Numerical Simulation Of Knocking Combustion Characteristics In A Premixed Natural Gas Dual-fuel Engine

Premixed natural gas dual-fuel engine will cause detonation combustion when it is under high load or high temperature,and that will not only reduce the engine power output,increase fuel consumption,exhaust emissions deteriorate,but also may cause mechanical damage to the engine.Because of the high temperature and high pressure,knock may cause mechanical damage to the engine and even threats to the safety.So it is of theoretical significance and practical value to study the detonation combustion characteristics of dual fuel engines and the influence of various factors on knock.In order to study the knock combustion characteristics of premixed natural gas dual fuel engine,the CFD simulation of the knock combustion for dual fuel engine was carried out by using Z19 DTH engine of General Company as the prototype.The CONVERGE software was used to simulate the engine,with the mass of natural gas intake,the mass of pilot diesel,the injection timing of ignition diesel,the initial temperature of combustion chamber and the revolution of engine as variable parameters.And the simulation results were reprocessed by the software which is named Ensight.Five monitoring points were selected in the combustion chamber.And then we made the curve of the pressure at the monitoring points from crank angle,analyzed the change of the pressure and the influence of the various parameters of the knock combustion characteristics.The post-processing and analysis results of the simulation show that the greater the natural gas intake,the greater the knocking intensity of the engine occur,the longer the knock lasts,reducing the natural gas intake can inhibit the occurrence of knock.The greater the amount of pilot diesel used,the greater the knock intensity occur,the longer the knock time lasts,reducing the amount of pilot diesel can release the occurrence of knock.The earlier the pilot diesel injected,the greater the knock intensity of the engine occur,the longer the knock lasts,in order to avoid the occurrence of knock,we should avoid injecting the pilot diesel earlier.The higher the initial temperature of the combustion chamber is,the greater the knock intensity is,the longer the knock lasts,depressing the intake air temperature of the engine,the occurrence of the knock could decrease.Knocking intensity increased with the engine revolution increased,and the knock time also increased;reducing the engine revolution appropriately,the engine knock will be weak in some certain extent.