A multistage throttling and expansion method for saving energy and reducing emissions of an engine, the engine comprising:
- a combustion chamber;
- a crankcase;
- a crevice passage with a multistage throttling and expansion function disposed between the combustion chamber and the crankcase;
- wherein, the crevice passage comprises a cylinder bore body with an inner wall, a piston body, a first compression piston ring, a second compression piston ring and an oil ring assembly;
- at least two stages of throttling and expansion are disposed in turn in the crevice passage underneath the combustion chamber, passing the piston body, the first compression piston ring, the second compression piston ring and the oil ring assembly to the crankcase, in each stage of throttling and expansion, the ratio of the radial dimension of the crevice passage at the position of the throttling to the radial dimension of the crevice passage at the position of the adjacent expansion is less than 1.0;
- and
- the multistage throttling and expansion method comprises the following steps:
- a. a first-stage throttling converts pressure energy of the high-pressure blow-by gas formed by part of the unburned high-pressure fuel-air mixture and the burned high-temperature and high-pressure gas inside the combustion chamber into kinetic energy of the high-velocity blow-by gas, and then the high-velocity blow-by gas with the kinetic energy and momentum converted from the pressure energy enters an adjacent first-stage expansion;
- b. the adjacent first-stage expansion expands and dissipates the incoming kinetic energy and momentum of the high-velocity blow-by gas into heat, and the pressure and momentum of the high-velocity blow-by gas are greatly reduced after a large amount of energy has been dissipated;
- c. the blow-by gas with the greatly reduced pressure and momentum enters a second-stage throttling and then experiences the above process of converting the pressure energy of the high-pressure blow-by gas into the kinetic energy and momentum of the high-velocity blow-by gas, then the high-velocity blow-by gas with the kinetic energy and momentum converted from the pressure energy enters an adjacent second-stage expansion, and the process of expanding and dissipating the kinetic energy and momentum of the high-velocity blow-by gas into heat is performed so that the pressure and momentum of the blow-by gas are greatly reduced again;
- and
- d. the above steps are repeated;
- and, after multiple times of the throttling and expansion processes with high dissipations, both the pressure energy and kinetic energy of the high-pressure blow-by gas have been exhausted, and the blow-by gas has no spare momentum to enter the crankcase, so that the purpose of preventing blow-by gas leakage is achieved.