New diesel engine concept powers up

The Cox Powertrain engine concept is based on a supercharged, two-stroke opposed piston diesel engine that features a Scotch Yoke crankshaft and a central injector position. This engine concept promises a power to weight ratio comparable with high performance petrol engines and it is also claimed that it will deliver diesel fuel consumption in a lightweight package that will be around half the weight of current performance diesel engines.

This engine concept has been developed by designer David Cox, who has worked with Formula 1 car teams. The Scotch Yoke concept replaces the crankshaft that is used in current engines and features a slot that is rigidly connected to the piston in which a pin attached to the crankshaft slides up and down to convert the motion of the piston into a rotary motion. The benefits of the concept are that the engine can be much more compact because pistons can be shorter and there are no big or small end bearings whilst the disadvantages are reported to be a higher wear factor in the pin and its slot. Cox has taken out several patents on the engine design so it can be assumed that they have overcome the wear problem.

The Cox engine is an opposed piston unit so that in effect opposing pistons will be fixed solidly together and linked by short piston rods and the Scotch Yoke. This will make the engine very compact and reduce its weight and these are two of the main advantages of the new engine. This compactness and lightweight will make the engine very suitable for outboard motor use and this is primarily why the MOD is backing this venture because it is a major user of powerful outboards on its assault and utility craft and would prefer to use diesel fuel as a fuel compatible with the mother ship and much less flammable. The basic engine module has been designed so that it can be stacked, combining two or more modules to increase the power output. The first units are likely to produce 200 and 300 hp but this can increase to 700 hp or more.

Cox Powertrain has worked with engineering consultancy company Ricardo to verify the engine concept and the first firing of the prototype engine has taken place at its Shoreham headquarters. In addition to military applications this diesel outboard is likely to find application as a power unit in super yacht tenders and many commercial applications where fuel compatibility with the mother ship is desirable.

This diesel outboard project is one of several taking place around the world to develop powerful diesel outboards.

By Dag Pike