Lower Pumping Loss Research Articles

Numerical and experimental study on fractal flow field for improving the performance of non-aqueous redox flow battery

The flow field design of the non-aqueous redox flow battery (RFB) decides the electrolyte flow and mass transfer of active species inside porous electrode, which has a significant influence on the operation of RFB. In this work, a fractal tree-like flow channel is proposed to enhance the electrolyte convection and optimize the concentration distribution of active species inside the graphite felt electrode, thus boosting the overall battery performance. Using the finite element simulation method, a three-dimensional numerical model of single cell is established to comparatively study the steady-state discharge process characteristics of deep eutectic solvent (DES) electrolyte-based vanadium‑iron RFBs with fractal and serpentine flow fields, respectively. Moreover, by assembling the single cell of this RFB and building the full cell test system, an experimental study is conducted to compare the discharging output voltage and power of the RFBs with serpentine flow field and fractal flow fields of different fractal dimensions. The numerical results show that the fractal tree-like flow field can improve the discharging power of RFB as well as reduce the pumping loss compared with the conventional serpentine flow field. That is mainly attributed to that fractal flow field is conducive to reducing the polarization loss and strengthening the convection in porous electrode simultaneously. What's more, the role of fractal dimension of flow field is also investigated numerically, thus knowing that large fractal dimension promotes lower pumping loss while small fractal dimension is in favor of higher output voltage. In addition, the experimental results also demonstrate that the fractal flow field could improve the output voltage and maximum discharging power of RFB compared to serpentine flow field. This work provides an optimization method for the flow field design of DES electrolyte-based vanadium‑iron RFB, and is expected to be employed in the other non-aqueous RFBs.

Investigating Mass Transfer Relationships in Stereolithography 3D Printed Electrodes for Redox Flow Batteries

AbstractPorous electrodes govern the electrochemical performance and pumping requirements in redox flow batteries, yet conventional carbon‐fiber‐based porous electrodes have not been tailored to sustain the requirements of liquid‐phase electrochemistry. 3D printing is an effective approach to manufacturing deterministic architectures, enabling the tuning of electrochemical performance and pressure drop. In this work, model grid structures are manufactured with stereolithography 3D printing followed by carbonization and tested as flow battery electrode materials. Microscopy, tomography, spectroscopy, fluid dynamics, and electrochemical diagnostics are employed to investigate the resulting electrode properties, mass transport, and pressure drop of ordered lattice structures. The influence of the printing direction, pillar geometry, and flow field type on the cell performance is investigated and mass transfer vs. electrode structure correlations are elucidated. It is found that the printing direction impacts the electrode performance through a change in morphology, resulting in enhanced performance for diagonally printed electrodes. Furthermore, mass transfer rates within the electrode are improved by helical or triangular pillar shapes or by using interdigitated flow field designs. This study shows the potential of stereolithography 3D printing to manufacture customized electrode scaffolds, which could enable multiscale structures with superior electrochemical performance and low pumping losses.

Exploring the potentials of lean-burn hydrogen SI engine compared to methane operation

The global rush for decarbonization and the more restrictive emission regulations are pushing the research for cleaner powertrains to the transport sector. In this sense, this work contributes with an experimental investigation of the performance and emissions of a single-cylinder SI engine operating under lean-burn hydrogen combustion. Its performance, combustion parameters, exhaust emissions, and indicated efficiency for a wide range of mixture dilutions are then compared to methane under similar engine load conditions. Hydrogen achieved stable combustion up to lambda 3.4, presenting zero CO emission and very low HC emission for all tested operating conditions. Hydrogen operation also presented zero NOx emissions for conditions leaner than lambda 2.2 and 3.0 at 2000 and 3000 rpm, respectively, however, the NOx emissions increase as the mixture is enriched. The high in-cylinder pressure rise rate limited the operation at mixtures richer than lambda 1.3 at 2000 rpm. When compared to methane, the hydrogen allows de-throttle the engine to burn lean mixtures maintaining a proper flame speed, resulting in lower pumping losses, lower pollutants emissions for most of the conditions tested, and higher indicated efficiency, making hydrogen a promising fuel to replace conventional fuels on cleaner SI engines.

Exploring the synergies of dynamic fuel management and propulsion electrification

Active fuel management is a technology that allows a multi-cylinder internal combustion engine to shut off a bank of cylinders to reduce engine power output as needed to match driving conditions and driver power demand. This variation in engine power is taken a step further with a technology known as dynamic fuel management, wherein individual cylinders of a multi-cylinder engine may be turned off as needed. This approach allows a finer resolution in engine power variation. Dynamic fuel management allows an engine to operate with lower pumping losses, thereby maximising the potential for capturing regenerative braking energy. In this paper, the synergies of such an engine equipped with dynamic fuel management, coupled to an electrified driveline incorporating a 48V P1 architecture, are investigated. Detailed MATLAB models are developed to understand the influence of system parameters as well as to identify the optimal engine/motor torque arbitration required for maximum fuel economy. It is shown that the combination of dynamic fuel management and P1 hybridisation can provide a substantial fuel economy improvement.

Exploring the synergies of dynamic fuel management and propulsion electrification

Active fuel management is a technology that allows a multi-cylinder internal combustion engine to shut off a bank of cylinders to reduce engine power output as needed to match driving conditions and driver power demand. This variation in engine power is taken a step further with a technology known as dynamic fuel management, wherein individual cylinders of a multi-cylinder engine may be turned off as needed. This approach allows a finer resolution in engine power variation. Dynamic fuel management allows an engine to operate with lower pumping losses, thereby maximising the potential for capturing regenerative braking energy. In this paper, the synergies of such an engine equipped with dynamic fuel management, coupled to an electrified driveline incorporating a 48V P1 architecture, are investigated. Detailed MATLAB models are developed to understand the influence of system parameters as well as to identify the optimal engine/motor torque arbitration required for maximum fuel economy. It is shown that the combination of dynamic fuel management and P1 hybridisation can provide a substantial fuel economy improvement.

Effect of supercharger system on power enhancement of hydrogen-fueled spark-ignition engine under low-load condition

Hydrogen energy has received much attention in recent years due to its reliability and non-carbon products. However, it has been found that the backfire phenomenon plays a major part in limiting power and torque in the hydrogen internal combustion engine (H2ICE). Much research in recent years has considered turbocharger as a useful method to improve the power of H2ICE. Although the result of boosting a system with turbocharger became enhanced when compared to the natural aspiration system. Unfortunately, there were unsolved problems in exhaust backpressure and pumping losses that hindering the practical utilisation of H2ICE. This paper investigated the experiment of 2.4 L supercharged port fuel injection engine at 2000 rpm. Air excess ratio (lambda) was varied from stoichiometric to 2.8 by adjusting the boosting amount in supercharger, and throttling of the air. The hydrogen injection amount were maintained the same with turbocharger condition; spark advance timing was set at maximum brake torque. It was observed that by boosting engine with supercharger, the lower pumping loss and higher indicated mean pressure had been obtained when compared to turbocharger boosted engine under low-load condition. However, some additional power required for supercharging that lowers output of the engine.

The effect of advanced ignition system on gasoline low temperature combustion

Engines operating in low temperature combustion during positive valve overlap operation offer significant benefits of high fuel economy over the low temperature combustion during negative valve overlap operation. Significant efficiency improvement was achieved by the increased gamma and lower pumping loss. However, NOx emissions were increased due to reliance on the flame-induced combustion. In this study, the corona ignition system was evaluated to reduce NOx emissions during positive valve overlap operation while maintaining the benefit of efficiency gain. The tests were performed in a 2.2-L multi-cylinder engine. The results show that the ignition delay is always shorter with the corona ignition system than with the spark plug. The corona ignition system is able to support stable combustion (coefficient of variation of indicated mean effective pressure <3%) in a lower load during positive valve overlap operation than the spark plug, which gives us additional efficiency benefit. Since the corona ignition system promotes simultaneous ignition of the mixture at multiple locations in the combustion chamber as opposed to ignition being limited to the spark gap channel, the dependence of the flame burn for stable combustion during positive valve overlap operation minimizes, which leads to lower NOx emissions over the spark plug.

A hierarchical interdigitated flow field design for scale-up of high-performance redox flow batteries

The pumping loss of redox flow batteries increases dramatically when scaling up to large-area cells, and becomes a key limiting factor for engineering high-performance cell stacks. This work proposes a hierarchical interdigitated flow field design that has independently regulated distribution/collection channels to lower pumping loss and enhance mass transport: a small quantity of primary branch channels with larger section area is engineered to transport the electrolyte across the length of the entire electrode with a relatively low pressure drop, while a large number of secondary branch channels with smaller section area serve to inject the electrolyte into the adjacent porous electrode with a relatively high velocity to ensure good mass transport. The analytical and experimental methods are combined to understand the mass transport phenomena in the presented flow field. It is shown that the hierarchical interdigitated flow field can significantly reduce the pumping loss by 65.9% and increase the pump-based voltage efficiency from 73.8% to 79.1% at 240 mA cm−2 and 3.0 mL min−1 cm−2 compared with the conventional interdigitated flow field, which demonstrates that the hierarchical interdigitated flow field presents a promising solution for scaling up the high-performance redox flow batteries.

Development of an aggressive Miller Cycle engine with extended Late-Intake-Valve-Closing and a two-stage turbocharger

This paper describes the development of an aggressive Miller cycle gasoline engine with stoichiometric combustion, a high expansion ratio of 12.5:1, a 65 crank angle degrees (CAD) longer duration Late-Intake-Valve-Closing (LIVC) cam, and a two-stage turbocharger. The full-load performance and part-load fuel consumption of the baseline and Miller cycle engines were assessed through engine dynamometer testing. The aggressive Miller cycle engine achieved the maximum Brake Mean Effective Pressure (BMEP) of 22 bar at 1500 rpm, which was enabled by the 65 CAD longer duration LIVC cam to further reduce the effective compression for controlling knock and by the two-stage turbocharger to provide significantly higher boost for maintaining and increasing trapped mass. It was shown that the more aggressive Millerization was realized while maintaining the specific output and advantages of current downsized boosted engines, such as lower friction and lower pumping losses. The aggressive Miller cycle engine achieved above 6% brake-specific fuel consumption (BSFC) reduction over the baseline turbocharged spark-ignition engine on average. The 65 CAD longer duration LIVC cam provided the benefit of pumping loss reduction with delayed intake valve closing and the benefit of hot residual dilution with relatively advanced intake cam phasing simultaneously, which provided the significant fuel economy improvement at non-knocking light-load conditions. Even without the latest technology enhancements and friction reduction methods on its base engine hardware, the aggressive Miller cycle engine achieved a very broad BSFC island of 230 g/kWh or lower, with the lowest BSFC of 223 g/kWh at 2000 rpm and 10 bar BMEP.

PREDIKSI PENGGANTIAN MINYAK PELUMAS MOTOR DIESEL GENERATOR SET BERDASARKAN LAJU PERUBAHAN VISKOSITAS DAN TOTAL BASE NUMBER DENGAN PENDEKATAN LINIERITAS

Diesel engine as the prime mover or as an auxiliary motor is still very dominant use on the ship. Diesel engines can operate with the same four-stroke cycle gasoline engine with: intake, compression, combustion and exhaust. One advantage of the diesel engine is the fuel consumption is better than gasoline engines due to lower pumping loss and high compression ratio. Conversely, there are drawbacks, such as vibration and noise during operation and large this state will increase along with the deterioration of the quality of lubricants. To detect the condition of lubricants can be done by measuring the viscosity and total base number (TBN) .. Nevertheless, every machine has different characteristics from each other, so as to know the condition of engine lubricant is casuistry anyway. In this case, replacement of engine lubricant boat with linearity approach is on a machine that has a high reliability aimed at determining the condition of engine lubricant according to the hours of operation.

Effects of application of variable valve timing on the exhaust gas temperature improvement in a low-loaded diesel engine

Engine manufacturers generally use aftertreatment systems to meet the strict emission criteria on automotive diesel engines. However, those systems operate inefficiently particularly at low-loaded cases of diesel engines since exhaust gas temperatures at aftertreatment inlet remain below 250°C. For those cases, variable valve timing (VVT) method can be applied to elevate exhaust temperatures and improve aftertreatment emission conversion efficiency. Therefore, in this study, intake valve closing (IVC) timing is advanced and retarded sufficiently from the base condition on a low-loaded diesel engine to increase aftertreatment inlet exhaust temperature above 250°C. A specially designed computer program, Lotus Engine Simulation (LES), is utilized to model the diesel engine. Experimental data of a similar study is used for the validation of the simulation. Engine loading (taken as brake mean effective pressure (BMEP)) is kept constant at 2.5bar by adjusting the fuel injection rate. The results show that there is a considerable exhaust temperature rise (up to 65°C) at aftertreatment inlet with the method and it is adequate for effective aftertreatment performance (Texhaust>250°C). It is also seen that the increase on exhaust temperature is due to the sudden reduction on volumetric efficiency (from 94% to 65%). Therefore, there is lower air induction into the cylinders and hence lower pumping losses which result in fuel-efficiency in the system. However, air flow reduction also causes a sharp decrease on the exhaust flow rate which affects the heat capacity of exhaust gases negatively in the system.

Fuel Efficiency Optimization for a Divided Exhaust Period Regulated Two-Stage Downsized Spark Ignition Engine

In our previous paper, a new gas exchange concept termed divided exhaust period regulated two-stage (DEP R2S) system has been proposed. In this system, two exhaust valves in each cylinder are separately functioned with one valve feeding the exhaust mass flow into the high-pressure (HP) manifold, while the other valve evacuating the remaining mass flow directly into the low-pressure (LP) manifold. By adjusting the timing of the exhaust valves, the target boost can be controllable while improving the engine's pumping work and scavenging is attainable which results in better fuel efficiency from the gas exchange perspective. This paper will continue this study by adding an appropriate knock model to examine the benefits this concept could bring to the combustion phasing. The results at full load showed that under knock limited spark advance (KLSA) and fully optimized exhaust valve timing condition, the DEP R2S system benefited from lower pumping loss and better scavenging due to the reduced backpressure and improved pulsation interference despite suffering from reduced expansion ratio and expansion work. The combustion phasing was advanced across the engine speed which is mainly attributed to the reduced residual and the reduced requirement of gross indicated mean effective pressure (IMEP). The net brake-specific fuel consumption (BSFC) was observed to improve by up to 3% depending on the engine operating points. At part load, the DEP R2S system could be used as a mechanism to extend the “duration” of the exhaust valve. This will reduce the recompression effect of the exhaust residuals during the beginning and the end of the exhaust stroke compared to the original R2S model with late exhaust valve opening and early exhaust valve opening. In addition, increased internal exhaust gas recirculation (EGR) due to the increased overlap between the LP and the intake valve is also beneficial for the improved pumping mean effective pressure (PMEP) as the throttle can be further opened to reduce the corresponding throttling loss. The average net BSFC improvement is expected to be approximately 6–7%.

CFD optimization of a 2-stroke range extender engine

A very promising concept for small range extenders (peak power less than 40 kW) is represented by the 2-stroke, direct injection spark ignition engine, with scavenging and exhaust ports controlled by the piston, and an external pump. The most important issue to be addressed on this type of engines is the compliance with stringent rules on pollutant emissions, which depends on combustion patterns and the quality of the scavenging process. The latter is generally hindered by the symmetry of ports timings, but this handicap can be canceled by adopting a patented rotary valve, controlling the flow through a set of auxiliary transfer ports, and using a piston pump for delivering air to the power cylinder and enhancing the balance of the crankshaft. The paper reviews the design of a virtual engine, rated at 35 kW at 5600 rpm, and developed according to the above mentioned concepts. Design has been driven by CFD simulation, using, whenever possible, experimentally calibrated numerical models, or experimental information derived from similar projects. Particular care has been devoted to characterize the scavenging process and the flow patterns within the cylinder and through the ports, analyzing the influence of the rotary induction valve. Engine performance parameters have been predicted by using a well-established commercial software (GT-Power, by Gamma Technologies), while CFD-3D analyses have been carried out by means of a customized version of the KIVA-3V code. The whole study is conceived as the basis for the construction of a physical prototype. The power target has been virtually achieved with a very light and compact engine (estimated weight without the close-coupled electric motor: 35 kg). A three-way catalyst allows the engine to comply with the most stringent emission regulations, without relevant penalizations on fuel efficiency. Furthermore, the engine can work with lean mixtures, achieving a minimum specific fuel consumption comparable to a current automotive Diesel engine (223 g/kWh). This excellent result is due to the low friction and pumping losses of the 2-Stroke engine, as well as to the compactness of the combustion chamber and the capability to stratify the charge.

Experimental study on the effects of high/low pressure EGR proportion in a passenger car diesel engine

An experimental study was conducted to investigate the effects of the proportion between high pressure and low pressure exhaust gas recirculation (HP/LP EGR) on engine operation. The study focused on the characteristics of combustion, emissions, and fuel consumption in a 2.2L passenger car diesel engine. The experiments were performed under three part-load and steady-state operating conditions. The LP EGR portion was swept from 0 to 1, while the mass flow rate of fresh air and boost pressure were fixed. The results showed that the intake manifold temperature decreased gradually as the LP EGR portion increased due to its greater cooling capability by a longer supply line and an intercooler. However, the required cooling power for the intercooler increased because the LP EGR gas, which has a higher temperature than the fresh air, was induced upstream of the compressor. The lowered intake manifold temperature with the increase of the LP EGR portion led to the prolonged ignition delay of pilot injections, which resulted in a slightly higher peak heat release rate in the main combustion. A higher LP EGR portion showed a lower fuel consumption level than the HP EGR only case because the variable geometry turbocharger (VGT) nozzle opened more widely to maintain the boost pressure, which means a lower pumping loss. Nitrogen oxide (NOx) emissions were also decreased as the LP EGR portion increased due to lowered intake charge temperature. Consequently, it was possible to improve the trade-off relationship between NOx emissions and fuel consumption with the increase of the LP EGR portion under steady-state operating conditions.

A Comparison of Valving Strategies Appropriate for Multimode Combustion Within a Downsized Boosted Automotive Engine—Part II: Mid Load Operation Within the SACI Combustion Regime

Spark assisted compression ignition (SACI) is a combustion mode that may offer significant efficiency improvements compared to conventional spark-ignited combustion systems. Unfortunately, SACI is constrained to a relatively narrow range of dilution levels and top dead center temperatures. Both positive valve overlap (PVO) and negative valve overlap (NVO) strategies may be utilized to attain these conditions at low and intermediate engine loads. The current work compares 1D thermodynamic simulations of PVO valving strategies and a baseline NVO strategy in a downsized boosted automotive engine with variable valve timing capability. As future downsized boosted engines may employ multiple combustion modes, the goal of this work is the definition of valving strategies appropriate for SACI combustion at low to moderate loads and spark ignition (SI) combustion at moderate to high loads for an engine with fixed camshaft profiles. PVO durations, valve opening timings, and peak lifts are investigated at low to moderate loads and are compared to a baseline NVO configuration in order to assess valving strategies appropriate for multimode combustion operation. A valvetrain kinematic model is used to translate the desired valve lift profiles into camshaft profiles while a kinematic analysis is used to calculate piston to valve clearances and to define the practical limits of the PVO strategies. The NVO and PVO strategies are also compared to throttled SI operation at part load to assess the overall efficiency benefit of operating under the thermodynamic conditions of the SACI combustion regime. While the results of this study are engine specific, there are several camshaft profiles that are appropriate for the use of PVO rebreathing type valve events. For the range of PVO valve events examined and taking into consideration piston to valve interference, the use of high exhaust and low intake lifts with early exhaust valve opening timing and long PVO durations enables high levels of internal exhaust gas recirculation (EGR) with relatively low pumping losses.

Output Selection and Its Implications for MPC of EGR and VGT in Diesel Engines

Control of exhaust gas recirculation (EGR) and variable geometry turbine in diesel engines is a challenging problem and model predictive control (MPC) seems to be a promising method. In MPC the choice of output variables, and thereby the criterion, has a direct impact on the optimization problem to solve and the resulting control performance. Different selections of outputs are investigated and discussed, proposing that it is beneficial to include EGR-fraction and pumping losses in the criterion while having the oxygen/fuel ratio as a constraint. The rational for this constraint is that, in diesel engines, it is allowed to have the oxygen/fuel ratio larger than a set-point. The proposed design also includes integral action of the EGR-fraction to handle model errors and prediction of engine load and speed. A comparison is made between the proposed MPC, a proportional-integral-derivative (PID) controller, and an MPC with intake manifold pressure and compressor flow as outputs, which is the common choice in the literature. Comparisons are performed in simulation on the European transient cycle showing the following two points. First, the proposed design gives 9% lower oxygen/fuel ratio error, 80% lower EGR-error, and 12% lower pumping losses compared to an MPC design with intake manifold pressure and compressor flow as outputs. Second, the proposed design gives 9% lower EGR-error and 6% lower pumping losses compared to a control structure with PID controllers with oxygen/fuel ratio and EGR-fraction as the main outputs.

The Effect of Intake Temperature in a Turbocharged Multi Cylinder Engine operating in HCCI mode

The operating range in HCCI mode is limited by the excessive pressure rise rate and therefore high combustion induced noise. The HCCI range can be extended with turbocharging which enables increased dilution of the charge and thus a reduction of combustion noise. When the engine is turbocharged the intake charge will have a high temperature at increased boost pressure and can then be regulated in a cooling circuit. Limitations and benefits are examed at 2250 rpm and 400 kPa indicated mean effective pressure. It is shown that combustion stability, combustion noise and engine efficiency have to be balanced since they have optimums at different intake temperatures and combustion timings. The span for combustion timings with high combustion stability is narrower at some intake temperatures and the usage of external EGR can improve the combustion stability. It is found that the standard deviation of combustion timing is a useful tool for evaluating cycle to cycle variations. One of the benefits with HCCI is the low pumping losses, but when load and boost pressure is increased there is an increase in pumping losses when using negative valve overlap. The pumping losses can then be circumvented to some extent with a low intake temperature or EGR, leading to more beneficial valve timings at high load.

Fuel economy and torque tracking in camless engines through optimization of neural networks

The feed forward controller of a camless internal combustion engine is modeled by inverting a multi-input multi-output feed forward artificial neural network (ANN) model of the engine. The engine outputs, pumping loss and cylinder air charge, are related to the inputs, intake valve lift and closing timing, by the artificial neural network model, which is trained with historical input–output data. The controller selects the intake valve lift and closing timing that will mimimize the pumping loss and achieve engine torque tracking. Lower pumping loss means better fuel economy, whereas engine torque tracking gurantees the driver’s torque demand. The inversion of the ANN is performed with the complex method constrained optimization. How the camless engine inverse controller can be augmented with adaptive techniques to maintain accuracy even when the engine parts degrade is discussed. The simulation results demonstrate the effectiveness of the developed camless engine controller.

Effect of Piston Behaviour around Top Dead Center on Thermal Efficiency

In reciprocating internal combustion engines, Otto cycle indicates the best thermal efficiency under the same compression ratio. To achieve this, combustion must take place instantaneously at top dead conter, but it is actually impossible. Meanwhile, if slower piston motion around top dead center was allowed, both the in-cylinder pressure and degree of constant volume would increase, leading to higher thermal efficiency. In order to verify this idea, an engine with slower piston motion by ideal constant volume comcustion was tested. It was revealed that the thermal efficiency could not be improved nevertheless an increase in degree of constant volume and lower pumping loss. Numerical analysis deduced that increased heat loss cancelled out the effect of the higher degree of constant volume and that faster piston motion around top dead center rather achieves an improvement of thermal efficiency in a case where rapid combustion was realized.

不等長圧縮膨張機関による熱効率改善の可能性(予混合圧縮着火燃焼と新燃焼(1),予混合圧縮着火燃焼と新燃焼)

In reciprocating internal combustion engines, the piston stops in a moment at top dead center, so there exists a necessary time to proceed combustion. However more slowing piston motion around top dead center, does it have a possibility to increase cylinder pressure and may lead to an increase of degree of constant volume? In order to verify this idea, the engine with slower piston motion by active piston control was tested. It was revealed that the increased heat loss cancelled out all other favorable features such as lower pumping loss and increase in degree of constant volume.