Engine performance under pressure
In the age of electronically controlled engines, financially constrained ship operators and environmental regulation, reliable monitoring of cylinder pressure is more important than ever.
Until the advent of electronically controlled engines nearly a decade ago, optimising two-stroke engine performance was a very different business. Engine combustion pressure (an important tuning parameter) was measured while the vessel was at full speed, and performed cylinder by cylinder. The result was that engines were optimised for only one speed, while differences in ambient conditions between measurements for each cylinder meant that it was hard to balance cylinder pressures across the whole engine.
Today’s modern engines feature electronic control and automatic tuning that eradicates those problems, measuring pressure across all cylinders for the whole voyage and constantly optimising the engine performance. The result is that these engines can boast an extended lifetime, lower maintenance costs and lower fuel consumption. The ease of monitoring also ensures that they operate to specification and in line with emissions regulations.
For the Swedish arm of ABB, producer of the Cylmate engine monitoring system, the emergence of such electronically controlled engines could have been a disaster. The engine designers’ moves into monitoring and control might have meant ABB’s own system lost sales, but there was a component that they couldn’t replace: the cylinder pressure transducer that was a vital piece of the Cylmate package is now an integral part of the MAN and WinGD designed electronically controlled engines as built by many licensees.
The Cylmate pressure sensor is based on ABB’s Pressductor magneto-elastic technology, with a blow-through design that simplifies the cleaning of combustion residues from the pressure sensor. The transducer is factory calibrated and designed for continuous combustion pressure measurement without any need for recalibration.
Measuring accuracy of the Cylmate pressure transducer is 0.5% over the full measuring range and is not influenced by any clogging or heat flash from the combustion gases - a problem common to other pressure sensors. The mean time between failures (MTBF) for the sensor is more than 10 years, with performance under warranty for five years.
Continuous measuring accuracy has a considerable impact on optimising fuel consumption. According to ABB, a deviation of just 1.0 bar in Pmax pressure measurement translates to a specific fuel oil consumption of 0.2g/kWh.
According to Björn Kindblom, area sales manager, Measurement & Analytics - Force Measurement, ABB, the company cooperated closely with engine designers when they were first designing their electronic controls. “The biggest challenge for engine designers in developing a closed-loop control system is to have a reliable pressure sensors. So when we started to work with them we had to prove that we had a sensor that was really reliable and could fit this purpose. That meant that they could come out with this functionality.”
Kindblom reports that Cylmate transducers installed in 2001 have been seen to be working as accurately as they had been when installed. That provable robustness and the lack of maintenance or calibration required have led to widespread use among engine builders. ABB reports that it has around 7,000 pressure transducers operational in the marine sector, equating to around 800 vessels.
While the company supplies mainly to engine builders rather than direct to ship operators, it is aware of the use of its transducers on engines operated by many major shipping lines, among them MSC, Euronav, COSCO, Mitsui OSK Line, CMA CGM and NSB. A notable reference is the original ship of Maersk’s Triple E class of container ships, the 18,270teu Maersk Mc-Kinney Møller, launched in 2013. The 400m loa, 165,000dwt vessel employs twin MAN Diesel & Turbo eight-cylinder, electronically controlled two-stroke engines, with Cylmate transducers in every cylinder.
The same sensors (with some additional certification required by engine designers) have also been used in dual-fuel engines, where pressure monitoring is even more important given the need to control knock characteristics. Pressure transducers feedback to the engine’s electronic controls, which regulate the fuel-air mixture to ensure that it is neither too lean (potentially causing knocking) nor too rich (which could cause cylinders to misfire). In fact, Cylmate pressure transducers were chosen for the very first ME-GI dual-fuel engine built by MAN, reports Kindblom.
In a tough market, fuel economy has never been more important, and ABB estimates conservatively that electronic control, enabled by accurate pressure monitoring, can lead to fuel savings of 1-2%. “Demand is increasing,” says Kindblom. “Another challenging aspect in the marine industry is that you have different crews coming onboard a ship. Having a sensor that needs maintenance or calibration would make measuring variable depending on the crew. With our sensors ship owners can have automatic tuning with a more than ten-year life.”
Durability, as well as reliability, will be a key factor as sensor technology is used more widely in engine monitoring. “Cabling could be damaged by mounting and unmounting as part of engine maintenance, but the mechanical part of the sensor could last longer than the engine itself,” claims Kindblom. “We’ve seen sensors come out of vessels after 15 years that are as accurate as when they were first installed.”
As demand for reliable, hard-wearing engine sensors increases, ABB believes that its long-established pressure transducer technology will keep it ahead of the curve.