Fig.6: PMI On-line cylinder pressure sensor of the strain-pin type, built into the cylinder cover. The sensor is mounted in a bottom-hole in the cylinder cover, without any direct contact with the corrosive combustion gases.
Since we realised this quite some time ago, we have been working on the development of a reliable system for long-term continuous cylinder pressure measurements. The first, successful, attempt involved the use of strain gauges on two cover studs on each cylinder, thus in fact using the cylinder cover itself as a 'pressure transducer'. A long-term test was carried out on the main engine of a Danish ferry about ten years ago and the system provided us with stable measurements over a period of more than 10,000 operating hours.
However, there was some electrical noise in the signals and we decided to use another system that had been introduced on the market in the meantime: the strain-pin type of pressure sensor. As can be seen in Fig.6, the pressure-sensing element is a rod located in a bottom-hole in the cylinder cover, in close contact with the bottom of the hole, close to the combustion chamber surface of the cylinder cover. Thus, the sensor measures the deformation of the cylinder cover caused by the cylinder pressure without being in contact with the aggressive combustion products and without having any indicator bore that can clog up. The position of the sensor also makes it easier to prevent electrical noise from interfering with the cylinder pressure signal.
The pressure transducer of the off-line system is used for taking simultaneous measurements for calibrating the on-line system. By feeding the two signals into the computer in the calibration mode, a calibration curve is determined for each cylinder. The fact that the same, high-quality, pressure transducer is used to calibrate all cylinders means that the cylinder-to-cylinder balance is not at all influenced by differences between the individual pressure sensors.
2.7 Electronic cylinder lubricator
The concept of the new electronic cylinder lubricator is illustrated in Fig.7 - this is described in more detail in [4]. A pump station delivers lube oil at 45 bar pressure to the lubricators. These have a small piston for each lube oil quill in the cylinder liner, and the power for injecting the oil comes from the 45 bar system pressure. Thus, the driving side is a conventional common rail system, whereas the injection side is a high-pressure positive displacement system, thus giving equal amounts of lube oil to each quill and the best possible safety margin against clogging of single lube oil quills.
For the large bore engines, each cylinder has two lubricators (each serving half of the lube oil quills) and an accumulator, while the small bore engines (with fewer lube oil quills per cylinder) are served by one lubricator per cylinder. The pump station includes two pumps (one operating, the other on stand-by with automatic start up), a filter and coolers. The computer unit comprises a main computer, controlling the normal operation, a switchover unit and a (simple) back-up unit. A shaft encoder (which can be shared with a PMI system, or the timing system on the Intelligent Engine) supplies the necessary timing signal.
The lubrication concept is intermittent lubrication a relatively large amount of lube oil is injected for each four (or five or six, etc.) revolutions, the actual sequence being determined by the desired dosage in g/bhph. The injection timing is controlled precisely and, by virtue of the high delivery pressure, the lube oil is injected exactly when the piston ring pack is passing the lube oil quills thus ensuring the best possible utilisation of the costly lube oil.
The first engines viz. a number of 12K90MC engines for Danish owner A.P.Mφller and the 6S90MC-C prototype engine, have been delivered, running on testbed with (prototype) electronic hardware and software. The first of the 12K90MC engines will be on sea trial in June this year. Furthermore, four stationary 12K90MC-S engines have been fitted With the system, and a 12K90MC container ship engine has just started service after being retrofitted with the system on all cylinders.
The status of development for series production is that the computer has passed the necessary tests (E 10), and the final approval by a number of Classification Societies took place in Copenhagen in April this year, paving the way for large-scale commercial deliveries. Production of the electronic hardware has started, and the first units have been delivered.
