RELIABILITY SAFEGUARD THROUGH STEP BY STEP DEVELOPMENT
The long history of the most popular S.E.M.T. Pielstick medium speed diesel engine started in 1963 with the launching of the 400-mm bore PC2.2 rated at 500 hp/cyl (368 kW/cyl) at 500/520 rpm.
Since that time, 3500 engines have been produced, with a major part for ship propulsion, in different versions with power ratings increasing over the years.
The latest development step allowed to reach with the PC2.6B a power of 750 kW/cyl, which means that the power has been doubled since the origin.
A similar step by step development has been used for the 280 mm bore PA6 engine, which has been recently focused on an 8.1 MW engine with low specific weight (5 kg/kW) for high speed ferries and navies applications.
As those latest developments had to cope with constraints linked to the environment protection, new systems are being introduced to reach as much as 75% NOx reduction.
The step by step development strategy allows to incorporate in each step the experience of previous versions which ensures, besides minimised risks for the engine designer, a maximised safety guarantee to the end user. This has been largely demonstrated by service experience results of medium-speed S.E.M.T. Pielstick engines, used for ship propulsion and manufactured by Japanese licensees.
S.E.M.T. Pielstick has developed, for over 50 years, four-stroke medium-speed (PC) and high-speed (PA) diesel engines in the power range of 1 to 26.5 MW. The developments have been always carefully oriented to fit the market requirements. While the major requirement for military application has been more or less always the same (high power density), the requirements for civil applications have been changing with economical and political situations.
When looking back at the evolution of the market requirements over the last 40 years, three main periods can be identified with different characteristics:
- a first period, lasting up to the fuel crisis in the 1970's, where the demand was mainly oriented towards constantly increased specific powers.
- a second period with a top priority given to low specific fuel consumption, as a consequence of the shock created by the 400% increase of the crude oil price resulting of the fuel crisis. This is the period when long stroke engines (PC20, PC30 and PC40) have been developed and peak combustion pressures increased.
- a last period, which started roughly 15 years ago, with tougher competition on engine first and total life-cycle costs on one hand, and the obligation to cope with emissions legislations on the other hand. New type of applications also appeared during this period, like high-speed ferries with special requirements i.e. low weight/power ratios.
Last but not least, there has been, and always will be, a permanent requirement of high reliability.
The step by step development strategy, to match market demands, has been used on the S.E.M.T. Pielstick best-sellers, namely: PC2, PC4 and PA6 engine families (Fig.1 to 3).