The Engineer

6 August 1999

 

"Diesel in demand"

"Over 50 years since they helped power German bombers in the Blitz, a new generation of diesel aeroengines is set to take to the air. Brian Davis looks at the UK and overseas players competing in this new market"

"Spurred by a move towards cheaper, more environmentally-friendly fuels, two UK firms are leading a revival in diesel engine technology.

The small-but-innovative engineering teams at Wilksch Airmotive and Diesel Air are targeting diesel engines at the home-built kit and light aircraft market. And the international competition is hotting up, with French, German and US firms also researching diesel technology.

Large diesel aero-engines were first developed in Germany in the 1930s, but were superseded by jet engines after the war.

In the light aircraft market, petrol engines have dominated because the Avgas they run on has been relatively cheap. And four-stroke petrol engines have remained popular, despite having a poorer power-to-weight ratio than diesel engines.

However, the diesel/Avtur fuel used by new diesel engines is a third of the price of conventional aviation fuel, and the engines are claimed to be cleaner, as diesel avoids lead emissions while cutting carbon monoxide and hydrocarbons output.

Diesel engines also run lean, with high compression ratios, making them more efficient than petrol engines. Avtur engines do not need priming to start, have no carburettor icing problems, no mixtures to fiddle with, and need less maintenance.

Australian engineer Mark Wilksch, founder of Wilksch Airmotive, learnt to fly at 16. Following spells as an engineer for the Royal Australian Air Force and the Flying Doctor service, he moved to the UK to work with the Arrow Formula One team, later joining Ford's European technical centre to develop petrol injection Systems.

With the help of a private backer and two DTI Smart awards worth £105,000, Wilksch left Ford to start his own company, and set about developing a two-cylinder, 80hp prototype diesel engine. Earlier this month his latest version, a three-cylinder WAM-120 engine, was fitted in Europa kit-built aircraft. It is due to start test flights later this year.

'At the start of the 1990s, many people thought my idea was crazy. Now everybody seems to believe this is the way to go,' says Wilksch. By 2001, 'with the help of a third, £300,000, Smart award, he hopes to secure orders for a family of diesel-powered engines.

Wilksch's two-stroke engine fires twice as often as a four-stroke and is claimed to run smoothly. The close coupling of the turbocharger also offers more efficient energy recovery at all running speeds.

The piston/con rod connection has a spherical joint instead of gudgeon pins, so the piston and rings are free to rotate, reducing wear on the piston.

The engine is inverted in line with integrated oil and cooling systems, and will be equipped with a mechanical blower to sustain idling and low-power settings.

The production version will about 100kg - lighter than rival Lycoming or Continental engines, but with the same power.

Once the engine is proven, Wilksch will apply for Joint Airworthiness Authority certification and a Federal Aviation Administration production licence for the US. He estimates the demand for diesel engines to be 1,000-2,000 a year.

But there are plenty of competitors on the horizon - including Diesel Air, formed in 1997 by David Soul, a Wilksch shareholder who left due to differences in opinion...

...Diesel Air plans to have a prototype DAIR 100 running on a Luscombe Silvaire light aircraft later this year. The engines will be available for aircraft builders next summer.

In Germany, Zoche has been developing a radical diesel engine for about 15 years. In France, Renault Moraine has a joint venture with Socata to develop a four-stroke horizontally-opposed, air-cooled 180-350hp diesel engine to run on Avtur. Flight trials have begun, aiming at certification by 2001.

In the US, Lyoming has bought a diesel engine 'project from Italian company VM, while continental is carrying out a research project with Perkins Technology on a uni-flow, scavenged two-stroke aviation engine. Both companies aim to develop larger engines for two to four-seater aircraft, rather than the 100-200bhp versions Wilksch is concentrating on.

'These are not direct competitors: they are far bigger, and are helping to legitimise the marketplace for diesel engines,' says Wilksch."