Research On The Emission Characteristics Of Heavy-duty Natural Gas Engine With Stoichiometric Operation Mode

The year 2020 will be the final year for China to complete the building of a moderately prosperous society in all respects.With the decline of subsidies for new energy vehicle and the national implementation of the CHINA VI emission regulation,Natural gas,as a clean energy,has been paid more attention to.In order to meet the emission requirements of the CHINA VI regulation,the traditional Lean-burn Heavyduty natural gas engine needs to be equipped with Selective Catalytic Reduction(SCR)and Ammonia Slip Catalyst(ASC)on the basis of the original Methane Oxidation Catalyst(MOC).Not only is the development difficult,but also the production cost increases obviously.However,the heavy-duty natural gas engine with stoichiometric operation and exhaust gas recirculation system can meet the requirements of pollutant emission level regulations only with three-way catalytic converter.In this study,the key parameters of natural gas engine with stoichiometric operation are calibrated.And the relationship between ignition advance angle,EGR rate etc and emission is explored.The key parameters of CNG engine were calibrated as a natural gas engine test bench is set up.The results show that with the increase of ignition advance angle,the cylinder volume decreases during combustion,which makes the cylinder pressure increase.The internal energy of the fuel is released in a short time.The brake specific gas consumption is reduced,the effective thermal efficiency of the engine is improved,and the economy is improved.At the same time,the nitrogen oxidation is improved the emission of hydrocarbon(mainly methane)increases,which has little impact on CO emission.With the increase of EGR rate,the oxygen content in the intake air of the engine decreases.the brake specific gas consumption increases and the fuel economy becomes worse.The COV of IMEP increases and the combustion stability becomes worse.Meanwhile,the NOx emission greatly reduces,and the hydrocarbon emission slightly increases.Under low and medium load,the CO emission first decreases and then increases with the increase of EGR rate due to the decrease of pump gas loss.Under high load,the influence of EGR rate on CO is not obvious.