Study On The Formation Process Of Unregulated Emissions From Engine Fueled With Methanol/F-T Diesel Blend

In the face of the urgent demand of energy saving and emission reduction,according to the characteristics of China's energy endowment,it is significant to study the application of coal-based F-T diesel and methanol in diesel engines and the generation process of emissions for finding alternative fuels and reducing the emission of pollutants from diesel engines.Conventional pollutants such as NOx,CO,HC and PM can be produced when F-T diesel and methanol are burned in diesel engines.In addition,unconventional pollutants such as aldehydes,ketones,aromatic hydrocarbons and olefin can also be produced,which has a certain impact on the environment.The research focused on the measurement method and formation process of unconventional pollutants in diesel engine fueled with methanol/F-T diesel mixture.The change ruel of methanol/F-T diesel fuel unconventional pollutants with methanol blending ratio and engine operating conditions was studied by means of diesel engine bench and special test.The kinetic model of fuel chemical reaction was established.The formation regularity of major unconventional pollutants was studied and the formation pathway of unconventional pollutants was analyzed.The theoretical research and experimental analysis were used to discuss the change ruel of density,kinematic viscosity,surface tension,cetane number and low calorific value of methanol/F-T diesel mixture with different blending ratios.The fitting formulas of characteristic parameters of methanol/F-T diesel mixture were put forward,and the effects of methanol blending ratio and ambient temperature on the physicochemical properties of the blend fuel were discussed.The results showed that with the increase of methanol blending ratio,the density and surface tension of the blend fuel increased,the viscosity,cetane number and low calorific value decreased.The density,viscosity and surface tension of the methanol/F-T diesel mixture decreased as the ambient temperature increased.A 493 non-road diesel engine test bench was built to measure combustion process and pollutants.The indicator diagram of methanol/F-T diesel mixture was collected and the combustion characteristic parameters were analyzed.Conventional pollutants such as NOx,smoke,HC and CO were measured,and the change ruel of conventional pollutants with methanol blending ratios was analyzed.The results showed that with the increase of methanol blending ratio,the peak pressure rise rate,the maximum explosive pressure in cylinder and the peak instantaneous heat release rate increased,and the corresponding crankshaft angle moved backward under rated condition.When diesel engine operated at rated speed and 25% load,the methanol blending ratio increased from 0 to 15%,the ignition delay period prolonged by 2.8°CA,and the combustion duration shortened by 6.1°CA.Under rated condition,the mixing ratio increased from 0 to 15%,the NOx and exhaust smoke decreased by 24.2% and 46.6%,respectively,and the HC and CO emissions increased.The measurement method of unconventional gaseous substances in methanol/F-T diesel blend fuel was discussed.The emission law of unconventional pollutants from 493 diesel engine fueled with methanol/F-T diesel mixture was analyzed.30 kinds of unconventional pollutants,such as aldehydes,ketones,olefins,alkanes and aromatic hydrocarbons,were measured and classified according to the concentration and chemical composition of the substances.The change ruel of unconventional substances such as acrolein,butadiene,n-hexane and benzene with methanol blending ratio and diesel engine operating conditions was studied.The results showed that propylene,butadiene,acrolein,benzene,toluene,ethylbenzene and p/m-xylene were unconventional pollutants with high concentration.Under the same conditions,the proportion of aromatic hydrocarbons in unconventional pollutants was the highest.With the increase of methanol blending ratio,the concentration of olefins,alkanes and aromatic hydrocarbons such as butadiene,n-hexane and benzene decreased,and the emission of aldehydes and ketones such as acrolein increased.When the methanol mixing ratio was constant,aromatic hydrocarbons,aldehydes,ketones and alkanes were the main unconventional pollutants under idle condition.At the maximum torque condition,the concentration of olefins increased,while the emissions of aromatic hydrocarbons,aldehydes,ketones and alkanes decreased.At the rated condition,the emissions of unconventional pollutants increased slightly compared with the maximum torque condition.According to the composition of fuel,the characteristic fuel of F-T diesel was determined,and the chemical reaction kinetics mechanism of methanol/F-T diesel blends was constructed.The formation process of substances was simulated by using reflection shock tube model and premixed flame model.The change ruel of the concentration and production rate of unconventional pollutants with initial conditions and methanol blending ratio was discussed.The results showed that with the increase of initial pressure,the production rate and the concentration peak of benzene increased.The initial temperature had little effect on the formation of formaldehyde.With the increase of initial temperature,the production rate and concentration of benzene increased,and the concentration peak of 1,3-butadiene and n-hexane decreased.With the increase of equivalent ratio,the emission of formaldehyde,benzene,1,3-butadiene and n-hexane increased.With the increase of methanol blending ratio,the concentration of formaldehyde increased,while the concentration of benzene,1,3-butadiene and n-hexane decreased.The contribution of reaction bewteen HCO and formaldehyde to formaldehyde consumption was gradually greater than that of formaldehyde hydrogenation.The production rates of the main elementary reactions of benzene formation and consumption decreased,and the reaction rate of benzene formation decreased greatly.O,H,OH and HO2 radicals had high activity and played a major role in the formation and consumption of unconventional pollutants.The research provided a reference for discussing the formation and control of unconventional pollutants in methanol/F-T diesel blends and promoting the application of methanol and F-T diesel in diesel engines.