Mercury Marine’s 3 Litre Diesel Spark Ignition

Issue 128 Mercury Marines 3 Litre Diesel Spark Ignition Military Issue Diesel Outboard Motors

Mercury Marine’s 3-litre Diesel Spark Ignition Diesel Outboard Review

For many years, Australia’s Navy has had a ban on outboards because traditional petrol engines – and the fuel itself – were considered too flammable to be aboard warships.

But now, Mercury has developed a new 3-litre DSI (Diesel Spark Ignition) diesel outboard specifically for military and other specialised commercial applications.

The high-performance DSI outboard differs significantly from a normal diesel engine which uses compression to cause the fuel to combust.

DSI motors, much like petrol engines, use a spark plug to ignite the fuel which has been finely atomised by a small charge of compressed air.

The DSI motors improves cold-weather starting and better idling.

Additionally, a ‘glow plug’ supports the spark plug for improved cold-weather starting and better idling.

Mercury’s OptiMax Diesel outboard weighs 234.5kg and delivers 175hp at the propshaft, with an operating range of 5000 to 6000 rpm. It is based on the 3-litre direct fuel-injected OptiMax platform and so behaves more like the 2-stroke gasoline engine it was derived from rather than a typical 4-stroke diesel engine.

The military-issue diesel outboard currently does not meet US exhaust emissions regulations so it cannot be released as a consumer engine. However, Mercury said that if it can find a way to meet the emissions standards in the future then these units may be released as consumer outboards as well.

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