Search Results (3)

When an engine burns methanol, which has a high latent heat of vaporization, if the injection parameters are not set reasonably, the engine will exhibit high combustion instability at low speeds. Therefore, in this study, two pre-injections are set up in an electric-plug-assisted compression ignition methanol engine to investigate the effects of the pre-injection ratio and pre-injection timing on combustion stability and to provide a theoretical basis for the calibration of the injection of the engine at low speeds. The test results show that, at low speeds, the pre-injection ratio and pre-injection timing have a significant effect on combustion stability. They also show that, at low speeds and high loads, by regulating the pre-injection strategy, the bimodal phenomenon observed in the cylinder pressure of the compression ignition methanol engine can be weakened, and the cylinder pressure fluctuation caused by afterburning can be improved. Specifically, the maximum cyclic fluctuation of cylinder pressure was improved by 32.8%, the maximum cyclic fluctuation of the engine’s indicated average effective pressure was improved by 8.12%, and the maximum cyclic fluctuation of engine peak pressure was improved by 16.96%. The start point and combustion center of gravity data were centralized. The concentration of the start point and combustion center of gravity data improved by 6 °CA and 5.87 °CA, respectively. Full article

The buckling failure of the afterburner cylinder is a serious safety concern for aero-engines. To tackle this issue, the buckling simulation analysis of the afterburner cylinder was carried out by using finite element method (FEM) software to obtain the buckling mode and critical buckling loads. It was found that the afterburner cylinder was susceptible to buckling when subjected to differential pressure or the compressive force of the rear flange. Buckling would occur when the differential pressure reached 0.4 times the atmospheric pressure or when the axial compressive force on the rear flange reached 222.8 kN. Buckling was also found at the front of the cylinder under the auxiliary mount load. Additionally, under various loads on the rear flange, buckling occurred in the rear section, with the buckling mode being closely related to the load characteristics. Based on the simulation results and structural design requirements, two structural improvements were proposed, including the wall-thickening scheme and the grid reinforcement scheme. FEM simulation analysis results showed that both schemes would improve the rigidity and stability of the afterburner cylinder. For the 0.3 mm increase in the wall thickness scheme, the critical buckling load increased by 17.86% to 66.4%; for the grid reinforcement scheme, the critical buckling load increased by 169% to 619%. Therefore, the grid reinforcement scheme had a stronger anti-buckling ability and was deemed the optimal solution. The findings of this paper could provide technical support for the structural design of large-sized and thin-walled components of aero-engines. Full article

Research was conducted on fuels with additives that selectively affect the rate of kinetic (dQ_k/dα) and diffusion (dQ_d/dα) combustion in the diesel engine cylinder. In addition to the base fuel (DFB), DFKA fuel with an additive reducing dQ_k/dα, DFDA fuel with an additive increasing dQ_d/dα, and DFS fuel with both additives were tested. The main purpose of such dQ/dα course control in the engine cylinder was to simultaneously reduce the emissions of nitrogen oxides (NO_x) and particulate matter (PM), and to increase the efficiency of the combustion process. Similar to the course of the dQ/dα, the course of the combustion temperature (T_c(α)) affects the NO_x produced and the number of afterburned solid particles; the influence of the fuel additives on the functional curves was analysed. In addition to analysis of the temperature T_c(α) calculated from the indicator diagrams, T_c(α) analysis was conducted using the two-colour method, which allows the analysis of the isotherm distributions locally and temporarily. The two-colour method required prior endoscopic visualisation of the fast-changing processes inside the engine cylinder. Parameters defined by pressure, temperature, heat release rate, and visualisation and thermovision in the engine cylinder (as a function of the crank angle) allowed for an in-depth cause and effect analysis. It was determined why combustion of DFS fuel with both additives produced a synergy resulting in the simultaneous reduction in NO_x and PM emissions in the exhaust gas and an increase in combustion efficiency. This publication relates to the field of Mechanical Engineering. Full article