Modification of a CI engine into SI mode and its performance evaluation on biogas
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Date
2007-07
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
In agriculture sector biogas is used in low horse power CI engines in dual fuel mode where about 30 percent diesel and 70 percent biogas are burnt in an engine to develop power. However, biogas has octane rating of 130 which is greater than the petrol (96) and therefore, there lies a potential to run such engines on 100 percent biogas by converting these engine into gas engines operating in SI mode.
A constant speed, low bhp (7.4 kW), single cylinder, four stroke, direct injection, Kirlosker make engine having compression ratio of 16.5:1 was converted into SI mode. Major modifications include the removal of diesel fuel supply system, reduction of compression ratio (13:1), installation of spark plug, mounting of ignition system and provision of mixing device for supply of air-biogas mixture. The studies were conducted to assess the performance of modified CI engine on 100 percent biogas with particular emphasis on operational issues and efficiency of converted engine. Observation on suitability from ease of installation and operation as well as care and maintenance using both battery and magneto ignition system were also evaluated. The engine was operated with ignition timing of 250 BTDC. A long duration test of a converted CI engine coupled with an alternator (7.5 kVA) was conducted to evaluate the crank case oil quality when operating on 100 percent biogas. The performance of converted CI engine in respect of generator load, brake specific biogas consumption, thermal efficiency and emission of HC and NOX on biogas was evaluated. The fuel properties of biogas were also studied.
The observed results of the experiment indicated that the CI engine converted to SI mode could develop maximum brake power of 4.5 kW on 100 percent biogas but at this output there was significant drop in engine speed. The drop in power is due to low heating value of biogas. It is therefore, suggested that the engine be operated at 1352 rpm developing 3 kW brake power for satisfactory operation of electrical devices through the coupled alternator and corresponding brake thermal efficiency was found to be 15.5 percent. The magneto ignition system found satisfactory for installation and operation than battery ignition system. The hydrocarbon and NOX emissions were observed lower on 100 percent biogas as compared to diesel and petrol. The long duration test of the converted engine on 100 percent biogas indicated no deterioration in crankcase oil quality however the engine should be operated for 500 hours for thorough evaluation of crankcase oil quality.
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