Research On High-Efficiency-Clean-Combustion Of Internal Combustion Engine Based On Coal To Liquid Diesel And Active Thermo-Atmosphere Control

With the increasing stringency of fuel consumption and pollutant emission regulations,energy and environmental sustainability have been the focus of global attention.China's energy structure is characterized by a shortage of oil,less gas and a richness of coal.The development of alternative fuels according to the distribution of our resources can give full play to the advantages of vast territory and the diversity of resources,so the development and synthesis of clean alternative fuels is attracting attention from all walks of life.At the same time,the new combustion modes of internal combustion engines require new fuel properties and molecular structures,and the physical and chemical properties of conventional fuels are difficult to match with the demands of the new combustion modes.Therefore,it is essential to optimize the engine combustion process by flexibly adjusting the in-cylinder active thermo-atmosphere with alternative fuels according to the needs of the new combustion model.In recent years,the efficient and clean combustion of internal combustion engines by means of fuel-engine synergy has gradually become a hot research topic.This study is based on the National Natural Science Foundation of China and the Natural Science Foundation of Jilin Province.For the application of coal to liquid diesel in compressionignition engines,based on the idea of synergy between the physicochemical properties of the fuel and the combustion mode.The effect of coal to liquid diesel/butanol blends reaction activity control combustion and dual fuel injection reaction activity stratified combustion and coal to liquid diesel/gasoline dual fuel injection reaction activity stratified combustion on combustion processes and emission pollutants in compression ignition engines is investigated.In conjunction with the adjustment of combustion boundary conditions such as intake and injection parameters,the potential for efficient and clean combustion in compression-ignition internal combustion engines is explored by adjusting the physical and chemical characteristics of the fuel and the activation heat atmosphere,and the combustion boundary condition control strategies are identified to match the fuel characteristics and combustion modes.Meanwhile,the methods of visualization and Numerical simulation analysis are used to investigate the mechanism and influence of fuel physicochemical properties and combustion boundary conditions on mixture formation,combustion processes,flame development and the history of pollutant generation.In this study,a thermodynamic engine test platform with two fuel injection systems,intake injection and in-cylinder direct injection,was built on the basis of an electronically controlled common rail four-valve diesel engine with an open ECU.The design and construction of a twostage analog supercharging system and an intercooled EGR system enables flexible adjustment of intake parameters.The combustion and emission measurement and control system of engine was built on the basis of eddy current dynamometer,combustion analyzer and high response transientemission analyzer,realizing real-time combustion and emission testing and analysis of compression ignition engines.The visualization platform was based on a four-stroke singlecylinder vertical water-cooled engine and a high-speed camera.The acquisition and analysis of the development of the flame in the cylinder of a compression-ignition engine has been achieved.The chemical reaction mechanism of coal-based synthetic diesel was constructed.And a threedimensional simulation platform was built for the thermodynamic engine used in this study,which enables the simulation of coal to liquid diesel/gasoline dual fuel injection reaction activity stratified combustion,creating the conditions for in-depth analysis of the combustion process of compression-ignition engines from the perspective of chemical reaction kinetics.The main research elements and conclusions are as follows:1.The effects of burning coal to liquid diesel and China VI petrochemical diesel fuel on the combustion process and pollutant emissions of compression-ignition engines was studied experimentally.It can be found that compared with the China VI diesel with low aromatic content,coal to liquid diesel has a higher reactivity,the cetane number is too high,the use of coal to liquid diesel in compression ignition engines shorten the ignition delay,resulting in a reduction in the proportion of premixed combustion,the boundary between premixed combustion and diffusion combustion is obvious.Due to the high proportion of diffuse combustion and the longer combustion duration,the combustion of coal to liquid diesel reduces engine NOx emissions but increases particulate mass emissions compared to the fossil diesel.2.Aiming at the problems of combustion of pure coal to liquid diesel such as the low proportion of premixed combustion,we adopt the coal to liquid diesel/butanol blends reaction activity control combustion and dual fuel injection reaction activity stratified combustion to improve the pre-mixed combustion ratio and thus the engine performance.It can be found that both the two combustion modes can increase the proportion of premixed combustion to improve the mixture generation and thus reduce the particulate emissions.Among them,the introduction of EGR in coal to liquid diesel/butanol activity control and activity stratified combustion can significantly reduce the high NOx emissions associated with the introduction of butanol and mitigate the trade-off between NOx emissions and particulate emissions.However,the higher latent heat of vaporisation of butanol and the delayed combustion phase result in a lower thermal efficiency of coal to liquid diesel/butanol reaction activity control combustion compared to pure coal to liquid diesel combustion.Relative to coal to liquid diesel/butanol blends reaction activity control combustion,the reaction activity stratified combustion mode with intake injection of butanol and direct in-cylinder injection of coal is more conducive to adjustment of the in-cylinder space distribution of the fuel to achieve stratification of the reactivity of the mixture and thus more flexible regulation of the in-cylinder activation heat atmosphere to achieve higher proportion of premixed combustion,resulting in a shorter combustion duration and a level of thermal efficiency comparable to that of pure coal to liquid diesel combustion during the activated stratified combustion process.However,the reaction activity stratified combustion produces high HC and CO emissions due to the incomplete combustion of butanol left between the piston rings and the cylinder liner during the intake and compression strokes.In combination with the fuel injection strategy and EGR rate optimisation,the emission optimum for a butanol ratio of 30% in the reaction activity stratified combustion mode reduces NOx emissions by 49.5% and particulate emissions by 40.9% relative to the emission optimum for pure coal to liquid diesel combustion.3.To investigate the flame development process and in-cylinder temperature field distribution under the coal to liquid diesel/butanol blends reaction activity control combustion and dual fuel injection reaction activity stratified combustion mode using an optical engine based visualization platform.It can be found that both the coal to liquid diesel/butanol blends reaction activity control combustion and dual fuel injection reaction activity stratified combustion can effectively reduce the flame area and flame luminosity during the combustion process of compression ignition engines,the average in-cylinder temperature is reduced and the temperature field is more uniformly distributed,which is conducive to reducing the soot KL factor and thus inhibiting soot generation,with the better effect of reaction activity control combustion.In the reaction activity stratified combustion mode,the pre-injected butanol into the intake precedes the low temperature reaction in the compression process to form ignition-friendly radicals that accelerate the diffusion combustion of coal to liquid diesel.In contrast to the reaction activity control combustion which only forms flame clusters around the cylinder walls,the coal to liquid diesel/butanol reaction activity stratified combustion process forms distinct flame clusters both in the central area of the cylinder and around the cylinder wall.4.To further increase the in-cylinder reaction activity gradient to achieve flexible regulation of the heat releaase to improve thermal efficiency and thus achieve efficient and clean combustion,the gasoline with lower reactivity and latent heat of vaporisation was adopted as the intake injection fuel,a study of the coal to liquid diesel/gasoline dual fuel reaction activity stratified mode based on a dual injection thermodynamic engine.In the dual fuel reaction activity stratified combustion mode with pre-injected gasoline in the intake,direct injection of the coal to liquid diesel with high cetane instead of the petrochemical diesel increases the reactivity gradient between the two fuels and thus increases the indicated thermal efficiency of engine,while helping to reduce the peak pressure rise rate and thus extending the load range of the reaction activity stratified combustion mode.In the coal to liquid diesel/gasoline dual fuel injection reaction activity stratified combustion mode,a moderate direct injection timing and gasoline ratio should be selected according to the engine operating conditions to obtain a high thermal efficiency while ensuring that the pressure rise rate does not exceed the limit.After the optimization of the fuel injection strategy,the coal to liquid diesel/gasoline reaction activity stratified combustion mode is able to increase engine indicated thermal efficiency by 2% compared to the petrochemical diesel/gasoline reaction activity stratified combustion mode,while reducing peak pressure rise rates and NOx emissions by 46.1% and 20.1% respectively.Compared to pure coal to liquid diesel direct injection combustion,coal to liquid diesel/gasoline reaction activity stratified combustion mode shows a 6.7% increase in indicated thermal efficiency and a 19.8% reduction in particulate mass emissions with little change in NOx emissions.5.Based on the the numerical simulation and analysis platform,the fuel evaporation,atomization mixing,combustion process and major pollutant generation history under coal to liquid diesel/gasoline dual fuel injection reaction activity stratified combustion mode are studied in depth.In the coal to liquid diesel /gasoline dual fuel injection reaction activity stratified combustion mode,increase the proportion of gasoline is conducive to reduce the proportion of diffusion combustion so that the distribution of temperature field more uniform.When the proportion of gasoline exceeds a certain limit it can be clearly observed that the process of gasoline spontaneous combustion from the distribution of temperature field.In the reaction activity stratified combustion mode,the premixed gasoline in the cylinder precedes the low temperature reaction to reserve a percentage of reactive radicals for the ignition of direct injection fuel,thereby facilitating the high temperature reaction while inhibiting the production of soot precursors.Advanced injection can accelerate the combustion process and improve the uniformity of the temperature field distribution,and the early injection significantly improves the distribution of incylinder mixture,thereby suppressing soot emissions.