We last covered the opposed piston engine concept back in 2011 (almost exactly 2 years ago). It was just a concept we covered then, but now? Now there’s a runner – and the British military is putting it through its paces as I type this.
The UK’s Ministry of Defense (MoD) has confirmed that it will continuing funding development of this new diesel outboard for the Royal Navy’s rigid inflatable boats. Currently under development by Cox Powertrain, the prototype marine engine concept uses opposed pistons to minimize thermal losses and help shift the Navy away from using gasoline on the water.
The opposed piston engine is part of a policy recently adopted by NATO countries for converting to heavy oil wherever possible, allowing member countries to simplify logistics and reduce the use of petroleum gasoline at sea. Naval forces currently need a wide variety of fuels to operate – from heavy diesel to avgas and gasoline – 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, gasoline is notoriously dangerous to use at sea, with an ever-present hazard of fire or explosion below decks much greater with gasoline than with diesel.
The concept uses opposed pistons, which means that the super-charged. two-stroke 3.6-liter motor has eight pistons housed in four cylinders but no cylinder “head”. Instead, each cylinder uses a centrally-placed injector and a set of paired pistons compresses the air/fuel mix in between them. A “Scotch Yoke” crankshaft converts the reciprocating movement of the pistons into rotary motion. The Cox engine, in this configuration, delivers some 350 bhp from a package that is about half the size of an equivalent, conventional diesel.