Research On Variable Compression Ratio Technology Of Natural Gas/Diesel Dual Fuel Engine

In recent years,with the development of alternative fuels for internal combustion engines and variable compression ratio technology,the research of natural Gas/diesel dual fuel engines has gradually attracted human attention.There are two working modes for natural gas/ diesel dual-fuel engines,namely pure diesel compression ignition mode and micro or small amount of diesel ignition natural gas mode.Natural gas and diesel have different compression ratios,so a fixed compression ratio cannot perfectly play the performance of a dual-fuel engine.Variable compression ratio technology has an important impact on the combustion and emissions of dual-fuel engines in different operating modes,and needs further study.This paper builds two GT-Power one-dimensional simulation model,namely 16V265 H locomotive diesel engine and a direct-injection diesel-ignition engine with dual fuel(diesel and natural gas)based on the modification of 16V265 H locomotive diesel engine.The effect of compression ratios of 14,16,18,and 20 on the cold start process of diesel engines was developed,and an experimental study on combustion and emission characteristics of that engine under compression ratios of 14,16,18,20 and diesel-ignition quality proportion of1%,2%,3%,4%,5% was investigated.The existing variable compression ratio mechanism is compared and summarized(research),and three mechanism schemes that can achieve variable compression ratio are proposed,which are the large-head eccentric ring type,the double-wedge dovetail groove type of the connecting rod,the Multi-hinge type of the connecting rod,using CAD/CAE/CAM software CREO to model each variable compression ratio mechanism components,complete the assembly and design,especially doing theoretical analysis for the variable compression ratio mechanism of the large rod eccentric ring of the connecting rod,some discussion on the influencing factors such as compression ratio range and eccentricity.Research indicates:(1)Under normal pressure and low temperature environment,increasing the compression ratio can effectively reduce the fuel consumption,HC and CO emissions during the cold start of the diesel engine,but it will cause a slight increase in NOx emissions.(2)During the cold start of the diesel engine,when the ambient temperature is-30 ℃,the use of a higher compression ratio can increase the diesel engine’s combustion efficiency in cylinder and the Net Indicated Mean Effective Pressure,effectively increase the fuel burned in the cylinder The ratio,but will slightly increase the Friction Mean Effective Pressure of each cylinder.(3)Increasing the compression ratio is beneficial to the combustion of the engine and the reduction of HC and CO emissions,but it will worsen the NOx emissions;increasing the amount of ignited diesel will cause the NOx and CO emissions to increase,but the HCemissions will decrease.(4)Theoretically analyze the diesel engine with variable compression ratio of the big-end of connecting rod which the eccentric ring installs at,and find that when the cylinder bore B is equal to the original diesel engine,the S/B decreases as the range of the compression ratio decreases;the performance of the diesel engine related to the piston movement process and Compared with the original diesel engine,there is almost no difference;the S/B value decreases as the maximum eccentricity of the eccentric ring decreases.