Peak Thermal Efficiency Research Articles

Numerical Investigation of a modified Kalina cycle system for high-temperature application and genetic algorithm based optimization of the multi-phase expander's inlet condition

As an alternative to the conventional steam Rankine Cycle, Kalina Cycle has witnessed a growing interest over the past years for high-temperature applications (A working fluid temperature of 500°C at the turbine inlet). However, the possibility of implementing an additional multi-phase expander on the weak ammonia-water solution loop of the Kalina cycle was hardly analyzed in the available literatures. In this research, two novel Kalina cycles (Kalina cycle-12A and Kalina cycle-12B) have been presented by integrating a multi-phase expander in addition to the turbine installed downstream of the Kalina evaporator. For Kalina cycle -12A, this additional multi-phase expander is positioned downstream of the Kalina separator and on the weak ammonia-water solution loop for Kalina Cycle-12B. A detailed mathematical model based on the thermodynamic laws has been developed to solve and optimize the Kalina Cycles. The influence of critical decision parameters, specifically the ammonia concentration on working fluid and evaporation pressure, were investigated. The optimization was performed based on the objective to maximize the net power output from the multi-phase expander under steady-state operating conditions. When the performance of the proposed Kalina cycles was compared with the conventional Kalina Cycle-12, both of them demonstrated superior performance, i.e., net power output and peak thermal efficiency increased by a maximum value of 3.23% for the proposed Kalina Cycle-12A cycle and 3.94% for the proposed Kalina Cycle-12B cycle. In terms of second law efficiency, Kalina Cycle-12A is 3.68 percent more efficient than Kalina Cycle-12, while Kalina Cycle-12B is 4.04 percent more efficient. Furthermore, 2nd law analysis also reveals, maximum destruction of exergy occurs at the condensers of the cycles.

Influence of twisted tape inserts on energy and exergy performance of an evacuated Tube-based solar air collector

Energy and exergy behaviour of an Evacuated Tube with Inserted Baffles Solar Air Collector (ETIBSAC) with various design configurations of twisted tape is analyzed through an analytical model. Among those configurations, Loose-Fit Perforated Twisted Tape (LFPTT) exhibits better performance in terms of energy effectiveness. Hence, LFPTT was selected for further investigation to identify the influence of helical twist ratio (y/D) and tape hole diameter ratio (d/D). The analytical model predicts the energy and exergy performance of the ETIBSAC with LFPTT inserts (y/D) = 2, 2.5 and 3 & (d/D) = 0.0714, 0.107 and 0.143. The results show that ETIBSAC with LFPTT produces the highest effective thermal and exergy efficiencies at lower airflow rates. The peak thermal efficiency of 62.33% was attained at 400 kg/h with (y/D) = 2 & (d/D) = 0.0714. The exergy efficiency attained its peak value of 3.91% and reduces with increasing airflow rate due to more exergy destruction. It is concluded that the proposed insertion of twisted tapes can be adopted for enhancing the performance of the system.

3-D numerical modelling and experimental investigation of coupled photovoltaic thermal and flat plate collector

Photovoltaic Thermal (PVT) systems generate hot water and electricity simultaneously. The grade of thermal energy generated by such PVT systems is low, resulting in limited application. To overcome this challenge, the coupling of the PVT system to a secondary flat plate collector (FPC) has been explored in this work. For the system's performance estimation, a 3-D numerical model has been developed for both glazed and unglazed PVT-FPC collector. Based on the numerical model, PVT collectors have been fabricated, and each is then connected in series to a commercially available FPC collector. Experiments conducted on the fabricated PVT-FPC system showed a close match between simulation and experiments. Further, experiments conducted on the unglazed PVT – FPC collector showed a peak outlet water temperature of 60–63 °C at 30 LPH. For the unglazed PVT collector, the peak electrical and thermal efficiency of 16% and 25% is reported respectively, whereas for the FPC collector, the thermal efficiency of 35% is reported. Compared to an individual unglazed PVT collector, 17 °C higher outlet water temperature is reported for the coupled system. Similarly, for the case of glazed PVT-FPC collector, the peak outlet water temperature reported is 65–67 °C at 30 LPH with 14–15 °C higher outlet water temperature.

The Impact of Advanced Fuels and Lubricants on Thermal Efficiency in a Highly Dilute Engine

<div class="section abstract"><div class="htmlview paragraph">In spark ignited engines, thermal efficiency is strongly influenced by the quality of the combustion process as initiated by the ignition system. Jet Ignition is a combustion concept that utilizes a small pre-chamber to produce reactive jets which distribute ignition energy throughout the main combustion chamber. This distributed ignition energy can be leveraged to induce ignition in traditionally difficult-to-ignite regimes, such as in highly dilute mixtures. Highly dilute jet ignition combustion has been proven to produce thermal efficiencies significantly higher than those of conventional spark ignition combustion.</div><div class="htmlview paragraph">To fully exploit the efficiency potential of active jet ignition, multiple aspects of the engine architecture and peripheral systems must be adjusted. Efficiency sensitivities to compression ratio, boost system, and intake port design have been explored extensively. Less well understood are the sensitivities of thermal efficiency and other jet ignition combustion parameters to fuel and lubricant properties. With increasing interest in investigating fuel-engine system interactions, it is imperative to understand how future lubricants and fuels could synergistically enhance this highly efficient combustion mode.</div><div class="htmlview paragraph">Experimental data is obtained using a 1.5L 3-cylinder jet ignition engine. The engine is tested with a range of lubricant and fuel formulations, commercial and proprietary, at multiple compression ratios. Results are analyzed for the different fuel/lubricant/hardware combinations. High load engine operation is limited by knock, peak cylinder pressure, and peak rate of cylinder pressure rise; the governing limitation changes according to the fuel/lubricant/hardware combination being utilized, with implications for both peak load and thermal efficiency. Engine results demonstrate a peak brake thermal efficiency of 43.6% with the optimal fuel and lubricant evaluated, representing a 1.5 percentage point increase over the baseline jet ignition configuration, and a 9% improvement in cycle average fuel economy.</div></div>

Effects of flame propagation speed on knocking and knock-limited combustion in a downsized spark ignition engine

Engine knock remains the key factor that ultimately restricts the peak thermal efficiency in modern downsized spark ignition (SI) engines. The flame propagation speed can affect knock tendency by the residence time and thermodynamic state of end-gas, which are competing with each other. The investigations in this study focus on flame propagation speed impacts on engine knock characteristics and thermal efficiency under a high load/low speed operating condition using three-dimensional numerical simulations. The results show that knock intensity (KI) increases first and thereafter decreases with the increase of SI flame speed under knocking condition. Behind the nonmonotonic relationship, the control mechanisms of end-gas auto-ignition are different. The low to moderate speed SI combustions are linked to local hot spots. Higher KI is caused by the interaction between the pressure waves induced by these hot spots. Then with the acceleration of SI flame, a homogeneous autoignition event occurs along the reaction front, leading to more intense pressure fluctuations. At the high-speed SI combustion, local hot spots disappear gradually, and the end-gas autoignition is dominated by flame-induced sequential auto-ignition. The corresponding KI decreases due to the reduction of available fresh gases. A posteriori analysis is also performed applying theories proposed by Zeldovich and Bradley. It’s shown that an increase in the SI flame speed results in lower first and thereafter higher temperature gradient in end-gas, leading to a drastic change in the auto-ignition behaviors. In addition, the relative effects of knock suppression and combustion duration reduction on thermal efficiency improvement are clarified.

The Influence of Charge Motion on Pre-Chamber and Main Chamber Combustion in a Highly Dilute Jet Ignition Engine

Though there are multiple viable powertrain options available for the automotive sector, those that contain internal combustion engines will continue to account for the majority of global sales for the next several decades. It is therefore imperative to continue the pursuit of novel combustion concepts that produce efficiency levels significantly higher than those of current engines. Introducing high levels of dilution in spark ignited (SI) engines has consistently proven to produce an efficiency benefit compared to conventional stoichiometric engine operation. However, this combustion mode can present challenges for the ignition system. Pre-chamber jet ignition enables stable, highly dilute combustion by both increasing the ignition energy present in the system and distributing it throughout the combustion chamber. Previous work by the authors have shown that jet ignition produces 15–25% increases in thermal efficiency over baseline SI engines with only relatively minor changes to engine architecture. Lean combustion in general and jet ignition in particular represent fundamentally different engine operating modes compared to those of conventional stoichiometric SI engines. Therefore, there are some system sensitivities not present in stoichiometric engines that must be investigated in order to fully optimize the jet ignition system. Differing types and magnitudes of charge motion are incorporated in SI engines to aid with mixture preparation but the influence of charge motion over lean combustion performance, particularly in jet ignition engines, is less well understood. This study analyzes the impact that charge motion has on both pre-chamber and main chamber combustion. A 1.5 L 3-cylinder gasoline engine is outfitted with multiple intake port configurations producing varying magnitudes and types of charge motion. Pre-chamber and main chamber combustion stability and other burn parameter responses are analyzed across multiple speeds and loads, including at critical operating points such as a catalyst heating condition. The results show that there is combustion sensitivity to charge motion, resulting in >1 percentage point spread in peak thermal efficiency for the configurations tested, and that this sensitivity manifests most significantly under low ignitability conditions such as heavy dilution. These results provide guidance for future system optimization of jet ignition engines.

Design and testing of additively manufactured high-efficiency resistojet on hydrogen propellant

This paper presents the design methodology and performance testing of an additively manufactured resistojet operating on hydrogen as propellant. Additive manufacturing allows to produce complex monolithic resistors, resulting in reliable high efficiency thrusters. The concept, to be used in combination with advanced cryogenic storage technologies, is proposed for short time and high specific impulse orbit transfers. The simplified two-dimensional thermal design approach adopted is discussed, and its application to the engineering of the resistor is shown for both Inconel 718 and tungsten. The paper reports the performance testing of the proof-of-concept version of the thruster, manufactured in Inconel 718. Experiments on hydrogen show near ideal performance, demonstrating a peak thermal efficiency of 96%. The thruster proves the validity of the design methodology proposed, and the feasibility of the approach to develop monolithic additively manufactured hydrogen resistojets as main propulsion units.

Numerical modeling and performance assessment of elongated compound parabolic concentrator based LCPVT system

In this work, a non-imaging low concentrating 2.5X Compound Parabolic Concentrator (CPC) truncated to 1.7X has been explored. CPCs inherently form non-uniform distribution of flux on the PVT module which has been mitigated by the integration of optimized homogenizer referred to as Elongated CPC (ECPC). The study involves detailed optical, thermal, and electrical modeling of the ECPC based Low Concentrating Photovoltaic Thermal (LCPVT) system. Optical simulations provide insight into the flux distribution on the PVT panel surface, which is further coupled with a thermal and electrical model for precise prediction of the performance of the system. These models are validated experimentally with a 315 Wp solar panel integrated with ECPC based LCPVT system. Performance evaluation of the system has shown peak thermal efficiency of ∼40% at ΔT of 16 °C, peak electrical efficiency of 12%, and an overall peak exergy efficiency of 15% at 38 Liters per hour (LPH) flow rate. A comparison of outlet water temperature results obtained from the numerical model and experiments has shown an excellent match with a relative error of 4%. Results also show that the increase in mass flow rate from 22 LPH to 38 LPH improves the electrical efficiency by 3% however a drop in ΔT of 2–3 °C is observed.

Experimental analysis of parabolic trough collector system with multiple receiver geometries and reflective materials

Solar parabolic trough collector systems provide an attractive solution especially for solar thermal power generation. The performance of these systems significantly depends on receiver geometries. Therefore, in the current study, an experimental analysis has been performed using three different receiver geometries along-with two reflective materials. These receiver geometries include: simple tube (reference geometry A), receiver tube with straight absorber plate (geometry B), and receiver tube with curved absorber plate (geometry C), whereas, the reflective materials include: aluminum and stainless steel. The experimentation was performed under subtropical climate conditions of Taxila, Pakistan. From experimentation, it was identified that peak heat gain obtained from receiver geometries C and B were 71%, and 30% higher as compared to the reference geometry A, respectively. The, thermal efficiency of the system with geometry A was 20%, geometry B was 28%, and geometry C was 34%. Furthermore, two reflective materials i.e. aluminum and Stainless steel were used on geometry C which yielded best results for further parabolic trough collector performance analysis. It was observed that peak thermal efficiencies were 34.8% and 31% with aluminum and stainless steel as reflector materials. The results indicated that aluminum reflector was approximately 12% efficient as compared to stainless steel reflector. The results will help to cultivate the advantages of innovative receiver geometries and alternative reflective materials.

An experimental study of an Organic Rankine Cycle utilizing HCFO-1233zd(E) as a drop-in replacement for HFC-245fa for ultra-low-grade waste heat recovery

The use of Organic Rankine Cycles (ORCs) for waste heat recovery can reduce energy consumption in data centers, which in turn benefits the environment through the reduction of carbon-based fuels. However, data center applications exist in the ultra-low temperature range (40 − 80℃), making efficient and economical operation challenging. The operating fluids that are viable in this temperature range are limited, so it can be a challenge to identify a suitable drop-in replacement for a proven fluid. In this study, the use of HCFO-1233zd(E) is explored to determine its suitability as a low Global Warming Potential and zero Ozone Depletion Potential alternative to the more common HFC-245fa in ultra-low temperature data center applications. This study features the first known comprehensive comparison between the alternative working fluid HCFO-1233zd(E) and HFC-245fa in a lab-scale experimental ORC under ultra-low-grade waste heat temperatures. The results of this study show that the lower HFCO-1233zd(E) saturated pressures impact the ORC operation by reducing the mass flow rate by 3–21%, thereby reducing the heat transfer across the evaporator and condenser. However, the peak thermal efficiency of the lab-scale system is seen to increase with the use of HCFO-1233zd(E) to a high of 5.0% from 4.6% with HFC-245fa. This work also identifies the minimum feasible waste heat temperature as 55 °C for a successful ORC application with both working fluids.

Implementation of Adaptive Neuro-fuzzy Model to Optimize Operational Process of Multiconfiguration Gas-Turbines

In this article, the adaptive neuro-fuzzy inference system (ANFIS) and multiconfiguration gas-turbines are used to predict the optimal gas-turbine operating parameters. The principle formulations of gas-turbine configurations with various operating conditions are introduced in detail. The effects of different parameters have been analyzed to select the optimum gas-turbine configuration. The adopted ANFIS model has five inputs, namely, isentropic turbine efficiency (Teff), isentropic compressor efficiency (Ceff), ambient temperature (T1), pressure ratio (rp), and turbine inlet temperature (TIT), as well as three outputs, fuel consumption, power output, and thermal efficiency. Both actual reported information, from Baiji Gas-Turbines of Iraq, and simulated data were utilized with the ANFIS model. The results show that, at an isentropic compressor efficiency of 100% and turbine inlet temperature of 1900 K, the peak thermal efficiency amounts to 63% and 375 MW of power resulted, which was the peak value of the power output. Furthermore, at an isentropic compressor efficiency of 100% and a pressure ratio of 30, a peak specific fuel consumption amount of 0.033 kg/kWh was obtained. The predicted results reveal that the proposed model determines the operating conditions that strongly influence the performance of the gas-turbine. In addition, the predicted results of the simulated regenerative gas-turbine (RGT) and ANFIS model were satisfactory compared to that of the foregoing Baiji Gas-Turbines.

Effect of hybrid nanofluids mixture ratio on the performance of a photovoltaic thermal collector

Solar photovoltaic-thermal (PV/T) collectors, are hybrid collectors used to convert solar radiation into usable thermal and electrical energy. Recently, the field of research on PV/T is has focused on improving the efficiency of the PV/T collector by replacing the conventional heat transfer fluids (HTFs) with nanofluids. This article investigates the effect of hybrid nanofluids mixture ratio on the useful energy and overall efficiency of a PV/T collector operating with Al2O3-ZnO water nanofluid as the HTF. Experiments to measure the thermophysical properties of the hybrid nanofluids were conducted for various temperatures, volume concentrations, and mixture ratios, furthermore, accurate correlation models were proposed. Metrological data and energy output readings collected from the PV solar farm at Cyprus International University were used to validate our model. The study observed that at the optimum mixture ratio (0.47 of Al2O3 in the hybrid), the electrical, thermal, and exergy efficiencies of the PV/T collector are 13.8%, 55.9%, and 15.13% respectively. Also, the cell temperature drops by 21% when the mass flow rate is 0.1 kg/s as compared to when it is 0.01 kg/s. Finally, the study concludes that by using the Al2O3-ZnO hybrid nanofluid an overall peak thermal efficiency of 91% can be attained, and this represents a 34% enhancement in the collector's performance when compared to water.

Experimental Investigation of a Novel Solar Micro-Channel Loop-Heat-Pipe Photovoltaic/Thermal (MC-LHP-PV/T) System for Heat and Power Generation

This paper aims to experimentally investigate a novel solar Micro-Channel Loop-Heat-Pipe Photovoltaic/Thermal (MC-LHP-PV/T) system which, making its first attempt to employ the co-axial tubular heat exchanger as the condenser, PV-bound multiple micro-channel tubes array as the PV/evaporator, the upper end liquid header with tiny holes as the liquid header and liquid/vapour separator, and the upper end vapour header as the vapour collector and distributor, can create the improved condensation and evaporation effects within the loop-heat-pipe (LHP) and thus, achieve significantly enhanced solar thermal and electrical efficiencies compared to traditional PV/T systems. Based on the results derived from our previous analytical study, a prototype MC-LHP-PV/T system employing R-134a as the working fluid was designed, constructed and tested, and the testing results were used to evaluate its operational performance including solar thermal and electrical efficiencies and their relevant impact factors. It is found that solar thermal efficiency of the MC-LHP-PV/T system varied with the inlet temperature and flow rate of coolant water, ambient temperature, as well as height difference between the condenser and evaporator. A lower inlet water temperature, a higher water flow rate, a higher ambient temperature, and a larger height difference between the condenser and the evaporator can help increase the solar thermal efficiency of the system. Under a range of testing conditions with the refrigerant charge ratio of 30%, a peak solar thermal efficiency (i.e., 71.67%) happened at solar radiation of 561W/m2, inlet water temperature of 18°C, water flow rate of 0.17m3/h, ambient temperature of 30°C, and height difference of 1.3m. This set of parametrical data is therefore regarded as the optimal operational condition of the MC-LHP-PV/T system. Under these specific operational condition and the real weather solar radiation, the solar thermal efficiency of the system was in the range 25.2% to 62.2%, while the solar electrical efficiency varied from 15.59% to 18.34%. Compared to the existing PV/T and BIPV/T systems, the new MC-LHP-PV/T system achieved 17.20% and 33.31% higher overall solar efficiency.

Effect of diesel injection timing on the combustion of natural gas/diesel dual-fuel engine at low-high load and low-high speed conditions

Past research has shown that advancing diesel injection timing is a promising approach to decrease the unburned methane and greenhouse gas (GHG) emissions of natural gas/diesel dual-fuel engines at lower engine loads. However, this benefit may not persist under medium to high load-low speed conditions. To explore this, the present paper uses experiments and detailed computational fluid dynamic (CFD) modeling to investigate the impacts of diesel injection timing on the combustion and emissions performance of a heavy-duty natural gas/diesel dual-fuel engine under four different engine load-speed conditions. The results showed that advancing diesel injection timing increases the peak pressure, thermal efficiency, and NOx emissions for all examined engine load-speed conditions. Advancing diesel injection timing also significantly decreases the unburned methane and CO2-equivalent (GHG) emissions of the dual-fuel engine under low load-low speed and medium load-high speed conditions. The concentration of OH and CH4 revealed that the central part of the combustion chamber is the main source of the unburned methane emissions under low load-low speed and medium load-high speed conditions, and advancing diesel injection timing significantly improves the combustion of natural gas-air mixture in this region. However, advancing diesel injection timing slightly increases the unburned methane emissions trapped in the crevice volume. However, this slight increase in the unburned methane emissions in the crevice volume is much lower than its significant decrease in the central region of the combustion chamber. At medium to high load-low speed conditions, there is almost no unburned methane in the central part of the combustion chamber, and the crevice region is considered as the main source of unburned methane emissions. As a result, advancing diesel injection timing does not improve the combustion of natural gas-air mixture in the central part of the combustion chamber but slightly increases the unburned methane trapped in the crevice region. This is the main reason that advancing diesel injection timing slightly increases the unburned methane emissions under medium to high load-low speed conditions. Overall, advancing diesel injection timing significantly increases thermal efficiency and decreases the unburned methane and GHG emissions under low load-low speed and medium load-high speed conditions. It improves the thermal efficiency under medium to high load-low speed conditions, but comes at the expense of increased methane and unchanged GHG emissions.

Experimental evaluation of a prototype hybrid CPV/T system utilizing a nanoparticle fluid absorber at elevated temperatures

Novel approaches for solar energy conversion continue to garner interest as a potential thermal and electrical energy source. Additionally, the need for systems capable of producing thermal energy at temperatures up to 300 °C is growing as a means to provide process heat to industry and distributed generation for small communities. An approach that has seen recent increased interest is the hybrid concentrating photovoltaic/thermal collector that can co-produce electricity and heat energy above 100 °C. One technique for this is to use nanoparticles in the heat transfer fluid to spectrally filter off wavelengths poorly utilized by the photovoltaic component. Here, we have demonstrated the first on-sun operation of a nanoparticle based hybrid CPV/T solar collector at temperatures exceeding 100 °C using a combination of gold and indium tin oxide nanoparticles in Duratherm S flowing in the receiver, with an aperture area a full order of magnitude larger than other tests. At 14× concentration the system achieved a photovoltaic efficiency of 4% while achieving a peak thermal efficiency of 61% with an outlet temperature of the fluid of 110 °C.

Design and off-design models of single and two-stage ORC systems on board a LNG carrier for the search of the optimal performance and control strategy

A diesel-electric propulsion system is generally used in large scale ships to allow a free placement of Internal Combustion Engines (ICEs), to acoustically decouple engines and hull, and reduce total weight and volume. On long voyages, the speed of a vessel can be more or less constant. Thus, to a first approximation, it can be considered that the engines operate most of the time at steady-state conditions. On this basis, Organic Rankine Cycle (ORC) systems can be conveniently installed aboard to generate additional electric power by recovering ICEs waste heat and increase in turn the overall system efficiency. The ICEs-ORC combined cycle system has to be designed properly to maximize the work production and guarantee at the same time a stable operation during both transient and steady-state working conditions.This paper presents the design and off-design dynamic and steady-state models of three ORC system configurations that exploit the waste heat of four dual fuel diesel ICEs on board a LNG carrier. One single-stage and two (subcritical or supercritical) two-stage ORC system configurations are considered. The available heat is taken from charge air, jacket and oil cooling systems, while the exhaust gases are not considered to be available being already used for other ship internal needs. Dynamic simulations are employed to define the control strategies that lead to stable operation of all the considered ORC system configurations after transients of the ship operation. Steady-state off-design models are then used to identify the best system design point taking into account the real ship operation during a reference year. Results show that the best performing single-stage ORC is designed for a ship speed of 16.5 knots on loaded voyage, and has an annual work production of 1665.8MWh with a peak thermal efficiency of 6.5%. The supercritical configuration reaches the best performance among the two-stage ORC systems, achieving a work production of 2306.6MWh and a thermal efficiency of 12.6% at 15.5 knots.

A novel cascade organic Rankine cycle (ORC) system for waste heat recovery of truck diesel engines

Waste heat recovery (WHR) of engines has attracted increasingly more concerns recently, as it can improve engine thermal efficiency and help truck manufacturers meet the restrictions of CO2 emission. The organic Rankine cycle (ORC) has been considered as the most potential technology of WHR. To take full advantage of waste heat energy, the waste heat in both exhaust gases and the coolant need to be recovered; however, conventional multi-source ORC systems are too complex for vehicle applications. This paper proposed a confluent cascade expansion ORC (CCE-ORC) system for engine waste heat recovery, which has simpler architecture, a smaller volume and higher efficiency compared with conventional dual-loop ORC systems. Cyclopentane is analyzed to be regarded as the most suitable working fluid for this novel system. A thermodynamic simulation method is established for this system, and off-design performance of main components and the working fluid side pressure drop in the condenser have been taken into consideration. System performance simulations under full engine operating conditions are conducted for the application of this system on a heavy-duty truck diesel engine. Results show that the engine peak thermal efficiency can be improved from 45.3% to 49.5% where the brake specific fuel consumption (BSFC) decreases from 185.6g/(kWh) to 169.9g/(kWh). The average BSFC in the frequently operating region can decrease by 9.2% from 187.9g/(kWh) to 172.2g/(kWh). Compared with the conventional dual-loop ORC system, the CCE-ORC system can generate 8% more net power, while the total volume of heat exchangers is 18% less.

Effects of biofuel blends on transient reactivity-controlled compression ignition engine combustion

Reactivity-controlled compression ignition is a low-temperature engine combustion strategy that utilizes in-cylinder blending of fuels with different autoignition characteristics to produce low NOx (oxides of nitrogen) and particulate matter emissions while maintaining high thermal efficiency. This study investigates reactivity-controlled compression ignition combustion in a light-duty, multi-cylinder, compression ignition engine over steady-state and transient operating conditions with both petroleum and bio-derived fuels. The engine experiments consisted of in-cylinder fuel blending with port fuel injection of gasoline or E20 and early-cycle, direct injection of ultra-low sulfur diesel or B20. Performance and emissions results were compared at steady-state and over an up-load change between 1 and 4 bar brake mean effective pressure at 1500 r/min. The results under steady-state operation showed that E20 offered reduced hydrocarbon emissions from the lower port fuel injection mass fraction. Port fuel injection mass fraction is defined as the mass fraction of the port fuel injection injected fuel compared to the total fuel injected, as calculated by [Formula: see text]. E20 also was shown to offer higher peak load capability and thermal efficiency than gasoline. Conversely, B20 was found to require a higher port fuel injection mass fraction with resulting higher hydrocarbon emissions. Peak load and efficiency were not affected by the use of B20. Steady-state NO and particulate matter emissions were unaffected by either of the biofuels. During the transient tests, E20 reduced hydrocarbon emissions while B20 increased hydrocarbon emissions. Both biofuels offered faster transient response to recover the CA50 to the steady-state CA50 value than gasoline or ultra-low sulfur diesel.

Analysis of an Internal Combustion Engine Using Porous Foams for Thermal Energy Recovery

Homogeneous and complete combustion in internal combustion engines is advantageous. The use of a porous foam in the exhaust gas in an engine cylinder for heat recovery is examined here with the aim of reducing engine emissions. The internal combustion engine with a porous core regenerator is modeled using SOPHT software, which solved the differential equations for the thermal circuit in the engine. The engine thermal efficiency is observed to increase from 43% to 53% when the porous core regenerator is applied. Further, raising the compression ratio causes the peak pressure and thermal efficiency to increase, e.g., increasing the compression ratio from 13 to 15 causes the thermal efficiency and output work to increase from 53% to 55% and from 4.86 to 4.93 kJ, respectively. The regenerator can also be used as a catalytic converter for fine particles and some other emissions. The regenerator oxidizes unburned hydrocarbons. Meanwhile, heat recovered from the exhaust gases can reduce fuel consumption, further reducing pollutant emissions from the internal combustion engine.

Heat transfer enhancement using rectangular vortex promoters in confined quasi-two-dimensional magnetohydrodynamic flows

Heat transfer efficiency from a duct side-wall in which an electrically conducting fluid flows under the influence of a transverse magnetic field is investigated. A quasi-two-dimensional magnetohydrodynamic model is employed to model the flow using high-resolution numerical simulation. The gap height and angle of attack of a rectangular cylinder, with aspect ratio α=1/2 and blockage ratio β=1/4, are independently varied to establish relationships between obstacle configuration and heat transfer efficiency. The heat transfer efficiency is measured through an efficiency index given by the ratio of heat transfer enhancement to pressure drop penalty in comparison to an empty duct case. At gap height ratios 1.15⩽G/Lc<2 for an upright cylinder above a heated lower wall, thermal enhancement and efficiency can be improved; with a peak thermal efficiency of η=1.6 occurring at G/Lc=1.5. Additional increases in thermal efficiency for an obstacle at the duct centre-line (G/Lc=2) can be achieved through inclining the cylinder at γ=-7.5°,γ=-37.5° and 0°<γ⩽22.5°. However, these configurations offered no improvement over simply offsetting an upright cylinder at a gap height ratio of G/Lc=1.5. For a cylinder offset at G/Lc=1.5, varying the incidence angle through -37.5°<γ⩽22.5°,-7.5°⩽γ<0° and 0°<γ⩽15° can lead to additional thermal efficiency benefits; with a global peak efficiency of η=1.7 occurring at γ=-37.5°. The streamwise distribution of the local time-averaged Nusselt number and the effect of Hartmann dampening for 100⩽Ha⩽2000 on heat transfer and flow dynamics are also investigated. A net power balance analysis reveals that in fusion applications the heat transfer enhancement dominates over the pumping power cost to produce net benefits for even modest heat transfer enhancement.