German IMES GmbH has developed a new type of very robust cylinder pressure sensor. CEO Stefan Neumann will present the[ds_preview] high robust sensor (HRS) during this year’s CIMAC congress. »Due to the trend to higher indicated mean effective pressure (IMEP) on small, medium and large gas engines with speed ranges of 100 to 1,800 rpm, the required cylinder pressure sensors are subject to increasing operating- and environmental conditions«, he says. »Thus a new era for extremely robust and high accurate cylinder pressure sensors with long-term stability has started.«
A new type of sensor with front membrane and M10 or rather M14 thread has been developed. This sensor is said to be »extremely robust« and to fulfil the demand of high accuracy with low dynamic- and static zero drift. The sensor transmits the pressure via a special designed measuring spring. Areas with equal tensile- and compressive strength are created on the measuring surface, which is a part of the measuring spring. As the measuring surface is subject to deformations a resistor bridge in high temperature thin film technology is applied on it. Depending on the amount of strain a voltage signal will be measured proportional to the pressure change.
Because of its particular construction the measuring spring is resistant to abnormal combustion with high pressure rise up to 1000 bar/ms and at the same time it achieves a high thermodynamic accuracy for engine control purposes. It is designed for >109 load cycles. A specially developed high temperature resistant ceramic for up to 400°C provides the basis for the electrical connection of the sensor. The resistance structure of the measuring spring and the ceramic pads are connected by wire bonding, as a result the electrical connection withstands temperatures of more than 350° C.
»Thermodynamic evaluations on a single cylinder test engine in comparison to a water-cooled piezoelectric reference sensor have confirmed its accuracy. Measurements of 18 bar IMEP at 1,500 rpm have a PMI deviation of 0.5 bar in comparison to the reference«, IMES states. The performance has also been tested on dual fuel ship’s engines. Since March 2017 the sensors are installed on the Swedish asphalt carrier »BIT Viking« and also on a power barge in the Caribbean on a 6 respectively 18 cylinder Wärtsilä dual-fuel engine. The result of the evaluation after 7,000 continuous operating hours was a span error of < 0.5% in comparison to the original calibration of the sensor.
