Theoretical and Practical analysis of the effect of charge air temperature and humidity in the combustion process of diesel engines at Heladhanavi Power Plant, Puttalam, Sri Lanka

Abstract: Heladhanavi 100MW Diesel Power Plant in Puttalam, Sri Lanka comprises of six 18V 46 Wartsila turbocharged air cooled engines. Fuel consumption of the engines varies with the ambient conditions. It has been seen in hotter days fuel consumption is higher comparatively to cooler days. This study was conducted as per the requirement to find out the reasons behind this variation of the fuel consumption and to quantify the effects on the efficiency with respect to the charge air properties in relation to temperature and humidity. In this study the effect of charge air temperature was analyzed performing two sets of experiments. A combustion analysis experiment (experiment 1) was performed to monitor what happens inside the combustion chamber during day and night times. This is to investigate the cause of efficiency variation and why and how it happens. Simultaneously a fuel consumption test was performed using the direct method with the fuel flow meter and energy dispatch readings taking in to the consideration. A humidity analysis inside the charge air receiver was carried out simultaneously to investigate the humidity effect on the combustion. A flue gas analysis test (experiment 2) was performed to determine the efficiency variation in day and night times through the indirect method. Along with this analysis the direct method was followed up to calculate fuel consumption to compare the results from the both tests. A humidity analysis inside the charge air receiver was carried out simultaneously to investigate the humidity effect on the combustion. For all the tests and analysis DG 02 at approximately Rhs: 55,000 was selected to conduct the measurements as 48,000 rhs major overhaul was completed recently. All the components in the fuel system such as pumping elements and injectors are in good condition. The cylinder head, liner and piston overhaul was also have been carried out. The experiments were planned so the lots other factors are not affecting the combustion efficiency during the process to isolate the ambient conditions. The experiments were also carried out during day and night times on the same day to minimize other factors such as fuel quality affecting the equations. Always the LHV of the incoming fuel was obtained for calculations to avoid further mistakes. The results are elaborated along with findings from the past studies in the Literature review. It was confirmed the fuel consumption is positively affected by the charge air temperature while the efficiency is negatively affected. From the literature review it was found out the humidity in charge air affects positively on the fuel consumption while efficiency is negatively affected. The charge air temperature affects the ignition delay period so that the peak pressure and then the combustion efficiency. The efficiency improvement is further confirmed by the flue gas analysis experiment as the loss in the flue gas reduces in night time comparatively to the day time. At Heladhanavi temperature and humidity in charged air behaves in completely opposite manner in day and night times. During day time temperature is high while humidity is low. For the night time case its vise versa. Finally it can be concluded that under the prevailing ambient conditions at the Heladhanavi Power Plant, Puttalam, Sri Lanka, the effect of charge air temperature is more prominent than the effect of humidity in the combustion process for the Wartsila 18 V 46 diesel engines, as a result the efficiency improves during the night time comparatively to the day time. Therefore, proper cleaning and maintaining of the charge air coolers are the most important factor to maintain the charge air temperature and relative humidity inside charge air receiver at a lowest value. Therefore to attain the best electrical efficiency and the fuel consumption for a certain fuel batch.