In the CHP gas engines of biogas plants, the lean, highly compressed mixture of biogas and intake air must be ignited with a powerful spark. High-quality and powerful spark plugs are used for this.
However, due to impurities in the combustion gas, deposits occur on the spark plugs over the operating time of the CHP units, which lead to a deterioration of the ignition function.
These deposits consist mainly of encrusted sulphur compounds resulting from the H2S content in the biogas. Furthermore, during combustion, the silicon compounds contained in traces in the biogas lead to the formation of particularly stable incrustations of silicon oxide. Another source of contamination is the entry of lubricating oil into the combustion chamber through the crankcase ventilation, the turbocharger and the cylinder inner wall itself. Insufficiently burnt lubricating oil residues lead to soot deposits (oil carbon) in the engine interior and especially on the spark plugs.
The consequence of dirty spark plugs is insufficient combustion in the CHP unit, which leads to a reduction in engine output and an increase in pollutant emissions.
To avoid unfavourable combustion and possible consequential damage, the condition of the spark plugs should be closely monitored and regular intensive ultrasonic cleaning is recommended.
After ultrasonic cleaning with a suitable cleaning preparation, the spark plugs regain their performance.
The main advantage of cleaning the spark plugs in the ultrasonic cleaning device compared to a wire brush is the better cleaning result in the gaps and avoidance of mechanical abrasion, which is unavoidable with a wire brush. Particularly in the case of pre-chamber spark plugs, which are used in MWM combined heat and power units, for example, ultrasound enables cleaning in the fine openings of the spark plug, which could not be reached with a brush.
After many years of testing, the service life of the spark plugs in a 500 kW GE Jenbacher CHP running on biogas was increased from 6,000 h previously to 8,000-10,000 h thanks to ultrasonic cleaning. Considering the costs of a spark plug set of approx. 4,000 euros, the investment in an ultrasonic cleaner pays for itself within one year. In addition, the ultrasonic cleaner can be used for other maintenance tasks, e.g. in a biogas plant.
