Speech by Dipl.-Ing. Claus Bruestle at the 26th Aachen Colloquium Automobile and Engine Technology on October 10, 2017: “THE FIRST TURBODIESEL OUTBOARD WITH TWIN CRANKSHAFT TECHNOLOGY”
Today’s marine engine market is divided into two major segments, commercial and recreational use of propulsion systems. At present no diesel outboard exists in the market segment of 30 to 52 kW (40 to 70 HP), a segment interesting for commercial use and which is defined by transport, hauling, commercial fishing and others. In the smaller engine segments with power below 75 kW (100 HP) gasoline engine technology is the dominant and sole available power. Due to their favorable compactness, ease of installation, serviceability, weight and also cost outboard engines govern the market.
The diesel torque to weight ratio, beneficial specific fuel consumption and the tax-free diesel fuel for commercial applications make diesel engines extremely attractive. Also other typical outboard engine applications like rescue boats on larger ships are much more comfortable and more economical with a diesel outboard. Here also an additional advantage steps in: No need to maintain dual fuel storage capacity onboard with all aspects of safety and logistics.
One focus on developing a diesel outboard engine is the vibration level. The typical diesel vibrations would make the whole boat shake.
The patented NEANDER Shark dual crankshaft design eliminates mass forces using the 2 counter rotating crankshafts. On top this design provides a role torque free operation of the engine on the transom. This leads to a smooth running behavior which is beside the NEANDER engine only achieved by multiple cylinder diesel engines!
The key enabler for a dual crankshaft engine with a constrained piston movement by two con-rods with theoretically no piston side forces is provision for forgiveness towards tolerances, which can lead to off-design positions of the piston in its cylinder bore and unfavorable mechanical effects like scuffing, sticking or simply higher friction as the least bad of effects.
Inventing and introducing a so-called space ball design resolved the problem, giving the piston the additional degree of freedom of rotational adjustment around the two piston pins.
The cylinder block of the engine is an Aluminum design, closed deck with dry cast iron cylinder sleeves pressed in for robustness and simple serviceability. The one-piece cylinder head, block and bedplate are joined by so called long bolts, which reach from the head into the bedplate main bearing saddles.
This design allows the structural aluminum parts to be under compressive stress only, which is favorable for the durability of all structural components. For vibrational rupture protection, dampening, the boltholes are connected via calibrated oil holes into the main oil gallery. This design strategy was applied successfully to other high performance marine engines in the past.