Analysis of the Cooling Performance of a Cylindrical Hole Designed for the Suction Side of the LS89 Vane under Transitional Conditions

Thermal performance of film cooling in a transonic high-pressure vane is studied by means of two different turbulence modelling strategies: the γ-ReΘ transition model and the fully turbulent k-ω SST model. Selected test case is the LS89 vane, appropriately modified to include a cylindrical film cooling device. The MUR237 transonic configuration is selected as representative of highly loaded vanes without shocks, with transonic Mach number over the suction side. The specifically designed cooling system is based on the non-dimensional geometrical and operating conditions of the high-pressure transonic MT1 cooled vane. Transition model constants are initially tuned to match the available experimental data for the original (uncooled) configuration. Eventually, results obtained with both models are compared with each other for several jet conditions, showing non-negligible influence of turbulence modelling on flow distribution and mixing between coolant and main-flow

Exploring the surface of the Moon and Mars: What kind of ground vehicles are required?

On the surface of the Moon and Mars, the astronauts must have at their disposal means for exploring a suitable area of the planet. A ground vehicle was tested for the first time outside Earth during the Apollo program, but the longer stay and the wider extent of the exploration will make similar vehicles designed for Mars larger, faster and more complex. In later missions, transportation on the planet will possibly require aerial vehicles and finally the realization of a whole transportation infrastructure. Furthermore, robotic rovers will be required to assist the astronauts in their exploration duties

Performance and Emissions of a Turbocharged Spark Ignition Engine Fuelled with CNG and CNG/Hydrogen Blends

An experimental investigation was performed on a turbocharged spark-ignition 4-cylinder production engine fuelled with natural gas and with two blends of natural gas and hydrogen (15% and 25% in volume of H2). The engine was purposely designed to give optimal performance when running on CNG. The first part of the experimental campaign was carried out at MBT timing under stoichiometric conditions: load sweeps at constant engine speed and speed sweeps at constant load were performed. Afterwards, spark advance sweeps and relative air/fuel ratio sweeps were acquired at constant engine speed and load. The three fuels were compared in terms of performance (fuel conversion efficiency, brake specific fuel consumption, brake specific energy consumption and indicated mean effective pressure) and brake specific emissions (THC, NOx, CO). The pressure trace was acquired in the four cylinders to perform a cycle-by-cycle and cylinder-by-cylinder analysis of the peak firing pressure and the indicated mean effective pressure as well as of the main combustion parameters. As far as MBT timing stoichiometric operations are concerned, the addition of hydrogen determines a reduction in the spark advance. The higher energy content of hydrogen with respect to methane determines lower brake specific fuel consumption values. Conversely,, similar values were found for the brake specific energy consumption, which is intimately related to the fuel conversion efficiency. The addition of H2 produces an appreciable reduction in THC which overcomes the mere reduction of HC in the blend. A small improvement can also be found for CO emissions whereas NOx turned out to be slightly affected by the H2 content in the fuel. The air/fuel ratio in the relative air/fuel ratio sweeps was varied in the rich and lean field up to the lean operation limit. The addition of hydrogen determined a marked reduction of the coefficient of variations in the lean field, thus allowing an extension of the lean operation limit with respect to CNG operation. The addition of hydrogen still determined a considerable THC reduction which turned out to be even more evident as one moved to the lean field. Regardless of the considered fuel, a significant cylinder-to-cylinder variation emerged, mainly to be attributed to the cylinder spatial distribution, which in turn affects the effectiveness of the cooling system and the uniform air/fuel mixture distribution

A model for the estimation of the residual driving range of battery electric vehicles including battery ageing, thermal effects and auxiliaries

Sustainable mobility has recently become a priority of research for on-road vehicles. Shifting towards vehicle electrification is one of the most promising solutions concerning the reduction in pollutant emissions and greenhouse gases, especially for urban areas. Nevertheless, battery electric vehicles might carry substantial limitations compared with other technologies. Specifically, the electric range could be highly affected by the ageing process, non-optimal thermal management of the battery and cabin conditioning. In this paper, a model for the estimation of the residual range of electric vehicles is proposed accounting for the influence of battery state of health, battery pack temperature, power consumption of the main vehicle auxiliaries, and battery pre-heating on the residual driving range. The results of the model application to an L7 battery electric vehicle highlighted that the electric range can be highly affected by several factors related to real-world driving conditions and can consistently differ from nominal values

Combustion chamber design for a high-performance natural gas engine: CFD modeling and experimental investigation

The present paper is focused on the development of a high-performance, monofuel, spark ignition engine running on natural gas, featuring a high volumetric compression ratio and a variable valve actuation system. More specifically, the cylinder head geometry effect has been analyzed and the compression ratio has been optimized by means of steady-state and transient simulation activity, as well as of an extensive experimental campaign. The compression ratio effect was mainly investigated by means of experimental tests but a few 3D simulations were also run in order to quantify its impact on the in-cylinder tumble and turbulence. The main novelty of the paper are, first, the adoption of very high engine compression ratio values, second, the combined optimization of the cylinder head design and compression ratio. The main results can be summarized as follows. The engine configuration with mask showed a decrease in the average discharge coefficient by 20–30% and an increase in the tumble ratio by around 200% at partial load. Moreover, the simulation of the engine cycle indicated that the presence of the piston modifies the tumble structure with respect to the steady-state simulation case. An increase in the tumble number and turbulence intensity by around 90% and 10%, respectively, are obtained for the case with mask at 2000 rpm and 4 bar. With reference to the combustion duration, on an average, the presence of the masking surface led to a reduction of the combustion duration (from 1% to 50% of mass fraction burned) between 2 and 6 degrees. As far as the engine compression ratio is concerned, the value of 13 was finally selected as the best compromise between combustion variability, engine performance at full load and fuel consumption at partial load

IDENTIFICATION OF FLUCTUATION MODES FOR A CYLINDRICAL FILM COOLING HOLE USING THE SPECTRAL PROPER ORTHOGONAL DECOMPOSITION METHOD

Film cooling is the main technology adopted to guarantee safe working conditions of vanes and blades in high-pressure turbine stages. Recent experimental investigations highlighted that unsteady interaction between the coolant jet and the hot gas contributes to the lateral dispersion of cold flow over the cooled surface. Hence, considering the harsh working environment of these devices, a fair prediction of their thermal performance requires accurate modelling of the interaction between cold and hot gases. In this paper, an experimental setup originally studied at the University of Karlsruhe during the EU-funded TATEF project is numerically investigated to determine the influence of high-frequency unsteady fluctuations on the thermal performance of the cooling device. The case study consists of a film cooling hole positioned on a flat plate, working at engine-like conditions. Unsteady Reynolds-Averaged Navier-Stokes equations are solved for a compressible flow in transonic regime on a hybrid mesh. Turbulence is modelled using the Scale-Adaptive Simulation method to correctly predict the interaction between the coolant and the main flow. Three different sets of conditions are analyzed by varying the blowing ratio from 0.5 to 1.5, aiming at highlighting the unsteady mechanisms occurring for different penetrations of the coolant into the hot gas. Time-averaged unsteady results are compared with the available experimental data to determine to what extent hybrid modelling allows for correctly predicting film cooling performance at different blowing ratios. Instantaneous solutions are then analyzed to investigate the time-dependent flow field in the vicinity of the jet exit section and on the cooled surface. Spectral Proper Orthogonal Decomposition is enforced to identify the principal fluctuation modes associated with the time-dependent coolant penetration into the main flow

Mixture formation and combustion behaviour analysis in a di ng engine with centrally mounted injector under different injection timings

The work presented in this paper was carried out by Politecnico di Torino, IFPEN, Renault and Continental within GasOn project of the European commission. The objective of this study has been to understand the fluid-dynamic behaviour in a natural gas engine using direct injection. The first part of the CFD activity has been focused on the characterization of the flow field and its interaction with the jet, with reference to different injection strategies. In the second part the ‘mixture breakdown’ at high speed has been detected, as the highest engine speed at which a sufficiently homogenous mixture can be obtained at the start of combustion. The third one has been related to the discussion of the mixing process and turbulence evolution at low speed and low load. The direct injection of NG in the combustion chamber allows several degrees of freedom to be considered, from the point of view of engine control. At full load, a late injection timing is preferable, whereas at partial load a better mixture quality is obtained for an early injection. For the engine under study, a significant deviation from the mixture homogeneity for engine speeds higher than 4500 rpm, can be detected

Modeling of an Organic Rankine Cycle Waste Heat Recovery system for automotive engine applications

The remarkable investments made by manufacturers over the last few decades have contributed to improving the performance of internal combustion engines in every aspect: lower polluting emissions, greater specific power and thermal efficiency. Despite this, on an average, about 40% of the thermal power theoretically available from the combustion of the fuel is still stored in the exhaust gases and therefore dispersed in the environment. In this work the modeling and validation of a waste heat recovery (WHR) plant will be described, combining the engine with a low temperature Organic Rankine Cycle (ORC) system, in order to investigate the feasibility of this system on board of a vehicle, analyzing the quantity of thermal power recovered and made available in the form of electrical power. The ORC plant is modeled using a 0D/1D thermo-fluid dynamic approach. Starting from experimental tests, a map-based model for the piston pump and the scroll expander has been developed. The model has been validated through the use of a vector optimization technique, exploiting a genetic algorithm (MOGA). Subsequently, this system has been coupled to a spark ignition engine for automotive applications, adapting its speed range to comply with the ORC experimental tests. To have an accurate control over the expander inlet temperature, a bypass circuit and two throttles actuated by a PI controller have been implemented. The simulations were performed by considering 18 engine points at maximum load and different rpm. An average thermal efficiency increase of the system of 2.6% was obtained by introducing the recovery plant, and wide improvement chance can be foreseen in the case of ORC full-power use