Comparative Investigation of the Performances of Subcritical and Transcritical Biomass-Fired ORC Systems for Micro-scale CHP Applications☆

Abstract The paper aims to analyse the energetic performances of Organic Rankine Cycles (ORCs) for biomass micro-scale CHP applications. Subcritical and transcritical cycles have been compared and the influence of internal regeneration on system behaviour has been evaluated. The investigation illustrates the noticeable influence of the operating conditions and ORC configuration on the main CHP performances. Furthermore, results reveal that the proper choice of the organic working fluid is fundamental to assure proper operations and optimise the system behaviour. The analysis shows that the transcritical cycle with internal regeneration offers the maximum electric performances, whereas the saturated cycle in simple configuration guarantees the highest thermal efficiency. Furthermore, all the investigated systems guarantee positive energy saving capabilities

Techno-economic Analysis of Biomass-fired ORC Systems for Single-family Combined Heat and Power (CHP) Applications☆

Abstract The aim of the paper is the investigation of the energetic performances and the economic feasibility of Organic Rankine Cycles (ORCs) for biomass single-family combined heat and power (CHP) generation. To this purpose, a parametric energy analysis has been performed to identify the proper system configurations. Subcritical and transcritical cycles, with saturated and superheated conditions at the turbine inlet, have been analysed and the impact of internal regeneration on system behaviour has been studied. The work reveals the large influence of the maximum temperature and the noticeable effect of the internal regeneration on the ORC system performances and the relative energy saving capabilities. An economic feasibility analysis has been performed for single-family users, taking into account the Italian scenario and the incentives for high efficiency cogeneration. The results in terms of return on investment and net positive value highlight that biomass-fired ORC system appears an attractive option for single-family CHP applications

energetic investigation of organic rankine cycles orcs for the exploitation of low temperature geothermal sources a possible application in slovakia

Abstract: The paper aims at analysing the energetic performances of Organic Rankine Cycles (ORCs) for the exploitation of low temperature heat sources. Specifically, the attention has been focused on low-enthalpy geothermal energy for small-scale applications. To this purpose a thermodynamic model has been developed and a parametric investigation has been performed considering different organic fluids (isobutane, isopentane, and R245ca). Saturated conditions at the expander inlet have been adopted and the effect of the internal regenerator on the system performances has been evaluated. The investigation highlights the large impact of the evaporation temperature on the ORC behaviour and the positive influence of the internal regenerator at the highest temperatures. Conversely, the effect of the internal heat exchanger reduces when the evaporation temperature decreases. Furthermore, a possible application in the Kosice Basin (Slovakia) has been analysed. The investigation demonstrates that the organic Rankine cycle represents an interesting option for efficient valorisation of low-enthalpy geothermal resources and electricity production in small-scale applications

A numerical analysis of energetic performances of active and passive aftertreatment systems

The present work aims to analyze the thermal and the energetic performances of an aftertreatment system with unidirectional and periodic reversal flow within the device. To this purpose a single-channel one-dimensional model was developed in order to assess the heat exchange between the aftertreatment system and the exhaust gas. Furthermore, the temperature profiles of the gas and solid phase were computed and the calculated temperatures were adopted to characterize the energy effectiveness of the aftertreatment system. The comparison between different control modes showed an increase in the heat retention efficiency of the system with reverse flow at low engine load conditions. Conversely, the system with passive thermal management presented higher temperatures of the monolith during the warm-up operations. Furthermore, the influence of unburned hydrocarbons oxidation on the effectiveness of the aftertreatment system was evaluated and the significant influence of the cycle time and the monolith length on the system performance was shown. Finally, the gas residence time was evaluated for different operating conditions. Copyright © 2008 John Wiley & Sons, Ltd

a comparative energetic analysis of active and passive emission control systems adopting standard emission test cycles

The present work aims at analysing and comparing the thermal performances of active and passive aftertreatment systems. A one-dimensional transient model has been developed in order to evaluate the heat exchange between the solid and the exhaust gas and to estimate the energy effectiveness of the apparatus. Furthermore, the effect of the engine operating conditions on the performances of emission control systems has been investigated considering standard emission test cycles. The analysis has demonstrated that the active flow control presents the higher thermal inertia and it appears more suitable to maintain the converter initial temperature level for a longer time after variations in engine load. Conversely, the traditional passive flow control is preferable when rapid "cooling" or "heating" of the solid phase is requested. Moreover, the investigation has highlighted the significant influence of the cycle time and converter length on the energetic performances of the aftertreatment apparatus

Development of a Lumped Model for the Characterisation of the Intake Phase in Spark-ignition Internal Combustion Engines

Abstract The present work aims to develop a control-oriented lumped model to investigate the fluid dynamic behaviour of multi-valve spark-ignition engines (ICEs). Specifically, the attention has been focused on the intake phase and in-cylinder air charge estimation. To this purpose, a spark-ignition engine has been characterised at a flow rig in terms of flow coefficients. The experimental data have been used to define the fluid dynamic behaviour of the different intake system components and to calibrate and validate the proposed model that has been developed in Matlab/Simulink environment. Furthermore, in order to evaluate the capability of the zero-dimensional code and to estimate the instantaneous in-cylinder mass flow in different operating conditions, the numerical data have been compared to the results of a one-dimensional commercial software. The comparison between numerical and experimental data shows a good agreement. The investigation highlights that the proposed control-oriented lumped model represents a useful and simple tool to evaluate the engine breathability and to define the proper valve timing

Analysis of a Trigeneration Plant under Transient Operating Conditions

Abstract A dynamic lumped-parameters model has been developed in order to analyse the performance of a combined cooling, heating and power (CCHP) plant during transient load variations. The plant allows the waste heat recovery from four Internal Combustion Engines (ICEs) to produce simultaneously refrigeration power for an absorption chiller, hot water for thermal user and electrical power. The heat recovery is realized through the exhaust gases, the jacket cooling water and the lubricant. The plant includes an auxiliary boiler, which maintains the water temperature levels to the values required by the absorption chiller, and a dry-cooler, which refrigerates the plant water before entering the internal combustion engines. Moreover, a three-way valve, which controls the water flow rate in order to satisfy both the refrigeration and the thermal loads, is considered. The simulations are carried out under thermal-drive and electric-drive strategy and the evaluation of the performance and time response of the CCHP apparatus are presented

Experimental investigation of the fluid dynamic efficiency of a high performance multi-valve internal combustion engine during the intake phase: Influence of valve-valve interference phenomena

The purpose of the present work is the analysis of the fluid dynamic behavior of a high performance internal combustion engine during the intake phase. In particular, a four-valve spark-ignition engine has been characterized at the steady flow rig. Dimensionless discharge coefficients have been used to define the global fluid dynamic efficiency of the intake system, while the Laser Doppler Anemometry (LDA) technique has been employed to evaluate the mean flow in the valve curtain area and to characterise the interference phenomena between the two intake valves. The investigation has shown the significant influence of the valve lift on the volumetric efficiency of the intake apparatus. Moreover, the experimental analysis has highlighted that the valve-valve interference phenomena have a relevant impact on the head breathability, on the flow development within the combustion chamber and on the velocity standard deviations

Energy Exploitation of High-Temperature Geothermal Sources in Volcanic Areas—a Possible ORC Application in Phlegraean Fields (Southern Italy)

This work aims to investigate the energy performances of small-scale Organic Rankine Cycles (ORCs) for the exploitation of high temperature geothermal sources in volcanic areas. For this purpose, a thermodynamic model has been developed, and a parametric analysis has been performed that considers subcritical and transcritical configurations, and different organic fluids (isobutane, isopentane, and R245ca). The investigation illustrates the significant effect of the temperature at the entrance of the expander on the ORC behaviour and the rise in system effectiveness when the internal heat exchange (IHE) is adopted. As a possible application, the analysis has focused on the active volcanic area of Phlegraean Fields (Southern Italy) where high temperature geothermal reservoirs are available at shallow depths. The work demonstrates that ORC systems represent a very interesting option for exploiting geothermal sources and increasing the share of energy production from renewables. In particular, the investigation has been performed considering a 1 kg/s geothermal mass flow rate at 230 °C. The comparative analysis highlights that transcritical configurations with IHE guarantee the highest performance. Isopentane is suggested to maximise the ORC electric efficiency (17.7%), while R245ca offers the highest electric power (91.3 kWel). The selected systems are able to fulfil a significant quota of the annual electric load of domestic users in the area