Pengaruh Panjang Rantai Karbon dan Derajat Ketidakjenuhan terhadap Karakteristik Pembakaran Droplet Asam Lemak Tunggal

This study aimed to investigate the effect of the different carbon chain lengths and the degree of unsaturation of six fatty acids as the constituent of vegetable oils. The droplet combustion was carried out at an ambient temperature and atmospheric pressure. The variation in the carbon chain length and the degree of unsaturation resulted in different physical and chemical properties of the fuel, which affect the droplet combustion characteristics. The increase of the carbon chain length results in longer ignition delay times and shorter burning durations, as well as higher droplet temperatures, burning rate constant, and specific power output. Conversely, an increase in the degree of unsaturation with the presence of double bond results in shorter ignition delay and longer burning duration, as well as higher droplet temperatures, but lower burning rate constant and specific power output. The droplet diameter evolution divides the combustion period into unsteady burning zones and quasi-linear burning zones. The flame dimension of unsaturated fatty acid is higher due to the soot formation at the top of the flame. A bluish flame related to the higher oxygen content in the molecule can be observed in saturated fatty acids. The short-chain saturated fatty acid has a large non-luminous zone because they are rich in oxygen. In contrast, the long-chain saturated fatty acid has a narrow non-luminous zone with high flame radiation.

The CFD-Based Simulation of a Horizontal Axis Micro Water Turbine

A horizontal axis micro water turbine generator has been designed for use as a source of power generation where the reservoir construction has only a low head. It uses the natural flow rate of water to generate a specific power output. The power is, however, limited by the flow rate of water which has to be sufficient to keep operating a suitable number of revolutions per minute for the blades. Tis research aimed to introduce a new blade can be disassembled and modular on the wheel blade and developing for optimum design of the horizontal axis micro water turbine generator. A 3D model of the wheel blade in the horizontal axis micro water turbine generator was created by using Autodesk Inventor Professional 2018 software. Computational Fluid Dynamics (CFD) analysis and structural Finite Element Analysis (FEA) are presented in this paper. CFD analysis was performed to obtain the velocity and pressure difference between the concave and convex regions of the wheel blade while FEA was used to obtain the structural response of the wheel blade due to the water velocity load applied in terms of stresses and displacements.

Thermodynamic and Mechanical Design Concept for Micro-Turbojet to Micro-Turboshaft Engine Conversion

In this work, a design concept for micro-turbojet to micro-turboshaft engine conversion is presented. This is motivated by a lack of available micro-turboshaft engines which is shown in the market survey conducted. Thus, the presented concept deals with the conversion of an existing micro-turbojet engine to a micro-turboshaft engine for a specific power output. The conversion is shown using the micro-turbojet engine OLYMPUS HP from AMT Netherlands. Furthermore, the simultaneously developed analytical preliminary design of the additional single-stage power turbine is shown besides a thermodynamic cycle simulation. This has been done to obtain the unknown gas generator outlet condition which is similar to the power turbine’s inlet condition. Within the cycle calculation, occurring losses due to the small dimensions have also been considered. During the design process, different combinations of work coefficient and mean diameter of the power turbine were investigated to minimize the required gear box ratio for a given rotor speed in terms of weight minimization. To keep losses in the power turbine low, the preliminary blade row has finally been improved using CFD calculations.

A Double-Bed Adsorptive Heat Transformer for Upgrading Ambient Heat: Design and First Tests

A full scale lab prototype of an adsorptive heat transformer (AHT), consisting of two adsorbers, an evaporator, and a condenser, was designed and tested in subsequent cycles of heat upgrading. The composite LiCl/SiO2 was used as an adsorbent with methanol as an adsorbtive substance under boundary temperatures of TL/TM/TH = −30/20/30 °C. Preliminary experiments demonstrated the feasibility of the tested AHT in continuous heat generation, with specific power output of 520 W/kg over 1–1.5 h steady-state cycling. The formal and experimental thermal efficiency of the tested rig were found to be 0.5 and 0.44, respectively. Although the low potential heat to be upgraded was available for free from a natural source, the electric efficiency of the prototype was found to be as high as 4.4, which demonstrates the promising potential of the “heat from cold” concept. Recommendations for further improvements are also outlined and discussed in this paper.

Numerical CFD Simulations and Indicated Pressure Measurements on a Sliding Vane Expander for Heat to Power Conversion Applications

The paper presents an extensive investigation of a small-scale sliding vane rotary expander operating with R245fa. The key novelty is in an innovative operating layout, which considers a secondary inlet downstream of the conventional inlet port. The additional intake supercharges the expander by increasing the mass of the working fluid in the working chamber during the expansion process; this makes it possible to harvest a greater power output within the same machine. The concept of supercharging is assessed in this paper through numerical computational fluid dynamics (CFD) simulations which are validated against experimental data, including the mass flow rate and indicated pressure measurements. When operating at 1516 rpm and between pressures of 5.4 bar at the inlet and 3.2 bar at the outlet, the supercharged expander provided a power output of 325 W. The specific power output was equal to 3.25 kW/(kg/s) with a mechanical efficiency of 63.1%. The comparison between internal pressure traces obtained by simulation and experimentally is very good. However, the numerical model is not able to account fully for the overfilling of the machine. A comparison between a standard and a supercharged configuration obtained by CFD simulation shows that the specific indicated power increases from 3.41 kW/(kg/s) to 8.30 kW/(kg/s). This large power difference is the result of preventing overexpansion by supercharging. Hence, despite the greater pumping power required for the increased flow through the secondary inlet, a supercharged expander would be the preferred option for applications where the weight of the components is the key issue, for example, in transport applications.

Performance Comparison and Parametric Analysis of sCO2 Power Cycles Configurations

A thermodynamic analysis and optimization of four supercritical CO2 Brayton cycles were conducted in this study in order to improve calculation accuracy; the feasibility of the cycles; and compare the cycles’ design points. In particular, the overall thermal efficiency and the power output are the main targets in the optimization study. With respect to improving the accuracy of the analytical model, a computationally efficient technique using constant conductance (UA) to represent heat exchanger performances is executed. Four Brayton cycles involved in this compression analysis, simple recaptured, recompression, pre-compression, and split expansion. The four cycle configurations were thermodynamically modeled and optimized based on a genetic algorithm (GA) using an Engineering Equation Solver (EES) software. Results show that at any operating condition under 600 °C inlet turbine temperature, the recompression sCO2 Brayton cycle achieves the highest thermal efficiency. Also, the findings show that the simple recuperated cycle has the highest specific power output in spite of its simplicity.

Experimental thermal survey of automotive turbocharger

Turbochargers are commonly used in the automotive industry due to their ability to increase the specific power output of internal combustion engines. Heat transfer from the turbine to the compressor can strongly influence the turbocharger performance. Therefore, it is essential to consider heat transfer properties of the turbochargers. Existing heat transfer models are generally limited to the specific situations on the turbocharger test rig or the engine test bench, which are different to the real conditions of engine operation in a vehicle. Accurate modeling and calculation of the heat transfer require a more precise measurement study. In this research, we evaluate the temperature distribution of the turbocharger walls using an engine test bench and also a vehicle that are both equipped with the same instrumented turbocharger. Thermocouple measurements and thermography pictures were used to determine the temperature distributions of the turbocharger. Different heat transfer phenomena of turbocharger have been measured and analyzed. In addition, the effect of heat transfer on compressor efficiency is investigated. Several tests have been conducted, including a vehicle on a flat surface and also during an uphill climb with a trailer load hitched. The results of vehicle warm-up test show that the compressor housing has a higher temperature gradient in comparison with the engine test bench. The velocity of the air around the turbocharger is a factor that contributed toward the differences between an engine test bench and typical vehicle conditions.

Experimental Investigations on Diesel Engine Forced Induction and Exhaust Gas Recirculation (EGR) Using Exhaust Gas Assisted Jet Compressor

Even though the conventional method of supercharging and turbocharging of an internal combustion engine increases the engine specific power output, part of the shaft power developed by the engine is consumed by the superchargers. The control system that is present in both the chargers further complicates the system. This study proposes a novel method of forced induction in a diesel engine by using a jet compressor run by exhaust gas recirculation (EGR). This method apart from increasing the specific power output reduces the NOx formation by the engine due to forced induction. Performance analysis of the jet compressor using exhaust gas as the motive stream and atmospheric air as the propelled stream was carried out. Using the standard available code, the governing equations were solved numerically to get the optimum operating conditions such as exhaust gas pressure, temperature, and flow rate for a three cylinder diesel engine. The dimensions of the jet compressor were determined by solving the energy balance equations obtained from the constant rate momentum change method. Using the commercial software fluent, the performance optimization of jet compressor used for forced induction in a diesel engine was made for different percentage of EGR input and estimated the power output. From the results obtained, a performance map was drawn for the three cylinder diesel engine to get the optimum boost pressure and maximum entrainment ratio for a given percentage of exhaust gas recirculation and power output. Experiments were conducted on a three cylinder diesel engine fitted with a fabricated jet compressor with EGR used for forced induction application. Results obtained from the experiments were in good agreement with the numerical results obtained from fluent analysis.

Is Gross Efficiency Lower at Acute Simulated Altitude Than at Sea Level?

Purpose:The purpose of this study was to test the assumption that gross efficiency (GE) at sea level (SL) is representative of GE at altitude (AL). It was hypothesized that an increased cost of ventilation and heart rate, combined with a higher respiratory-exchange ratio, at AL might result in a decrease in GE.Methods:Trained men (N = 16) completed 2 maximal incremental tests and 2 GE tests, 1 at SL and 1 at an acute simulated AL of 1500 m (hypobaric chamber). GE was determined during submaximal exercise at 45%, 55%, and 65% of the altitude-specific power output attained at VO2max.Results:GE determined at the highest submaximal exercise intensity with a mean RER ≤1.0, matched for both conditions, was significantly lower at AL (AL 20.7% ± 1.1% and SL 21.4% ± 0.8%, t15 = 2.9, P < .05).Conclusion:These results demonstrate that moderate AL resulted in a significantly lower GE during cycling exercise than SL. However, it might be that the lower GE at AL is caused by the lower absolute exercise intensity.