| China’s plateau area is vast,and the territory with an average altitude of 2000 m～4500m accounts for about one-third of the country’s land area.The low oxygen content and low air pressure in the plateau area pose a challenge to the combustion process of diesel engines.This environment can lead to deterioration of diesel engine performance and incomplete combustion,resulting in more emissions such as NOx,CO and Soot.In response to the environmental and performance challenges of diesel engines in highland areas,research on new fuels and combustion chambers is key to solving environmental problems and improving energy use efficiency.The main research elements of this thesis are as follows:1、A model of a six-cylinder four-stroke diesel engine combustion chamber is established,the sub-model required for calculation is determined and the boundary conditions and initial conditions are set by combining the test data and theoretical analysis.By comparing the simulation data with the test data,it is found that the error of cylinder pressure curve is within the allowable error range,which verifies the feasibility of the simulation model and provides an important method for theoretical research under different altitudes.2、The effect of altitude change on diesel engine performance was studied and analyzed based on numerical simulation results.It is found that when the altitude increases,the incylinder pressure of the diesel engine decreases,the maximum temperature increases and the sauter mean diameter increases,while the combustion thermal efficiency decreases.In addition,NO,CO and Soot emissions also increase gradually and significantly.3、Four different blends were prepared,D90N10,D80N20,D70N30 and D60N40,where D is for diesel,N is for n-butanol and the numbers represent their volume fractions.By analyzing the physicochemical properties of these four blends,it was found that the oxygen content and latent heat of vaporization values of the blends increased with increasing proportions of n-butanol,while the viscosity,density,cetane number and low heating value decreased.4、Simulations are performed at an altitude of 4500 m with four different proportions of blended fuels and pure diesel fuel at rated operating conditions.It is found that with the increase of n-butanol,the cylinder pressure increases and the peak time is delayed.The temperature and heat release rate in the cylinder also increase,while the sauter mean diameter is reduced.In terms of emission,NO emission increased and increased obviously with the increase of n-butanol,while CO and Soot emission decreased accordingly.5、According to the characteristics of the combustion of highland diesel engines,the shape of the original combustion chamber was optimised and the influence of the geometry of the original combustion chamber(SCC)and the modified combustion chamber(MCC)on the in-cylinder combustion process was compared and analysed.It is found that the optimised MCC combustion chamber has a faster turbulence speed,a more complete mixing of fuel and air,a higher combustion efficiency and is more conducive to improving the performance and power recovery of the diesel engine.6、MCC offers higher combustion efficiency and lower pollutant emissions compared to SCC combustion chambers.One of the main advantages of the MCC model is the reduction in emissions of pollutants such as NO,CO and Soot.In addition,the combustion process of D90N10 fuel in both combustion chambers was investigated.The results show that incylinder pressure and temperature and NO emissions increase in both combustion chambers when using D90N10 fuel,but this increase is lower in the MCC combustion chamber than in the SCC chamber.In addition,emissions of Soot and CO are reduced,more significantly in the MCC chamber. |
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