A Lightweight, V-4, Two-Stroke Diesel for Aviation
4 May 2006
|DeltaHawk diesel engine.|
DeltaHawk Engines, a small Wisconsin company, is developing a family of lightweight, V-4, two-stroke, turbo- and super-charged diesel engines for a variety of general aviation and non-aviation uses. The engines will run on Jet A (JP5) fuel, or #2 diesel where ambient temperatures are high enough to avoid gelling (above 20° F).
There are other diesel aviation engines—“aero-diesels”—available in the international market, but Deltahawk is poised to become the first US-based vendor.
Thielert Aircraft Engines GmbH (TAE) (Lichtenstein, Germany) builds the Centurion 1.7, for example, a 1.7-liter, 4-cylinder, 4-stroke, 4-valve, in-line diesel cycle engine with common rail direct injection. It can burn Jet A1 and Diesel (EN 590) in any mixture ratio.
(TAE has begun maintenance training in the US in anticipation of its bringing it to market.)
SMA (Bourges, France) offers an opposed-cylinder diesel cycle engine that burns Jet A fuel.
There are also several diesel aviation engines under development. US-based Teledyne Continental Motors began working on a two-stroke 4.7-liter, horizontally-opposed diesel cycle engine (TCM GAP) fueled by Jet A in 1997. Zoche in Munich, Germany is developing an air-cooled, radial two-stroke diesel with 4 cylinders per row. It features two stage charging (turbo- and super-charger), direct fuel injection and intercooling.
Interest in aero-diesels stretches back to the 1930s, with the introduction of several models of the Junker Jumo two-stroke, 6-cylinder, vertically-opposed engine. Given a variety of factors, general interest in the diesel cycle for aviation waned until recently.
With carbon dioxide issues and the cost and availability of fuel increasingly an issue for general and commercial aviation, the lower fuel consumption (and lower CO2 emissions of the diesel cycle is becoming increasingly attractive.
In 1998, the president of Lycoming, a leading manufacturer of general aviation engines, said that the time was right to develop and to market aero-diesels.
The wide availability of jet fuel makes diesel engines attractive as powerplants. Plus, the increased fuel efficiency fits well with aircraft engine design goals. With new lighter alloys, we can also see significant reductions in the dry weight of these engines, long known as efficient, but heavy—Jim Koerner, Lycoming
(Koerner made those remarks during the announcement of a partnership with Detroit Diesel to develop such an engine. The engine, according to Andre Teissier-duCros, the publisher of DieselAir Newsletter, was sold to DaimlerChrysler which then abandoned it. )
|A top view of the DeltaHawk, with a comparison to the footprint of the Lycoming IO-360. Click to enlarge.|
The DeltaHawk engine. The DeltaHawk engine is an upright 90ª V-4, super- and turbo-charged, direct drive, liquid-cooled (glycol/water) two-stroke diesel with oil pump and external air-oil separator/sump.
The compact two-stroke design—which offers a higher power density than a four-stroke engine—results in a lower part count and fewer potential leakage points than the current 4-cylinder gasoline-powered aircraft engines. There is no camshaft or valve train, nor head gasket or head bolts.
|Fuel consumption comparison. Click to enlarge.|
It comes in 160 hp (119 kW) and 200 hp (149 kW) models and weighs about 327 pounds. DeltaHawk says that its engine delivers 20–30% more range per gallon, and a BSFC (brake specific fuel consumption) of .37 lb/hp/hr versus current avgas-powered aviation engine book BSFC of .59 lb/hp/hr at 75% and above.
The fuel issue. Conventionally, aviation fuels are classified into two general groups: aviation gasolines for reciprocating piston engines, and kerosene-type aviation turbine fuels for use in turbo-propeller and turbo-jet engines. Those turbine fuels—of which Jet A is a member—can also be used in a compression ignition (diesel) reciprocating engine.
The rising cost of fuel is one of the most critical issues faced by both commercial and general aviation. (Emissions are another.)
Thus, one of the next major technology challenges for the entire airline industry is the development of alternative fuels that are cleaner-burning, and lower in cost than the petroleum-based fuels, according to Giovanni Bisignani, Director General & CEO of the International Air Transport Association (IATA).
While synthetic fuels (e.g., Fischer-Tropsch fuels) are of great interest for commercial and military aviation, blending biodiesel with the existing kerosene-based fuels is a route that many researchers are exploring.
One of the main issues with biodiesel in aviation is the gelling at low-temperature.
As one approach to resolving that issue, researchers at Purdue developed a 40% biodiesel, 60% Jet A blend that meets ASTM D-1655 (Jet A) fuel specifications for cold temperature behavior (freezing at a temperature not higher than -40° C).
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