Simulations of engine knock flow field and wave-induced fatigue of a downsized gasoline engine

Abstract

A mathematical correlation is developed, based on the thermodynamic model of a downsized gasoline engine, to establish the numerical relationship among the thermodynamic parameters of the combustion chamber. In the developed numerical model, the in-cylinder pressure curves of various operation conditions are simulated by varying the air–fuel ratio in the cylinder, and the associated knock characteristics are recorded. The accuracy of the numerical simulation results is verified against the knock excitation experiment. Then, based on the Rover K16 gasoline engine, a simulation model is developed to simulate the engine knock in the combustion chamber and observe the force acting on the top surface of the piston. The results show that the forces, which act on the piston top surface, are varying at various locations at the same time, and the largest forces occur at the edge of the piston and followed by the piston centre. Then, by comparing the thermo-mechanical coupling strength of the piston under different operating conditions, the results show that the occurrence of the knocking does not exceed the piston’s strength limit. However, the stress and deformation value of the piston is increased significantly, and the failure point of the piston position is changed. Finally, based on the calibrated strength results, the piston durability is predicted for various engine knock conditions. The results show that there is an initial damage of piston in the process of detonation at the surface of the piston pin hole and the joint of the piston cavity. The gasoline engine finally has a predicted mileage of 2,53,440 km continuously, which meet the prescribed mileage of 2,20,000 km.

Numerical simulation research on the influence of the parameters of water injection on the GDI engine

“…[7][8][9] Knock restricts the advancement of ignition timing, the increase in CR, and the increase in boost pressure, greatly limiting the optimization of gasoline engine power, economy, and emission characteristics. [10][11][12][13] Since the appearance of gasoline engines, domestic and foreign scholars' research on knock phenomena has continued to progress with the innovation of research methods and the improvement of gasoline engine technology. Kawahara et al 14 used high-speed photography to find that the spontaneous combustion of the terminal mixture is caused by flame propagation and shock waves.…”

Evaluation of ASTM D6424 standard for knock analysis using unleaded fuel candidates on a six cylinder aircraft engine

“…51,52 In this method, the end-gas auto-ignition is modeled with the solution of a detailed chemical kinetic mechanism. 53,54 The drawback of this approach are: (1) it is computationally expensive, (2) accurate reaction mechanisms are not available for all fuels in the market, and (3) the development of reaction mechanisms for commercial fuels is not easy. 55,56 This method becomes more computationally extensive when it is integrated with 3D computational fluid dynamics models, 57 where solving thousands of reactions and transporting the hundreds of related species between zones becomes impractical for realtime implementation.…”

Experimental assessment of ignition characteristics of lubricating oil sprays related to low-speed pre-ignition (LSPI)

“…These pre-ignitions may in turn lead either to super-knock, heavy-knock, slight-knock or non-knock, most of them leading to a direct damage to the engine. 4–6…”

“…These pre-ignitions may in turn lead either to super-knock, heavy-knock, slightknock or non-knock, most of them leading to a direct damage to the engine. [4][5][6] As a consequence, researchers have focused on describing mechanisms causing LSPI, [7][8][9][10][11] in order to reduce its occurrences through design. The most likely causes for this phenomenon include lubricating oil droplets or solid deposits released in the combustion chamber, either being a source for pre-ignition or acting as a hot spot locally increasing the air-fuel mixture temperature.…”