1-D Modelling Comparative Study to Evaluate Performance and Emissions of a Spark Ignition Engine Fuelled with Gasoline and LNG

In this study, a spark-ignition engine fuelled with gasoline and LNG was modelled in 1-D at wide open throttle by using Ricardo-Wave software. Different engine speeds ranging from 1500rpm to 4500rpm with an increment of 500rpm were studied to evaluate the effects of gasoline and LNG on engine performance and exhaust emissions. It is determined that LNG decreases engine performance and emissions as well, at especially high speeds

Brush seal temperature distribution analysis

Brush seals are designed to survive transient rotor rubs. Inherent brush seal flexibility reduces frictional heat generation. However, high surface speeds combined with thin rotor sections may result in local hot spots. Considering large surface area and accelerated oxidation rates, frictional heat at bristle tips is another major concern especially in challenging high-temperature applications. This study investigates temperature distribution in a brush seal as a function of frictional heat generation at bristle tips. The two-dimensional axisymmetric computational fluid dynamics (CFD) analysis includes the permeable bristle pack as a porous medium allowing fluid flow throughout the bristle matrix. In addition to effective flow resistance coefficients, isotropic effective thermal conductivity as a function of temperature is defined for the bristle pack. Employing a fin approach for a single bristle, a theoretical analysis has been developed after outlining the brush seal heat transfer mechanism. Theoretical and CFD analysis results are compared. To ensure coverage for various seal designs and operating conditions, several frictional heat input cases corresponding to different seal stiffness values have been studied. Frictional heat generation is outlined to introduce a practical heat flux input into the analysis model. Effect of seal stiffness on nominal bristle tip temperature has been evaluated. Analyses show a steep temperature rise close to bristle tips that diminishes further away. Heat flux conducted through the bristles dissipates into the flow by a strong convection at the fence-height region

1-D Modelling Comparative Study to Evaluate Performance and Emissions of a Spark Ignition Engine Fuelled with Gasoline and LNG

In this study, a spark-ignition engine fuelled with gasoline and LNG was modelled in 1-D at wide open throttle by using Ricardo-Wave software. Different engine speeds ranging from 1500rpm to 4500rpm with an increment of 500rpm were studied to evaluate the effects of gasoline and LNG on engine performance and exhaust emissions. It is determined that LNG decreases engine performance and emissions as well, at especially high speeds

Flame Radius Effects on a Sequential Ignition Engine Characteristics

The effects of the flame radius and flame propagation have been investigated at a sequential ignition engine with numerically. A single cylinder of the sequential ignition engine was modeled in STAR-CD/es-ice software for the gasoline usage taking into account all components related to the combustion chamber. The effect of flame on engine characteristics is the function of flame radius and flame thickness. In the numerical analysis, compression ratio is 10.8:1, air-fuel ratio is 1.2, ignition advance at 30-25 CAD, engine speed is 3000 rpm and the flame thickness is 0.0001 m were kept constant. The analysis, k-? RNG turbulence model, Angelberger wall interaction and G-equation combustion model were used and optimum flame radius value was determined. Three different analysis were carried out to determine the effect of the flame radius and the flame radius was changed to 0.0005 m, 0.0010 m and 0.0020 m, respectively. As a result of the study, images of flame formation and propagation were obtained for the time period up to the top dead center at the time of sequential ignition. The effects of flame radius on CO2 formation and NOx formation were evaluated. The net work area was obtained from the highest engine power and pressure-volume graph when the flame radius was 0.0010 m for the specified operating conditions

Düz güneş enerjisi toplayıcılarında yutucu plakada oluşan ısı transferinin parametrik analizi

Güneş enerjisi uygulamalarındaki artışa paralel olarak, güneş enerjisinin faydalı ısı enerjisine dönüştürüldüğü düz güneş enerjisi toplayıcılarından ısı transferinin verimli olarak gerçekleştirilmesinin önemi giderek artmaktadır. Bu çalışmada, düz toplayıcılarda güneş ışınım enerjisinin ısı taşıyıcı akışkana aktarıldığı yutucu plakanın ısıl analizi yapıldı. Geliştirilen analitik formülasyonda yutucu plaka tek boyutlu bir kanat olarak incelendi. Yutucu plaka üst yüzeyinde güneşten gelen ışınım akısı ve çevreye olan ısı kaybı tanımlanırken, alt yüzey ideal olarak yalıtılmış kabul edildi. Kanat ısı transfer denklemleri analitik olarak çözülerek, yutucu plaka üzerindeki sıcaklık dağılımını ve plakadan akışkana olan ısı geçişini veren bağıntılar elde edildi. Sıcaklık dağılımı ve ısı geçişi üzerindeki etkili parametreler temel olarak; geometrik boyutlar, akışkan sıcaklığı, yutucu plaka malzemesinin ısı iletim katsayısı, ışınım ısı akısı, çevre sıcaklığı ve çevreye olan toplam ısı kayıp katsayısıdır. Bu parametrelerin etkileri metodik olarak incelendi, inceleme sonucunda; yüksek ısı iletim katsayısına sahip yutucu plakadaki sıcaklık seviyesinin ve akışkana geçen ısı akısının arttığı tespit edildi. Toplayıcıda elde edilen faydalı ısı enerjisinin kullanılabilirliğini belirleyen, pratik çalışma şartlarında ulaşılabilecek maksimum akışkan sıcaklığı, güneş ışınım şiddetinin fonksiyonu olarak elde edildi. Elde edilen tüm sonuçlara bağlı olarak, toplayıcı verimi üzerindeki parametrelerin etkileri tespit edildi.Importance of efficient heat transfer in straight solar energy collectors, where solar energy is converted into useable heat energy, has been ever increasing with demanding solar energy applications. In this study, thermal analysis of the absorber plate, where solar radiation energy is transferred to tie fluid carrying heat in the straight solar collector, have been performed. In the analytical formulation developed, the absorber plate has been treated as a one-dimensional fin. Radiation flux coming from the sun and heat loss to the environment are defined at the upper face of the absorber plate while the lower face is assumed to be ideally insulated. By solving the fin heat transfer equations analytically, relations giving temperature distribution on the absorber plate and heat transfer from the absorber plate to the working fluid have been derived. Effective parameters on temperature distribution and heat transfer are mainly: geometrical dimensions, fluid temperature, heat conduction coefficient of the absorber plate, radiation heat flux, environmental temperature, and total heat loss coefficient to the environment. Effects of these parameters are methodically investigated. One of the investigation results is that the absorber plate with high heat conduction coefficient yields increased temperature level and heat flux transferred to the working fluid. The achievable maximum fluid temperature at the practical working conditions, which quantifies the availability of useable heat energy obtained in the collector, has been determined as a function of incident solar radiation. Effects of the parameters dominating the collector efficiency have been investigated by evaluating all the analysis results

Effects of geometry on brush seal pressure and flow fields - Part II: Backing plate configurations

Brush seal dynamic behavior is strongly related to pressure and flow fields. Developments in brush seal design have led to geometric modifications to control flow field and consequent brush seal issues including blow-down, hang-up, and pressure stiffening. Some of the geometric enhancements have been found to have common use as backing plate modifications. Over the two decades of brush seal evolution, many backing plate configurations have been suggested in numerous patent disclosures. Even so, literature on the effects of geometric modifications on pressure and flow fields remains limited. This study numerically investigates brush seal pressure and flow fields for such common conceptual backing plate configurations as single and multiple grooves, with and without by-pass passages. The CFD analysis presented employs a bulk porous medium approach for the bristle pack. The effectiveness of various backing plate configurations outlining important flow features is discussed. Results indicate that backing plate configurations have a decisive role in shaping seal pressure fields. In general, it has been found that all cases having bypass configuration leak more. Moreover, the major portion of the seal leakage through fence height is fed from the backing plate cavity. The single backing plate groove forms a constant pressure behind the bristle pack. In contrast, multiple grooves form multiple constant pressure regions

Investigation of flow behavior and porous medium resistance coefficients for metallic-cloth fibers

The flow through porous metallic-cloth fibers influences the cloth seal leakage performance. Measuring the actual seal leakage proves difficult with challenging turbine operating conditions. A non-Darcian porous medium Computational Fluid Dynamics (CFD) model was employed for the flow within porous metallic-cloth fibers. CFD analyses need leakage data depending on the pressure load to calibrate flow resistance coefficients. A test rig was built to measure leakage with respect to the pressure load and weave orientation in four directions. The Sutherland-ideal gas approach was utilized to determine the flow resistance coefficients for Dutch twill metallic-cloth fibers as a function of pressure load. The results show that metallic-cloth fiber leakage is a linear function of pressure load. The best–worst order for leakage performance was the warp, diagonal, shute, and cross directions. For the best sealing performance, the flow direction in metallic-cloth fibers would be the warp direction. The flow resistance coefficients depend on the evaluation of the pressure level, which changes over the weave flow thickness. This is represented with the pressure constant (Cdown). The best match between the test and CFD leakages was obtained for the weave directions of warp (0.9), shute (0.9), diagonal (0.7), and cross (0.0). Calibrating the resistance coefficients with respect to the pressure and temperature enables performing CFD analyses in turbine conditions

Effect of shear heat on hydrodynamic lift of brush seals in oil sealing

Due to their superior performance and stable leakage characteristics, brush seals are one of the dynamic seals used in oil and oil mist applications in aero-engines and turbines. The viscous medium between the high speed rotor surface and bearing surfaces formed by brush seal bristles generates a hydrodynamic lifting force that determines seal clearance and leakage rate in oil sealing applications. The analytical solution to bristle lifting force can be found by using Reynolds formulation. Following a short bearing approximation, a closed form solution of the lifting force has been previously presented. However, the solution suggests a strong dependence of hydrodynamic lift force and seal clearance on oil temperature and viscosity. This work presents an analytical solution to oil temperature rise due to shear heating. The hydrodynamic lift force relation has been expanded to include oil temperature variability due to rotor speed and lift clearance. Results are also compared with the experimental data obtained from the dynamic oil seal test rig