Powertrain & Energy - September 26, 2012 - 16

tech Report
Are diesel aircraft coming soon to an airport near?
The application of the two-stroke diesel concept to aircraft engines is anything but a novelty. For example, Junkers built a very successful series of these engines in the late 1930s named JUMO. The main advantage offered by such an engine is fuel efficiency; even in 1938, the JUMO engine was capable of a brake SFC of 213 g/kW·h—impressive even by modern standards. Fuel consumption is very important for aircraft performance, since a relevant portion of the aircraft total weight (sometimes up to 50%) is due to fuel storage. The main reason for the outstanding fuel economy of two-stroke diesel engines is the high mechanical efficiency ensuing from the two-stroke cycle. Besides the possibility of having no poppet valves and the associated driving system, mechanical friction losses over the cycle are about halved in comparison to a four-stroke engine having the same crank and piston and crankcase design, due to the double cycle frequency. The two-stroke cycle is a good match for aircraft engines, since it is possible to achieve high power density at low crankshaft speed, allowing direct coupling to a propeller without the need for a reduction drive (which is heavy and expensive, besides adsorbing energy). Supercharging further improves power density and fuel efficiency, as well as enhancing altitude performance. Diesel combustion allows a higher boosting level, in comparison to spark-ignited (SI) engines, limited by knocking. In addition,

For modeling uniflow scavenged engines, researchers referenced a modern aircraft two-stroke turbocharged diesel powerplant, named WAM 100/120, produced by Wilksch Airmotive, with a top brake power of 100-120 hp.

September 26, 2012

SAE Powertrain & Energy

Powertrain & Energy - September 26, 2012

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