New 300hp (224 kW) Diesel Outboard

At the recent international defence exhibition and conference (DSEi) in London, a new lightweight diesel engine was on display. The British company Cox Powertrain Limited ( is developing, together with Ricardo UK a modular, power dense engine with target output of 300 hp (224 kW) @ 4,000rpm from a 3.6 liter supercharged 2-stroke diesel engine, weighing 300 lbs (136 kg). Such a high power to weight ratio opens up a variety of application opportunities such as marine outboard motor and powered flight e.g. UAVs.


Caption: Impression of the Cox 300hp Diesel Outboard.
Image Credit: Cox Powertrain Ltd.

 The four cylinder, eight piston engine module features an unusual opposed piston (OP) configuration, whereby twin pistons reciprocate with a stroke of 130mm in opposing directions in a common cylinder of bore 98mm. This generates the high compression required for combustion of the diesel fuel without the need for massive cylinder heads. The fuel system is a Common Rail type with direct injection. While OP has been around since the early 20 century the Cox engine uses a Scotch Yoke* cranking arrangement to change the reciprocating piston movements into rotation, thereby substantially saving weight and the number of moving parts.

 As the 2015 deadline for the withdrawal of gasoline from NATO fleets approaches, due to considerations of on board fuel safety and logistics, the search for alternative high power/density engines that run on standard fleet fuels such as F76/JP8 aviation kerosene is increasing. To this end, the UK MOD has invested in the Cox engine project as a viable replacement for gasoline outboard motors.

 The modular construction of the engine allows two modules to be siamesed to produce an engine unit of 700+hp. Some variants may be able to deliver up to 900 hp.

 This is an ongoing development and Beta testing will commence in 2014 with an estimated launch date for the outboard motor version in 2016.


Caption: Cox 3.6 liter, four cylinder, OP single engine module with target out put of 300 hp (224 kW) @ 4,000 rpm. The supercharged diesel engine is expected to have a weight of only 300 lbs (135 kg). Image Credit: Cox Powertrain Ltd.

*An animation of the Scotch Yoke can be seen at: 


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