100 hp diesel engine designed to be direct 0-200 replacement
A new diesel aero engine, albeit one its maker freely acknowledges is based on the most successful design of the past, was shown at the PFA Rally this July. The Diesel Air is a 1.8 litre opposed-piston flat twin two-stroke with a dry weight of 90 kilos (excluding radiators and intercooler). It is rated at 100 hp, at a propeller speed of 2,500 rpm.In layout, the Diesel Air resembles one end of the highly-developed Jumo 207 diesel of the mid 1940s (see pg 31); pairs of pistons share bores in the centre of the engine and they drive geared-together crankshafts mounted-in this case, either side of the engine. The blower is a modified production turbocharger compressor and is driven from a step-up gear train via a quill shaft and epicyclical gear set. The 600 bar rotary injection pump is also a modified version of a standard automotive item. Although a turbocharger can be added for extra power, a mechanically-driven blower was chosen for the base engine because a turbocharger alone would not provide sufficient off-load boost to keep the engine running during low-power phases like the final approach. One novelty, the detail design of which Diesel Air is keeping very close to its chest, is a 'torque limiter' which protects the propeller from the diesel engine's characteristically harsh firing impulses, especially at low speed.
  Above: The Diesel Air opposed-piston flat twin 2- stroke on display at Cranfield. & the Diesel Air installed in a Luscombe Silvaire.
Below: The drawing shows the two pistons per bore and the crankshafts eith side of the engine.
Intended as an 0-200 replacement, the new diesel has been carefully dimensioned to fit within the conventional engine's cowlings and its cast-in crankcase mounting lugs are designed to mate up with existing engine mounts. Unlike the old Continental, the Diesel Air is water-cooled. The intention is to use a pair of small radiators, sited behind the normal cowl intakes. Together with the necessary intercooler, they will take the installed weight very close to the air-cooled 0-200's typical figure, eliminating the need for any weight adjustment of ballasting to preserve the C of G. Either Avtur or diesel fuel can be used. Substantial fuel cost savings are projected for the engine, on the basis that it will consume 4.2 gph, compared with 5 gph for the equivalent gasoline engine. If duty-free 'red' diesel can be used, aircraft are, of course off-road' machines, the potential saying is vast. Diesel Air has already made a trial installation in a Luscombe 8A Silvaire. Once the current programme of bed testing has been completed (the engine has already run for over 1,000 hours under development), the engine will be mounted in the Luscombe for flight trials "in a couple of months time", according to company MD David Soul. Diesel Air is not keen on making public predictions of production targets or certification dates. The potential for such a direct replacement for 0-200s and the like is obvious, but its chosen approach is to supply engines, in the first instance, to PFA types. It is anticipated that this will allow production to be built up in stages as experience is gathered from operators. A larger version of the engine is under development for airship use.