1,720,968 research outputs found
Combustion chamber design for a high-performance natural gas engine: CFD modeling and experimental investigation
Full text linkThe 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
A model for the estimation of the residual driving range of battery electric vehicles including battery ageing, thermal effects and auxiliaries
Full text linkSustainable 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
Mixture formation and combustion behaviour analysis in a di ng engine with centrally mounted injector under different injection timings
No full textThe 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
Decentralized Control for CACC Systems Accounting for Uncertainties
No full textTraditional CACC systems utilize inter-vehicle wireless communication to maintain minimal yet safe inter-vehicle distances, thereby improving traffic efficiency. However, introducing
communication delays generates system uncertainties that jeopardize string stability, a crucial requirement for robust CACC performance. To address these issues, we introduce a
decentralized model predictive control (MPC) approach that incorporates Kalman filters and state predictors to counteract the uncertainties posed by noise and communication delays. We validate our approach through MATLAB/Simulink simulations, using stochastic and mathematical models to capture vehicular dynamics, Wi-Fi communication errors, and sensor noises. In addition, we explore the application of a reinforcement learning (RL)-based algorithm to compare its merits and limitations against our decentralized MPC controller, considering factors like feasibility and reliability
Analysis of the Cooling Performance of a Cylindrical Hole Designed for the Suction Side of the LS89 Vane under Transitional Conditions
Full text linkThermal 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?
No full textOn 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
Technology review and thermodynamic performance study of a biogas-fed micro humid air turbine
No full textBiogas is a proven and valuable energy source today for the combined production of heat and electricity (CHP). One of the most reliable and efficient technologies for the CHP application using biogas is represented by microturbine (MT). This prime mover not only shows a very flexible behavior towards change in the fuel composition, but it also sticks out for its reliability, small size, and low weight. Moreover, micro humid air turbine (mHAT) cycle, which is still under development, provides a relatively simple and inexpensive solution to increasing the power output of the microturbines. In this paper, the thermodynamic model of a novel CHP system based on a 500 kW micro humid air turbine (mHAT) in a wastewater treatment plant (WWTP) is presented and discussed. Furthermore, some considerations regarding an appropriate biogas treatment system and heat recovery module are discussed.
The results presented in this paper show how the proposed biogas-fed plant can achieve an electrical efficiency of 46.6% together with a CHP efficiency of 81.2%. The impact of integration with WWTPs is beneficial where both biogas and required water for inlet air humidification are available
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Modeling of an Organic Rankine Cycle Waste Heat Recovery system for automotive engine applications
No full textThe 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
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