Zhang F, Xu H, Zhang J, Tian G, Kalghatgi G (2011) Investigation into Light Duty Dieseline Fuelled Partially-Premixed Compression Ignition Engine, SAE International Journal of Engines 4 (1) pp. 2124-2134
Conventional diesel fuelled Partially-Premixed Compression Ignition (PPCI) engines have been investigated by many researchers previously. However, the ease of ignition and difficulty of vaporization of diesel fuel make it imperfect for PPCI combustion. In this study, Dieseline (blending of diesel and gasoline) was looked into as the Partially-Premixed Compression Ignition fuel for its combination of two fuel properties, ignition-delay-increasing characteristics and higher volatility, which make it more suitable for PPCI combustion compared to neat diesel. A series of tests were carried out on a Euro IV light-duty common-rail diesel engine, and different engine modes, from low speed/load to middle speed/load were all tested, under which fuel blend ratios, EGR rates, injection timings and quantities were varied. The emissions, fuel consumption and combustion stability of this dieseline-fuelled PPCI combustion were all investigated. The results showed that dieseline had great advantages as a PPCI combustion fuel in terms of emission reduction. This was particularly significant at high-speed engine mode. It was also found that with a blend of 50% gasoline in diesel, the particle numbers total concentration could be reduced by 90% while low NOx level and high brake fuel conversion efficiency (around 30%) were maintained at all the loads tested. © 2011 SAE International.
Li Y, Tian G, Xu H (2012) Application of Biodiesel in Automotive Diesel Engines, In: Zhen F (eds.), Biodiesel - Feedstocks, Production and Applications 14 pp. 387-406
Lu Y, Wang L, Tian G, Roskilly T (2012) Study on a small scale solar powered organic Rankine cycle utilizing Scroll expander,
Tian G, Xu H, Daniel R, Li Y (2010) Spray characteristics and engine adaptability of 2, 5-dimethylfuran, Journal of Automotive Safety and Energy (2)
Al-Weshahi MA, Anderson A, Tian G (2012) Exergy efficiency enhancement of MSF desalination by heat recovery from hot distillate water stages, Applied Thermal Engineering
This detailed exergy analysis of a 3800 m 3/h Multi-Stage Flash (MSF) desalination plant is based on the latest published thermodynamics properties of water and seawater. The parameters of the study were extracted from a validated model of MSF desalination using IPSEpro software. The results confirmed that the overall exergy efficiency of the unit is lower than would be desirable at only 5.8%. Exergy inputs were destroyed by 55%, 17%, 10%, 4.3%, and 14% respectively, in the heat recovery stages, brine heater, heat rejection stages, pumps and brine streams disposal. Moreover, the detail of the study showed that the lowest exergy destruction occurs in the first stage, increasing gradually in heat recovery stages and sharply in heat rejection stages. The study concludes that recovering the heat from the hot distillate water stages can improve unit exergy efficiency from its low 5.8% to a more economical 14%, with the hot water parameters suitable for powering other thermal systems such as absorption chiller and multi-effect desalination. © 2012 Elsevier Ltd. All rights reserved.
Tian G, Li H, Xu H, Li Y, Mohan Raj S (2010) Spray characteristics study of DMF using phase doppler particle analyzer, SAE International Journal of Passenger Cars - Mechanical Systems 3 (1) pp. 948-958
2,5-dimethylfuran (DMF) is currently regarded as a potential alternative fuel to gasoline due to the development of new production technology. In this paper, the spray characteristics of DMF and its blends with gasoline were studied from a high pressure direct injection gasoline injector using the shadowgraph and Phase Doppler Particle Analyzer (PDPA) techniques, This includes the spray penetration, droplet velocity and size distribution of the various mixtures. In parallel commercial gasoline and ethanol were measured in order to compare the characteristics of DMF. A total of 52 points were measured along the spray so that the experimental results could be used for subsequent numerical modeling. In summary, the experimental results showed that DMF and its blends have similar spray properties to gasoline, compared to ethanol. The droplet size of DMF is generally smaller than ethanol and decreases faster with the increase of injection pressure. The mean velocity of DMF spray droplets is similar to gasoline and higher than ethanol. Ultimately, the spray characteristics of DMF are better suited to the gasoline engine technology than its counterpart, ethanol. © 2010 SAE International.
Tian G, Wang Z, Ge Q, Wang J, Shuai S (2007) Mode switch of SI-HCCI combustion on a GDI engine, SAE Technical Papers
Multi-mode combustion is an ideal combustion strategy to utilize HCCI for internal combustion engines. It combines HCCI combustion mode for low-middle load and traditional SI mode for high load and high speed. By changing the cam profiles from normal overlap for SI mode to the negative valve overlap (NVO) for HCCI mode, as well as the adjustment of direct injection strategy, the combustion mode transition between SI and HCCI was realized in one engine cycle. By two-step cam switch, the throttle action is separated from the cam action, which ensures the stabilization of mode transition. For validating the feasibility of the stepped switch, the influence of throttle position on HCCI combustion was carefully studied. Based on the research, the combustion mode switch was realized in one engine cycle; the whole switch process including throttle action was realized in 10 cycles. The entire process was smooth, rapid and reliable without any abnormal combustion such as knocking and misfiring. Copyright © 2007 SAE International.
Wang Z, Wang JX, Tian GH, Shuai SJ, Zhang Z, Yang J (2008) Research on steady and transient performance of an HCCI engine with gasoline direct injection, SAE Technical Papers
In this paper, a hybrid combustion mode in four-stroke gasoline direct injection engines was studied. Switching cam profiles and injection strategies simultaneously was adopted to obtain a rapid and smooth switch between SI mode and HCCI mode. Based on the continuous pressure traces and corresponding emissions, HCCI steady operation, HCCI transient process (combustion phase adjustment, SI-HCCI, HCCI-SI, HCCI cold start) were studied. In HCCI mode, HCCI combustion phase can be adjusted rapidly by changing the split injection ratio. The HCCI control strategies had been demonstrated in a Chery GDI2.0 engine. The HCCI engine simulation results show that, oxygen and active radicals are stored due to negative valve overlap and split fuel injection under learn burn condition. This reduces the HCCI sensitivity on inlet boundary conditions, such as intake charge and intake temperature. The engine can be run from 1500rpm to 4000rpm in HCCI mode without spark ignition. The COV of IMEP within and among cylinders are less than 2%. NOx emission is from 0.1 to 2 g/kW.h before TWC. The lowest BSFC is 240g/kW.h at 2000r/min. © 2008 SAE International.
Wang Z, Wang J, Tian G, Shuai S (2006) Study of Multi-mode Combustion System with Gasoline Direct Injection, ASME Trans. J. Gas Turbine and Power
Daniel R, Tian G, Xu H, Shuai S (2012) Ignition timing sensitivities of oxygenated biofuels compared to gasoline in a direct-injection SI engine, Fuel 99 pp. 72-82
Global concerns over atmospheric carbon dioxide (CO 2) levels and the security of fossil fuel supply have led to the development of biofuels; a potentially carbon-neutral and renewable fuel strategy. One new gasoline-alternative biofuel candidate is 2,5-dimethylfuran (DMF). In this paper, the potential of DMF is examined in a direct-injection spark-ignition (DISI) engine. Focus is given to the combustion performance and emissions sensitivity around the optimum spark timing, especially at 10 crank angle degrees retard (SR10). Such spark retard strategies are commonly used to reduce catalyst light-off times, albeit at the cost of reduced engine performance and increased CO 2. The results for DMF are compared to gasoline, ethanol, butanol and methanol so that its sensitivity can be positioned relatively. The overall order of spark sensitivity at the highest load (8.5 bar IMEP) was: gasoline > butanol > DMF > ethanol > methanol. The four biofuels widen the spark window due to improved anti-knock qualities and sometimes increased charge-cooling. This allows the increase of CO 2 to be better minimized than with gasoline. Furthermore, DMF is the only biofuel to produce high exhaust gas temperatures, similar to gasoline and helpful for fast catalyst light-off, whilst maintaining high combustion stabilities. This demonstrates the potentially favorable characteristics of DMF to become an effective cold-start fuel. © 2012 Elsevier Ltd. All rights reserved.
Bohl T, Tian G, Zeng W, He X, Roskilly A (2014) Optical investigation on diesel engine fuelled by vegetable oils, Energy Procedia 61 pp. 670-674
© 2014 The Authors.In the present paper the combustion behaviour and soot generation of different neat vegetable oils on a direct injection optical diesel engine have been investigated using in-cylinder pressure based combustion analysis and high-speed two colour method. A singlecylinder optical diesel engine with an electronically controlled common-rail fuel injection system has been used for this study. Four different vegetable oils, Jatropha, Croton, Rapeseed and Sunflower oil, have been tested at 120 MPa injection pressure and fuel temperatures of 60 and 90 °C. All tests were performed at fixed injection timings and fixed engine speed at 1200 rev/min with pilot and main injection. The experimental results show that although all four bio-oils have very similar physiochemical properties, some differences in their combustion and soot generation behaviour have been observed. It was concluded that sunflower oil (SFO) had very good combustion properties at lower temperatures compared to other fuels. While croton oil (CO) did not have outstanding combustion behaviour at any conditions, the combustion of Jatropha oil (JO) was improved at higher fuel injection temperatures.
Jia B, Jia B, Zuo Z, Tian G, Feng H, Roskilly AP (2015) Development and validation of a free-piston engine generator numerical model, Energy Conversion and Management 91 pp. 333-341
© 2014 Elsevier Ltd. All rights reserved. This paper focuses on the numerical modelling of a spark ignited free-piston engine generator and the model validation with test results. Detailed sub-models for both starting process and steady operation were derived. The compression and expansion processes were not regarded as ideal gas isentropic processes; both heat transfer and air leakage were taken into consideration. The simulation results show good agreement with the prototype test data for both the starting process and steady operation. During the starting process, the difference of the in-cylinder gas pressure can be controlled within 1 bar for every running cycle. For the steady operation process, the difference was less than 5% and the areas enclosed on the pressure-volume diagram were similar, indicating that the power produced by the engine and the engine efficiency could be predicted by this model. Based on this model, the starting process with different starting motor forces and the combustion process with various throttle openings were simulated. The engine performance during stable operation at 100% engine load was predicted, and the efficiency of the prototype was estimated to be 31.5% at power output of 4 kW.
Wang Z, Wei M, Peng F, Liu H, Guo C, Tian G (2016) Experimental evaluation of an integrated electric vehicle AC/HP system operating with R134a and R407C, Applied Thermal Engineering 100 pp. 1179-1188
Al-Weshahi MA, Tian G, Anderson A (2014) Performance enhancement of MSF desalination by recovering stage heat from distillate water using internal heat exchanger, Energy Procedia 61 pp. 381-384
© 2014 The Authors. Published by Elsevier Ltd.The paper presents an attempt to enhance unit performance of an existing 1274 m3/h Multi Stage Flash (MSF) desalination plant through sensible heat recovery from hot distillate water at the MSF stages to warm up the make-up seawater using internal heat exchange. The extraction of the distillate from stages could increase water production by 2% and reduces steam consumption by 5%. In addition, a reduction of seawater feed flow which also results in a drop of pump power consumption were observed. Environmentally, the modification could decrease CO2 emissions by 2300 tonnes annually.
Al-Weshahi MA, Anderson A, Tian G (2013) Exergy efficiency enhancement of MSF desalination by heat recovery from hot distillate water stages, Applied Thermal Engineering 53 (2) pp. 226-233
© 2012 Elsevier Ltd.This detailed exergy analysis of a 3800 m3/h Multi-Stage Flash (MSF) desalination plant is based on the latest published thermodynamics properties of water and seawater. The parameters of the study were extracted from a validated model of MSF desalination using IPSEpro software. The results confirmed that the overall exergy efficiency of the unit is lower than would be desirable at only 5.8%. Exergy inputs were destroyed by 55%, 17%, 10%, 4.3%, and 14% respectively, in the heat recovery stages, brine heater, heat rejection stages, pumps and brine streams disposal. Moreover, the detail of the study showed that the lowest exergy destruction occurs in the first stage, increasing gradually in heat recovery stages and sharply in heat rejection stages. The study concludes that recovering the heat from the hot distillate water stages can improve unit exergy efficiency from its low 5.8% to a more economical 14%, with the hot water parameters suitable for powering other thermal systems such as absorption chiller and multi-effect desalination.
Wang Z, Wang J, Shuai S, Tian G (2006) Experimental and Computational Studies on Gasoline HCCI Combustion Control Using Injection Strategies, ASME Trans. J. Gas Turbine and Power 128
Wang Z, Wang J, Shuai S, Tian G (2006) Study of the Effect of Spark Ignition on Gasoline HCCI Combustion, Proceedings of the Institution of Mechanical Engineers Part D-Journal of Automobile Engineering 220 (6) pp. 817-825
Jia B, Tian G, Smallbone A, Feng H, Zuo Z, Roskilly A (2015) A fast response free-piston engine generator numerical model for control application, Applied Energy 162 pp. 321-329
Daniel R, Tian G, Xu H, Wyszynski ML, Wu X, Huang Z (2011) Effect of spark timing and load on a DISI engine fuelled with 2,5-dimethylfuran, Fuel 90 (2) pp. 449-458
Currently, bioethanol leads the automotive fuel market as the main substitute for gasoline in spark-ignition engines. However, worldwide interest has been triggered in the potential of 2,5-dimethylfuran, known as DMF, since the discovery of improved production methods. Although the energy content of DMF is comparable to that of gasoline, little is known about its combustion characteristics and emissions. Therefore, this work examines the effect of DMF in a single cylinder direct-injection spark-ignition engine. The results are compared to ethanol and gasoline using the optimized spark timings for gasoline and the respective fuel. In summary, DMF produces competitive combustion and emissions qualities to gasoline, which, in some cases surpass ethanol. The two biofuels have a higher burning rate and lower initial combustion duration than gasoline. They also produce greater combustion efficiency, which helps to lower hydrocarbon and carbon monoxide emissions. These initial results highlight how DMF, which was originally only considered as an octane improver, has the potential to become a competitive renewable gasoline alternative. © 2010 Elsevier Ltd. All rights reserved.
Al-Weshahi M, Anderson A, Tian G, Makhdoum B (2013) Validation of simulation model for cogeneration power and water desalination plant, Int J Mod Opt 3 (1) pp. 46-53
Daniel R, Wang C, Xu H, Tian G, Richardson D (2012) Dual-injection as a knock mitigation strategy using pure ethanol and methanol, SAE Technical Papers
For spark ignition (SI) engines, the optimum spark timing is crucial for maximum efficiency. However, as the spark timing is advanced, so the propensity to knock increases, thus compromising efficiency. One method to suppress knock is to use high octane fuel additives. However, the blend ratio of these additives cannot be varied on demand. Therefore, with the advent of aggressive downsizing, new knock mitigation techniques are required. Fortuitously, there are two well-known lower alcohols which exhibit attractive knock mitigation properties: ethanol and methanol. Both not only have high octane ratings, but also result in greater charge-cooling than with gasoline. In the current work, the authors have exploited these attractive properties with the dual-injection, or the dual-fuel concept (gasoline in PFI and fuel additive in DI) using pure ethanol and methanol. The single cylinder engine results at 1500 rpm (»=1) show benefits to indicated efficiency and emissions (HC, CO and CO2) at almost every load (4.5 bar to 8.5 bar IMEP) compared to GDI. This is because the spark timing can be significantly advanced despite the use of relatively low blends (d50%, by volume), which lowers the combustion duration and improves the conversion of fuel energy into useful work. Overall, these results reinforce the potential of the dual-injection concept to provide a platform for aggressive downsizing, whilst contributing to a renewable energy economy. Copyright © 2012 SAE International.
Wu X, Daniel R, Tian G, Xu H, Huang Z, Richardson D (2011) Dual-injection: The flexible, bi-fuel concept for spark-ignition engines fuelled with various gasoline and biofuel blends, Applied Energy 88 (7) pp. 2305-2314
Dual-injection strategies in spark-ignition engines allow the in-cylinder blending of two different fuels at any blend ratio, when simultaneously combining port fuel injection (PFI) and direct-injection (DI). Either fuel can be used as the main fuel, depending on the engine demand and the fuel availability. This paper presents the preliminary investigation of such a flexible, bi-fuel concept using a single cylinder spark-ignition research engine. Gasoline has been used as the PFI fuel, while various mass fractions of gasoline, ethanol and 2,5-dimethylfuran (DMF) have been used in DI. The control of the excess air ratio during the in-cylinder mixing of two different fuels was realized using the cross-over theory of the carbon monoxide and oxygen emissions concentrations. The dual-injection results showed how the volumetric air flow rate, total input energy and indicated mean effective pressure (IMEP) increases with deceasing PFI mass fraction, regardless of the DI fuel. The indicated efficiency increases when using any ethanol fraction in DI and results in higher combustion and fuel conversion efficiencies compared to gasoline. Increasing the DMF mass fraction in DI reduces the combustion duration more significantly than with increased fractions of ethanol or gasoline in DI. The hydrocarbon (HC), oxides of nitrogen (NOx) and carbon dioxide (CO2) emissions mostly reduce when using any gasoline or ethanol fraction in DI. When using DMF, the HC emissions reduce, but the NOx and CO2 emissions increase. © 2011.
Li Y, Tian G, Zhang J, Xu H (2010) Comparative experimental study on microscopic spray characteristics of RME, GTL and diesel, SAE Technical Papers
In this paper, the microscopic spray characteristics of diesel, Rapeseed Methyl Ester (RME) and Gas-to-Liquid (GTL) fuel, were studied at different injection pressures and measuring positions using Phase Doppler Anemometry (PDA) technique and the velocity development and size distributions of the fuel droplets were analysed in order to understand spray atomisation process. The injection pressures ranged from 80MPa to 150MPa, and the measuring position varied from 20mm to 70mm downstream the nozzle. It was found that the data rate is quite low in the near nozzle region and at high injection pressure. Sauter Mean Diameter (SMD) of all fuels obviously decreases when the injection pressure increases from 80MPa to 120MPa; but the injection pressure has little promotion on the axial velocity of droplets. The SMD decreases with increasing axial distance from the nozzle from 40mm to 70mm downstream the nozzle for the given fuels at the injection pressure of 120MPa while relatively stable at 80MPa injection pressure. Moreover, the droplet velocity development of GTL and RME exhibits a similar tendency, compared with that of diesel at given injection pressure. GTL has the smallest SMD, compared with diesel and RME at the given test condition. For RME and diesel, SMD does not show obvious difference at 80MPa injection pressure. However, diesel obtained a smaller SMD when injection pressure was increased to 120MPa. Copyright © 2010 SAE International.
Jia B, Zuo Z, Feng H, Tian G, Roskilly AP (2014) Development Approach of a Spark-Ignited Free-Piston Engine Generator, SAE Technical Papers 2014-October
Copyright © 2014 SAE International.The free-piston engine generator (FPEG) is a novel type of energy conversion device; it integrates a two stroke combustion engine and a linear electric machine into a single unit. As an alternative to conventional engines, the FPEG is a promising power generation system due to its simplicity and high thermal efficiency and has attracted considerable research interests recently. This paper presents the development for a spark-ignited free-piston engine generator prototype, and the design of major sub-systems is introduced. The electrical linear machine is operated as a motor to start the engine and switched to a generator after successful ignition. Ignition is one of the most crucial problems for the generating process, thus a unique control sub-system to generate ignition signals at the correct ignition timing based on the piston position was completed. Then experiments of the starting process were carried out with the prototype. The results indicate that with a fixed motor force of 110N, the maximum in-cylinder gas pressure can reach 12 bar and the compression ratio can reach 8:1. Moreover, the experiment results show a good agreement with the simulation prediction. According to the performance of the starting process, the development of the prototype is acceptable and further research on the generating process will be undertaken soon.
Tian G, Daniel R, Li H, Xu H, Shuai S, Richards P (2010) Laminar burning velocities of 2, 5-dimethylfuran compared with ethanol and gasoline, Energy & Fuels 24 (7) pp. 3898-3905
Tian G, Wang Z, Wang J, Xu H, Shuai S (2009) Effects of key factors on the engine combustion mode switching between HCCI and SI, Journal of Engineering for Gas Turbines and Power: Transactions of the ASME 131 (1)
Wang Z, Shuai SJ, Wang JX, Tian GH (2006) A computational study of direct injection gasoline HCCI engine with secondary injection, Fuel 85 (12-13) pp. 1831-1841
The detailed intake, spray, combustion and pollution formation processes of compression ignition engine with high-octane fuel are studied by coupling multi-dimensional computational fluid dynamic (CFD) code with detailed chemical kinetics. An extended hydrocarbon oxidation reaction mechanism used for high-octane fuel was constructed and a modeling strategy of 3D-CFD/chemistry coupling for engine simulation is introduced to meet the requirements of execution time acceptable to simulate the whole engine physicochemical process including intake, compression, spray and combustion process. The improved 3D CFD/chemistry model was validated using the experimental data from HCCI engine with direct injection. Then, the CFD/chemistry model has been employed to simulate the intake, spray, combustion and pollution formation process of gasoline direct injection HCCI engine with two-stage injection strategy. The models account for intake flow structure, spray atomization, droplet evaporation and gas phase chemistry in complex multi-dimensional geometries. The calculated results show that the periphery of fuel-rich zone formed by the second injection ignited first, then the fuel-rich zone ignited and worked as an initiation to ignite the surrounding lean mixture zone formed by the first injection. The two-zone HCCI leads to sequential combustion, this makes ignition timing and combustion rate controllable. In addition, HCCI load range can be extended. However, the periphery of fuel-rich zone leads to fierce burning, which results in slightly high NOx emissions. © 2006 Elsevier Ltd. All rights reserved.
Ma H, Xu H, Schnier T, Wang J, Tian G (2012) A real-time control oriented HCCI combustion model in 4-stroke HCCI/SI GDI engine and model-based fast calibration development, SAE Technical Papers
For Homogeneous Charge Compression Ignition (HCCI) combustion, the auto-ignition process is very sensitive to in-cylinder conditions. This includes the change in in-cylinder temperature, the composition of chemical components and their concentrations. This sensitivity presents a major challenge for the accurate control of reliable and efficient HCCI combustion. This paper outlines our recent work: 1. a real-time control oriented gasoline-fueled HCCI combustion model and its implementation in Simulink with fixed step for the conversion into dSPACE Hardware-in-the-Loop (HIL) simulation purpose. 2. The development of model-based fast calibration for the best fuel efficiency and hydrocarbon emissions via evolutionary algorithm (EA). The model reported in this paper is able to run in real-time cycle-to-cycle under engine speeds below 4000rpm and with fixed simulation steps. This aims to achieve cycle-to-cycle performance calculation for Model based Predictive Control (MPC) and HIL simulation. With the aim of controlling the desired amount of trapped Exhaust Gas Recirculation (EGR) from the previous cycle, the phase of the Intake Valves Opening (IVO) and Exhaust Valves Closing (EVC) are designed to vary in this model. The model is able to anticipate the auto-ignition timing, MFB, combustion duration, in-cylinder pressure and hydrocarbon emissions etc. The validation has been conducted by comparing experimental data obtained from a Jaguar HCCI/SI V6 GDI engine at the University of Birmingham. This comparison shows good agreement between the simulation results and experimental data. Copyright © 2012 SAE International.
Zhang J, Tian G, Xu H, Zhang F, Daniel R (2010) The application of two closely coupled DPFs as the after-treatment system, SAE Technical Papers
In this study, the application of two closely coupled Diesel Particle Filters (DPFs), composed of an assistant DPF and a main standard honeycomb DPF, was investigated. A series of tests were carried out on a light-duty common-rail Euro 4 diesel engine and the emissions were measured and compared with those when a standard DOC+DPF system was used for the after-treatment. Replacing the DOC with an assisting DPF (ADPF) showed significant advantages in the reduction of particles, which had a direct impact in reducing the soot loading rate of the main DPF by up to 30%. Its oxidation characteristics not only showed equivalent exhaust-conversion efficiency, which concern the regulated gaseous emissions (CO and HC) under most engine conditions, but also continuously regenerated the soot it trapped. The impacts on the particle size and distributions were investigated, based on the new regulations on particle number limits; as well as the increased back pressure which is an unavoidable compromise. The overall performance of this DPF+DPF strategy showed great potential to be adopted in the future, Not only can this cope with tighter emissions regulations but it also has great cost benefits as main DPF's size and weight can be reduced. It also encourages more options for other cheaper materials as less soot is collected. Copyright © 2010 SAE International.
Wang Z, Shuai SJ, Wang JX, Tian GH, An XL (2006) Modeling of HCCI combustion: From 0D to 3D, SAE Technical Papers
The detailed chemical kinetics was implemented into the 0D single-zone model, 1D engine cycle model and 3D CFD model respectively. Both simulation and experiment were carried out on a four-stroke gasoline HCCI engine with direct injection. The 0D model (HRG) was developed to study the isolating effect of HCCI parameters. The 1D engine cycle model with HRG was established to study the gas exchange process and the direct injection strategy in the gasoline HCCI engine with two-stage direct injection (TSDI) and negative valve overlap (NVO). The 3D model with HRG was constructed to study the ignition control mechanism in "two-zone HCCI" combustion via analysis the auto-ignition spots distribution in combustion chamber. "Two-zone HCCI" is defined in this paper as premixed ultra-lean compression ignition combining with premixed ultra-rich compression ignition. The three models were validated by experiments. The simulated results provided a detailed insight into the processes governing combustion and pollutant formation in the HCCI engine. TSDI fuel strategy and two-zone HCCI combustion are adopted to resolve the two stubborn problems of HCCI ignition timing control and high load extension. Copyright © 2006 SAE International.
Tian G, Wang Z, Ge Q (2007) Control of SI/HCCI Mode Transition on a GDI Engine, Proceedings of the Institution of Mechanical Engineers Part D-Journal of Automobile Engineering 221 pp. 867-875
Al-Weshahi MA, Anderson A, Tian G (2014) Organic Rankine Cycle recovering stage heat from MSF desalination distillate water, Applied Energy 130 pp. 738-747
This investigation addresses the potential for heat recovery from Multi Stage Flash (MSF) desalination plant hot distillate water to power an Organic Rankine Cycle (ORC), comparing R134a and R245fa refrigerants as the working fluid. Using design characteristics of an existing ORC unit, the model was first validated against its measured output. The distillate hot water from MSF stages is utilised to provide heat to the ORC and performance is investigated for both working fluids and for the number of MSF stages for heat recovery. For the specific MSF plant investigated, the net produced ORC power is found the highest with extraction up to MSF powering stage 8, generating 359. kW when R245fa is used and 307. kW when R134a is used. Both refrigerants exhibit an increase of power output and decrease of energy efficiency as heat is recovered from more MSF stages. The influence of variation of the evaporator and cooling temperature on ORC performance is demonstrated to be significant for both refrigerants, with R245fa performing better in this specific application. © 2014 Elsevier Ltd.
Abdullah N, Wyszynski M, Tsolakis A, Mamat R, Xu H, Tian G (2010) Combined effects of pilot quantity, injection pressure and dwell periods on the combustion and emissions behaviour of a modern V6 diesel engine, Archivum Combustionis
Jia B, Zuo Z, Feng H, Tian G, Roskilly AP (2014) Investigation of the starting process of free-piston engine generator by mechanical resonance, Energy Procedia 61 pp. 572-577
© 2014 The Authors. Published by Elsevier Ltd.As an alternative to conventional engines, free-piston engine generator (FPEG) is a promising power generation system due to its simplicity and high thermal efficiency. One crucial technical challenge in the FPEG operation is the initial process of overcoming the compression force to achieve a certain speed which allows a stable and continuous operation, i.e. starting process. This paper proposes a novel method to start the engine by mechanical resonance. A closed-loop control model was developed and implemented in a prototype FPEG which was driven by a linear machine with a constant driving force. Both numerical and experimental investigation was carried out. The results show that once the linear motor force have overcome the initial friction force, both the in-cylinder peak pressure and the amplitude of the piston motion would increase gradually by resonance and quickly achieve the target for ignition. With a fixed motor force of 110N, within 0.8 second, the maximum in-cylinder pressure can achieve 12 bars, the compression ratio can reach 9:1, and the engine is ready for ignition. The results demonstrated that it is feasible to start the FPEG by mechanical resonance in a constant motor force in the direction of the natural bouncing motion.
Tian G, Liu Z, Wei M, Song P, Lu Y, Ashby G, Roskilly T (2015) Modelling and Optimisation on scroll expander for Waste Heat Recovery Organic Rankine Cycle,
Daniel R, Wang C, Xu H, Tian G (2012) Effects of combustion phasing, injection timing, relative air-fuel ratio and variable valve timing on SI engine performance and emissions using 2,5-dimethylfuran, SAE Technical Papers
Ethanol has long been regarded as the optimal gasoline-alternative biofuel for spark-ignition (SI) engines. It is used widely in Latin and North America and is increasingly accepted as an attractive option across Europe. Nevertheless, its low energy density requires a high rate of manufacture; in areas which are deficient of arable land, such rates might prove problematic. Therefore, fuels with higher calorific values, such as butanol or 2,5-dimethylfuran (DMF) deserve consideration; a similar yield to ethanol, in theory, would require much less land. This report addresses the suitability of DMF, to meet the needs as a biofuel substitute for gasoline in SI engines, using ethanol as the biofuel benchmark. Specific attention is given to the sensitivity of DMF to various engine control parameters: combustion phasing (ignition timing), injection timing, relative air-fuel ratio and valve timing (intake and exhaust). Focus is given to the window for optimization; the parameter range which sustains optimal IMEP (within 2%) but provides the largest reduction of emissions (HC or NOx). The test results using a single cylinder SI research engine at 1500rpm show how DMF is less sensitive to key engine parameters, compared to gasoline. This allows a wider window for emissions optimization because the IMEP remains optimal across a greater parameter range. Copyright © 2012 SAE International.
Daniel R, Wang C, Xu H, Tian G (2012) Split-injection strategies under full-load using DMF, a new biofuel candidate, compared to ethanol in a GDI engine, SAE Technical Papers
It is well known that direct-injection (DI) is a technology enabler for stratified combustion in spark-ignition (SI) engines. At full-load or wide-open throttle (WOT), partial charge stratification can suppress knock, enabling greater spark advance and increased torque. Such split-injection or double-pulse injection strategies are employed when using gasoline in DI (GDI). However, as the use of biofuels is set to increase, is this mode still beneficial? In the current study, the authors attempt to answer this question using two gasoline-alternative biofuels: firstly, ethanol; the widely used gasoline-alternative biofuel and secondly, 2,5-dimethylfuran (DMF); the new biofuel candidate. These results have been benchmarked against gasoline in a single-cylinder, spray-guided DISI research engine at WOT (»=1 and 1500rpm). Firstly, single-pulse start of injection (SOI) timing sweeps were conducted with each fuel to find the highest volumetric efficiency and IMEP. The resulting optimum SOI timing for gasoline was then used as the first injection (SOI1) with each fuel in the split-injection tests. In this instance, second SOI timing (SOI2) sweeps were made using two split-ratios (SOI1:SOI2 = 1:1 and 2:1). For the single-pulse SOI timing sweeps, the change in IMEP when using ethanol is symmetrical either side of the maximum. However, when using gasoline and DMF, the behavior is asymmetrical, with maximums later and earlier than with ethanol, respectively. For split-injection, the maximum IMEP increases when fuelled with the biofuels, whilst maintaining acceptable engine stability. This increase, however, is much more dependent on SOI2 timing than with gasoline, due to the deterioration of in-cylinder mixing and slower combustion. Copyright © 2012 SAE International.
Zhang R, Fan W, Xing F, Song S, Shi Q, Tian G (2015) Experimental study of slight temperature rise combustion in trapped vortex combustors for gas turbines, Energy 93 pp. 1535-1547
Turner D, Tian G, Xu H, Wyszynski ML, Theodoridis E (2009) An experimental study of dieseline combustion in a direct injection engine, SAE Technical Papers
The differences between modern diesel and gasoline engine configurations are now becoming smaller and smaller, and in fact will be even smaller in the near future. They will all use moderately high compression ratios and complex direct injection strategies. The HCCI combustion mode is likely to lead to the merging of gasoline and diesel engine technologies to handle the challenges they are facing, offering a number of opportunities for the development of the fuels, engine control and after-treatment. The authors' recent experimental research into the HCCI combustion quality of gasoline and diesel blend fuels has referred to the new combustion technology as 'Dieseline'. It is found that this kind of fuel blend provides some unexpected benefits to the expansion of the operating window and reduction of hydrocarbon emissions in HCCI engines, and these benefits include extended low misfire limit, increased engine stability, reduced peak cylinder pressures and reduced emissions within the whole HCCI operating window. It was shown that the lean limit of lambda can almost reach up to 2.0 when the engine is operated with moderate compression ratios. It is shown that the combustion of the blended fuel offers promise to the desired ignition quality, which reduces the dependence of HCCI on EGR trapping or intake heating for a wide range of CR. The HCCI operating region for the unheated NVO can be significantly extended into lower IMEP values and the audible knocking is restrained to the highest values of air fuel ratio at high load boundary for the highest mixture temperatures. Copyright ©2009 SAE International.
Wu X, Li Q, Fu J, Tang C, Huang Z, Daniel R, Tian G, Xu H (2012) Laminar burning characteristics of 2,5-dimethylfuran and iso-octane blend at elevated temperatures and pressures, Fuel 95 pp. 234-240
2,5-Dimethylfuran, known as DMF, is a promising second-generation biofuel candidate. The potential of 2,5-dimethylfuran as an additive in iso-octane (used as gasoline fuel substitute in this study) was studied. Using outwardly spherical flame method and high speed schlieren photography, laminar burning characteristics of 2,5-dimethylfuran/iso-octane (20%/80% vol., designated as D20)/air mixtures were experimentally investigated. Laminar flame speeds and Markstein lengths of D20-air mixtures were empirically organized as a function of initial pressures and temperatures. Onset of cellular structures at the flame front was observed at relatively higher initial pressures due to the combined effect of diffusional-thermal and hydrodynamic instabilities. Laminar flame speeds of D20-air mixtures are higher than those of iso-octane-air mixtures when the equivalence ratio is greater than 1.2. © 2012 Elsevier Ltd. All rights reserved.
Jia B, Tian G, Feng H, Zuo Z, Roskilly AP (2014) An experimental investigation into the starting process of free-piston engine generator, Applied Energy
© 2015 Elsevier Ltd.This paper presents an experimental investigation of the starting process of a prototype free piston engine generator (FPEG). Experimental test results show that during the motoring stage, the peak in-cylinder pressure and compression ratio increase in a non-linear manner and trend to reach a stable state after a number of cycles. The motoring force is suggested to be within a reasonable range. With a fixed starting force of 125. N, the in-cylinder air fuel mixture was successfully ignited at the fourth cycle with a compression ratio of over 9:1. The peak in-cylinder pressure for the first combustion cycle reached over 40. bar. The piston ran at high and relatively constant speed at the middle portion of the stroke. The peak piston velocity increases significantly to around 4.0. m/s. Cycle-to-cycle variation of the piston movement was significant and the engine misfired frequently. During the misfire cycles, the peak piston velocity decreased to nearly 2.5. m/s; and the piston dynamics were similar to the motoring process. Based on these, discussion on misfire and further stable running control, as well as the linear electric machine mode switch were presented.
Tian G, Zhang Y, Roskilly T (2014) Semi-dynamic simulation of ORC based diesel engine WHR system, Energy Procedia 61 pp. 695-699
© 2014 The Authors.Organic Rankine Cycle (ORC) based engine waste heat recovery (WHR) has been recognised as a promising technology as it can potentially improve the total engine efficiency significantly and has no noticeable effect on engine operation. In this paper, a model based investigation in this technology has been presented. A semi-dynamic model has been developed which consists of a detailed 1-D engine acoustic model, an ideal ORC thermodynamic model and a bridging model that couples the two sub-models and enables a dynamic data transfer between these two models, thus enables a semi-dynamic simulation. A parametric analysis has been carried out for working fluid selection that allows the best match of the engine working conditions. Water, R134a and R245fa were selected as working fluid candidates, and the simulation results suggest that despite water has the highest cycle efficiency, it is unsuitable to use it because as a wet fluid, water cannot be heated to superheated steam in most of the conditions. For the two organic refrigerants, R245fa is superior to R123a in terms of cycle efficiency. A cyclic simulation following a WHSC engine operation cycle suggests that the control of working fluid flow rate is necessary to maintain a high ORC cycle efficiency. A preliminary optimal control can achieve 8.1% fuel economy improvement throughout the whole cycle.
Jia B, Zuo Z, Feng H, Tian G, Smallbone A, Roskilly T (2016) Effect of closed-loop controlled resonance based mechanism to start free piston engine generator: Simulation and test results, Applied Energy 164 pp. 532-539
Tian G, Xu H, Daniel R (2011) DMF - A New Biofuel Candidate, In: Dos Santos Bernardes MA (eds.), Biofuel Production-Recent Developments and Prospects 19 pp. 487-520 InTech
This book aspires to be a comprehensive summary of current biofuels issues and thereby contribute to the
understanding of this important topic. Readers will find themes including biofuels development efforts, their
implications for the food industry, current and future biofuels crops, the successful Brazilian ethanol program,
insights of the first, second, third and fourth biofuel generations, advanced biofuel production techniques,
related waste treatment, emissions and environmental impacts, water consumption, produced allergens and
toxins. Additionally, the biofuel policy discussion is expected to be continuing in the foreseeable future and the
reading of the biofuels features dealt with in this book, are recommended for anyone interested in
understanding this diverse and developing theme
In this study, the particle emission characteristics of 10% alternative diesel fuel blends (Rapeseed Methyl Ester and Gas-to-Liquid) were investigated through the tests carried out on a light duty common-rail Euro 4 diesel engine. Under steady engine conditions, the study focused on particle number concentration and size distribution, to comply with the particle metrics of the European Emission Regulations (Regulation NO 715/2007, amended by 692/2008 and 595/2009). The non-volatile particle characteristics during the engine warming up were also investigated. They indicated that without any modification to the engine, adding selected alternative fuels, even at a low percentage, can result in a noticeable reduction of the total particle numbers; however, the number of nucleation mode particles can increase in certain cases. For all the fuels tested, the increase of engine load results in a general reduction of particle numbers and an increase of particle mean diameters while increasing EGR leads to increased total particle numbers, which are mainly in the nucleation mode. The engine particle emissions suffer much higher numbers of the nucleation mode non-volatiles during warming up than during normal operations. © 2010 SAE International.
Depletion of oil resources and increase in energy demand have driven the researchers to seek ways to convert the waste products into high quality oils that could replace fossil fuels. Plastic waste is in abundance and can be converted into high quality oil through the pyrolysis process. In this study, pyrolysis oils were produced from polyethylene (LDPE700), the most common used plastic, and ethylene-vinyl acetate (EVA900) at pyrolysis temperatures of 700oC and 900oC respectively. The oils were then tested in a four cylinder diesel engine, and the performance, combustion and emission characteristics were analysed in comparison with mineral diesel. It was found that the engine could operate on both oils without the addition of diesel. LDPE700 exhibited almost identical combustion characteristics and brake thermal e ciency to that of diesel operation, with lower NOX, CO and CO2 emissions but higher unburned hydrocarbons (UHC). On the contrary, EVA900 presented longer ignition delay period, lower e ciency (1.5?2%), higher NOX and UHC emissions and lower CO and CO2 in comparison to diesel. The addition of diesel to the EVA900 did not significantly improve the overall engine performance.
In this paper, the macroscopic spray characteristics of four next-generation biofuels, namely, hydrotreated vegetable oil (HVO), Palm oil methyl ester (PME), Soybean oil methyl ester (SME) and used cooking oil methyl ester (UCOME) were investigated in detail using a constant volume spray vessel, and benchmarked against reference mineral diesel (B0). During experiments, fuels were heated to 80 °C to achieve an engine-like environment before being injected at various compression ignition engine relevant operating conditions. The fuel spray tip penetration, spray cone angle and spray area were investigated analysing images obtained using a direct photography technique. Furthermore, a modified spray model was proposed to extend its scope to include alternative fuels by considering fuel density as part of the spray model. The results show that HVO with the lowest density of all fuels achieves the shortest penetration distance and the highest cone angle, resulting in a more distributed fuel-air mixture. All fuels have very similar spray areas for the same injection conditions, but the specific spray area per injected mass is highest for HVO followed by the three methyl esters. It was concluded that the fuel liquid viscosity was a significant factor on the observed air-fuel mixing process. The spray characteristics were compared with our engine test results and can be used to explain observed engine behaviour when fuelled with biofuels.
Waste heat recovery from exhaust gas with organic Rankine cycle (ORC) systems is a promising method to improve the overall thermal efficiency of engines. The performance of a diesel engine integrated with an ORC system is evaluated in this paper. Simulation models of the diesel engine and the ORC system are developed in GT-suite separately, and a combined system model is developed in Simulink environment. The engine simulation results are validated experimentally. The steady performance evaluation of the engine with ORC system at different engine conditionsis presented, and the acceleration performance of the diesel engine with and without ORC is evaluated. The performance of the engine during the ORC expander start-stop process is also discussed. The steady performance simulation results indicate that, the net power output increment, the brake specific fuel consumption (BSFC) reduction and the thermal efficiency improvement of the engine with ORC system can be up to 4.13 kW, 3.61 g/(kW·h) and 0.66 %, respectively. The transient performance simulation results show that the ORC system has minimal effects on the acceleration performance of the engine.
Plastic waste is an ideal source of energy due to its high heating value and abundance. It can be converted into oil through the pyrolysis process and utilised in internal combustion engines to produce power and heat. In the present work, plastic pyrolysis oil is manufactured via a fast pyrolysis process using a feedstock consisting of different types of plastic. The oil was analysed and it was found that its properties are similar to diesel fuel. The plastic pyrolysis oil was tested on a four-cylinder direct injection diesel engine running at various blends of plastic pyrolysis oil and diesel fuel from 0% to 100% at different engine loads from 25% to 100%. The engine combustion characteristics, performance and exhaust emissions were analysed and compared with diesel fuel operation. The results showed that the engine is able to run on plastic pyrolysis oil at high loads presenting similar performance to diesel while at lower loads the longer ignition delay period causes stability issues. The brake thermal efficiency for plastic pyrolysis oil at full load was slightly lower than diesel, but NOX emissions were considerably higher. The results suggested that the plastic pyrolysis oil is a promising alternative fuel for certain engine application at certain operation conditions.
This paper presents the investigation of engine optimisation when plastic pyrolysis oil (PPO) is used as the primary fuel of a direct injection diesel engine. Our previous investigation revealed that PPO is a promising fuel however the results suggested that control parameters should be optimised in order to obtain a better engine performance. In the present work, the injection timing was advanced, and fuel additives were utilised to overcome the issues experienced in the previous work. In addition, spray characteristics of PPO were investigated in comparison with diesel to provide in-depth understanding of the engine behaviour. The experimental results on advanced injection timing (AIT) showed a reduced brake thermal efficiency and increased carbon monoxide, unburned hydrocarbons and nitrogen oxides emissions in comparison to standard injection timing. On the other hand, the addition of fuel additive resulted in a higher engine efficiency and lower exhaust emissions. Finally, the spray tests revealed that the spray tip penetration for PPO is faster than diesel. The results suggested that AIT is not a preferable option while fuel additive is a promising solution for long-term use of PPO in diesel engines.
Energy saving and emission reduction of engines were taken seriously, especially for vehicular diesel engines.
Exhaust heat recovery based on organic Rankine cycle (ORC) system has been considered as an effective
approach for improving engine fuel economy. This article presents the investigation of water or air cooling
method for an ORC exhaust heat recovery system on a heavy duty truck through simulations. The models of
the truck engine and the ORC system were developed in GT-suite, and the integration system model was
developed in the Simulink environment. The validity of the models was verified experimentally. The
performance of the vehicular engine with ORC system using water or air cooling method was comparatively
analyzed. The simulation results indicated that water cooling method is more suitable for the vehicular ORC
system than air cooling method. The relation between benefit and penalty of the ORC system and cooling system
was discussed. The operating condition of the cooling system was confirmed having significant effects on the
combined system performance, especially the fan speed. The performance improvement of the engine with the
use of ORC system was further evaluated under different engine operating conditions and ambient temperatures.
Lower ambient temperature had positive impacts on the engine fuel economy. The mass flow rate of exhaust
gas for heat recovery should be regulated for better performance under high ambient temperature.
Polypropylene is the most common type of plastic found in municipal solid waste. The production of polypropylene is expected
to increase due to the widespread utilization in daily life, resulting in even higher amounts of polypropylene waste. Sending this
plastic to landfill not only exacerbates environmental problems, but also results in energy loss due to the elevated energy content of
polypropylene. Pyrolysis is a process that can effectively convert polypropylene waste into fuel, which can then be used to generate
power and heat. In the present study, the ect of the pyrolysis temperature on the pyrolysis of polypropylene was investigated, and
the oils produced at 700oC (PP700) and 900oC (PP900) were used to fuel a four cylinder diesel engine. The engine's combustion,
performance and emission characteristics were analysed and compared to diesel operation. The results showed that both PP700
and PP900 enabled stable engine operation, with PP900 performing slightly better in terms of efficiency and emissions. However,
PP700 and PP900 were found to have longer ignition delay periods, longer combustion periods, lower brake thermal efficiencies,
higher NOX, UHC and CO emissions, and lower CO2 emissions in comparison to diesel operation. Nonetheless, the addition of a
small quantity of diesel improved the overall performance of the oil blends, resulting in comparable results to diesel in the case of
The increase in worldwide greenhouse gas emissions and costs for fossil fuels are forcing fuel suppliers and engine manufacturers to consider more sustainable alternatives for powering internal combustion engines. One very promising equivalent to mineral diesel fuel is hydrotreated vegetable oil (HVO) as it is highly paraffinic and offers similar combustion characteristics. This fuel offer the potential of not requiring further engine hardware modification together with correspondingly lower exhaust gas emissions and better fuel consumption than mineral diesel.
In this paper the spray and combustion characteristics of HVO and its blends are investigated and compared with mineral diesel (European standard). Evidence of the reported reductions in NOx emissions has proven contradictory with some researchers reporting large reductions, whilst others measured no differences.
This paper reports the results from comparison of three different experimental tests methods using diesel/HVO binary fuel blends. The macroscopic spray characteristics have been investigated and quantified using a constant volume spray vessel. Engine performance and exhaust emissions have also been characterised using a HD diesel engine in its original configuration (mineral diesel fuel-ready) and then in a recalibrated configuration optimised for HVO fuel.
The results show that the engine injection control and also the fuel quality can influence the formation of NOx and particulate matter significantly. In-particular a potential pilot injection proved highly influential upon whether NOx emissions were reduced or not. When optimising the fuel injection, a reduction in NOx emissions of up to 18% or reductions of PN of up to 42?66% were achieved with simultaneous savings in fuel consumption of 4.3%.
Diesel particulate matter (PM) was collected at different tailpipe positions where the sampling temperature was different. The PM samples were pre-treated in air at high temperature until 40% mass loss. Then, the partially oxidized PM samples were aged in air for 40 days, and the physicochemical properties of partially oxidized PM before and after aging in air were tested. The results showed that the oxidation activity of partially oxidized PM was appreciably restored by aging in air. The morphology, diameter distribution of primary particles and nanostructures of partially oxidized PM changed slightly after aging in air. The amorphous carbon adsorbing on PM surface were faintly observed through high resolution transmission electron microscope (HRTEM) images. The adsorption of oxygen-containing functional groups (carbonyl and hydroxy) and organic compounds were evidenced through Fourier transform infrared spectroscopy (FTIR) and Raman parameter AD3/AG. The crystallite size calculated using Raman parameter decreased slightly after aging in air.
Diesel particulate matter (PM) samples were collected at different tailpipe positions where sampling
temperature differed greatly. All the samples were pre-heated in air at high temperature until 40%
mass was burnt out. Physicochemical properties of diesel PM both before and after partial oxidation
were analyzed, and to further figure out the reasons of oxidation activity changes in the oxidation
process. The results showed that ignition temperature of PM whose sampling temperature was
higher than 208 °C differed greatly from PM sampled below that temperature. After partial
oxidation, sample 3 presented the hugest oxidation activity decreasing with burn out temperature
increasing by 14.7 °C. Primary particle size distribution shifted to smaller diameter direction after
partial oxidation, and particle stacking degree decreased evidently. Nanostructures of diesel PM
transferred from onion like structures with randomly arranged crystallite to core-shell like structures
with void inner cores. Oxygen-containing functional groups (carbonyl and hydroxy) decreased
evidently after PM partial oxidation that was obtained from Fourier transform infrared spectroscopy
(FTIR) spectra, it was consistent with the results of Raman parameter ID3/IG.
In this research, a one-way fluid-thermal-solid numerical coupling model of a scroll expander for a waste heat recovery system was developed and used to investigate the deformation of the scroll pair. The pressure and thermal loads were firstly calculated by a CFD model, and the surface pressure and body temperature distributions of the scroll members were used as boundary conditions in the FEM model to obtain the deformation distributions of the scroll parts. Three time instants that may have significant adverse impacts on the maximum forces were selected to determine the most critical time for the occurrence of the maximum deformation of the scroll wraps. The results showed that the deformations induced by inertial force only occurred at the orbiting scroll tail, whereas the deformations in other regions negligible. At the time instants of t/T equaled to 13/15 and 1, the deformations induced by pressure loads had the opposite direction compared to that of the thermal loads and thus the two deformations canceled each other out and the coupling deformations decreased. The deformations induced by pressure loads were less significant than the thermal loads, therefore the coupling deformation was dominated by the thermal loads. The results also confirmed that the critical time at t/T equaled to 7/20 for the occurrence of the largest deformation resulted from the maximum axial forces that were exerted on the fixed scroll.
Scroll expanders are currently attracting interest for integration in small scale organic Rankine cycle (ORC) waste
heat recovery applications and have been subject to significant research over the last two decades. The most common
geometrical design uses a scroll profile generated by the involute of a circle with a constant wall thickness. A major
disadvantage of this approach is that the increase of the geometric expansion ratio is constrained, since it is accompanied
with a large increase in the scroll profile length and is associated with a decreased efficiency. In this paper, the
published literature related to scroll expander geometry is reviewed. Investigations regarding the influence of varying
scroll geometrical parameters on the performance of scroll expanders with a constant wall thickness are first examined.
The use of variable wall thicknesses and their effects on the performance are then considered. Finally, the impact of
scroll expander geometries using unconventional scroll profiles and scroll tip shape variations on the performance is
discussed and summarised. The major conclusion to be drawn from this review is that scroll expanders with variable
wall thickness scrolls should be further designed and developed. It is possible to increase the geometric expansion ratio
without increasing the length of the scroll profiles. CFD simulations are a promising tool to illustrate and understand
the non-uniform and asymmetric inner flow and temperature fields. The related benefits could lead to scroll devices
with variable wall thickness not only improving the performance of organic Rankine cycle (ORC) systems but also
opening a broad new field of applications such as refrigeration cycles and other power cycles where a high pressure
ratio is preferred.
In an Organic Rankine cycle (ORC) system, the working fluid pump plays an important role in the system performance. This paper focused on the operating characteristics of a multistage centrifugal pump at various speed and condensation conditions. The experimental investigation was carried out to assess the influence of the performance of the pump by the ORC system with special attention to actual net power output, thermal efficiency as well as back work ratio (BWR). The results showed that an increase in the pump speed led to an increase in the mass flow rate and expand in the operating range of the outlet pressure. The mass flow rate decreased nonlinearly with the increase of the outlet pressure from 0.22 to 2.41 MPa; the electric power consumption changed between 151.54 and 2409.34 W and the mechanical efficiency of the pump changed from 7.90% to 61.88% when the pump speed varied from 1160 to 2900 RPM. Furthermore, at lower pump specific speed the ORC system achieved higher thermal efficiency, which suggested that an ultra-low specific speed pump was a promising candidate for an ORC system. The results also suggested that the effects of condensation conditions on the pump performance decreased with the pump speed increasing and BWR was relatively sensitive to the condensation conditions, especially at low pump speed.
Catalytic converters mitigate carbon monoxide, hydrocarbon, nitrogen oxides and particulate matter emissions from internal combustion engines, and allow meeting the increasingly stringent emission regulations. However, catalytic converters experience light-off issues during cold start and warm up. This paper reviews the literature on the thermal management of catalysts, which aims to significantly reduce the light-off time and emission concentrations through appropriate heating methods. In particular, methods based on the control of engine parameters are easily implementable, as they do not require extra heating devices. They present good performance in terms of catalyst light-off time reduction, but bring high fuel penalties, caused by the heat loss and unburnt fuel. Other thermal management methods, such as those based on burners, reformers and electrically heated catalysts, involve the installation of additional devices, but allow flexibility in the location and intensity of the heat injection, which can effectively reduce the heat loss in the tailpipe. Heat storage materials decrease catalyst light-off time, emission concentrations and fuel consumption, but they are not effective if the engine remains switched off for long periods of time. The main recommendation of this survey is that integrated and more advanced thermal management control strategies should be developed to reduce light-off time without significant energy penalty.