Disclosed is a homogeneous charge compression ignition and diffusion compression ignition combined ignition control method for low-octane gasoline, using a diffusion compression ignition control mode as a forced ignition measure, to ignite a premixed homogeneous lean oil and gas mixture, and meanwhile to achieve homogeneous charge compression ignition of the oil and gas mixture. During an intake stroke, a fuel is partially injected into the cylinder or an intake manifold, to form a low-concentrated, homogeneous, premixed oil and gas mixture. Before the piston reaches a top dead center during the compression stroke, the remaining part of fuel is injected into the cylinder, diffuses in the air, and spontaneously ignites, thus achieving diffusion compression ignition. A flame is generated in the diffusion compression ignition, and ignites the premixed oil and gas mixture in the cylinder, to achieve ignition and combustion of the homogeneous lean fuel. As the temperature and the pressure rise in the cylinder, multi-point spontaneous ignition occurs within the homogeneous lean oil and gas mixture, thus achieving homogeneous charge compression ignition. Such a combined ignition control method achieves a high compression ratio, lean combustion, stratified combustion, and fast combustion, without causing any knocks. Also disclosed are an insulation method of an internal combustion engine exhaust system, and a product thereof.