Aeoliki Marine introduces Imes engine pressure meter
Aeoliki Marine introduces Imes engine pressure meter
Keyword: Pressure
Background information
Cylinder pressure is the fundamental variable that determines a combustion engine's operating state. This is done through cylinder pressure sensors used to control diesel engines, allowing detection of start and end of combustion events, to reduce NOx, smoke, and soot emissions. Recent interest has focused in air-fuel ratio control for turbocharged engines, mostly in the interest of reducing the NOx levels.
Most of the diesel engine use of cylinder pressure sensors has, however, been in the area of engine balancing and monitoring. Larger diesel engines, typically with six or more cylinders, are frequently prone to cylinder-to-cylinder variability requiring periodic re-balancing and frequent adjustments. In some older marine engines, periodic balancing on a monthly basis is required, in order to maintain nominal engine operating and emission characteristics.
Most recently, cylinder pressure monitoring has become popular in the area of condition based maintenance (CBM), as shipowners attempt to eliminate the traditional scheduled maintenance in favour of CBM. Based on cylinder pressure evolution over time, various diagnostic and prognostic techniques have been reported leading to early detection of such problems as piston scuffing,overheating, cracking of cylinder heads, fuel injection system failures, or bearing failure.
Thin film technology sensor – the heart of the Imes engine pressure meter
To date the widespread use of cylinder pressure based monitoring and control systems has been hampered by one overriding factor: the lack of a cost-effective, reliable, and durable combustion pressure sensor. Piezoelectric-quartz pressure transducers that have been used over decades in engine development and calibration are subject to electromagnetic interference effects, have limited lifetime, and are unacceptably expensive.
Lower cost piezoceramic devices, such as spark plug washers and boss-type sensors, do not offer high accuracy under all engine conditions, are subject to electrical interference problems, are prone to large temperature errors, and questionable durability.
For new and demanding applications in measuring and control technology more and more sensors are used employing the thin film technology. In co-operation with STW, Imes has developed a high temperature measuring cell (as used in the Imes engine pressure meter) capable of withstanding the extreme conditions prevailing on diesel and gas engines. This development led to high quality,innovative products for cylinder pressure measurement, including hardware and software, thus opening the way to new options in engine control.
In addition to the common quality requirements for pressure sensors, such as small hysteresis, good linearity, and small temperature dependence, the following requirements must also be met:
long temperature stability and resistance to temperature peaks in the pressure medium of up to 1,700°C;
load frequencies greater than 108 are typical during sensor life;and
thermal shock error due to extremely fast variations in the pressure medium temperature has to be small.
The performance of the Imes sensor (as used in the Imes engine pressure meter) displays all these characteristics.
For further information contact Thomas Andreou, Business Co-ordinator,Aeoliki Marine Ltd, Holly House, 12 Elm Gardens, Welwyn Garden City AL8 6RY, UK. Tel: +44 1707 329000; Fax: +44 1707 696254; E-mail aeoliki@ntlworld.com
