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Research on knocking combustion is vitally essential since it impacts engine performance regarding noise and emissions, fuel consumption, power density, and durability. Because of end-gas auto-ignition, current SI engines may experience conventional knock, which restricts increasing the compression ratio to increase thermal efficiency. Therefore, this paper examined the in-cylinder pressure and vibration of a port fuel-injected gasoline engine under knocking and non-knocking conditions. The heat release rate was calculated from pressure traces where the crank angle resolutions were not constant, and the conversion from the time domain to the frequency domain of knock sensor signals by using the Fourier Transform was performed. The result reveals that more heat is released during knocking combustion than during non-knocking combustion. When there is a knock, the temperature variation increases. This would facilitate the use of heat transfer studies to detect knock occurrences. Moreover, knocking is caused by an ignition timing that is too advanced, 22°BTC, compared to the non-knocking spark case, 14°BTC. In the frequency domain, the amplitude of the knocking combustion is higher than the amplitude of the non-knocking combustion, indicating the engine’s noise and vibration. [ABSTRACT FROM AUTHOR]

For the fourth-order partial differential equation proposed by Fushchich for mathematical description of heat and mass transfer processes, the class of uniqueness and the class of correctness of the Cauchy problem have been established. Using the Fourier transform, a solution to the Cauchy problem is found in an explicit analytical form. It is shown that the new equation does not improve the properties of the classical heat conduction equation, but it allows one to describe heat transfer processes taking into account relaxation effects within the framework of the Galileo-invariant mathematical theory of transfer. [ABSTRACT FROM AUTHOR]

In this paper, two special-shaped separated heat pipes with different condensation section structures are designed. The working medium is water, and the filling rate is 65%. The evaporation section is placed in the hot water tank, and the condensation section is equipped with a cold water jacket. The effects of different structures of condensing section on the thermal performance of separated heat pipes are experimentally studied, and the temperature changes of the two separated heat pipes during start-up and stable operation under different heating power are analyzed. The results show that the heat transfer characteristics of the two separated heat pipes are different due to the different structures of the condensation section, and the heat transfer capacity of sample 2 is higher. At the same time, the temperature fluctuation in the condensing section of sample 2 is also quite different from that in the condensing section of sample 1, and the temperature fluctuation in the condensing section of sample 2 is greater. The wall temperature fluctuates periodically in a steady-state, and a fast Fourier transform is used to analyze the temperature fluctuation. [ABSTRACT FROM AUTHOR]

• Semi-analytic methods are used to solve 3D DPL problems. • Compared with FEM, the semi-analytic method has higher computational efficiency. • The phase lag of heat flow and the phase lag of temperature gradient have influence on the temperature response speed and the formation of temperature field. With the development of picosecond laser technology, the dual-phase-lagging (DPL) model is more suitable to describe the heat transfer problem with micro-scale effect and micro-time effect. In this paper, a three-dimensional dual-phase-lagging heat transfer model for picosecond laser processing is established. Then Fourier transform (FT) and Laplace transform (LT) are used to derive the frequency response functions (FRFs) of the problem in the frequency domain, and the inverse Laplace transform (ILT) and discrete-convolution fast Fourier transform (DC-FFT) algorithm are used to solve the temperature field. The calculation accuracy of this method is verified and the effect of phase lag constants on temperature field is studied. The results show that the semi-analytical method has a high accuracy for solving the dual-phase-lagging heat conduction model, and the phase lag of heat flux will affect the heating rate in the heating stage, and the phase lag of temperature gradient will delay the formation of temperature field. The effect of phase lag constants on temperature-time history is investigated and the related phenomena are explained by using the two-step heat transfer theory. This semi-analytical method provides a new approach to solve the problem of three-dimensional dual-phase-lagging heat transfer. [ABSTRACT FROM AUTHOR]