Showing papers on "Thermal efficiency published in 2003"

Porous glass electroosmotic pumps: design and experiments.

Abstract: An analytical model for electroosmotic flow rate, total pump current, and thermodynamic efficiency reported in a previous paper has been applied as a design guideline to fabricate porous-structure EO pumps. We have fabricated sintered-glass EO pumps that provide maximum flow rates and pressure capacities of 33 ml/min and 1.3 atm, respectively, at applied potential 100 V. These pumps are designed to be integrated with two-phase microchannel heat exchangers with load capacities of order 100 W and greater. Experiments were conducted with pumps of various geometries and using a relevant, practical range of working electrolyte ionic concentration. Characterization of the pumping performance are discussed in the terms of porosity, tortuosity, pore size, and the dependence of zeta potential on bulk ion density of the working solution. The effects of pressure and flow rate on pump current and thermodynamic efficiency are analyzed and compared to the model prediction. In particular, we explore the important tradeoff between increasing flow rate capacity and obtaining adequate thermodynamic efficiency. This research aims to demonstrate the performance of EOF pump systems and to investigate optimal and practical pump designs. We also present a gas recombination device that makes possible the implementation of this pumping technology into a closed-flow loop where electrolytic gases are converted into water and reclaimed by the system.

The Impact of Exhaust Gas Recirculation on Performance and Emissions of a Heavy-Duty Diesel Engine

Abstract: This work studies the complex interactions resulting from the application and control of Exhaust Gas Recirculation (EGR) on a production heavy-duty diesel engine system, and its effectiveness in reducing NOx emissions. The coupling between EGR, the Variable Geometry Turbocharger (VGT) and the EGR cooler critically affects boost pressure, air/fuel ratio (A/F), combustion efficiency and pumping work. It is shown that EGR provides an effective means for reducing flame temperatures and NOx emissions, particularly under low A/F ratio conditions. However, engine thermal efficiency tends to decrease with EGR as a result of decreasing indicated work and increasing pumping work. Combustion deterioration is predominant at higher load, low speed and low boost conditions, due to a significant decrease of A/F ratio with increasing EGR. For conditions allowing the VGT to maintain high enough boost and hence A/F ratio, efficiency losses with increased EGR are largely attributed to increased pumping work. Finally, the total system heat rejection increases significantly due to EGR cooling.

Analysis of biomass-residue-based cogeneration system in palm oil mills

Abstract: Palm oil mills in Malaysia operate on cogeneration system using biomass residue as fuel in the boiler. The boiler produces high pressure and temperature steam which expands in a backpressure steam turbine and produces enough electric power for the internal needs of the mill. The exhaust steam from the turbine goes to an accumulator which distributes the steam to various processes in the mill. The study were made on seven palm oil mills in the Perak state in Malaysia. The primary objectives of the study are to determine boiler and turbine efficiencies, energy utilization factor, oil extraction rate and heat/power ratio for various palm oil mills working under similar conditions and adopting same processes. The palm oil industry is one of those rare industries where very little attempt is made to save energy. The energy balance in a typical palm oil mill is far from optimum and there is considerable scope for improvement. Bench-marking is necessary for the components in the mill. Energy-use bench-marking can give an overview of energy performance of the mills. The calculations were done to get net gain in power when back pressure turbine is replaced by a condensing turbine. It was found that the boiler and turbine have low thermal efficiencies compared to conventional ones used in power plants due to non-homogeneity and non-uniform quality of the fuel. The extraction rate was around 0.188. The use of condensing turbine increase the power output by 60% and the utilization factor was found to be 65% for the cogeneration system.

The Effect of Cooled EGR on Emissions and Performance of a Turbocharged HCCI Engine

Abstract: This paper discusses the effects of cooled EGR on a turbo charged multi cylinder HCCI engine. A six cylinder, 12 liter, Scania D12 truck engine is modified for HCCI operation. It is fitted with port fuel injection of ethanol and n-heptane and cylinder pressure sensors for closed loop combustion control. The effects of EGR are studied in different operating regimes of the engine. During idle, low speed and no load, the focus is on the effects on combustion efficiency, emissions of unburned hydrocarbons and CO. At intermediate load, run without turbocharging to achieve a well defined experiment, combustion efficiency and emissions from incomplete combustion are still of interest. However the effect on NOX and the thermodynamic effect on thermal efficiency, from a different gas composition, are studied as well. At high load and boost pressure the main focus is NOX emissions and the ability to run high mean effective pressure without exceeding the physical constraints of the engine. In this case the effects of EGR on boost and combustion duration and phasing are of primary interest. It is shown that CO, HC and NOX emissions in most cases all improve with EGR compared to lean burn. Combustion efficiency, which is computed based on exhaust gas analysis, increases with EGR due to lower emissions of CO and HC.

Optimizing the Scavenging System for a Two-Stroke Cycle, Free Piston Engine for High Efficiency and Low Emissions: A Computational Approach

Abstract: A free piston internal combustion (IC) engine operating on high compression ratio (CR) homogeneous charge compression ignition (HCCI) combustion is being developed by Sandia National Laboratories to significantly improve the thermal efficiency and exhaust emissions relative to conventional crankshaft-driven SI and Diesel engines. A two-stroke scavenging process recharges the engine and is key to realizing the efficiency and emissions potential of the device. To ensure that the engine’s performance goals can be achieved the scavenging system was configured using computational fluid dynamics (CFD), zero- and onedimensional modeling, and single step parametric variations. A wide range of design options was investigated including the use of loop, hybrid-loop and uniflow scavenging methods, different charge delivery options, and various operating schemes. Parameters such as the intake/exhaust port arrangement, valve lift/timing, charging pressure and piston frequency were varied. Operating schemes including a standard uniflow configuration, a low charging pressure option, a stratified scavenging geometry, and an over-expanded (Atkinson) cycle were studied. The computational results indicated that a stratified scavenging scheme employing a uniflow geometry, and supplied by a stable, low temperature/pressure charge will best optimize the efficiency and emissions characteristics of the engine. The operating CR can be maximized through substantial replacement of the burned charge, while short-circuiting emissions can be controlled by late fuel introduction. The in-cylinder flows are important to both NOx and short-circuiting emissions with inadequate mixing (and resulting temperature stratification) the predominant driver of NO production, and fuel penetration to the exhaust valve region the main cause of unburned hydrocarbon emissions.

Hydrogen IC Engine Boosting Performance and NOx Study

Abstract: Hydrogen Internal Combustion Engine (H 2 ICE) powered vehicles have been considered a low emission, low cost, practical method to help establish a hydrogen fueling infrastructure. However, the naturally aspirated H 2 ICE operating lean has performance issues requiring either increased displacement or induction boost to have comparable power to the modern gasoline powered IC engine. Ford Scientific Research Laboratory has continued its H 2 ICE system investigation, conducting dynamometer engine-boosting experiments utilizing a 2.0 L Zetec engine (with compression ratios of 14.5:1 and 12.5:1), and a 2.3L Duratec HE-4 engine'(with a compression ratio of 12.2:1) with boosted manifold air pressure up to 200 kPa. Test data of brake torque and exhaust emissions are reported at various boost pressures. Results of a detailed NOx study, conducted at University of California - Riverside, with EGR and aftertreatment for a naturally aspirated 2.0L Zetec engine are also reported. The trade off between engine compression ratio and thermal efficiency, power density, and NOx emission control strategy is discussed.

Effects of process parameters of the IS process on total thermal efficiency to produce hydrogen from water

Abstract: Thermal efficiency of the IS (sulfur-iodine) thermochemical hydrogen production cycle process was investigated. The heat and mass balance of the process were calculated with various operating conditions, and the effects of these conditions on the thermal efficiency were evaluated. The flowsheet of the H2SO4 decomposition designed by Knoche et al. (1984) was used. An electro-electrodialysis (EED) cell for the concentration of HI and a hydrogen permselective membrane reactor for decomposition of HI were applied to the process. Sensitivities of four operating conditions (the HI conversion ratio at the HI decomposition reactor, the reflux ratio at the HI distillation column, the pressure in the HI distillation column, and the concentration of HI after the EED cell) were investigated. The concentration of HI had the most significant effect on thermal efficiency. The difference of the efficiency was 13.3%. Other conditions had little effects within 2% of the efficiency. Effects of nonideality of the process (electric energy loss in the EED cell, loss at heat exchangers and loss of the waste heat recovery as electric energy) were evaluated. The difference of the efficiencies by the loss in the EED cell was 11.4%. The efficiency decreased by 5.7% by the loss at heat exchangers. The loss of the waste heat recovery lowered the efficiency by 6.3%. The result shows that the development of the EED cell, heat exchangers and electric recovery is effective in improving thermal efficiency. The operating conditions such as the HI concentration after the EED cell should be optimized to obtain the maximum thermal efficiency after the developments of the apparatuses. Change of the state of nonideality needs the optimization of the concentration. The thermal efficiency of the total process was 56.8% with ideal operating conditions of the EED cell, heat exchangers and high performance waste heat recovery.

System with an internal combustion engine, a fuel cell and a climate control unit for heating and/or cooling the interior of a motor vehicle and process for the operation thereof

Abstract: A system with an internal combustion engine which has a heat transfer circuit, a fuel cell and a climate control unit which is accommodated in the heat transfer circuit of the internal combustion engine. The system has a heat transfer arrangement for transferring the exhaust heat of the fuel cell to the heat transfer circuit and a bypass for bridging a segment of the heat transfer circuit which runs through the internal combustion engine so that, in the bypassed operating state, an isolated circuit is formed. In stationary operation, this enables an optimized operating mode since the internal combustion engine is no longer heated and the exhaust heat of the fuel cell is fully available for heating purposes. The climate control unit can have a fuel cell and an arrangement for transferring the heat produced by the fuel cell to the vehicle interior has a fan unit by which an air flow can be produced for cooling the fuel cell and a heating unit which is powered by the fuel cell and by which the air flow for heating the vehicle interior can be additionally heated. For cooling or heating the interior of a motor vehicle, the system can have a cooling circuit with a compressor, a condenser, an expansion element, and a first evaporator and an APU or a fuel cell to electrically power the compressor, and a second cooling circuit a second evaporator, the second cooling circuit being connected to the first cooling circuit.

Residual-effected homogeneous charge compression ignition at a low compression ratio using exhaust reinduction

Abstract: Studies have been conducted to assess the performance of homogeneous charge compression ignition (HCCI) combustion initiated by exhaust reinduction from the previous engine cycle. Reinduction is achieved using a fully flexible electrohydraulic variable-valve actuation system. In this way, HCCI is implemented at low compression ratio without throttling the intake or exhaust, and without preheating the intake charge. By using late exhaust valve closing and late intake valve opening strategies, steady HCCI combustion was achieved over a range of engine conditions. By varying the timing of both valve events, control can be exerted over both work output (load) and combustion phasing. In comparison with throttled spark ignition (SI) operation on the same engine, HCCI achieved 25–55 per cent of the peak SI indicated work, and did so at uniformly higher thermal efficiency. This was accompanied by a two order of magnitude reduction in NO emissions. In fact, single-digit (ppm) NO emissions were realized und...

Steam reforming of methane and water-gas shift in catalytic wall reactors

Abstract: Catalytic wall reactors permit high heat-transfer rates between exothermic and endothermic reactions taking place catalytically on opposite sides of a thin wall, because they eliminate resistance to heat transfer in thermal boundary layers, thus making them compact and efficient. A parallel plate catalytic wall reactor was built in which exothermic methane combustion on platinum and endothermic methane steam reforming on rhodium occurred on walls in alternate channels. This reactor gave 95% conversion of methane to synthesis gas with a residence time of ∼70 ms at a steam/methane ratio of 1/1 with a thermal efficiency of ∼60%. A preheat pass was added on the combustion side that enabled heat exchange between hot combustion products and cold combustion inlet gases to increase temperature upstream and decrease it downstream. This two-pass reactor gave H2/CO ratios of ∼14/1 with a residence time of ∼170 ms at a steam/methane ratio of 4/1. To increase the H2/CO ratio, the endothermic channel length was also extended, with a platinum-ceria wall coating on the extended region to further reduce downstream temperatures and promote water-gas shift. This reactor gave downstream temperatures as low as 200°C, and produced H2/CO ratios as high as 42/1 with a residence time of ∼300 ms at a steam/methane ratio of 4/1. The extended reactor shows good potential for producing high H2/CO ratio product streams suitable for preferential oxidation and subsequent use in fuel cells in a scalable configuration.

The universal power and efficiency characteristics for irreversible reciprocating heat engine cycles

Abstract: The performance of irreversible reciprocating heat engine cycles with heat transfer loss and friction-like term loss is analysed using finite-time thermodynamics. The universal relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, and the optimal relation between power output and the efficiency of the cycles are derived. Moreover, analysis and optimization of the model were carried out in order to investigate the effect of cycle processes on the performance of the cycle using numerical examples. The results obtained herein include the performance characteristics of irreversible reciprocating Diesel, Otto, Atkinson and Brayton cycles.

A High-Efficiency Solid Oxide Fuel Cell Hybrid Power System Using the Mercury 50 Advanced Turbine Systems Gas Turbine

Abstract: The conceptual design of a 20 MWe-class hybrid power generating system that integrates a Siemens Westinghouse pressurized solid oxide fuel cell generator with a Mercury 50 gas turbine is discussed. The Mercury 50 was designed and developed by Caterpillar/Solar Turbines during the U.S. Department of Energy (DOE) Advanced Turbine Systems (ATS) program, and the hybrid system design concept was evaluated during a recently completed project that was part of the DOE high efficiency fossil power plant (HEFPP) program. While achieving a high power system efficiency by the hybrid cycle approach was important, the focus of the design study was to select the solid oxide fuel cell (SOFC) generator capacity such that the low specific cost of the ATS gas turbine and the high efficiency of the more expensive pressurized solid oxide fuel cell (PSOFC) generator would combine optimally to produce an attractively low cost of electricity (COE) for the overall power system. The system cycle and physical characteristics are described; power, efficiency, and emissions estimates are presented; and estimates of system cost and COE are provided. In addition, two bottoming cycle options (steam turbine and ammonia turbine) are described, and performance and cost projections for each are reviewed.

Experimental investigation of heat losses in a ceramic coated diesel engine

Abstract: Ever since the invention of this reliable workhorse of the automotive world, the quest for increasing the efficiency of an internal combustion engine has been going on. In recent times, much attention has been focused on achieving this goal by reducing energy lost to the coolant during the power stroke of the cycle. A cursory look at the internal combustion engine heat balance indicates that the input energy is divided into roughly three equal parts: energy converted to useful work, energy transferred to coolant and energy lost to exhaust. The reduction in, or the elimination of, in-cylinder heat transfer to either the coolant and/or the environment does not violate the second law of thermodynamics and, moreover, according to the first law, has the potential of producing more work. Added to this, another important advantage of the concept is the great reduction in parasitic losses due to elimination of cooling system, thus increasing the brake horsepower of the engine. The main purpose of this study is to evaluate the heat losses at different engine loads and speeds with and without ceramic-coated diesel engine. The results showed a reduction in heat losses to the coolant and an increase in exhaust energy at all load levels.

Design of a Microfabricated Rankine Cycle Steam Turbine for Power Generation

Abstract: This paper presents the system-level and component design of a micro steam turbine power plant-on-a-chip which implements the Rankine cycle for micro power generation. The microfabricated device consists of a steam turbine that drives an integrated micropump and generator. Two-phase flow heat exchangers are also integrated on-chip with the rotating components to form a complete micro heat engine unit, converting heat to electricity. The system-level design includes cycle analysis and overall performance predictions, accounting for the expected performance of miniaturized components, thermal and structural integrity of the microsystem, and system-level trade-offs for optimal overall performance. Operating principles and design studies are also presented for the core component, with emphasis on a multistage, planar, radial microturbine and a spiral groove viscous pump. Design consideration for two-phase flow heat exchangers, microbearings, seals and micro-generators are also presented. Expected power levels range from 1–12 W per chip with energy conversion efficiency in the range of 1–11%. This suggests power density of up to 12 kW/kg for this technology, which is an order of magnitude greater than competing technologies, such as thermoelectrics. This study suggests the viability of a micro Rankine power plant-on-a-chip, but also identifies critical engineering challenges that must be met for practical implementation.Copyright © 2003 by ASME