Study On Low Temperature Combustion And Coolhot Flame Conversion Of Diesel Based On Simplified Mechanism

Diesel engines are widely used in engineering and special vehicles because of their high power and high torque.Under extreme cold conditions,diesel engines may have difficulty in ignition,deterioration in the combustion process in the cylinder,and reduced thermal efficiency,which is not conducive to the normal operation of diesel engines.Studying the low-temperature combustion process of diesel and revealing the process of the hot and cool flame conversion and microscopic mechanism are of great significance for optimizing the low-temperature combustion process of diesel engines,improving their operating characteristics at low temperatures,and achieving low-temperature combustion control of diesel engines.In this paper,a three-dimensional computation grid coupled with a CFD simulation method to simplify the chemical reaction mechanism is used to study the diesel low-temperature combustion process and the conversion law of hot and cool flames.Based on a low-temperature constant-volume combustion system for basic research,a solid model of a constant-volume chamber was established,and the boundary,initial conditions and grid generation strategy were set in the CONVERGE to obtain a three-dimensional calculation grid.Select n-heptane as the mark fuel,adopt the widely used and verified San Diego n-heptane simplified mechanism containing 64 primitives and 301-step primitive reactions,obtain a CFD simulation model,and verify and calibrate it based on experimental data,as the basis for subsequent research.Based on the verified CFD model,the low-temperature combustion process of diesel and the conversion between hot and cool flames at different initial temperatures,initial pressures and injection temperatures were studied.The results show that when the initial temperature is low,only cool flames are generated during the diesel combustion process.When the initial temperature is higher(> 753K),there is a significant temperature and pressure jump after the cool flame is generated,and the cool flame is converted into a hot flame.As the initial temperature increases,the timing of generating the cool flame and the hot flame gradually advances.Studies have shown that the lowest critical initial temperature that can convert cool flame to hot flame under simulated temperature and pressure conditions is 753K;The initial pressure has an effect on the conversion of cool flame into hot flame during diesel combustion.With the increase of the initial pressure,the cool flame is more easily converted into hot flame.The research shows that the minimum critical initial pressure for the conversion of cool flame into hot flame under the conditions of simulation temperature and pressure is 1MPa;The lower temperature of the fuel injection also has a certain inhibitory effect on the conversion of cool flame to hot flame.As the temperature of the fuel injection increases,the cool flame is more easily converted into hot flame.Studies have shown that the lowest critical fuel injection temperature that can transform cool flame into hot flame under simulated temperature and pressure conditions is 273K;In addition,compared with the fuel injection temperature,the initial temperature has a more obvious effect on diesel combustion,and the cool flame is more easily converted into a hot flame.