A recent directive from the European Community requires that ships and maritime craft reduce exhaust emissions. While the directive could undermine the economic viability of many maritime transportation services, it could also prompt ship companies to introduce new technical innovations aimed at reducing overall ship fuel consumption. There are already bulk carrier vessels on the ocean with airfoil type sails mounted to the deck, that use wind power to assist in ship propulsion (and reduce overall fuel consumption). As well, companies such as Kite-ship offer kite-sails that help tow a vessel sailing in the direction of trade winds.

Wave Power:

Waves are a form of wind energy and for many years, researchers have sought to use wave power to propel maritime craft. At the present time, some small craft powered by wave energy have been able to sail at speeds of 6 to 8-knots. There appears to be scope to further develop the technology to assist in propelling a vessel at higher speed. Before the technology is developed to carry containers and bulk cargo across the oceans, it may have application in the Mediterranean tour boat industry and perhaps be combined with wind power to attract environmentally conscious tourists.

Clean Energy Storage:

There are rechargeable, emissions-free propulsion technologies that may have possible application in short-distance maritime transportation involving an oversize tug being coupled to the stern of a ship-size barge or a train of coupled barges. The tug may carry grid-scale batteries that provide several megawatt-hours (Mw-hrs) of stored energy and capable to undertaking extended-distance ferry voyages. It may also carry multiple pressure vessels of high-pressure saturated water with optional insulated tanks of molten thermal storage compounds. While certain (low cost) thermal energy storage technologies offer greatly extended service life expectancies, they can only provide energy for short-distance ferry-type voyages.

Natural Gas:

The USA is beginning to export natural gas to Europe, via ships. There have been successful conversions of large-scale maritime diesel engines to burning natural gas. A ship carrying liquefied natural gas may divert a small portion of the cargo to propulsion. Alternatively, a large ocean tug may carry LNG as fuel as it pushes and navigates a barge carry LNG across the North Atlantic, possibly even across the North Pacific to Asian ports. At the present time, American natural gas prices are at record low levels compared to diesel and to bunker fuel.

Biomass:

Several European companies are converting coal-fired power stations to wood and biomass combustion and are importing wood product and biomass from North American suppliers. During an earlier period, ships and boasts operated of solid fuel and used steam engines to drive propellers. Under the Kyoto Accord, bio-fuel is regarded as being ‘environmentally neutral’ while bunker oil is not. New European ship exhaust emissions standards may open the door for ships and boats powered by biomass. One propulsive option may involve gas turbine engines powered by sawdust (or powdered biomass) while the other option may involve steam engines.

Steam Engine Options:

While large-scale steam piston engines are no longer produced, there is scope to adapt off-the-shelf steam turbine engines for maritime propulsion, using electrical transmissions. There may be scope to adapt modern rotary engines such as the sliding vane engine and the Quasiturbine engine to steam power, to directly drive a ship propeller. These engines may be arranged in a sequence of increasing ‘displacement’ to operate on high-pressure, intermediate-pressure and low-pressure steam. For small vessels, there have been successful conversions of 2-stroke diesel engines to steam power for rural power generation in Australia.

An early 1980’s proposal to convert V-16 diesel engine converted to steam power involved operating 4-cylinders on high-pressure steam and the remaining 12-cylinders on low-pressure steam. Borrowing from the precedent of the Skinner triple expansion marine steam engine, a modern 7-cylinder 2-stoke diesel engine can be converted to operate with a single cylinder on high-pressure steam, 2-cylinders on intermediate pressure and 4-cylinders on low-pressure steam. A 9-cylinder engine conversion may operate 3-cylinders on high-pressure steam and 6-cylinders on lower-pressure stream. There may be scope to adapt the precedent of multi-stage expansion on steam piston engines to internal combustion engines.

Multi-Stage IC Engines:

Gas turbine engines operate multi-stage expansion downstream of the combustion chambers, using high-pressure and low-pressure turbines. Some engines (Rolls Royce) use 3-stage expansion of combustion gas. There are precedents of exhaust gas from a diesel piston engine driving a power turbine installed on a drive shaft. Such engines are best suited to running at continuous steady speed over prolonged durations of time, such as trans-oceanic maritime service. Some designs of piston engine can be adapted to allow further expand combustion gas in an adjacent ‘trailing’ cylinder, a form of ‘extended-stroke’ operation to improve engine efficiency.

Crank throws are spaced 90-degrees apart in 90-degree 4-stroke V-8 engines, allowing 4-cylinders to operate compression and combustion with an adjacent trailing cylinder (by 90-degrees) further expanding the combustion gas. The option of using an adjacent cylinder for compound expansion would be possible on modified 4-stroke inline-8, V-8 and V-16 engines as well as on modified (with head breathing) 2-stroke inline-4, inline-6, V-8, V-12 and V-16 engines such as models offered by GM Edison and adapted to maritime propulsion. Under full load, the engines will fire all cylinders and operate compound expansion when at part load.

Leverage:

The compound expansion IC engine would use leverage to provide additional power output. As the combustion cylinder approaches bottom-dead-center, the leverage between the con-rod and crank would rapidly diminish while trailing cylinder leverage between con-rod and crank would be near maximum. When the trailing cylinder passes top-dead center (TDC), an interconnecting passage would open between the leading and trailing cylinders to allow combustion gas to exert pressure on the trailing piston. The arrangement would combine short-stroke compression with long-stroke expansion, a variation of the Atkinson cycle that has been proven to improve engine efficiency.

Ceramic Engine Parts:

Some commercial duty engines are now available with ceramic coatings on top of the pistons and under the valves. Ceramic coatings improve engine efficiency by reducing heat transfer and heat loss from the combustion area immediately following combustion. Some of these engines actually produce hotter exhaust gases to energize the turbocharger, often with enough residual energy available to drive a downstream engine. Ceramic-coated engine parts would enhance the performance of ‘extended-stroke’ engines possibly with enough exhaust heat to drive a turbocharger. The combination of stricter emissions regulations and higher fuel prices see such engines becoming commercially available.

Conclusions:

Europe’s drive to enforce stricter exhaust emissions from ship engines could introduce alternative fuels, re-introduce modified technology from an earlier era and introduce new propulsion innovations to maritime transportation. The cost of fuel oil along with stricter emissions standards could prompt introduction of natural gas and biomass to maritime propulsion. There also exists much proven technology that could be further developed and adapted to improve efficiency and reduce exhaust emissions in maritime transportation. However, such technology would benefit smaller vessels as the largest vessels afloat operate at high propulsive efficiency with low levels of exhaust emissions per container (per ton).