Method and system for achieving ultralow emission of natural gas engine

Abstract

The invention discloses a method for achieving ultralow emission of a natural gas engine, and relates to the technical field of engine aftertreatment. The technical problem that ultralow emission of an existing aftertreatment mode is difficultly achieved is solved. The method comprises the following steps that an emission control mode of a TWC catalyst, an SCR catalyst and an ASC catalyst is adopted; the air-fuel ratio in a cylinder is controlled by taking the conversion efficiency of HC and CO in the TWC catalyst as a target, so that the emission of HC and CO treated by the TWC catalyst reaches regulation limit values; and the oxygen concentration of a tail gas treated by the TWC catalyst is increased, so that the emission of NOx treated by the SCR catalyst reaches a regulation limit value; and the invention further discloses a system for achieving the ultralow emission of the natural gas engine. According to the method and system for achieving the ultralow emission of the natural gas engine, the air-fuel ratio in the cylinder is controlled by taking the conversion efficiency of HC and CO in the TWC catalyst as the target, so that the TWC catalyst performs efficient conversion on HC and CO, and then the oxygen concentration of the tail gas treated by the TWC catalyst is increased, NOx is efficiently converted through the SCR catalyst, ultralow emission is achieved, and the regulation limit value is met.

Description

technical field [0001] The invention relates to the technical field of engine aftertreatment, and more specifically, it relates to a method and system for realizing ultra-low emission of natural gas engines. Background technique [0002] In order to meet the requirements of National VI emission regulations (GB17691-2018) for heavy-duty commercial vehicles and engines (emission limit requirements NOx control≤0.46g / kWh, CH4≤0.5g / kWh, NMHC≤0.16g / kWh, NH3≤10ppm), currently Natural gas engines generally adopt the combustion technology route of equivalent + EGR + TWC + ASC. First, the engine controls the original exhaust NOx, NMHC, CH4 and CO to a certain level through internal control technologies such as engine body design, combustion optimization and external cooling EGR strategy, and then combined with external purification (TWC+ASC) Emissions are controlled within the limits of China 6 emission regulations. [0003] The current technical solution three-way catalytic convert...

AI Technical Summary

Problems solved by technology

[0003] The current technical solution three-way catalytic converter (TWC) has higher requirements on air-fuel ratio control accuracy (such as figure 1 Shown): There is a certain difference in the most efficient conversion window of NOx, CO and HC, and the conversion efficiency of NOx, CO and HC cannot be maximized at the same time if the exhaust gas concentration is too lean or too rich. The current scheme is limited by the air-fuel ratio window It is more difficult to achieve ultra-low emission control, resulting in a small margin for the overall engine emission compared with the National VI emission limit, and there are great technical challenges in meeting the emission regulations of the next stage, especially the durability of the catalytic converter is difficult to be guaranteed

Images