Centurion Engines

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The Centurion is a series of diesel cycle aircraft engines for general aviation built by Thielert. They are based on Mercedes-Benz automotive engines, albeit heavily modified.

Each Centurion engine is water cooled and turbocharged. It has a one-control digital engine management system (FADEC) which simplifies engine management for the pilot as well as improving reliability as it prevents the engine being operated improperly. The engine runs on either jet fuel or diesel fuel. The high compression ratio of the engine combined with the digitally controlled fuel injection system dramatically reduces emissions as well, putting it on par with modern automobile engines.[citation needed]

A Centurion engine is always fitted with a (variable pitch) constant speed propeller which allows the engine to be operated at it optimum speed at all times. However, the engine rotates far too quickly for any suitable propeller and so the propeller is driven through a reduction gear which is also fitted as standard. The CSU and reduction gear result in a propeller tip speed 10-15% lower than comparable conventional avgas engines, considerably reducing propeller noise.

The high compression of a diesel engine results in much better fuel efficiency. Also, the higher RPM of the Centurion (in comparison to conventional aircraft piston engines) allows higher power to be developed from smaller cylinder displacement.

Several of the standard features of a Centurion engine are available also as options for the conventional aviation engines against which the Centurion is marketed. The CSU, turbocharger, FADEC, and reduction gearbox are necessary (and not optional) on a Centurion engined aircraft.

An aircraft engine fitted with turbocharger and constant speed unit can often replace one of higher maximum power output which does not have these two features. During take off a CSU allows full power to be developed by allowing the engine to run at a quicker, optimum speed. During the cruise a CSU allows the engine to be operated at full power without overspeeding the engine. A turbocharged engine allows greater power to be developed at altitude in comparison to a naturally aspirated engine.

A Centurion engine complete with CSU, reduction gearbox, turbocharger and FADEC engine management system is considerably heavier that the ubiquitous conventional Continental and Lycoming engines against which it is marketed. This weight disadvantage is compensated by the Centurion's considerably lower fuel consumption, which, for certain journeys, may allow for the same useful load to be carried.

The Centurion engine, although it lacks the magnetos and spark plugs of the conventional Lycoming and Continental engines against which it competes, is considerably more complex than those engines.

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[edit] Centurion 1.7

The Centurion 1.7 was the first product introduced by Thielert, a 1689 cm³ (103 in³) engine producing 135 DIN-hp (99 kW) is based on OM 668 engine from Mercedes-Benz A-Class A 170 CDI (W168) with 80 mm bore and 84 mm stroke.

Aircraft manufactured with Centurion 1.7 engines include:

The engine is also available as a retrofit for the Cessna 172 and Piper PA28 aircraft.

The Diamond DA40 is available as the Centurion powered DA40-TDI and also as the DA40-XL powered by a conventional avgas engine, a 180hp Lycoming. Comparing these otherwise nearly identical aircraft with each other and with a 1985 Cessna 172P (which can be retrofitted with the Centurion 1.7) is interesting:

Aircraft & engine DA40-TDI
Centurion 1.7		 DA40-XL
Lycoming IO-360-M1A		 Cessna 172P (1985)
Lycoming O-320-D
Fuel Jet A, Jet A1, Diesel Avgas Avgas
Fuel delivery Injectors, turbocharged Injectors Carburettor
Drive chain & propeller type Reduction gear. Constant speed (variable pitch) Direct. Constant speed (variable pitch) Direct. Fixed pitch
Engine controls FADEC (one lever) Propeller speed, manifold pressure, fuel mixture Throttle, fuel mixture, carburettor heat
Max RPM: prop & engine 2300 & 3900 2700 2700
Power (sea level) 135 hp 180 hp 160 hp
Engine system weight 134 kg  ? 104 kg (180 hp C172R)
Payload 370 kg 400 kg 429 kg
Max cruise speed 142 kt TAS @ 6000 ft 158 kt TAS 123 kt TAS
Cruise speed
power @ altitude
fuel consumption		 125 kt TAS
70% @ 10000 ft
4.9 US gal/hr		 150 kt TAS
75% @ 6000 ft
10 US gal/hr
Takeoff roll & to clear 50 ft obstacle 1099 ft & 2083 ft 1027 ft & 1140 ft 890 ft & 1625 ft

Some indication of the improvement in engine design can be seen by comparing the 1.7 to the engines it is aimed to replace, notably the Lycoming O-320, and to a lesser degree the Lycoming IO-360 and Continental O-300. The O-320 delivers 150 hp (112 kW) from 320 in³ (5.2 L), while the 1.7 delivers 135 hp (101 kW) from 103 in³ (1.7 L). This represents a dramatic increase in specific power, from the O-320's 0.47 hp/in³ (21 kW/L) to the 1.7's 1.31 hp/in³ (60 kW/L). The 1.7 is slightly heavier however, 295 lb (134 kg) vs the O-320 at 278 lb (126 kg). As a result of the greatly increased compression ratio of the diesel cycle, fuel economy is likewise improved, the 1.7 has a specific fuel consumption of 0.36 lb/(hp·h) (0.22 kg/(kW·h)), while the O-320 gets only 0.42 lb/(hp·h) (0.26 kg/(kW·h)).

Combining the better fuel economy, higher performance at altitude, and the somewhat greater energy density of diesel fuel, aircraft range is dramatically increased. For instance, replacing the O-320 with the 1.7 in a Cessna 172 drops the fuel consumption by half, increasing range from 575 to 900 nautical miles (1100 to 1700 km). Fuel costs fall dramatically as a result, notably in Europe where avgas is much more expensive than in North America.

Until the end of 2006, when production ceased in favor of the Centurion 2.0, more than 1,500 Centurion 1.7 had been built. The in service record of the 1.7 has been poor, with a combination of design, service and support issues causing widespread customer disatisfaction and resulting in Diamond designing its own engines to compete with Thielert.

[edit] Centurion 2.0

Since late 2006 production has switched from the Centurion 1.7 to its successor, the Centurion 2.0. The main difference is a new cylinder block from OM 640 engine from Mercedes-Benz A 200 CDI (W169) with a displacement of 1991 cm3 (Ø83 x 92 mm). Other improvements include a more compact FADEC, a lighter cast gearbox housing, interfaces for glass cockpits and a new service tool that allows the FADEC to be programmed in the field. Dimensions of the Centurion 2.0 and 1.7 are nearly identical and the install kits are compatible, so a 1.7 at the end of its life can be easily replaced with a 2.0.

Currently the Centurion 2.0 is rated for a power output of 135 hp (99 kW), the same as the 1.7. The engine itself, however, is already EASA and FAA certified for 155 hp (114 kW) and it seems reasonable to expect that after acquiring STC's for the different aircraft types in which the engine is used, it will be officially uprated to this power level.

Albeit the engine's more complex design, it has accumulated more than 1,000,000 flight hours without mechanical failures as of April 2008.

[edit] Centurion 4.0

The 1.7 generated intense interest in the aviation market, and many pilots were soon asking for a larger engine to replace the 300 hp (224 kW) class engines of several 6 seat aircraft making up much of the rest of the GA market. The result was a new V8 design, the 350 hp (261 kW) Centurion 4.0, developed from OM 629engine. This engine had at first two turbochargers, later this was changed to a larger single turbocharger. The 4.0 is currently certified only for Jet A/A1.

The Centurion 4.0 is certified for use in the Cirrus SR-22 and the Cessna 206. For the latter a retrofit kit is available. Further STC's are sought by Thielert for the Cessna 340, 414 and 421. There is also a project by Martin Hagensieker in collaboration with Gomolzig Flugzeug- und Maschinenbau GmbH for a Centurion 4.0 conversion of the Beechcraft Duke. A Duke with an early 310 hp (228 kW) version of the Centurion 4.0 already flew in late 2005, however work has been stopped for the time being. According to Hagensieker this is due to capacity problems at Thielert, who are right now too busy with other projects and therefore not able to provide adequate support. He hopes that work can restart in 2008.

[edit] Centurion 3.2

A third model, the Centurion 3.2, is supposed to fill the gap between the Centurion 2.0 and the 4.0. It will produce 230hp, making it suitable for larger 4 seat aircraft including, e.g., the Cessna 182. In a Thielert press release the engine was announced to be available by 2009, later this was changed to 2008. However, according to a Thielert employee at the Aero 2007 exhibition, whereas engine development is largely complete, other priorities mean that the project has been put on hold. Furthermore the engine is considered as too heavy and it is assumed that it would probably be better to start over with a more modern base engine. This would mean that the engine would be available only as late as 2011 or 2012.

[edit] See also