Numerical Simulation On Combustion System Optimization And Matching For High Efficiency Heavy Duty Diesel Engine

As energy issues and carbon emission regulations become prominent,improving the thermal efficiency of diesel engines,and reducing brake specific fuel consumption（BSFC）and CO₂ emission are always the research hotspots of internal combustion engine research community.At the same time,the operating condition is also an important affect of the BSFC of diesel engine.It is very valuable to carry out explorations on how to improve the thermal efficiency and make the low BSFC zone falling into the target operating range of the highest possibility.The current study should have important engineering value to reduce the production utilization costs of engine.In this paper,numerical models of target diesel engine were set up based on GT-Power and CONVERGE packages.A one-dimensional simulation was carried out to explore the influence of compression ratio and the parameter of air system on the minimum BSFC range of diesel engine.A combustion system scheme was proposed to meet the requirements of different application scenarios of engine.The results show that the low BSFC zone can be moved to various target conditions by matching turbocharger and combustion chamber appropriately.When the compression ratio was increased to 19.5,combined with turbocharger configurations optimized at low speed,the minimum BSFC range can be moved to low speed condition,with BSFC upmost reduction of 3.1%.When the compression ratio was increased to 18.5,together with turbocharger optimization,the minimum BSFC range can be moved to medium speed condition,with BSFC reduction of 1.6%.Similar approach has been applied at high speed and high load with elevated peak in-cylinder pressure limit,within which a relatively larger turbine was adopted,and the BSFC at high speed and high load can be greatly reduced.Furthermore,a three-dimensional simulation of improving the thermal efficiency of diesel engine by optimizing the combustion chamber structure and injection system parameters were carried out.Results show that the combustion chamber geometry greatly affected the spatial distribution of the fuel-air mixture.By optimizing the combustion chamber,the combustion duration can be reduced,resulting in higher thermal efficiency.Increasing the compression ratio by reducing the piston cup depth and pit radius can reduce the lean zone and shorten combustion duration.More fuel entered the top of the combustion chamber,and thermal efficiency increased first then started to drop with the piston cup diameter（edge）increasing.The distance between the fuel and the wall was shortened,more fuel entered the top of the combustion chamber,and the BSFC decreased first then started to increase with the contracted throat diameter decreasing.With the increase of nozzle cone angle,the position of fuel hitting the wall moved up,and there were more fuel entered the top of combustion chamber.When there were little fuel entering the top of the combustion chamber,a bigger piston cup diameter,smaller contracted throat diameter and bigger nozzle angle can make the distribution of fuel more reasonable,and the thermal efficiency increased.When the piston cup diameter was 91mm,contracted throat diameter was69mm,the nozzle angle was 144°,combined with supercharging system optimization,the thermal efficiency increased by 3.3%.In a conclusion,the present work has studied the potential of improving engine thermal efficiency and making the minimum BSFC range matching different conditions by optimizing the combustion system and combustion chamber structures,and the optimization schemes were put forward.Therefore,the current research has important guiding significance and engineering application value for the development of combustion system of improving the thermal efficiency of diesel engine and making the minimum BSFC range of diesel engine meet the requirements of different application scenarios.