Elia Distaso

Laminar flame speed correlations for methane, ethane, propane and their mixtures, and natural gas and gasoline for spark-ignition engine simulations

The laminar flame speed plays an important role in spark-ignition engines, as well as in many other combustion applications, such as in designing burners and predicting explosions. For this reason, it has been object of extensive research. Analytical correlations that allow it to be calculated have been developed and are used in engine simulations. They are usually preferred to detailed chemical kinetic models for saving computational time. Therefore, an accurate as possible formulation for such expressions is needed for successful simulations. However, many previous empirical correlations have been based on a limited set of experimental measurements, which have been often carried out over a limited range of operating conditions. Thus, it can result in low accuracy and usability. In this study, measurements of laminar flame speeds obtained by several workers are collected, compared and critically analyzed with the aim to develop more accurate empirical correlations for laminar flame speeds as a function of equivalence ratio and unburned mixture temperature and pressure over a wide range of operating conditions, namely ϕ = 0 . 6 - 1 . 7 , p u = 1 - 50 atm and T u = 298 - 800 K . The purpose is to provide simple and workable expressions for modeling the laminar flame speed of practical fuels used in spark-ignition engines. Pure compounds, such as methane and propane and binary mixtures of methane/ethane and methane/propane, as well as more complex fuels including natural gas and gasoline, are considered. A comparison with available empirical correlations in the literature is also provided.

Effects of lubricant oil on particulate emissions from port-fuel and direct-injection spark-ignition engines:

This work presents experimental tests where lubricant oil was added to the engine in order to highlight its contribution to particle emissions from both gasoline and compressed natural gas spark-ignition engines. Three different ways of feeding the extra lubricant oil and two fuel-injection modes—port fuel injection and direct injection—were investigated to mimic the different ways by which lubricant may reach the combustion chamber. In particular, in the tests using compressed natural gas, the oil was injected either into the intake manifold or directly into the combustion chamber, whereas in both the port-fuel-injection and direct-injection tests using gasoline, the oil was premixed with the fuel. The experiments were performed on a single-cylinder, optically accessible spark-ignition engine, running at 2000 r/min under stoichiometric and full-load conditions, and requiring no lubrication. Particle size distribution functions were measured in the range from 5.6 to 560 nm by means of an engine exhaust particle sizer. Particle samples were taken directly from the exhaust flow, just downstream of the valves. Opacity was measured by an AVL 439 opacimeter, and gaseous emissions were measured by means of an exhaust gas analyzer in order to globally monitor the combustion process. Detailed analysis of the recorded total particulate number and particle size distributions allowed to determine the size ranges and relative amounts associated with the lubricant-oil-derived particles. Oil addition produced a significant increase in the particles emitted in the lowest range size, independent of the way lubricant was added. Only when lubricant was injected directly into the combustion chamber (either blended with the fuel or by itself), an increase in the number of particles with sizes larger than 50 nm was recorded.

A Review of Direct Drive Proportional Electrohydraulic Spool Valves: Industrial State-of-the-Art and Research Advancements

This paper reviews the state of the art of directly driven proportional directional hydraulic spool valves, which are widely used hydraulic components in the industrial and transportation sectors. Firstly, the construction and performance of commercially available units are discussed, together with simple models of the main characteristics. The review of published research focusses on two key areas: investigations that analyse and optimize valves from a fluid dynamic point of view, and then studies on spool position control systems. Mathematical modelling is a very active area of research, including Computational Fluid Dynamics (CFD) for spool geometry optimisation, and dynamic spool actuation and motion modelling to inform controller design. Drawbacks and advantages of new designs and concepts are described in the paper.

Accurate Radial Vaneless Diffuser One-Dimensional Model

A simplified one-dimensional model for the performance estimation of vaneless radial diffusers is presented. The starting point of such a model is that angular momentum losses occurring in vaneless diffusers are usually neglected in the most common turbomachinery textbooks: It is assumed that the angular momentum is conserved inside a vaneless diffuser, although a nonisentropic pressure transformation is considered at the same time. This means that fluid-dynamic losses are taken into account only for what concerns pressure recovery, whereas the evaluation of the outlet tangential velocity incoherently follows an ideal behavior. Several attempts were presented in the past in order to consider the loss of angular momentum, mainly solving a full set of differential equations based on the various developments of the initial work by Stanitz (1952, “OneDimensional Compressible Flow in Vaneless Diffusers of Radial or Mixed-Flow Centrifugal Compressors, Including Effects of Friction, Heat Transfer and Area Change,” Report No. NACA TN 2610). However, such formulations are significantly more complex and are based on two empirical or calibration coefficients (skin friction coefficient and dissipation or turbulent mixing loss coefficient) which need to be properly assessed. In the present paper, a 1D model for diffuser losses computation is derived considering a single loss coefficient, and without the need of solving a set of differential equations. The model has been validated against massive industrial experimental campaigns, in which several diffuser geometries and operating conditions have been considered. The obtained results confirm the reliability of the proposed approach, able to predict the diffuser performance with negligible drop of accuracy in comparison with more sophisticated techniques. Both preliminary industrial designs and experimental evaluations of the diffusers may benefit from the proposed model. [DOI: 10.1115/1.4029482]

Accurate Radial Vaneless Diffuser 1D Model

A simplified one dimensional model for the performance estimation of vaneless radial diffusers is presented. The starting point of such a model is that angular momentum losses occurring in vaneless diffusers are usually neglected in the most common turbomachinery textbooks: it is assumed that the angular momentum is conserved inside a vaneless diffuser, although a non-isentropic pressure transformation is considered at the same time. This means that fluid-dynamic losses are taken into account only for what concerns pressure recovery, whereas the evaluation of the outlet tangential velocity incoherently follows an ideal behavior.Several attempts were presented in the past in order to consider the loss of angular momentum, mainly solving a full set of differential equations based on the various developments of the initial work by Stanitz. However, such formulations are significantly more complex and are based on two empirical or calibration coefficients (skin friction coefficient and dissipation or turbulent mixing loss coefficient) which need to be properly assessed.In the present paper, a 1D model for diffuser losses computation is derived considering a single loss coefficient and without the need of solving a set of differential equations. The model has been validated against massive industrial experimental campaigns, in which several diffuser geometries and operating conditions have been considered. The obtained results confirm the reliability of the proposed approach, able to predict the diffuser performance with negligible drop of accuracy in comparison with more sophisticated techniques. Both preliminary industrial designs and experimental evaluations of the diffusers may benefit from the proposed model.Copyright