Britain’s Ministry of Defence (MoD) has confirmed that it is continuing funding for a new diesel outboard engine for the Royal Navy’s rigid inflatable craft. Currently under development by Cox Powertrain, the prototype marine engine concept uses opposed pistons. It is part of a policy adopted by NATO countries for converting to heavy oil wherever possible, to simplify logistics and reduce the use of petrol at sea.

Naval forces need a wide variety of fuels to operate. There’s heavy diesel for the ship’s engines, aviation fuels for planes and helicopters, and petrol for small boats. The problem is that these different fuels mean different supply lines and a logistical nightmare during a large deployment, that might see a warship on station without any petrol for the boats.

Worse, petrol is notoriously dangerous to use at sea, with an ever-present hazard of fire or explosion below decks. For this reason, the Royal Navy is joining other NATO countries in converting as much as possible to a single heavy fuel for all vessels.

The Cox Powertrain concept is being developed in collaboration with the engineering R&D firm Ricardo. The project has already attracted £6.7 million (US$10.1 million) in private investment, in addition to previous MoD funding. The concept is based on an invention of Cox Powertain’s founder, former F1 designer David Cox, and is specifically designed for outboard use.

CAD model of the Cox Powertrain concept

The concept uses opposed pistons, which means that the super-charged. two-stroke 3.6-liter motor has eight pistons housed in four cylinders. There’s no cylinder head, but rather each cylinder uses a centrally-placed injector, and the piston pair compresses the fuel/air mixture in the middle. Meanwhile, a Scotch Yoke crankshaft converts the reciprocating movement of the pistons into rotary motion.

With this layout, the Cox Powertrain concept achieves 350 bhp (261 kW) per engine module, yet is half the size of an equivalent conventional diesel engine. It can also be configured in multiple modules up to 700 bhp (522 kW).

The Cox Powertrain concept has completed its detailed design phase and the first firing is expected this month at Ricardo. The companies also foresee the development of variations for civilian applications and UAVs.

Source: Ricardo