Advantages- No carburettor icing
- No magnetos
- No spark to cause radio interference
- No mixture control
- Can be run on Jet A (if injection pump can cope with lower lubricity compared to automotive diesel fuel)
- Fuel system less susceptable to vapour lock
- Max torque occurs at lower rpms
- Does not require stoichiometric fuel/air ratio
- Usually offers significant reduction in fuel consumption
- Fuel does not boil off at altitude
Disadvantages- High compression ratio requires stronger and heavier components
- Torque reversal at low rpms is damaging to reduction drives and alternators (torsional damper required on reduction drive and sprag clutch on alternator)
- Technology for aircraft use is still maturing
- The USA, the largest potential market, does not offer big cost savings on the fuel, only on efficiency of operation
- Fuel is heavier
- Leaks on high pressure fuel pipes a fire risk if near hot surfaces
Four stroke diesels allow engines to be based on automotive units, such as Thielert, Austro Diesel, Peugeot etc.
The French SMA engine is four stroke but does not appear to be based on a car engine.
Two strokes such as the Wilksch WAM125 and Weslake W100, offer more firing cycles per revolution.
The most proven diesel engines in aircraft were the Junkers Jumo 205 and 207 engines used in the Junkers Ju86 Bomber and the Blohm & Voss BV138 flying boat. These were built under licence as the Napier Culverin, which was developed into the Napier Deltic Engine used in minesweepers and locomotives. Napier also made the Nomad compound diesel engine which was intended for the Avro Shackleton but never used in it. The Nomad was for a long time (may still be?) the most fuel efficient aero engine ever built.