Experimental Research On Engine Performance And Combustion And Emission Characteristics Of Methanol-Biodiesel Dual Fuel With Intelligent Charge Compression Ignition Combustion

To alleviate the increasingly grim situation of the oil crisis and environmental problems,developing the newly combustion modes is an effective way aimed at achieving high-efficiency and ultra-low emissions for internal combustion engines.Evidence showed that the key to solving the above problems is the controllable and accurate mixture organization process in the cylinder.Based on this,the intelligent charge compression ignition combustion mode was proposed in which the concentration and reactivity stratifications of the fuel-gas mixture is formed to adapt to the different engine loads through the flexible and controllable cross-injection strategies,thereby improving thermal efficiency and reducing emissions.applications of alcohol and biodiesel in internal combustion engines have raised widespread concerns,but there is still huge scope for improvements in efficiency and emissions.Methanol and biodiesel are commonly used as alternative fuels for vehicles.The complementarities in their reactivity,volatility,and latent heat supporting them to form a concentration-reactivity gradient in the cylinder.In this paper,the prospective experiment of methanol-biodiesel dual fuel in intelligent charge compression ignition（ICCI）mode was conducted to study the effects of injection parameters,injection strategies,intake conditions,and load expansion on engine combustion,emission characteristics,and engine performance.The experiment was carried out on a modified four-stroke single-cylinder compression-ignition engine.Methanol and biodiesel were independently directly injected into the cylinder in succession to investigate the effects of injection parameters on engine combustion and emissions characteristics.Controlled variables consist of methanol energy ratios（30,40,50,60%）,methanol injection pressures（30,35,40 MPa）,fuel injection timings(SOI_Me&SOI_Bio).Results show that in ICCI mode the effects of methanol and biodiesel injection timings on ICCI combustion and emissions presented different tendencies spatially and temporally.Concretely,the earlier combustion phase,increasing combustion rate,and higher indicated thermal efficiency were mainly attributed to the slight postponement of biodiesel injection timing,while the distribution uniformity and mixing sufficiency of the fuel-air mixture were primarily improved by the advanced injection of methanol.As the methanol energy ratio increases,the combustion phase is delayed and the combustion duration is shortened.Besides,the indicated thermal efficiency is increased and emissions of gaseous pollutants and particulate matter are reduced.Besides,it is necessary to adaptively postpone the biodiesel injection timing to maintain a proper combustion phase and the peak in-cylinder pressure and heat release rate.In ICCI experiments,indicated thermal efficiency（ITE）reaching up to53.5%and NOx emissions well below 0.6 g/k Wh were obtained,accompanied with acceptable CO and HC emissions with the optimal fuel injection timings and energy ratios supplemented with appropriate injection pressure and intake conditions.To strengthen the stratifications of concentration and reactivity in the cylinder the methanol two-stage injection strategy was experimentally investigated based on the single-stage injection of methanol.According to the preceding results,research objects are chosen as follows:the injection interval between methanol two-stage injection,biodiesel injection timings,and the overall phase of methanol two-stage injection.Results indicate that the overall combustion phase was advanced and the combustion efficiency was increased by about 1～2%with the methanol two-stage injection strategy compared with methanol one-shot injection.What’s more,it can further reduce the emissions of formaldehyde and NOx and significantly improve the worsening in-cylinder combustion and emissions caused by the late injection of methanol one-shot injection.The optimal interval between two injections of methanol is 60°CA.To further explore the overall engine performance with load expansion,the indicated mean effective pressure increased from 8 bar to 12 bar with ICCI combustion mode.As the load increases,emissions of hydrocarbons,carbon dioxide,and formaldehyde decrease accompanied with thermal efficiency rising from 48%to 53.5%.Furthermore,the number of nucleation and accumulation particulate matter is reduced.The two-stage biodiesel injection strategy biodiesel can retard the overall combustion phase and can effectively reduce the excessive pressure rise rate under high load.