The first cargoships powered by SEMT-Pielstick diesel engines entered service more than 25 years ago and became the forerunners of a fleet that at present aggregates more than 1,000 vessels propelled by the modern PC2-5, PC3, and PC4 versions of the now famous Pielstick design.
During the past year SEMT-Pielstick, along with other marine diesel designers, had to face the second fuel crisis, which had two main consequences: the cost of a ton of fuel increased above $200, and the oil refineries developed new processes and will supply lower quality fuels for marine uses.
To cope with these problems, SEMT-Pielstick concentrated research and development on a decrease in fuel consumption and use of the worst quality fuel. It has developed new engine models with higher cylinder output and, particularly, lower specific fuel consumption. These engines, with the same bore and stroke as their predecessors, have been designed with all the experience already gained with them.
The PC2-6, with bore of 400 mm and stroke of 460 mm, has a maximum continuous rating of 750 bhp per cylinder at 520 rpm, and specific fuel consumption of 136 grams per horsepower-hour at 85 percent of mcr. The PC4-2 has a bore of 570 mm, stroke of 620 mm, and mcr of 1,650 horsepower per cylinder at 400 rpm. This engine has specific fuel consumption of 134 grams per horsepower-hour at 85 percent of mcr.
These two engines are also offered in an economical, derated version. The PC2-6-E has an mcr of 675 horsepower per cylinder at 520 rpm, and specific fuel consumption of 134 grams per horsepower-hour at 85 percent of mcr. The PC4-2-E, with mcr of 1,500 horsepower per cylinder at 400 rpm, has specific fuel consumption of 132 grams per horsepower-hour at 85 percent of mcr. The new engine specifications permit the burning of fuels with gravity lower than 0.99, viscosity of 600 cst at 50 C, and sulphur content of 5 percent.
Another solution is the design of an economical engine room, which can easily be adapted to the particular needs of almost any type ship, thanks to two basic advantages of medium-speed engines: the necessary use of a reduction gear allows the selection of the most economical propeller speed, resulting in a decrease of the propulsion power by about 3 percent for each 10 rpm propeller speed decrease; the heat that can be recovered from a medium-speed engine is some 60 to 70 percent higher than that from a low-speed engine of the same power.
As a consequence, it is possible to supply the full electrical demand at sea on bulk carriers and general cargo ships at service power as low as 8,000 horsepower. Some 15 ships are already equipped with turbogenerators running on steam produced by the exhaust gas energy, without any diesel generator sets operating while at sea.
Super-economical engine room designs make full use of waste heat recovery possibilities. The waste heat can be used for ship's service purposes or for heating condensate water. It can use the calories eliminated in the first stage of the air cooler to create a second stage of steam pressure.
The power of the turbogenerator exceeding the ship's electrical demand can be fed to the propeller, either by mechanical coupling of the steam turbine of the turbogenerator to the gear box through a power take-off, or by the use of a static frequency converter supplying its regulated current to a shaft generator used as a motor.
Such super-economical installations, the first versions of which are already in operation and the second versions under construction, provide a total specific fuel consumption as low as 120 grams per horsepower-hour, operate any given ship with the lowest possible propulsion power, eliminate diesel generator operation at sea, and burn the poorest quality fuel.