Study of biomethanol as sustainable replacement of Autogas at variable ignition timing

Abstract

Bio-methanol has recently interested researchers looking for a suitable alternative due to its low carbon/hydrogen (C/H) ratio. Adding methanol to Autogas could thereby improve combustion while lowering emissions. In the present investigation, testing is conducted at a compression ratio of 14:1 on various fuel ratios (55/45 to 75/25 with a 5% change) of methanol/Autogas with ignition timing ranging from 28°CA bTDC to 14°CA bTDC. The results indicate improvements due to the addition of 65% methanol. Improved brake thermal efficiency (BTE) by 6.27%, peak pressure (P_max) by 0.36%, heat release rate (HRR_max), peak temperature (T_max) by 0.89%, and rise in exhaust gas temperature (EGT). Simultaneously, combustion duration, HC & CO emissions, and the coefficient of variations in indicated mean effective pressure (CoV_IMEP) are reduced. With methanol, the volumetric efficiency (η_vol) improves continuously. Optimal ignition timing is shown to advance with increasing methanol concentration. With ignition retard, the flame development phase (CA10) decreases by 1.7%/2°CA ignition retard, whereas the flame propagation phase (CA10-90) decreases to a minimum and then increases. Due to combustion instability, ignition retard increases the Cyclic variation and CoV_IMEP, while P_max, HRR_max, T_max, and BTE increase to a maximum and then drop. Ignition retard is an effective way of reducing NO_x emissions, although CO and HC emissions increase significantly. Due to reduced carbon supply, carbon emissions are extremely low even at higher methanol concentrations than Autogas-rich fuel. NOx emissions are also extremely low (62.5 % of the ignition angle at 24°CA), revealing that a higher methanol ratio could be used with minimal risk of power loss.