Comparison of performance of a Greener direct-injection stratified-charge (DISC) engine with a spark-ignition engine using a simplified model

The direct-injection stratified charge (DISC) engine is a hybrid between spark ignition (SI) and compression-ignition engines, it combines many of the best features of both with some unique advantages of its own. This includes multi-fuel capability, high thermal efficiency, low NOx production, and low particulate emissions.This work shows how simple semi-global models can predict the performance of the SI and DISC engines with reasonable accuracy, without going to details of modeling for internal processes such as: swirl, mixing and detailed combustion kinetics.The operating variables studied were inlet manifold pressure p_i, exhaust manifold pressure p_e, engine speed N, equivalence ratio Φ, and volumetric efficiency η_v at different loads. The corresponding performance parameters were the brake mean effective pressure bmep, brake power P_b, and brake thermal efficiency η_b,th. The main contribution of this work is the production of friendly set of curve-fitting correlations for engine performance. The bmep and the P_b increase with the load for both engines. For spark ignition engines the bmep increases by about 70% when load increases from 50% to 100%. With the DISC engine, this ratio increases to 75%. The percent improvement in η_b,th for the DISC to the SI engine is around 50% which increases with part load, lower compression ratio r_c and p_i.     

Optimisation of operating parameters on the performance characteristics of a free piston engine linear generator fuelled by CNG–H2 blends using the response surface methodology (RSM)

The free piston engine linear generator (FPELG) is a simple engine structure with few components, making it a promising power generation system. However, because the engine works without a crankshaft, the handling of the piston motion control (PMC) is the main challenge influencing the stability and performance of FPELGs. In this article, the optimal operating parameters of FPELG for maximising engine performance and reducing exhaust gas emissions were studied. Moreover, the influence of adding hydrogen (H₂) to compressed natural gas (CNG) fuel on FPELG performance was investigated. The influence of operating parameters on in-cylinder pressure was also analysed. The single-piston FPELG fuelled by CNG blended with H₂ was used to run the experiments. The response surface methodology (RSM), including the central composite design (CCD), was used. Then, adequacy models were developed and verified by ANOVA. Three independent factors on seven responses were utilised for optimisation. Results showed that the optimal operating conditions of lambda, ignition velocity, and injection position were 0.96, 0.53 m/s, and ?14.9 mm, respectively. The best-predicted values were as follows: indicated mean effective pressure (IMEP) of 7.6 bar, in-cylinder pressure of 27.87 bar, combustion efficiency of 39.64%, CO of 9531.41 ppm, CO₂ of 2.4%, HC of 551.75 ppm, and NO_X of 113.737 ppm. Furthermore, results showed that the experimental data could be fitted well with the predicted quadratic model.     

Energy,exergy, and environmental (3E) assessments of an integrated molten carbonate fuel cell (MCFC), Stirling engine and organic Rankine cycle (ORC) cogeneration system fed by a biomass-fueled gasifier

In this paper, a novel syngas-fed combined cogeneration plant, integrating a biomass gasifier, a molten carbonate fuel cell (MCFC), a heat recovery steam generator (HRSG) unit, a Stirling engine, and an organic Rankine cycle (ORC), is introduced and thermodynamically analyzed to recognize its potentials compared to the previous solo/combined systems. For the proposed system, energetic, exergetic as well as environmental evaluations are performed. Based on the results, the gasifier and the fuel cell have a significant contribution to the exergy destruction of the system. Through a parametric study, the current density and the stack temperature difference are known as the main effective factors on the plant performance. Meanwhile, dividing the whole system into three sub-models, i.e., model (1): power production plant including the gasifier and MCFC without including Stirling engine, HRSG, and ORC unit, model (2): the cogeneration system without ORC unit, and model (3): the whole cogeneration system, an environmental impact assessment is carried out regarding CO₂ emission. Considering paper as biomass revealed that maximum value of exergy efficiency is 50.18% with CO₂ emissions of 28.9 × 10⁻² t.MWh⁻¹ which compared to the solo MCFC system indicates 28.40% increase and 13.3 × 10⁻² t.MWh⁻¹ decrease in exergy efficiency and CO₂ emission, respectively.     

船用2 MW级天然气发动机及动力系统研发

天然气作为优质高效、绿色清洁的低碳能源,正逐步成为我国主体能源之一,具有重要的战略意义和显著的经济效益。介绍了新近推出的自主品牌M23G天然气发动机的开发历程、性能及主要技术特点。针对气体发动机的性能特点,提出了船舶天然气动力系统配置、设计中须关注的关键技术,以及天然气发动机在陆用能源的应用方向。     

Improved model for solar cells with up-conversion of low-energy photons

In this paper we analyze the system proposed by Trupke T, Green MA, Würfel P. [Improving solar cell efficiencies by up-conversion of sub-band-gap light. J Appl Phys 2002; 92: 4117–22] to increase solar cells efficiency. The system consists in adding to the cell a so-called up-converter, which is a device able to convert the low-energy (sub-band gap) incident solar photons into photons of higher energy. The main novelty of the present model consists in taking into account appropriately the refractive index of solar cell and converter materials. Two configurations are studied: cell and rear converter (C–RC) and front converter and cell (FC–C), respectively. The main conclusions of this work are as follows: (1) The maximum solar energy conversion efficiency increases in case of the C–RC system as compared to the efficiency of a solar cell operating alone, especially at higher values of the concentration ratio; (2) the solar energy conversion efficiency of the C–RC system increases by increasing both the cell and the up-converter refractive indices; (3) the energy conversion efficiency does not increase by adding a front up-converter to the cell, whatever the value of the concentration ratio is.     

Evaluation of vibration characteristics of a hydroxyl (HHO) gas generator installed diesel engine fuelled with different diesel–biodiesel blends

There are two main reasons of alternative fuel search of scientists: environmental problems resulted from combustion of fossil fuels and limited reserves of crude oil. Biodiesel and Hydrogen (H₂) are two of the most promising alternative fuels with their environmental friendly combustion profiles. The aim of this study was to evaluate vibration level of a hydroxyl (HHO) gas generator installed and diesel engine using different kinds of biodiesel fuels. In this study, at different flow rates, the effect of HHO gas addition on engine vibration performance was investigated with a Mitsubishi Canter 4D34-2A diesel engine. HHO gas introduced to the test engine via its intake manifold with 2, 4 and 6 L per minute (LPM) flow rates when the engine was fuelled with sunflower, canola, and corn biodiesels. The vibration data was collected between 1200 and 2400 rpm engine speeds by 300 rpm intervals. Finally, artificial neural network (ANN) approach was conducted in order to predict the effect of fuel properties and HHO amount on engine vibration level.     

喷油率形状可变的增压式压电共轨喷射系统

柴油机的低排放与经济性是相互矛盾的，为降低制造成本和运行费用，必须进一步采取机内净化措施降低柴油机的原始排放和燃油耗，其中燃油喷射系统依然起着十分重要的作用。Bosch公司正在研制的一种增压式压电共轨喷射系统(APCRS)，不但能以较低的共轨压力获得比一般共轨系统高得多的喷油压力，而且除能进行多次预喷射和后喷射外，还能使主喷射的喷油率形状从矩形变化到斜坡形直至靴形，与柴油机的运转工况达到最佳的匹配，在宽广的发动机特性曲线范围内显示出明显降低排放和燃油耗的潜力。     

A comparative study of lumped equivalent circuit models of a lithium battery for state of charge prediction

Battery modeling plays an important role in remaining range prediction and battery management system development. An accurate and realistic battery model is essential to design an efficient electric storage system. The goal of this paper is to investigate the performance of different circuit topologies for diffusion process in the equivalent circuit models (ECMs). The theory of diffusion process approximation by using resistive‐capacitor (RC) networks is explained in frequency domain. The terminal voltage predictive capabilities of the ECMs are compared and validated with test data. The numerical simulation results show that model prediction accuracy and computation burdens increase along with the number of RC pairs. The ECM with three RC networks is the best choice in terms of the balance between accuracy and complexity for ternary lithium batteries. In addition, a novel method of combining unscented Kalman filter (UKF) algorithm with initial state of charge (SOC) acceleration convergence for SOC estimation is proposed. The results of urban dynamometer driving schedule (UDDS) show that ECM with three RC networks has the best comprehensive performance on calculation cost and SOC estimation accuracy.     

Performance assessment of steam Rankine cycle and sCO2 Brayton cycle for waste heat recovery in a cement plant: A comparative study for supercritical fluids

The main objective of this study is to investigate the feasibility of a waste heat recovery (WHR) closed Brayton cycle (BC) working with supercritical carbon dioxide (sCO₂). For this aim, an actual WHR steam Rankine cycle (RC) in a cement plant was evaluated thermodynamically. After, a sCO₂-BC was theoretically adapted to the actual WHR system for the performance assessment. Both systems were analyzed comparatively in terms of energy and exergy. According to the results, the sCO₂-BC showed higher performance than the actual steam RC with a net electricity generation of 9363 kW where it was calculated as 8275 kW for the actual cycle. In addition, the energy efficiencies were found to be 27.6% and 24.18% where the exergy efficiencies were calculated as 58.22% and 51.39% for sCO₂-BC and steam RC, respectively. In the following part of the study, the closed BC was examined for different supercritical working fluids, namely, CO₂, pentafluoroethane (R125), fluoromethane (R41), and sulfur hexafluoride (SF6). Parametrical analyses were conducted to determine the effects of the system parameters such as turbine inlet temperature, compressor inlet temperature, and pressure ratio on the cycle performance. The simulation results of the comparative study showed that, among the supercritical fluids, the CO₂ demonstrated a higher performance for the closed BC with an energy efficiency of 27.9% followed by R41, SF6, and R125. As a result, the utilization of sCO₂-BC for WHR can be sustainably adapted and extended for environmentally friendly energy generation.     

Thermal stability of hexamethyldisiloxane (MM) as a working fluid for organic Rankine cycle

The high temperature organic Rankine cycle (ORC) has recently attracted much interest for its excellent performance in renewable energy utilization and industrial waste heat recovery. The thermal stability of working fluids is the important property for fluid selection studies because of the possible decomposition at high temperatures. Siloxanes are good selections for high temperature ORCs in previous studies. However, study on the thermal stability of siloxanes for high temperature ORCs is scant. This paper studied the thermal stability of siloxanes, using hexamethyldisiloxane (MM) as a representative fluid. An experimental method with two test systems was designed to identify the compositions of decomposition products. Linear siloxanes, such as octamethyltrisiloxane (MDM), were found to be the main decomposition products of MM. The influences of pressure, temperature, and time on the decomposition were then determined experimentally. The decomposition mechanism of MM and the influences of the decomposition on ORCs were also analyzed based on the experimental results.     

实现小型二冲程汽油机分层扫气的膜片式喷射化油器

发明并研究了一种结构简单的膜片式喷射化油器（ＤＩＣ）,其工作原理是利用曲轴箱峰值压力给燃油加压,由一组膜片机构将进气喉口处的压差转换到燃油主量孔两侧,使供油量与进气量成正比,从而实现燃油的计量和喷射。本系统和适当的扫气系统结合起来,可实现小型二冲程汽油机的分层扫气,减少燃油的短路损失,大幅度降低油耗和未燃碳氢排放。本文还提出了保留常规化油器的低负荷供油系统,用来解决一般简单喷射系统低负荷性能恶化的问题,又使燃油系统结构大为简化。本文描述了ＤＩＣ的基本概念和工作原理,并在３０ｃｍ３试验专用汽油机上进行了膜片式喷射化油器供油特性和发动机性能的对比试验。     

一种新型复合函数凸轮型线的设计研究

在对几种常见车用发动机凸轮型线分析研究的基础上,以复合摆线Ⅱ型凸轮型线(FB2)为研究对象,研究了影响FB2型凸轮型线性能的主要因素。根据FB2型凸轮型线设计灵活的特点,寻找出了复合函数型线各主要设计参数对型线性能的影响规律和设计调整方法。提出了通过改变型线的3个主要参数m、n、p,来实现改变丰满系数、正负加速度峰值、凸轮桃尖处的凸轮-挺柱接触应力等性能的设计思路。在此基础上,开发出一种能够更好地调节负加速度段的新型复合函数凸轮型线FH1。     

Exergetic analysis and evaluation of a new application of gas engine heat pumps (GEHPs) for food drying processes

In this study, three medicinal and aromatic plants (Foeniculum vulgare, Malva sylvestris L. and Thymus vulgaris) were dried in a pilot scale gas engine driven heat pump drier, which was designed, constructed and installed in Ege University, Izmir, Turkey. Drying experiments were performed at an air temperature of 45 °C with an air velocity of 1 m/s. In this work, the performance of the drier along with its main components is evaluated using exergy analysis method. The most important component for improving the system efficiency is found to be the gas engine, followed by the exhaust air heat exchanger for the drying system. An exergy loss and flow diagram (the so-called Grassmann diagram) of the whole drying system is also presented to give quantitative information regarding the proportion of the exergy input dissipated in the various system components, while the sustainability index values for the system components are calculated to indicate how sustainability is affected by changing the exergy efficiency of a process. Gas engine, expansion valve and drying ducts account for more than 60% amount of exergy in the system. The exergetic efficiency values are in the range of 77.68–79.21% for the heat pump unit, 39.26–43.24% for the gas engine driven heat pump unit, 81.29–81.56% for the drying chamber and 48.24–51.28% for the overall drying system.     

Thermodynamic analysis of combustion and pollutants formation in a wood-gas spark-ignited heavy-duty engine

Awareness of limitations of petroleum based liquid fuels as for example used in spark-ignited heavy-duty engines for power generation, has led engineers to propose various solutions such as the use of alternative/renewable energy sources. Wood-gas is an alternative gaseous fuel generated from the gasification of wood, which could be used as a full supplement fuel in conventional heavy-duty spark-ignited engines fuelled with natural gas. Previous related research studies have shown that the main disadvantage of the wood-gas combustion is its negative impact on brake engine efficiency compared to the normal natural gas operation, while NO and CO emissions are also increased. Compression ratio and spark timing are some of the engine parameters, which influence significantly the combustion mechanism inside the combustion chamber of a wood-gas powered spark-ignited engine. In order to examine the effect of these parameters on the performance and exhaust emissions of a heavy-duty, turbocharged, spark-ignited engine fuelled with wood-gas, a theoretical investigation is conducted in this work by using a numerical simulation. The results concern engine performance characteristics, NO and CO emissions for various engine operating conditions (i.e. air to fuel excess ratios), by using a comprehensive two-zone phenomenological model. The predictive ability of the thermodynamic model was tested against experimental measurements, which were obtained from the operation of a multi-cylinder, four-stroke, turbocharged, spark-ignited engine fuelled with wood-gas fuel at various loads. The experimental results are found to be in good agreement with the respective computed ones obtained from the simulation model. The main objective of the comparative assessment shown in the present work is to record and comparatively evaluate the relative impact of each one of the above mentioned parameters (compression ratio and spark timing) on the engine performance characteristics and emitted pollutants. Furthermore, an effort is made to determine the optimum combinations between these parameters, since at high engine load conditions their simultaneous increase may lead in undesirable results concerning the engine performance characteristics. The conclusions from the present investigation are valuable for the use of wood-gas as a full supplement energy source in conventional, natural gas fuelled, heavy-duty, spark-ignited engines used for electric power generation.     

Anatomy of a sub-tropical Positive Energy Home (PEH)

Zero energy buildings (ZEB) and zero energy homes (ZEH) are a current hot topic globally for policy makers (what are the benefits and costs), designers (how do we design them), the construction industry (can we build them), marketing (will consumers buy them) and researchers (do they work and what are the implications). This paper presents initial findings from actual measured data from a 9 star (as built), off-ground detached family home constructed in south-east Queensland in 2008. The integrated systems approach to the design of the house is analysed in each of its three main goals: maximising the thermal performance of the building envelope, minimising energy demand whilst maintaining energy service levels, and implementing a multi-pronged low carbon approach to energy supply. The performance outcomes of each of these stages are evaluated against definitions of net zero carbon/net zero emissions (site and source) and net zero energy (onsite generation vs primary energy imports). The paper will conclude with a summary of the multiple benefits of combining very high efficiency building envelopes with diverse energy management strategies: a robustness, resilience, affordability and autonomy not generally seen in housing.     

Energy, exergy and cost analysis of a micro-cogeneration system based on an Ericsson engine

Hot air engines (Stirling and Ericsson engines) are well suited for micro-cogeneration applications because they are noiseless, and they require very low maintenance. Ericsson engines (i.e. Joule cycle reciprocating engines with external heat supply) are especially interesting because their design is less constrained than Stirling engines, leading to potentially cheaper and energetically better systems. We study the coupling of such an Ericsson engine with a system of natural gas combustion. In order to design this plant, we carry out classic energy, exergy and exergo-economic analyses. This study does not deal with a purely theoretical thermodynamic cycle. Instead, it is led with a special attempt to describe as accurately as possible what could be the design and the performance of a real engine. It allows us to balance energetic performance and heat exchanger sizes, to plot the exergy Grassmann diagram, and to evaluate the cost of the thermal and electric energy production. These simple analyses confirm the interest of such systems for micro-cogeneration purposes. The main result of this study is thus to draw the attention on Ericsson engines, unfortunately unfairly fallen into oblivion.     

Effect of exhaust gas recirculation (EGR) temperature for various EGR rates on heavy duty DI diesel engine performance and emissions

DI diesel engines are well established today as the main powertrain solution for trucks and other relevant heavy duty vehicles. At the same time emission legislation (mainly for NO_x and particulate matter) becomes stricter, reducing their limit to extremely low values. One efficient method to control NO_x in order to achieve future emissions limits is the use of rather high exhaust gas recirculation (EGR) rates accompanied by increased boost pressure to avoid the negative impact on soot emissions. The method is based on the reduction of gas temperature level and O₂ availability inside the combustion chamber, but unfortunately it has usually an adverse effect on soot emissions and brake specific fuel consumption (bsfc). The use of high EGR rates creates the need for EGR gas cooling in order to minimize its negative impact on soot emissions especially at high engine load were the EGR flow rate and exhaust temperature are high. For this reason in the present paper it is examined, using a multi-zone combustion model, the effect of cooled EGR gas temperature level for various EGR percentages on performance and emissions of a turbocharged DI heavy duty diesel engine operating at full load. Results reveal that the decrease of EGR gas temperature has a positive effect on bsfc, soot (lower values) while it has only a small positive effect on NO. As revealed, the effect of low EGR temperature is stronger at high EGR rates.     

涡轮增压柴油机高海拔(低气压)性能试验研究

在内燃机高海拔(低气压)模拟试验台上，对不同模拟海拔高度下的涡轮增压柴油机性能进行了试验研究。分析了海拔高度的变化对涡轮增压柴油机动力性、经济性的影响，研究了涡轮增压柴油机最大转矩、最低燃油消耗率随海拔高度的变化规律，为进一步提高高海拔地区涡轮增压柴油机的性能提供了重要的理论依据。     

Free piston Stirling engines: A review

This paper presents a detailed review on free piston Stirling engines (FPSEs) technology. Generally, the Stirling engines can be categorized into two broad classes comprising kinematic and dynamic converters among which FPSEs are known as the dynamic type. Other well-known dynamic Stirling converters are Fluidyne and thermosacoustic engines among which the thermosacoustic ones are the most advanced Stirling converters recently presented. In this research, the dynamic Stirling engines are first introduced and reviewed. Then, the review work is directed toward the FPSEs, one of the most reliable dynamic Stirling converters utilized in different applications such as combined heat and power systems (CHPs). Subsequently, the working principles of different types of FPSEs and their performance are summarized. Next, several manufactured FPSEs, as well as their corresponding features and applications, are discussed. Finally, the article is conducted to analysis and modeling approaches of FPSEs. Accordingly, linear and nonlinear analytical techniques of FPSEs are introduced, and some comparative data are provided to verify the modeling schemes. Then, various design parameters affecting the engine performance are introduced and studied. The outcomes of this review work demonstrate the potential of FPSEs for different applications and reveal that the perturbation-based model is likely the most comprehensive nonlinear method for modeling and design of the FPSEs.     

船用柴油机主轴承盖对轴承油膜润滑的影响研究

基于AVL Excite PU软件,采用弹性流体动力学耦合有限元法对某20V船用柴油机主轴承油膜进行了仿真分析。研究了不同材料、不同结构的主轴承盖对油膜润滑工作状态的影响。结果表明:同样结构的主轴承盖,采用铁材料比钢材料对轴承润滑更加有利;主轴承盖承压面两侧挖槽,在保证刚度的前提下,可以有效降低主轴承边缘压力峰值和平均热载峰值。