Research On The Combustion Characteristics Of PODE/Methanol Dual-fuel Based On Optical Engine

The carbon neutral fuels provide a strong support for the internal combustion engine industry to achieve carbon neutrality goals.Polyoxymethylene dimethyl ethers(PODE)and methanol as carbon-neutral fuels contribute to the realization of a fully closed carbon cycle of CO2-fuel-CO2 in internal combustion engines and alleviate the global greenhouse effect.At the same time,the effective combination of high-activity PODE and low-activity methanol based on the fuel design concept is of great significance to achieve high efficiency and low emissions of internal combustion engines.However,there are few studies on PODE/methanol dual-fuel combustion,and it is not clear how to effectively combine PODE/methanol dual-fuel with advanced combustion modes to achieve efficient and clean combustion of the engine.Therefore,in this paper,the combustion characteristics and flame development characteristics of PODE/methanol dual-fuel are studied in detail based on an optical engine.First,the effects of fuel injection amount,intake air temperature and injection timing on the combustion characteristics of PODE were investigated.The results show that with the increase of fuel injection amount,the low temperature reaction is first advanced and then delayed due to the influence of the endothermic inhibition of fuel evaporation and the promotion of reaction activity.The increase in intake air temperature can improve the combustion stability of PODE.With the delay of injection time,the ignition delay period is shortened,the position of fuel impinging on the wall changes,and the combustion of PODE changes from homogeneous compression ignition to diffusion combustion.Secondly,the combustion characteristics and ignition characteristics of PODE/methanol blended fuels were explored.The results show that with the increase of methanol ratio,the combustion phase is delayed,the heat transfer loss and the negative compression work are reduced.Under the conditions of high intake air temperature and low methanol ratio,the combustible mixture has higher activity,and a new initial fire nucleus will be formed during the flame propagation process,and the combustion speed is faster.As the injection time advances,the ignition delay period is prolonged,and the premixed gas content increases,the proportion of blue premixed flame increases,and the initial fire core gradually moves from the center of the combustion chamber to the edge of the optical window.Finally,the effects of different injection strategies on PODE/methanol combustion are compared.The results show that for port and in-cylinder co-injection PODE/methanol blended fuel,with the increase of port injection ratio,the low temperature reaction is promoted,combustion stability is improved,and the maximum pressure rise rate is reduced.For port injection methanol,in-cylinder direct injection PODE,It can prolong the ignition delay period,delay the combustion phase,reduce the negative work of compression and heat transfer loss,and improve the thermal efficiency of the engine.Therefore,port and in-cylinder co-injection PODE/methanol blended fuel injection strategy is more suitable for PODE/methanol dual-fuel combustion under low load and high load conditions,while port injection methanol and in-cylinder direct injection PODE injection strategies are suitable for medium load conditions of PODE/methanol dual-fuel combustion.In this paper,the combustion characteristics and flame development characteristics of PODE/methanol are studied by visualization technology,which provides theoretical guidance for the efficient and clean utilization of PODE and methanol in internal combustion engines.