The aircraft diesel engine or aero diesel is a diesel-powered aircraft engine. They were used in airships and tried in aircraft in the late 1920s and 1930s, but were never widely adopted until recently. Their main advantages are their excellent specific fuel consumption, the reduced flammability and somewhat higher density of their fuel, but these have been outweighed by a combination of inherent disadvantages compared to gasoline-fueled or turboprop engines. The ever-rising cost of avgas and doubts about its future availability have spurred a resurgence in aircraft diesel engine production in the early 2010s.
Using diesel engines in aircraft is additionally advantageous from the standpoint of environmental protection as well as the protection of human health, since the tetraethyllead antiknock ingredient of avgas has long been known to be highly toxic as well as polluting.
Development
Early diesel aircraft A number of manufacturers built diesel aero engines in the 1920s and 1930s; the best known were the Packard air-cooled radial, and the Junkers Jumo 205, which was moderately successful, but proved unsuitable for combat use in World War II. The Blohm & Voss BV 138 trimotor maritime patrol flying boat, however, was powered with the more developed Junkers Jumo 207 powerplant, and was more successful with its trio of diesel Jumo 207s conferring upwards of a maximum 2,100 km (1,300 mile) combat radius upon the nearly 300 examples of the BV 138 built during World War II.
The first successful diesel engine developed specifically for aircraft was the Packard DR-980 radial diesel of 1928–1929, which was laid out in the familiar air-cooled radial format similar to Wright and Pratt & Whitney designs, and was contemporary with the Beardmore Tornado used in the R101 airship. The use of a diesel had been specified for its low fire risk fuel. The first successful flight of a diesel powered aircraft was made on September 18, 1928, in a Stinson model SM-1DX Detroiter registration number X7654. Around 1936 the heavier but less thirsty diesel engines were preferred over gasoline engines when flight time was over only 6–7 hours.Odel, Axel. "Teknikken i luftfartens tjeneste" page 18-20 Ingeniøren, 2 May 1936. Accessed: 28 December 2014.
Entering service in the early 1930s, the two-stroke Junkers Jumo 205 opposed-piston engine was much more widely used than previous aero diesels. It was moderately successful in its use in the Blohm & Voss Ha 139 and even more so in airship use. In Britain Napier & Son license-built the larger Junkers Jumo 204 as the Napier Culverin, but it did not see production use in this form. A Daimler-Benz diesel engine was also used in Zeppelins, including the ill-fated LZ 129 Hindenburg. This engine proved unsuitable in military applications and subsequent German aircraft engine development concentrated on gasoline and jet engines.
The Soviet World War II-era four-engine strategic bomber Petlyakov Pe-8 was built with Charomskiy ACh-30 diesel engines; but just after the war's end, both its diesels, and gasoline-fueled Mikulin inline V12 engines for surviving Pe-8 airframes were replaced with Shvetsov-designed radial gasoline engines because of efficiency concerns. The Yermolaev Yer-2 long-range medium bomber was also built with Charomskiy diesel engines.
Other manufacturers also experimented with diesel engines in this period, such as the French Bloch (later Dassault Aviation), whose MB203 bomber prototype used Clerget diesels of radial design. The Royal Aircraft Establishment developed an experimental compression ignition (diesel) version of the Rolls-Royce Condor in 1932, flying it in a Hawker Horsley for test purposes.
Postwar development Interest in diesel engines in the postwar period was sporadic. The lower power-to-weight ratio of diesels, particularly compared to turboprop engines, weighed against the diesel engine. With fuel available cheaply and most research interest in turboprops and jets for high-speed airliners, diesel-powered aircraft virtually disappeared. The stagnation of the general aviation market in the 1990s saw a massive decline in the development of any new aircraft engine types.
Napier & Son in Britain had developed the Napier Culverin, a derivative of the Junkers Jumo 205, before World War II, and took up aero diesel engines again in the 1950s. The British Air Ministry supported the development of the Napier Nomad, a combination of piston and turboprop engines, which was exceptionally efficient in terms of brake specific fuel consumption, but judged too bulky and complex and canceled in 1955.
Modern developments Several factors have emerged to change this equation.McLanahan, J. Craig. "Diesel Aircraft Engines: A Delayed Promise from the 1930's". SAE Transactions, vol. 108, 1999, pp. 1103–1112. First, a number of new manufacturers of general aviation aircraft developing new designs have emerged. Second, in Europe in particular, avgas has become very expensive. Third, in several (particularly remote) locations, avgas is harder to obtain than diesel fuel. Finally, automotive diesel technologies have improved greatly in recent years, offering higher power-to-weight ratios more suitable for aircraft application.
Certified diesel-powered light planes are currently available, and a number of companies are developing new engine and aircraft designs for the purpose. Many of these run on readily available jet fuel (kerosene), or on conventional automotive diesel.
Simulations indicate lower maximum payload due to the heavier engine, but also longer range at medium payload.Vassilios Pachidis. Clean Sky Technology Evaluator Environmental Performance Assessment of Rotorcraft , page 36. Cranfield University, 20 October 2015.
Applications
Airships
The zeppelins LZ 129 Hindenburg and LZ 130 Graf Zeppelin II were propelled by reversible diesel engines. The direction of operation was changed by shifting gears on the camshaft. From full power forward, the engines could be brought to a stop, changed over, and brought to full power in reverse in less than 60 seconds.
Nevil Shute Norway wrote that the demonstration flight of the airship R100 was changed from India to Canada, "when she got petrol engines, because it was thought that a flight to the tropics with petrol on board would be too hazardous. It is curious after over twenty years to recall how afraid everyone was of petrol in those days (c. 1929), because since then aeroplanes with petrol engines have done innumerable hours of flying in the tropics, and they don't burst into flames on every flight. I think the truth is that everyone was diesel-minded in those days; it seemed as if the diesel engine for aeroplanes was only just around the corner, with the promise of great fuel economy".
Hence, the ill-fated diesel-engined R101 — which crashed in 1930 — was to fly to India, though her diesel engines had petrol starter engines, and there had only been time to replace one with a diesel starter engine. The R101 used the Beardmore Tornado aero diesel engine, with two of the five engines reversible by an adjustment to the camshaft. This engine was developed from an engine used in railcars.
Certified engines Manufacturer Model Certification Power Prop. RPM Weight Specific power Technify Motors TAE 125 2007-03-06 Technify Motors TAE 125-02-125 2020-07-22 DieselJet TDA CR 1.9 8V 2010-06-11 118 kW (160 hp) 2450 Austro Engine E4P 2015-03-26 2300 DeltaHawk DH180 2023-05 134.2 kW (180 HP) 2700 162 kg (357 lb) DieselJet TDA CR 2.0 16V 2016-03-08 142 kW (193 hp) 2306 SMA SR305-230 2001-04-20 2200 SMA SR305-260 2019-02-15 2200 Technify Motors Centurion 3.0 2017-06-20 2340 Technify Motors Centurion 4.0 2007-09-26 RED Aircraft RED A03 2014-12-19 368 kW (500 hp) 2127
Technify Motors Continental Motors, Inc. subsidiary Technify Motors GmbH of Sankt Egidien, Germany, is the new TC holder of the Thielert TAE 110 certified by the EASA on 8 March 2001, a 4-cylinder, four stroke engine with common rail direct injection, turbocharger, 1:1.4138 reduction gearbox and FADEC producing at takeoff at 3675 rpm and continuously at 3400 rpm for . The TAE 125-01, certified 3 May 2002, is the same with a 1:1.689 gearbox, weighs and outputs maximum at 3900 rpm, like the later TAE 125-02-99 certified on 14 August 2006, then the TAE 125-02-114 on 6 March 2007 for at 3900 rpm, and the TAE 125-02-125 outputting at 3400 rpm for .
The Centurion 4.0 is a four stroke 8-cylinder, with common rail, 2 turbochargers, 1:1.689 reduction gearbox, propeller governor and FADEC weighting and certified on 26 September 2007 for up to maximum, continuous at 3900 rpm. The centurion 4.0 V8 has not been certified for installation in any airframes.
EASA certified on 20 June 2017, the Centurion 3.0 is a four stroke V6, also with common rail, turbocharger, Electronic Engine Control Unit (EECU) and 1 : 1.66 reduction gearbox, weighting and outputting 221 kW (300 HP) at take-off, 202 kW (272 HP) continuously, both at 2340 propeller RPM.
Thielert Thielert, based in German Lichtenstein, Saxony was the original TC holder of the 1.7 based on the Mercedes A-class turbo diesel, running on diesel and jet A-1 fuel. It was certified for retrofitting to Cessna 172s and Piper Cherokees, replacing the Lycoming O-320 Avgas engine. The of the 1.7 engine is similar to the O-320 but its displacement is less than a third and it achieves maximum power at 2300 prop RPM instead of 2700.
Austrian aircraft manufacturer Diamond Aircraft Industries offered its single-engine Diamond DA40-TDI Star with the 1.7 engine, and the Diamond DA42 Twin Star with two, offering a low fuel consumption of . Robin Aircraft also offered a DR400 Ecoflyer with the Thielert engine.
In May 2008, Thielert went bankrupt and although Thielert's insolvency administrator, Bruno M. Kubler, was able to announce in January 2009 that the company was "in the black and working to capacity," by then Cessna had dropped plans to install Thielert engines in some models, and Diamond Aircraft has now developed its own in-house diesel engine: the Austro Engine E4. Several hundred Thielert-powered airplanes are flying.
SMA Engines SMA Engines, located in Bourges, France, have designed the SMA SR305-230: a direct drive four-stroke, air and oil-cooled, turbo-diesel of four horizontally opposed cylinders displacing with an electronically controlled mechanical pump fuel injection, it obtained EASA certification on 20 April 2001 for at 2200 rpm, weighting . A SR305-260 was certified in February 2019. The SR305-230 obtained US FAA certification in July 2002. It is now certified as retrofit on several Cessna 182 models in Europe and the US, and Maule is working toward certification of the M-9-230. SMA's engineering team came from Renault Sport (Formula 1) and designed it from the ground up.
SMA develops a six cylinder version, the SR460. At AERO Friedrichshafen 2016, SMA debuted a high power density engine demonstrator: a 135 hp (100 kW), 38-cubic-inch (0.62 liter) single cylinder four-stroke for 215 hp (160 kW) per liter, scalable from and up to 1.5 hp/lb. (2.5 kW/kg) power density with a specific fuel consumption of 0.35 lb/hp/hr (210 g/kwh).
Austro Engine Austro Engine GmbH, based in Wiener Neustadt, Austria had the E4 engine certified by EASA on 28 January 2009. It is a 4-cylinder, 1991 cm³ four stroke engine with common rail direct injection, turbocharger, 1:1.69 reduction gearbox and an Electronic Engine Control Unit. It produces at Take-off and continuously, at 2300 propeller RPM for . The same weight E4P was certified on 26 March 2015 for at Take-off at the same speed, and continuously at 2200 propeller RPM.
In 2011, Austro Engine was developing a 6-cylinder in cooperation with Steyr Motors, based on their block, to be used in the Diamond DA50.
DieselJet