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Cox Powertrain and Ricardo receive MoD development contract for advanced engine concept; supercharged, opposed-piston diesel

Cox Powertrain CAD model
Single-module Cox powerhead unit. Click to enlarge.

The UK Ministry of Defense (MoD) has confirmed its order for the next prototype stage of development of a new high-performance, lightweight diesel engine intended for marine outboard applications on the fast, rigid inflatable boats used by the Royal Navy. The Cox Powertrain engine concept—with many patents pending—is based on a supercharged, two-stroke diesel opposed piston architecture with Scotch Yoke crankshaft and a central injector position.

This engine topology promises a power to weight ratio comparable with high performance gasoline engines, whilst delivering diesel fuel consumption and a package volume around half that of a state-of-the-art diesel engine. The engine is being developed towards the demanding operating conditions of a military application in which extreme diesel performance, light weight and small package size are critical to mission performance, and must be delivered alongside robustness and high reliability of operation.

The core Cox module is a 4-cylinder, 8-piston, supercharged 2-stroke diesel with a capacity of 3.6 liters that delivers up to 350 hp (261Kw) per module; which can be scaled up or down in capacity and configured in multiple modules, depending on requirement. The engines can be specified in units of 200hp to 350hp, with twin modules of up to 700hp per application drive.

Principle benefits are increased responsiveness combined with reduced size, mass and parts count when compared with conventional diesels of similar power output and improved fuel efficiency and storage safety compared to gasoline engines of similar power output.

Cox Powertrain approached Ricardo at an early stage to provide assistance both in developing the Cox engine concept and in supporting the growth and development of the Cox Powertrain business from a small start-up operation to one capable of taking the fully developed product to market.

Cox Powertrain re-located to secure premises at the Ricardo Shoreham Technical Centre site in 2011 and with Ricardo support, has now successfully completed the detailed design phase. This has included an intensive computer aided engineering (CAE) program using both commercial and proprietary Ricardo software tools, in order to optimize and validate the design to an extremely high level prior to prototype manufacture.

Having concluded the design phase the new MoD contract will support Cox Powertrain and Ricardo as they pursue preparation and further development of the engine in prototype form. The partners anticipate the first fire of the engine will be carried out at Ricardo in February of this year, marking the start of the prototype development phase.

The Cox opposed piston engine concept—the original invention of the company’s founder, former F1 designer David Cox—has been the subject of fully subscribed private investment rounds raising development capital of £6.7 million (US$10.5 million), and has already attracted previous external funding from the MoD to support the accelerated development of its detailed design.

The Cox engine concept is specifically designed for its intended purpose as an outboard power unit, but further variants are already under consideration for military inboard power, civilian marine applications and UAVs.



Good firms with good specs - good luck.


Unfortunately no information on engine weight is provided.


Looks like a compact design - cannot tell.

Since they use a Scotch Yoke and say; "Scotch Yoke crankshaft" I assume there is only one crankshaft?


It is a variation of the OPOC (Opposed Piston Opposed Cylinder) concept with a single Scotch Yoke mechanism.

See http://www.sumobrain.com/patents/wipo/Internal-combustion-engines/WO2012160376A2.pdf which is a patent application that has some reasonable drawings.

It may have an advantage in that the piston force is in a straight line.


Aha; thanks, the drawings help a lot.

Apparently there are 4 pistons per cylinder, with the inner pistons connected to a central crank, more or less conventionally with a Scotch yoke.

The outer pistons are connected via a “cage” or with rods that connect to two adjacent crank throws (180 degrees from the 1st).

The engine shown in the drawings has 2 cylinders, but only one more crank throw is needed, for a total of 4.

And the engine is apparently completely balanced.

With 4 pistons in each cylinder, it is rather “tall” but likely not 4 times a normal in-line engine.

I have no idea how those rods all fit in or how well they will work but they are generally in tension during the compression and power strokes (and there ARE NO other strokes).

This is one weird engine; it requires sealing rings around the injectors and though it has 8 pistons, it fires only twice per revolution (every 180 degrees) while an 8 cylinder 2-stroke engine might fire as many as 8 times per revolution (every 44 degrees).

It certainly would appear to be light weight and compact
• No head
• No valves
• No cam shafts
• Short piston skirts (maybe)
• No con rods (they are replaced by the shorter
Scotch yoke assembly and the heavier rods)


Context http://www.gizmag.com/cox-diesel-powertain/26032/

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