Abstract: The invention belongs to the technical field of metal ceramics, in particular to a metal ceramic and a preparation method thereof. The hard phase is formed by at least four kinds of crystal grains with different compositions and shapes; and in the scanning electron microscope photograph of the metal ceramic, it can be observed the first hard phase comprising black titanium nitrocarbide, a thin ring and a thick ring wherein the core phase is pure black; the second hard phase in the form of a dark gray core-ring structure particles; the third hard phase in the form of a high-brightness white core-gray ring; and the fourth hard phase in the form of a homogenous gray phase and off-white core-gray ring structure particles. In addition, a white binder phase can also be observed, and the binder phase is at least one of cobalt and nickel.

Abstract: A method and a system for controlling an air-fuel ratio for a gas engine are provided. Current outlet pressure of the nozzle is calculated based on current pressure in an intake pipe and a current rotational speed, without detecting the outlet pressure of the nozzle by a sensor. A fluid state of the gas can be determined based on a ratio of the current outlet pressure to the current inlet pressure of the nozzle collected by a sensor, such that a flow rate characteristic corresponding to the fluid state can be selected to calculate power-on duration for the nozzle, so as to set the air-fuel ratio based on the power-on duration. The power-on duration can be calculated based on flow rate characteristics of the gas in respective fluid states, thereby achieving an air-fuel ratio with high accuracy.

Abstract: The present invention relates to a light selective absorbing coating and a production process thereof. The light selective absorbing coating consists of a composite material film deposited by reaction of iron chromium alloy and a non-metal gas with vacuum deposition technology. Said non-metal gas comprises gases of nitrogen and oxygen elements. The present invention also relates to a solar energy heat collecting element or solar energy selective absorbing coating system comprising said light selective absorbing coating and a production process thereof. The present invention further relates to use of said composite material film as a light selective absorbing coating of a solar energy heat collecting element or of a solar energy selective absorbing coating system.