Influence of Maintenance Intervals on Performance and Emissions of a 192 kWel Biogas Gas Otto CHP Unit and Results of Lubricating Oil Quality Tests—Outcome from a Continuous Two-Year Measuring Campaign

In the present work, we focus on long-term and permanent measurements of approximately two years on a 192 kWel Gas Otto CHP (combined heat and power) unit at a full-scale research biogas plant. In detail the influence of 600 h and 1800 h maintenance intervals on electrical efficiency consumption and exhaust gas emissions such as NOx and CO have been studied under real life conditions. Lubricating oil quality analyses throughout the CHP operation time are presented to show the destructive changes in property and its influence on condition based maintenance. The results confirm the well-known fact that after readjustment of the air-fuel ratio after 1800 h maintenance the emission values for NOx decline while CO increases. The emission-optimized operation mode leads to lower engine efficiency. The maintenance tasks carried out at 600 h intervals lead to lower NOx emissions in nine cases while in 14 cases the emissions remained unchanged. The permanent measurements proved their legitimacy showing various emission deviations from the limiting values prior and post maintenance. The results show that by monitoring the lubricating oil quality, the oil change intervals can be maximized while ensuring that engine performance is not endangered, and a longer engine lifespan can be expected. The OPEN ACCESS Energies 2013, 6 2820 oil analyses allow the operator to reduce maintenance expenditures while minimizing wear.