Numerical study of the waste heat recovery potential of the exhaust gases from a tractor engine

The paper presents an analysis of the possibilities of exhaust gas heat recovery for a tractor engine with an output power of 110 kW. On the basis of a literature review, the Rankine cycle seems to be the most effective way to recover the exhaust gas energy. This approach reduces the fuel consumption and allows engines to meet future restrictions on carbon dioxide emissions. A simulation model of the engine by means of a one-dimensional approach and a zero-dimensional approach was built into the simulation code AVL BOOST, and a model of the Rankine cycle was implemented. The experimental values of the effective power of the engine, the mass flow and the exhaust gas temperature were used to validate the engine model. The energy balance of the engine shows that more than 28.9% of the fuel energy is rejected by exhaust gases. Using the engine model, the energy and the exergy of the exhaust gases were studied. An experimental study of the real working cycle of a tractor engine revealed that the engine operates most of the time at a constant speed (n = 1650 r/min) and a constant load (brake mean effective pressure, 10 bar). Finally, Rankine cycle simulations with four working fluids were carried out at the most typical operating point of the engine. The simulation results reveal that the output power of the engine and the efficiency of the engine increase within the range 3.9–7.5%. The highest value was achieved with water as the working fluid while the lowest value was obtained with the organic fluid R134a. The power obtained with water as the working fluid was 6.69 kW, which corresponds to a Rankine cycle efficiency of 15.8%. The results show good prospects for further development of the Rankine cycle

Possibilities of waste heat recovery on tractor engines

International audienceTractor engines present significant possibilities of waste heat recovery due to their high power and their operation cycles. The waste heat recovery system based on Rankine cycle seems to be the most effective way of reducing the fuel consumption, respectively the emission of CO2. Experimental studies of the real working cycles of a tractor engine reveal that such type of engines operate at high load close to the maximum most of the time when the tractors run on the fields. The aim of the article is to evaluate the energy and exergy available at different location points in the exhaust system of the tractor engine. A combination of 1D and 0D approaches is used to build the engine model in the software AVL BOOST. The experimental results such as: fuel consumption, effective power, mass flow, wasted energy in the cooling system, temperature in the exhaust system etc. have been used for calibration of the model. The energy balance of the engine shows that more than 35% of the fuel energy is lost by exhaust gases on the most typical operating points. Finally, the energetic and exergetic analysis at a certain point of the exhaust system is presented. The results show good prospects for further research on the Rankine system mounted on the tractor engine studied here

Stockage d’électricité sous forme thermodynamique et impact des hautes températures sur les turbomachines utilisées

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Working fluid selection of rankine-hirn cycle according to the heat source (pdf download available)

International audienceThis paper presents our simulation model of Rankine-Hirn cycle. This model is developed for sizing and for the working fluid choice of a test bench of Rankine-Hirn cycle for engine waste heat recovery. The heat source characteristics were measured on a diesel tractor engine during work in field. The simulation tool allows to study some of static operating points. An iterative calculation is used to find the best parameters as pressure or working fluid flow rate according to some constraints such as heat exchanger surface or maximum pressure. We identify that each fluid is adapted for a limited range of temperature heat source. For our application, ethanol and water are the adapted working fluids. These results define the future control laws of the waste heat recovery system

Thermal Electricity Storage by a Thermodynamic Process: Study of Temperature Impact on the Machines

International audienceThis paper presents different ways of storing electricity to overcome the intermittency of renewable energies. After reviewing existing storage technologies, a new way of storing electricity thermodynamically on a large scale is presented. This system is based on the principle of a high temperature heat pump that converts electricity into heat. This thermal energy is stored in refractory materials, and at a later stage converted into electricity by means of a Joule cycle. The first mode -of energy storage- requires the use of turbomachinery - compressors and turbines - to operate under conditions different from those usually encountered. In particular, for the process to be efficient, the compressor must operate at high temperatures (500 to 1000° C). This represents a major technological barrier in the process due to the market unavailability of compressors capable of operating under such conditions. In this study the latest advances in the field of gas turbines are presented, including those concerning high pressure turbine blades, in order to adapt them to the compressor. These advances result mainly in changes in the composition of nickel-based superalloys and their implementation (single crystals) to achieve maximum wall temperatures around 950 °C

ETUDE PARAMETRIQUE D’UN CYCLE DE RANKINE POUR LA RECUPERATION D’ENERGIE DES GAZ D’ECHAPPEMENT D’UN MOTEUR D'AUTOMOBILE

International audience. La réduction des émissions de CO2 des moteurs à combustion interne et des futurs véhicules est une préconisation importante de l'Union Européenne. La récupération d’énergie des gaz d’échappement par cycle de Rankine est une méthode permettant d’améliorer l’efficacité globale des moteurs. Dans cet article une modélisation d’un système de récupération d’énergie des gaz d’échappement d’un moteur a été réalisée. Un modèle statique du cycle de Rankine est développé utilisant le langage Python (x,y). Les paramètres du fluide de travail sont déterminés grâce à la base de donnée CoolProp. Dans cette étude, le modèle d'un moteur à combustion interne a été développé. Ce moteur est un moteur diesel de 2.0 litre à injection directe pilotée électroniquement. Le modèle du moteur a été élaboré avec le code de simulation AVL Boost et validé sur la courbe de pleine charge à partir des données constructeur. L’eau a été choisie comme fluide de travail pour le système de récupération. Une étude paramétrique a été conduite de façon à optimiser le système en fonction de la plage de fonctionnement du moteur

Optimization of automotive Rankine cycle waste heat recovery under various engine operating condition

International audienceAn optimization study of the Rankine cycle as a function of diesel engine operating mode is presented. The Rankine cycle here, is studied as a waste heat recovery system which uses the engine exhaust gases as heat source. The engine exhaust gases parameters (temperature, mass flow and composition) were defined by means of numerical simulation in advanced simulation software AVL Boost. Previously, the engine simulation model was validated and the Vibe function parameters were defined as a function of engine load. The Rankine cycle output power and efficiency was numerically estimated by means of a simulation code in Python(x,y). This code includes discretized heat exchanger model and simplified model of the pump and the expander based on their isentropic efficiency. The Rankine cycle simulation revealed the optimum value of working fluid mass flow and evaporation pressure according to the heat source. Thus, the optimal Rankine cycle performance was obtained over the engine operating map

Injection timing strategy for exhaust heat recovery optimization on a turbocharged diesel engine

International audienceThe paper presents a numerical analysis of injection timing effect on engine output power and heat rejected by exhaust gas in a turbocharged direct injection diesel engine implemented for a tractor application. The engine performance and exhaust gas enthalpy were studied by means of an engine computational model built in advanced simulation code AVL Boost. A Rankine-Hirn cycle model was developed due to estimate recovery potential of the exhaust gas. Injection timing optimization was carried out at the most commonly used engine operating points (n=1650rpm and variable load). The maximum engine output power was chosen as a target parameter to determine the optimal injection timing. A combination of Rankine-Hirn cycle using water as working fluid and injection timing optimization increased the maximum engine output power by 7.4%. The results revealed that in order to optimize overall engine efficiency in case of waste heat recovery system is applied it is necessary to reduce injection advance by 2deg to 5deg

Development of 0d simulationalmodel for rankine-hirn cycle heat exchanger optimisation

International audienceThe article presents a 0D model development of the heat exchanger intended for a Rankine-Hirn cycle waste heat recovery system in internal combustion engines. The heat transfer in the exchanger was estimated as the volume was separated by small elements. For each of the elements the heat transfer was calculated depends on the temperature variation, surface of the transfer and total heat transfer coefficient. An estimation code based on the model was developed in Python. CoolProp simulation code was used for working fluid parameters determination. Numerical estimation of the heat transfer was presented with different working fluids at the most commonly used operating point of a tractor engine. Finally, a study of the working fluid mass flow rate effect on heat transfer effectiveness was conducted as water was used into the Rankine-Hirn cycl

Efficiency of automotive electric supercharging compressors

International audienceThe automotive electric supercharger provides high torque at low engine speeds. During accelerations, it fills the power gap due to the turbocharger's inertia and avoids turbo lag. Its operation is of short duration because once this deficit has been juggled, it must be stopped in order not to generate unnecessary electricity consumption and to avoid overheating of the electric motor which would compromise its lifetime. Usually the power of automotive turbocharger is calculated assuming an adiabatic air compression and the adiabatic efficiency is assessed. At low speed or for low compression ratio, which is the case of electric supercharger, this hypothesis is no more valid and special experiments have to be done. On our test bench the compressor is driven by a turbine supplied with cold compressed air. Between the compressor and the turbine, a torque meter is inserted to measure the power given to the compressor shaft. The tests were conducted with a non-insulated compressor and an insulated compressor for eight iso-speeds. Additional tests were carried out to assess the actual power supplied to the fluid including bearing losses measurements and to assess the influence of different preload springs used to counter the axial thrust of the compressor. This article presents and analyses the results of this work