Abstract
In this paper, the visualization experiments of spray, ignition, and combustion of diesel under variable injection pressure (from 90 to 130 MPa) were studied by using a constant volume vessel and impinging combustion plate system. With the development of the down-sizing of diesel engines, the wall impinging combustion without liquid spray collision will be the research focus in the diesel engine combustion process. The flame natural luminosity in the experiment represents the soot formation of diesel combustion. Besides, the detailed information of diesel spray mixing combustion was obtained by using the CFD (Computational Fluid Dynamics) simulation of alternative fuels in CONVERGE™. The specific conclusions are as follows. The high velocity of the spray under the higher injection pressure could reduce the low-mixing area near the impinging wall by entraining more air. Under higher injection pressure in simulation, the gas diffused more extensively, and more heat was released after combustion. Therefore, a large amount of soot formed in the early stage of combustion and then oxidized in high-temperature regions, which agreed with the conclusions in the experiments. Under the influence of the superposition of image pixels of the flame, the change of soot generation with injection pressure is smaller than the actual value, so the visualization experiment can be used as the basis of combustion prediction.
Highlights
Diesel engines have been widely used in various fields because of their advantages of low fuel consumption, high torque, reliability, and durability
The effects of injection pressure on the wall impingement, flame propagation, and soot generation of diesel were studied by the simulation of fuel combustion in the constant volume vessel of the CONVERGETM (Version 2.4.0, Convergent Science, Inc., Madison, WI, USA)
The spray, combustion temperature, and soot generation evaluation of diesel in the constant volume vessel were simulated by using fuel n-Heptane (C7 H16 ), which is often used in heavy duty diesel engine simulation
Summary
Diesel engines have been widely used in various fields because of their advantages of low fuel consumption, high torque, reliability, and durability. The research on the combustion in the constant volume vessel under fixed-injections condition showed that with the increase of injection pressure, the gas spray spreading diameter along the impinging wall plate and fuel-air mixing area near the impinging wall became larger [22]. The effect of fuel injection pressure needs deep study by modern engine design, especially when the wall impinging phenomenon exists, which will further affect the flame diffusion process and the final emission after combustion. Based on the experiment of a single hole injector in the constant volume combustion vessel, this article studied the complete evolution process of diesel fuel from spray to ignition to combustion flame wall under different injection pressure conditions by using CFD simulation. The effects of injection pressure on the wall impingement, flame propagation, and soot generation of diesel were studied by the simulation of fuel combustion in the constant volume vessel of the CONVERGETM (Version 2.4.0, Convergent Science, Inc., Madison, WI, USA)
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