جستجوی مقالات مرتبط با کلیدواژه "پاشش سوخت" در نشریات گروه "مکانیک"

In this study, the flow physics of two-dimensional liquid jets discharged into still ambient are experimentally studied. Three injectors with thickness of 0.35 mm and aspect ratios of 30, 60 and 90 were manufactured from stainless steel to produce two-dimensional liquid jets. The experiments were conducted for a wide range of liquid volume flow rate varying from 10 to 120 L/h. High speed photography was used to visualize and capture the instantaneous structure of fluid flow at different flow conditions. Based on the visualizations, the behavior of two-dimensional liquid jets was recognized and for the first time categorized into four regimes. These regimes are dripping, column, triangular and perforation. Moreover, different parameters of the liquid sheet including convergence angle, convergence length, retraction velocity and jet length were measured. It was shown that the sheet convergence length increases with aspect ratio. Also, it was observed that the convergence angle and retraction velocity are independent from aspect ratio and manifest similar behavior in all jets. Empirical relations were proposed to describe convergence angle, convergence length and retraction velocity.

In a liquefied gas turbine combustor, due to the limited length of the premix tube, the evaporation process of fuel droplets is not completely carried out inside the tube and the droplets enter the combustion chamber. The presence of droplets in the combustor causes the reactions occur in the non-premix mode and the emission of NOx increases as a result. To avoid the emission of this pollutants, it’s necessary the droplets are evaporated completely in a limited space. In here, a mechanism is proposed for spraying the droplets. In which, fuel droplets with hollow-cone spray pattern are injected in the opposite direction of the air. In this type of injection, due to the relative velocity of droplets and subsequent enhancement of the droplet break-up and evaporation processes, it is possible to achieve this goal. To verify, various patterns of injection are modeled using an Eulerian-Lagrangian approach. The validity of turbulence, heat and mass transfer models, as well as the influence of gas molecules penetration into droplets has been evaluated. The results showed that using this type of injection, in addition to full evaporation of droplets in a limited space, the fuel vapor in the tube outlet is more evenly distributed.

Homogeneous charge compression ignition (HCCI) is an advantageous combustion concept in terms of efficiency and pollutant emissions. However, its limited operating range suppressed its successful utilization. One applicable method to use this concept is to combine it with other combustion strategies. Direct fuel injection into the combustion chamber is an applicable strategy aiming at this target. To make this concept an applicable one for engines, there should be validated models both for performance prediction and control applications. Single zone models are good and rapid performance predictors and can be used in control applications. Due to the intrinsic characteristics of HCCI being a kinetically controlled combustion, chemical kinetics should be incorporated in modeling it. Therefore, in this study a stand-alone single-zone thermo-kinetic model is developed and validated against experimental measures. Since the main assumption of the developed model is the immediate vaporization of the injected liquid fuel, the validity of the model confirms the idea which states that in the case of early direct fuel injection, in-cylinder combustion can be regarded as HCCI. Furthermore, the results show good agreement with the measurements. The model predicts combustion phasing within 0.5 crank angle degrees while engine power is estimated with an acceptable accuracy of 90 percent.

Homogeneous charge compression ignition (HCCI) is an advantageous combustion concept for internal combustion engines in terms of efficiency and pollutant emissions. However, the limited operating range of this combustion concept suppressed its successful utilization. One applicable method to use this combustion concept in engines is to combine it with other similar combustion strategies, such as diesel and partially premixed combustion (PPC), while each combustion concept come into work during its optimum operating range. In this study, the transition from partially premixed combustion (PPC) to homogeneous charge compression ignition (HCCI) combustion is determined based on investigating the performance and emission characteristics obtained from experimental data. The determination is based on the fact that in the direct-injection (DI) HCCI combustion, the stratification generated from the fuel injection is not an influencing factor. The results reveal that in the case of very early fuel injection timing (when the whole injection is completed before 60 crank angle degrees to top dead center) the HCCI combustion regime is obtained.