had its supercharger geared for increased power ratings at low altitudes, and the Merlin 70 series that were designed to deliver increased power at high altitudes. While

6000-472: The Merlin 66-powered Spitfire IXs of two Air Defence of Great Britain (ADGB) squadrons were cleared to use the new fuel for operational trials, and it was put to good use in the summer of 1944 when it enabled Spitfire L.F. Mk. IXs to intercept V-1 flying bombs coming in at low altitudes. 100/150 grade fuel was also used by Mosquito night fighters of the ADGB to intercept V-1s. In early February 1945, Spitfires of

6125-408: The Merlin X. The later Merlin XX incorporated the two-speed drive as well as several improvements that enabled the production rate of Merlins to be increased. The low-ratio gear, which operated from takeoff to an altitude of 10,000 ft (3,000 m), drove the impeller at 21,597 rpm and developed 1,240 hp (920 kW) at that height; while the high gear's (25,148 rpm) power rating

6250-553: The Merlin ran only on 100-octane fuel, and the five-minute combat limitation was raised to +18 pounds per square inch (224 kPa; 2.3 atm). In late 1943 trials were run of a new "100/150" grade (150-octane) fuel, recognised by its bright-green colour and "awful smell". Initial tests were conducted using 6.5 cubic centimetres (0.23  imp fl oz ) of tetraethyllead (T.E.L.) for every one imperial gallon of 100-octane fuel (or 1.43 cc/L or 0.18 U.S. fl oz/U.S. gal), but this mixture resulted in

6375-527: The Merlin was largely superseded by the Rolls-Royce Griffon for military use, with most Merlin variants being designed and built for airliners and military transport aircraft . The Packard V-1650 was a version of the Merlin built in the United States. Production ceased in 1950 after a total of almost 150,000 engines had been delivered. Merlin engines remain in Royal Air Force service today with

SECTION 50

#1732852077611

6500-516: The Merlin's components itself. Hillingdon required "a great deal of attention from Hives" from when it was producing its first complete engine; it had the highest proportion of unskilled workers in any Rolls-Royce-managed factory”. Engines began to leave the production line in November 1940, and by June 1941 monthly output had reached 200, increasing to more than 400 per month by March 1942. In total 23,675 engines were produced. Worker absenteeism became

6625-425: The Merlin's technical improvements resulted from more efficient superchargers , designed by Stanley Hooker , and the introduction of aviation fuel with increased octane ratings . Numerous detail changes were made internally and externally to the engine to withstand increased power ratings and to incorporate advances in engineering practices. The Merlin consumed an enormous volume of air at full power (equivalent to

6750-402: The Peregrine and Vulture were both cancelled in 1943, and by mid-1943 the Merlin was supplemented in service by the larger Griffon . The Griffon incorporated several design improvements and ultimately superseded the Merlin. Initially the new engine was plagued with problems such as failure of the accessory gear trains and coolant jackets. Several different construction methods were tried before

6875-474: The Spitfire and Hurricane, although the majority of the production run was for the four-engined Avro Lancaster heavy bomber. The Merlin continued to benefit from a series of rapidly-applied developments, derived from experiences in use since 1936. These markedly improved the engine's performance and durability. Starting at 1,000 horsepower (750 kW) for the first production models, most late war versions produced just under 1,800 horsepower (1,300 kW), and

7000-520: The Spitfire used a variation of this exhaust system fitted with forward-facing intake ducts to distribute hot air out to the wing-mounted guns to prevent freezing and stoppages at high altitudes, replacing an earlier system that used heated air from the engine coolant radiator. The latter system had become ineffective due to improvements to the Merlin itself which allowed higher operating altitudes where air temperatures are lower . Ejector exhausts were also fitted to other Merlin-powered aircraft. Central to

7125-444: The U.S. became available, the engine was adapted to use a conventional liquid-cooling system. The Hart was subsequently delivered to Rolls-Royce where, as a Merlin testbed , it completed over 100 hours of flying with the Merlin C and E engines. In 1935, the Air Ministry issued a specification, F10/35 , for new fighter aircraft with a minimum airspeed of 310  mph (500  km/h ). Fortunately, two designs had been developed:

7250-500: The V12 engines with a further 8,600 hours of testing on the V-twins. The fate of the six Crecy engines remains unknown. The Crecy proved a unique exercise and Rolls-Royce did not develop any other two-stroke aero engines, the whole concept of advanced piston engines at that time being overtaken by the advent of the practical jet engine . In the summer of 1941, Supermarine Spitfire Mk II P7674

7375-443: The aircraft remained at Hucknall until it was scrapped on 11 September 1945. From 1943 a number of postwar transport projects were considered, taking advantage of the Crecy's unique characteristics for land, sea and air applications. None got further than the drawing-board. Data from The Rolls-Royce Crecy. Related development Comparable engines Related lists Two-stroke engine Two-stroke engines often have

7500-477: The altitude performance of the Merlin engine necessitated the employment of a two-stage supercharger. As the Merlin evolved so too did the supercharger; the latter fitting into three broad categories: The Merlin supercharger was originally designed to allow the engine to generate maximum power at an altitude of about 16,000 ft (4,900 m). In 1938 Stanley Hooker, an Oxford graduate in applied mathematics, explained "... I soon became very familiar with

7625-475: The basic design of the Merlin was set. Early production Merlins were unreliable: common problems were cylinder head cracking, coolant leaks, and excessive wear to the camshafts and crankshaft main bearings . The prototype, developmental, and early production engine types were the: The Merlin II and III series were the first main production versions of the engine. The Merlin III was the first version to incorporate

SECTION 60

#1732852077611

7750-423: The bore diameter for reasonable piston ring life. Beyond this, the piston rings bulge into the exhaust port and wear quickly. A maximum 70% of bore width is possible in racing engines, where rings are changed every few races. Intake duration is between 120 and 160°. Transfer port time is set at a minimum of 26°. The strong, low-pressure pulse of a racing two-stroke expansion chamber can drop the pressure to -7 psi when

7875-459: The combustion chamber, and then is deflected downward. This not only prevents the fuel/air mixture from traveling directly out the exhaust port, but also creates a swirling turbulence which improves combustion efficiency , power, and economy. Usually, a piston deflector is not required, so this approach has a distinct advantage over the cross-flow scheme (above). Often referred to as "Schnuerle" (or "Schnürle") loop scavenging after Adolf Schnürle,

8000-466: The company convention of naming its piston aero engines after birds of prey, Rolls-Royce named the engine the Merlin after a small, Northern Hemisphere falcon ( Falco columbarius ). Two more Rolls-Royce engines developed just prior to the war were added to the company's range. The 885 hp (660 kW) Rolls-Royce Peregrine was an updated, supercharged development of their V-12 Kestrel design, while

8125-488: The construction of the Merlin supercharger and carburettor ... Since the supercharger was at the rear of the engine it had come in for pretty severe design treatment, and the air intake duct to the impeller looked very squashed ..." Tests conducted by Hooker showed the original intake design was inefficient, limiting the performance of the supercharger. Hooker subsequently designed a new air intake duct with improved flow characteristics, which increased maximum power at

8250-453: The crankshaft commonly spins in the same axis and direction as do the wheels i.e. "forward". Some of the considerations discussed here apply to four-stroke engines (which cannot reverse their direction of rotation without considerable modification), almost all of which spin forward, too. It is also useful to note that the "front" and "back" faces of the piston are - respectively - the exhaust port and intake port sides of it, and are not to do with

8375-415: The cycle's potential for high thermodynamic efficiency makes it ideal for diesel compression ignition engines operating in large, weight-insensitive applications, such as marine propulsion , railway locomotives , and electricity generation . In a two-stroke engine, the exhaust gases transfer less heat to the cooling system than a four-stroke, which means more energy to drive the piston, and if present,

8500-480: The design of the two-stage supercharger forged ahead, Rolls-Royce also continued to develop the single-stage supercharger, resulting in 1942 in the development of a smaller "cropped" impeller for the Merlin 45M and 55M; both of these engines developed greater power at low altitudes. In squadron service the LF.V variant of the Spitfire fitted with these engines became known as the "clipped, clapped, and cropped Spitty" to indicate

8625-533: The end of its production run in 1950, 168,176 Merlin engines had been built; over 112,000 in Britain and more than 55,000 under licence in the U.S. The existing Rolls-Royce facilities at Osmaston, Derby were not suitable for mass engine production although the floor space had been increased by some 25% between 1935 and 1939; Hives planned to build the first two or three hundred engines there until engineering teething troubles had been resolved. To fund this expansion,

8750-469: The engine before discharging the exhaust stream on the outboard side of the UPP nacelle. As a result, sound levels were reduced by between 5 and 8 decibels . The modified exhaust also conferred an increase in horsepower over the unmodified system of 38 hp (28 kW), resulting in a 5 knot improvement in true air speed. Still-air range of the aircraft was also improved by around 4 per cent. The modified engine

8875-400: The engine from end loads. Large two-stroke ship diesels are sometimes made to be reversible. Like four-stroke ship engines (some of which are also reversible), they use mechanically operated valves, so require additional camshaft mechanisms. These engines use crossheads to eliminate sidethrust on the piston and isolate the under-piston space from the crankcase. On top of other considerations,

9000-499: The exceptionally loud two-stroke exhaust was estimated as being equivalent to a 30% increase in power at the propeller on top of the rated output of the engine. The power of the engine was interesting in its own right, but the additional exhaust thrust at high speed could have made it a useful stop gap between engines such as the Rolls-Royce Merlin and anticipated jet engines. Serial numbers were even, because Rolls-Royce practice

9125-415: The exhaust port in the cylinder, the hottest part of the engine, where piston lubrication is at its most marginal. The front face of the piston is also more vulnerable since the exhaust port, the largest in the engine, is in the front wall of the cylinder. Piston skirts and rings risk being extruded into this port, so having them pressing hardest on the opposite wall (where there are only the transfer ports in

9250-409: The exhaust port, and direct injection effectively eliminates this problem. Two systems are in use: low-pressure air-assisted injection and high-pressure injection. Since the fuel does not pass through the crankcase, a separate source of lubrication is needed. For the purpose of this discussion, it is convenient to think in motorcycle terms, where the exhaust pipe faces into the cooling air stream, and

9375-413: The fresh intake charge into the upper part of the cylinder, pushing the residual exhaust gas down the other side of the deflector and out the exhaust port. The deflector increases the piston's weight and exposed surface area, and the fact that it makes piston cooling and achieving an effective combustion chamber shape more difficult is why this design has been largely superseded by uniflow scavenging after

9500-428: The fuel supply line together with a diaphragm fitted in the float chamber, jocularly nicknamed " Miss Shilling's orifice ", after its inventor, went some way towards curing fuel starvation in a dive by containing fuel under negative G; however, at less than maximum power a fuel-rich mixture still resulted. Another improvement was made by moving the fuel outlet from the bottom of the S.U. carburettor to exactly halfway up

9625-526: The great Ford factory at Manchester started production, Merlins came out like shelling peas ...". Some 17,316 people worked at the Trafford Park plant, including 7,260 women and two resident doctors and nurses. Merlin production started to run down in August 1945, and finally ceased on 23 March 1946. Total Merlin production at Trafford Park was 30,428. As the Merlin was considered to be so important to

9750-443: The intake and exhaust ports in some two-stroke designs can also allow some amount of unburned fuel vapors to exit in the exhaust stream. The high combustion temperatures of small, air-cooled engines may also produce NO x emissions. Two-stroke gasoline engines are preferred when mechanical simplicity, light weight, and high power-to-weight ratio are design priorities. By mixing oil with fuel, they can operate in any orientation as

9875-428: The level maximum speed of the Spitfire by 10 mph (16 km/h) to 360 mph (580 km/h). The first versions of the ejector exhausts featured round outlets, while subsequent versions of the system used "fishtail" style outlets, which marginally increased thrust and reduced exhaust glare for night flying. In September 1937 the Spitfire prototype, K5054 , was fitted with ejector type exhausts. Later marks of

10000-481: The maximum boost pressure at which the engine could be run using 87-octane fuel was +6 pounds per square inch (141 kPa; 1.44  atm ). However, as early as 1938, at the 16th Paris Air Show , Rolls-Royce displayed two versions of the Merlin rated to use 100-octane fuel. The Merlin R.M.2M was capable of 1,265 hp (943 kW) at 7,870 feet (2,400 m), 1,285 hp (958 kW) at 9,180 feet (2,800 m) and 1,320 hp (980 kW) on take-off; while

10125-469: The model year. The Monte Carlo Rally variant, 750-cc (with a filled crankshaft for higher base compression), generated 65 hp. An 850-cc version was available in the 1966 SAAB Sport (a standard trim model in comparison to the deluxe trim of the Monte Carlo). Base compression comprises a portion of the overall compression ratio of a two-stroke engine. Work published at SAE in 2012 points that loop scavenging

10250-428: The most advanced two-stroke aero-engines ever built. The engine never reached flight trials and the project was cancelled in December 1945, overtaken by the progress of jet engine development. The engine was named after the Battle of Crécy , after Rolls-Royce chose battles as the theme for naming their two-stroke aero engines. Rolls-Royce did not develop any other engines of this type. Sir Henry Tizard , Chairman of

10375-424: The number of required sub-contracted parts such as crankshafts, camshafts and cylinder liners eventually fell short and the factory was expanded to manufacture these parts "in house". Initially the local authority promised to build 1,000 new houses to accommodate the workforce by the end of 1938, but by February 1939 it had only awarded a contract for 100. Hives was incensed by this complacency and threatened to move

10500-476: The oil leaks that had been a problem with the early Merlin I, II and III series. The process of improvement continued, with later versions running on higher octane ratings, delivering more power. Fundamental design changes were also made to all key components, again increasing the engine's life and reliability. By the end of the war the "little" engine was delivering over 1,600 hp (1,200 kW) in common versions, and as much as 2,030 hp (1,510 kW) in

10625-399: The oil pump of a modern two-stroke may not work in reverse, in which case the engine suffers oil starvation within a short time. Running a motorcycle engine backward is relatively easy to initiate, and in rare cases, can be triggered by a back-fire. It is not advisable. Model airplane engines with reed valves can be mounted in either tractor or pusher configuration without needing to change

10750-483: The other - the inlet pipe having passage to the crankcase only when the two cutouts coincide. The crankshaft itself may form one of the members, as in most glow-plug model engines. In another version, the crank disc is arranged to be a close-clearance fit in the crankcase, and is provided with a cutout that lines up with an inlet passage in the crankcase wall at the appropriate time, as in Vespa motor scooters. The advantage of

10875-434: The piston covering and uncovering the ports as it moves up and down in the cylinder. In the 1970s, Yamaha worked out some basic principles for this system. They found that, in general, widening an exhaust port increases the power by the same amount as raising the port, but the power band does not narrow as it does when the port is raised. However, a mechanical limit exists to the width of a single exhaust port, at about 62% of

11000-440: The piston is at bottom dead center, and the transfer ports nearly wide open. One of the reasons for high fuel consumption in two-strokes is that some of the incoming pressurized fuel-air mixture is forced across the top of the piston, where it has a cooling action, and straight out the exhaust pipe. An expansion chamber with a strong reverse pulse stops this outgoing flow. A fundamental difference from typical four-stroke engines

11125-550: The power band. Such valves are widely used in motorcycle, ATV, and marine outboard engines. The intake pathway is opened and closed by a rotating member. A familiar type sometimes seen on small motorcycles is a slotted disk attached to the crankshaft , which covers and uncovers an opening in the end of the crankcase, allowing charge to enter during one portion of the cycle (called a disc valve). Another form of rotary inlet valve used on two-stroke engines employs two cylindrical members with suitable cutouts arranged to rotate one within

11250-632: The premises in October, one month after the outbreak of war. The factory was fully occupied by September 1940. A housing crisis also occurred at Glasgow, where Hives again asked the Air Ministry to step in. With 16,000 employees, the Glasgow factory was one of the largest industrial operations in Scotland. Unlike the Derby and Crewe plants, which relied significantly on external subcontractors , it produced almost all

11375-466: The principles remain the same, the mechanical details of various two-stroke engines differ depending on the type. The design types vary according to the method of introducing the charge to the cylinder, the method of scavenging the cylinder (exchanging burnt exhaust for fresh mixture) and the method of exhausting the cylinder. Piston port is the simplest of the designs and the most common in small two-stroke engines. All functions are controlled solely by

11500-511: The production of the Rolls-Royce Avon turbojet and others, the factory was closed in 2005. The Ford Motor Company was asked to produce Merlins at Trafford Park , Stretford , near Manchester , and building work on a new factory was started in May 1940 on a 118-acre (48 ha) site. Built with two distinct sections to minimise potential bomb damage, it was completed in May 1941 and bombed in

11625-474: The project. Crecy s/n 10 achieved 1,798 horsepower (1,341 kW) on 21 December 1944 which after adjustment for the inclusion of an exhaust turbine would have equated to 2,500 horsepower (1,900 kW). Subsequent single-cylinder tests carried out on the Ricardo E65 engine achieved the equivalent of 5,000 brake horsepower (3,700 kW) for the complete engine. By June 1945 a total of 1,060 hours had been run on

11750-480: The propeller. These motors are compression ignition, so no ignition timing issues and little difference between running forward and running backward are seen. Rolls-Royce Merlin The Rolls-Royce Merlin is a British liquid-cooled V-12 piston aero engine of 27-litre (1,650 cu in) capacity . Rolls-Royce designed the engine and first ran it in 1933 as a private venture. Initially known as

11875-450: The prototype high-altitude Vickers Wellington V bomber, Rolls-Royce started experiments on the design of a two-stage supercharger and an engine fitted with this was bench-tested in April 1941, eventually becoming the Merlin 60. The basic design used a modified Vulture supercharger for the first stage while a Merlin 46 supercharger was used for the second. A liquid-cooled intercooler on top of

12000-806: The same in the 1970s. Production of two-stroke cars ended in the 1980s in the West, due to increasingly stringent regulation of air pollution . Eastern Bloc countries continued until around 1991, with the Trabant and Wartburg in East Germany. Two-stroke engines are still found in a variety of small propulsion applications, such as outboard motors , small on- and off-road motorcycles , mopeds , motor scooters , motorized bicycles , tuk-tuks , snowmobiles , go-karts , RC cars , ultralight and model airplanes. Particularly in developed countries, pollution regulations have meant that their use for many of these applications

12125-473: The same month. At first, the factory had difficulty in attracting suitable labour, and large numbers of women, youths and untrained men had to be taken on. Despite this, the first Merlin engine came off the production line one month later and it was building the engine at a rate of 200 per week by 1943, at which point the joint factories were producing 18,000 Merlins per year. In his autobiography Not much of an Engineer , Sir Stanley Hooker states: "... once

12250-471: The shortened wingspan , the less-than-perfect condition of the used airframes , and the cropped supercharger impeller. The use of carburettors was calculated to give a higher specific power output, due to the lower temperature, hence greater density, of the fuel/air mixture compared to injected systems. Initially Merlins were fitted with float controlled carburettors. However, during the Battle of Britain it

12375-437: The side, which allowed the fuel to flow equally well under negative or positive g. Further improvements were introduced throughout the Merlin range: 1943 saw the introduction of a Bendix-Stromberg pressure carburettor that injected fuel at 5 pounds per square inch (34  kPa ; 0.34 bar ) through a nozzle directly into the supercharger, and was fitted to Merlin 66, 70, 76, 77 and 85 variants. The final development, which

12500-438: The spark plugs reduced detonation , allowing higher compression ratios or supercharger boost. Supercharger throttling was used as well to achieve idling. The supercharger throttles were novel vortex types, varying the effective angle of attack of the impeller blades from 60 to 30 degrees. This reduced the power required to drive the supercharger when throttled, and hence fuel consumption at cruising power. Later testing involved

12625-431: The success of the Merlin was the supercharger. A.C. Lovesey , an engineer who was a key figure in the design of the Merlin, delivered a lecture on the development of the Merlin in 1946; in this extract he explained the importance of the supercharger: The impression still prevails that the static capacity known as the swept volume is the basis of comparison of the possible power output for different types of engine, but this

12750-425: The supercharger casing was used to prevent the compressed air/fuel mixture from becoming too hot. Also considered was an exhaust-driven turbocharger , but although a lower fuel consumption was an advantage, the added weight and the need to add extra ducting for the exhaust flow and waste-gates meant that this option was rejected in favour of the two-stage supercharger. Fitted with the two-stage two-speed supercharger,

12875-511: The top or bottom of the piston. Regular gasoline two-stroke engines can run backward for short periods and under light load with little problem, and this has been used to provide a reversing facility in microcars , such as the Messerschmitt KR200 , that lacked reverse gearing. Where the vehicle has electric starting, the motor is turned off and restarted backward by turning the key in the opposite direction. Two-stroke golf carts have used

13000-408: The two-speed superchargers designed by Rolls-Royce, resulting in increased power at higher altitudes than previous versions. Another improvement, introduced with the Merlin X, was the use of a 70%–30% water-glycol coolant mix rather than the 100% glycol of the earlier versions. This substantially improved engine life and reliability, removed the fire hazard of the flammable ethylene glycol , and reduced

13125-420: The use of a conventional lubrication system, instead of the total-loss type found in many two-stroke engines. Stratified charge was used: the fuel was injected into a bulb-like extension of the combustion chamber where the twin spark plugs ignited the rich mixture. Operable air-fuel ratios of from 15 to 23:1 were available to govern the power produced between maximum and 60%. The rich mixture maintained near

13250-465: The use of an exhaust turbine which was a half-scale version of that used in the Whittle W.1 turbojet , the first British jet engine to fly. Unlike a conventional turbocharger the turbine was coupled to the engine's accessory driveshaft and acted as a power recovery device . It was thought that using the turbine would lower fuel consumption allowing the engine to be used in larger transport aircraft. This

13375-610: The very latest version as used in the de Havilland Hornet over 2,000 horsepower (1,500 kW). One of the most successful aircraft engines of the World War II era, some 50 versions of the Merlin were built by Rolls-Royce in Derby , Crewe and Glasgow , as well as by Ford of Britain at their Trafford Park factory , near Manchester . A de-rated version was also the basis of the Rolls-Royce/Rover Meteor tank engine. Post-war,

13500-403: The volume of a single-decker bus per minute), and with the exhaust gases exiting at 1,300 mph (2,100 km/h) it was realised that useful thrust could be gained simply by angling the gases backwards instead of venting sideways. During tests, 70 pounds-force (310 N ; 32  kgf ) thrust at 300 mph (480 km/h), or roughly 70 hp (52 kW) was obtained, which increased

13625-625: The war effort, negotiations were started to establish an alternative production line outside the UK. Rolls-Royce staff visited North American automobile manufacturers to select one to build the Merlin in the U.S. or Canada. Henry Ford rescinded an initial offer to build the engine in the U.S. in July 1940, and the Packard Motor Car Company was selected to take on the $ 130,000,000 Merlin order (equivalent to $ 2.83 billion in 2023 dollars ). Agreement

13750-488: The whole operation, but timely intervention by the Air Ministry improved the situation. In 1940 a strike took place when women replaced men on capstan lathes , the workers' union insisting this was a skilled labour job; however, the men returned to work after 10 days. Total Merlin production at Crewe was 26,065. The factory was used postwar for the production of Rolls-Royce and Bentley motor cars and military fighting vehicle power plants. In 1998 Volkswagen AG bought

13875-528: The worth of further research into a two-stroke sleeve-valved design. Both these engines had initially been converted to diesel sleeve-valved operation with a lower power output than the original design being noted along with increased mechanical failures, although one converted Kestrel was subsequently used successfully by Captain George Eyston in a land-speed record car named Speed of the Wind . The second engine

14000-426: Was 1,175 hp (876 kW) at 18,000 ft (5,500 m). These figures were achieved at 2,850 rpm engine speed using +9 pounds per square inch (1.66  atm ) (48") boost. In 1940, after receiving a request in March of that year from the Ministry of Aircraft Production for a high-rated (40,000 ft (12,000 m)) Merlin for use as an alternative engine to the turbocharged Hercules VIII used in

14125-522: Was 32,377. The original factory closed in March 2008, but the company maintains a presence in Derby. To meet the increasing demand for Merlin engines, Rolls-Royce started building work on a new factory at Crewe in May 1938, with engines leaving the factory in 1939. The Crewe factory had convenient road and rail links to their existing facilities at Derby. Production at Crewe was originally planned to use unskilled labour and sub-contractors with which Hives felt there would be no particular difficulty, but

14250-617: Was concentrated on civil derivatives of the Merlin. Development of what became the "Transport Merlin" (TML) commenced with the Merlin 102 (the first Merlin to complete the new civil type-test requirements) and was aimed at improving reliability and service overhaul periods for airline operators using airliner and transport aircraft such as the Avro Lancastrian , Avro York (Merlin 500-series), Avro Tudor II and IV (Merlin 621), Tudor IVB and V (Merlin 623), TCA Canadair North Star (Merlin 724) and BOAC Argonaut (Merlin 724-IC). By 1951

14375-525: Was confirmed during testing, but failures due to severe overheating and drive shaft fractures were experienced. The following table summarises the test running programme, hours run, and highlights some of the failures experienced. Data from: The progress of jet engine development overtook that of the Crecy and replaced the need for this engine. As a result, work on the project ceased in December 1945 at which point only six complete examples had been built, however an additional eight V-twins were built during

14500-404: Was delivered to Hucknall and fitted with a Crecy mock-up to enable cowling drawings and system details to be designed. It was planned for the first production Spitfire Mk III to be delivered to Hucknall in early 1942 for fitting of an airworthy Crecy, but this never took place. A Royal Aircraft Establishment report (No. E.3932) of March 1942 estimated the performance of the Spitfire fitted with

14625-984: Was designated the "TMO" and the modified exhaust system was supplied as kit that could be installed on existing engines either by the operator or by Rolls-Royce. Power ratings for the civil Merlin 600, 620, and 621-series was 1,160 hp (870 kW) continuous cruising at 23,500 feet (7,200 m), and 1,725 hp (1,286 kW) for take-off. Merlins 622–626 were rated at 1,420 hp (1,060 kW) continuous cruising at 18,700 feet (5,700 m), and 1,760 hp (1,310 kW) for take-off. Engines were available with single-stage, two-speed supercharging (500-series), two-stage, two-speed supercharging (600-series), and with full intercooling, or with half intercooling/charge heating, charge heating being employed for cold area use such as in Canada. Civil Merlin engines in airline service flew 7,818,000 air miles in 1946, 17,455,000 in 1947, and 24,850,000 miles in 1948. From Jane's : Most of

14750-409: Was fitted to the 100-series Merlins, was an S.U. injection carburettor that injected fuel into the supercharger using a fuel pump driven as a function of crankshaft speed and engine pressures. At the start of the war, the Merlin I, II and III ran on the then standard 87-octane aviation spirit and could generate just over 1,000 hp (750 kW) from its 27-litre (1,650-cu in) displacement:

14875-462: Was found that if Spitfires or Hurricanes were to pitch nose down into a steep dive, negative g -force ( g ) produced temporary fuel starvation causing the engine to cut-out momentarily. By comparison, the contemporary Bf 109E , which had direct fuel injection , could "bunt" straight into a high-power dive to escape attack. RAF fighter pilots soon learned to avoid this with a "half-roll" of their aircraft before diving in pursuit. A restrictor in

15000-414: Was further converted to petrol injection which then gave a marked power increase over the standard Kestrel. Single-cylinder development began in 1937 under project engineer Harry Wood using a test unit designed by Ricardo. The Crecy was originally conceived as a compression ignition engine and Rolls-Royce had previously converted a Kestrel engine to run on Diesel. By the time they started development of

15125-430: Was no mechanical time limit mechanism, but pilots were advised not to use increased boost for more than a maximum of five minutes, and it was considered a "definite overload condition on the engine"; if the pilot resorted to emergency boost he had to report this on landing, when it was noted in the engine log book, while the engineering officer was required to examine the engine and reset the throttle gate. Later versions of

15250-580: Was refining the Merlin. As a result, the Peregrine saw use in only two aircraft: the Westland Whirlwind fighter and one of the Gloster F.9/37 prototypes. The Vulture was fitted to the Avro Manchester bomber, but proved unreliable in service and the planned fighter using it – the Hawker Tornado – was cancelled as a result. With the Merlin itself soon pushing into the 1,500 hp (1,100 kW) range,

15375-575: Was the desire of the Air Ministry to develop a type of sprint engine for home defence....there was the question as to how far fuel consumption could be disregarded. Mr Ricardo had raised this point in a recent conversation by enquiring whether a high fuel consumption might not be permissible under certain circumstances, for if so, an investigation of the possibilities of the two-stroke petrol engine appeared to be attractive." Previous experience gained between 1927 and 1930 using two converted Rolls-Royce Kestrel engines through an Air Ministry contract had proven

15500-473: Was to have even numbers for engines rotating clockwise when viewed from the front. The reciprocating sleeve valves were open-ended, rather than sealing in a junk head . The open end uncovered the exhaust ports high in the cylinder wall at the bottom of the sleeves' stroke, leaving the ports cut into the sleeve to handle the incoming charge only. The sleeves had a stroke of 30% of the piston travel at 1.950 in (49.5 mm) and operated 15 degrees in advance of

15625-530: Was used in conjunction with the expansion chamber exhaust developed by German motorcycle manufacturer, MZ, and Walter Kaaden. Loop scavenging, disc valves, and expansion chambers worked in a highly coordinated way to significantly increase the power output of two-stroke engines, particularly from the Japanese manufacturers Suzuki, Yamaha, and Kawasaki. Suzuki and Yamaha enjoyed success in Grand Prix motorcycle racing in

#610389