Role of global fuel-air equivalence ratio and preheating on the behaviour of a biogas driven dual fuel diesel engine

The practice of the green renewable fuels in diesel engines is increasing concerning the progressive deterioration of the green environment and the scarcity of the fossil fuels. In these aspects, several experiments in dual fuel mode (DFM) at different global fuel-air equivalence ratio (Phi(global)), intake charge preheating and loads have been carried out considering biogas as the inducted renewable fuel. The Phi(global) was varied from 0.30 to 0.89 from part to higher loads with biogas flow rate (BFR) of 0.67-3.99 kg/h. The maximum diesel replacements (DR) and biogas energy share (BES) are found to be 92.49% and 97.55%, respectively. However, at higher Phi(global), the brake thermal efficiency (BTE) reduces drastically. Although with preheating, there is an increment of BTE by 5.72% and 2.60% at loads of 4.36 N center dot m and 21.78 N center dot m, respectively. At lower Phi(global) in DFM and with preheating, the diesel like trends of BTE is achieved. Overall combustion behaviour deteriorates at higher Phi(global). However, it significantly improved with the preheating and at controlled Phi(global). Higher cycle-to-cycle variation of cylinder peak pressure (CPP) is noticed at higher Phi(global). With preheating, at part and higher loads the reduction of CO of 29.41% and 65.49% are estimated. At higher load (21.78 N center dot m) and with preheating a reduction of 53.33% of HC is noticed. The drastic reduction of NOx is observed with the increment of Phi(global). The superior performance is achieved at each of the tested loads at the optimum Phi(global) and with preheating.