Before World War II, diesel engines were utilized in aircraft, such as the rigid airship LZ 129 Hindenburg, powered by four Daimler-Benz DB 602 diesel engines, and in several Junkers aircraft with Jumo 205 engines.
In 1929, the Packard Motor Company in the United States developed the Packard DR-980, an air-cooled, 9-cylinder radial diesel engine. This engine received the first-ever Approved Type Certificate for an aircraft diesel engine from the U.S. Department of Commerce on March 6, 1930. It was used in various record-breaking distance or endurance flights, as well as the first successful ground-to-air radiophone communication demonstration.
Some advantages of diesel engines at the time included reduced risk of post-crash fires and better high-altitude performance.
Unfortunately, issues like noxious exhaust fumes, cold-start problems, vibration, engine structural failures, the death of the developer, and the economic challenges of the Great Depression led to the discontinuation of the program.
MODERN ERA OF DIESEL ENGINES IN AIRCRAFT
From the late 1970s, diesel engines were not widely used in aircraft. Karl H. Bergey, co-designer of the Piper Cherokee, even considered the likelihood of a general aviation diesel engine in the near future to be remote in 1978.
However, in the 1970s, the energy crisis and environmental concerns led to renewed interest in diesel engines for aircraft. Diesel engines do not require leaded fuel, which is necessary for high-compression piston aircraft engines running on aviation gasoline ("avgas"). The aviation community feared potential bans or discontinuation of leaded avgas due to environmental concerns.
Moreover, avgas is a specialty fuel in low demand compared to other fuels, making it less attractive to refiners. Outside the United States, avgas became harder to find at airports, while diesel-compatible fuels like Jet-A became more prevalent.
In the late 1990s and early 2000s, diesel engines began appearing in light aircraft. Frank Thielert and his Austrian engine enterprise played a pivotal role in developing diesel engines to replace gasoline/piston engines in common light aircraft. The Diamond DA42 Twin Star was one of the first aircraft to successfully use these engines, demonstrating exceptional fuel efficiency. Subsequently, other companies, including Continental Aerospace Technologies, joined the development of aircraft diesel engines.
By 2007, jet-fueled piston aircraft had accumulated over 600,000 hours of service. By early 2019, a diesel engine model for general aviation aircraft was nearing completion. As of late 2022, Continental reported the success of its "Jet-A" fueled engines, with over 2,000 engines in operation today and over 9 million flight hours, becoming a preferred choice for various aircraft models.
In recent years, diesel engines have also found application in unmanned aircraft (UAV) due to their reliability, durability, and low fuel consumption.