Method and system for controlling combustion of natural gas engine

A method for controlling combustion of a natural gas engine, comprising:

• determining, based on a current operation parameter of a natural gas engine, an operation state of the natural gas engine;
• calculating a total injection quantity of natural gas and pilot diesel required by the natural gas engine in the operation state;
• adopting a direct injection diffusion combustion mode in a case that the operation state is an idle state or a low load state, wherein the direct injection diffusion combustion mode is a mode in which the diesel is injected at a top dead center of compression, and then the natural gas is injected;
• adopting a natural gas homogeneous hybrid active control compression-ignition mode in a case that the operation state is a medium load state, wherein the natural gas homogeneous hybrid active control compression combustion mode is a mode in which the natural gas is injected after an intake valve is closed and the diesel is injected at a position before the top dead center of compression;
• configuring the total injection quantity into three parts including a compression-ignition natural gas injection quantity, a pilot diesel injection quantity, and a diffusion-combustion natural gas injection quantity in a case that the operation state is a high load state;
• injecting natural gas with the compression-ignition natural gas injection quantity into a combustion chamber so as to be mixed with air inside the combustion chamber, in an early stage of a compression stroke of the natural gas engine;
• injecting, at a position near the top dead center of compression or at a large diesel injection advance angle, diesel with the pilot diesel injection quantity into the combustion chamber so as to ignite the pre-injected natural gas;
• and
• injecting, after a predetermined time interval, natural gas with the diffusion-combustion natural gas injection quantity into the combustion chamber,
• wherein the early stage of the compression stroke starts from a time instant when a crankshaft rotates at least 10 degrees after the intake valve is closed,
• wherein in the case that the operation state is the high load state, distribution of the compression-ignition natural gas injection quantity, the pilot diesel injection quantity, and the diffusion-combustion natural gas injection quantity is optimized according to a following rule during the combustion of the natural gas engine:
• decreasing the compression-ignition natural gas injection quantity and decreasing the pilot diesel injection quantity, and increasing the diffusion-combustion natural gas injection quantity, with increasing of load of the natural gas engine.