Sweden: Diesel monitoring system simplifies maintenance, cuts fuel consumption
Cylmate, the world's first continuous diesel engine monitoring system that can guarantee a power calculation better than 2%, has been introduced by ABB Automation Technology Products of Västeraså Sweden. The system, currently completing a program of trials with engines on a Maersk container ship and a Baltic ferry, is designed to provide a continuous stream of combustion performance data for low and medium-speed diesel engines.
The new technology now makes it possible to continuously identify variations in the power output of up to 20 individual cylinders in up to 10 engines simultaneously. Since power output can vary with each piston stroke, this information enables fuel injectors to be adjusted so that each cylinder is generating exactly the same horsepower. This makes it possible to control all aspects of the engine's performance and to significantly reduce vibration, fuel consumption and engine wear.
Cylmate is claimed to be suitable for any type of low or medium-speed diesel application, including ship propulsion and offshore power plants. Its monitoring capability is derived from improved accuracy in measuring the position of the pistons. This information is used in conjunction with data from pressure transducers that continuously measure cylinder pressure. The result is that vital engine performance parameters can be calculated for each cylinder while it is in operation.
Magneto-electric principle
Unlike earlier systems that were only capable of providing a "snapshot" of conditions within an engine's combustion chamber, the Cylmate pressure transducer provides data throughout the entire combustion cycle. This is achieved through permanent attachment of the transducer to the cylinder's indicator bore where it uses ABB's patented Pressductor technology, which is based on a magneto-elastic principle.
When the engine is in use, the combustion pressure enters a thin-walled Inconel tube. The tube is held within a sensor that employs the Pressductor principle to measure minute changes in its shape caused by pressure variations within the cylinder. The pressure changes are measured and relayed to the system's control unit where the information is matched with data showing the precise position of the cylinder piston at exactly the same moment.
The Cylmate pressure transducer can continuously measure piston pressures up to 250 bar at high temperatures to an accuracy of within 0.5%. The transducer can operate for long periods without maintenance because any build-up of deposits within the tube has no effect upon the pressure measurements. However, when maintenance is considered necessary, this can be undertaken simply by opening the indicator valve mounted on the top of the transducer, so that the tube can be blown through.
For the pressure measurements to provide any benefit they must be related to the position of the piston within the cylinder at exactly the same time. This is achieved by accurate measurement of the flywheel angle. A patented angle transducer is employed that uses the pulsed eddy current principle to register the flywheel teeth as they pass beneath it. A grooved tooth provides the central reference point and the device is capable of finding the magnetic center of each tooth to an accuracy of within 0.05°. During commissioning, the transducer "learns" the shape and position of every tooth on the flywheel. The result is that in one rotation of the flywheel the system obtains 720 samples of crank angle and cylinder pressure for up to 20 cylinders.
Twist compensation
The importance of accurate crank angle measurement becomes apparent in the final calculation as a 1° error can result in an 8% error in the calculated power. Consequently further precision is added to the angle measurements via a mathematical engine model that takes account of the weight of the swinging masses and other factors affecting the components. It is used by the control unit in real time to compensate for any twist or deflection of the piston crank, which can be as much as 1°.
Information collected by the sensors is presented as a visual display at the PC operator station. This uses high resolution graphics in a Windows based environment to create graphs showing the relationship between cylinder power output and the position of the piston. Any discrepancies are immediately visible and can be linked to an alarm, if desired. This helps optimize performance for fuel cost reduction and also minimizes the maintenance cost.
For more information contact Martin Ottosson, ABB Automation Technology, Force Measurement. Tel: +46 21 34 21 51, Fax: +46 21 34 00 05, Email:[email protected]
