In the present study, the two installation methods in combining Darrieus machine to Savonius machine were applied. First, Savonius machine was directly mounted to the main shaft of Darrieus machine and another one it was mounted to the main shaft via one-way bearing. The result shows that the self-starting ability of Darrieus machine could increase of about 60% by combining it with drag device such as Savonius machine. However, the net power extracted by this combination is significantly decrease. In the combination of Darrieus-Savonius machine where the Savonius was directly mounted on the main shaft without one-way bearing gives power reduction 53%, while in the combination of Darrieus-Savonius machine where the Savonius was mounted on the main shaft with one-way bearing gives power reduction of about 29%. Savonius machine mounted to the main shaft via one-way bearing gives relatively lower impact in power extraction reducing of Darrieus machine instead of Savonius was directly mounted to the main shaft without one-way bearing. As conclusion that the combination of Darrieus-Savonius machines should be addressed to improve the starting ability only, it should not be addressed to improve the power extraction capability of Darrieus machine.

No abstract

The use of coal which is dominated by hard coal is projected as the main energy source (± 25%) in 2050 according to the Indonesian Government Regulation No. 79 of 2014. The use of low-rank coal as a substitute for hard coal through the Upgrading Brown Coal (UBC) process is supported by the Indonesian Government Regulation No. 77 of 2014 concerning the obligation to increase the added value of mining products. The use of UBC products can reduce the amount of coal consumption by up to 50% of the use of low-rank coal The UBC process is still being developed, as in this study, a mixture of low-rank coal and waste cooking oil is used as a coating material to cover the coal pores after the watering process. The variation in the mixing ratio of low-rank coal and waste cooking oil is 1:1; 1:2; and 1:3, with a variation of the heating temperature and mixing mixture of 100°C; 125°C; 150°C; 175°C; and 200°C. The analysis showed that the best conditions are found at a ratio of 1: 3 with a temperature of 175°C, wherein the results of the inherent moisture showed a decrease of 21.95% with a calorific value of 7462.82 cal/g. The high calorific value obtained was proven by the flame that occurred for 14 minutes for 50 g of the UBC product sample in the best variable with ash content of 2.92 %, and volatile matter by 64.77%.

Energi angin merupakan salah satu sumber energi terbarukan yang melimpah di Indonesia. Potensi angin yang besar ini dapat dimanfaatkan dengan menggunakan turbin angin sebagai teknologi yang ramah lingkungan. Turbin angin Savonius dan turbin angin Darrieus merupakan turbin angin sumbu vertikal yang sesuai dengan karakteristik angin yang tersedia. Pada penelitian ini, turbin Darrieus dikombinasikan dengan turbin Savonius dalam rangka memperbaiki kemampuan self-starting turbin tersebut. Untuk mendapatkan performansi turbin yang lebih baik, daya yang dihasilkan oleh turbin Savonius juga dimanfaatkan sehingga tidak semata-mata berfungsi sebagai perangkat starting saja. Untuk tujuan itu, rotor Savonius dipasang pada poros dengan menggunakan one way bearing sehingga masing-masing rotor dapat beroperasi secara terpisah dan memiliki kecepatan putaran yang berbeda. Profil sudu yang digunakan dalam penelitian ini adalah airfoil NACA 0018 untuk rotor Darrieus dan modifikasi airfoil e377-il untuk rotor Savonius. Tujuan utama penelitian ini adalah mengevaluasi peningkatan peformansi yang diperoleh pada kombinasi turbin Darrieus Savonius poros kembar bila dibandingkan dengan kombinasi poros tunggal. Pada kombinasi poros tunggal, rotor Savonius terpasang tetap pada poros turbin Darrieus dan hanya digunakan sebagai starting, sedangkan pada kombinasi poros kembar, daya yang dihasilkan oleh kedua rotor dimanfaatkan. Hasil dari pengujian ini memperlihatkan bahwa daya yang dibangkitkan oleh kombinasi poros kembar mengalami peningkatan yang signifikan dibandingkan oleh kombinasi poros tunggal yaitu sebesar 28.54% (0.528 W) pada kecepatan angin 4.38 m/s.