TDM - Transports Durables et Mobilité

TRain ENergy Efficiency via Rankine-cycle exhaust Gas heat recoverY – TRENERGY

TRain ENergy Efficiency via Rankine-cycle exhaust Gas heat recoverY

Assessing the interest of using a Rankine thermodynamic cycle to recover part of the heat dissipated in the exhaust gas of diesel engines and thus increase the efficiency of the «power packs« providing propulsion for Diesel-electric trains.

Main issues and objective

Up to now, Rankine systems have been mainly used for stationary equipment (power plants, heat recovery from boilers and furnaces, ...), although applications to transport have been studied (for trains, trucks, and more recently, cars) or even implemented, in the case for large ships. For lighter transportation means, several scientific and technical bottlenecks need to be removed before Rankine systems can be considered cost-effective devices for increasing energy efficiency. Among the main problems of Rankine systems for mobile applications, we can recall those posed by the rapid and uncontrolled variations of the heat source as well as by the limited cooling capacity of the system.<br /> <br />The main objective of the project is to design and test at the engine test bench an organic Rankine cycle (ORC) for waste heat recovery on board regional trains with diesel-electric propulsion. The purpose of this system is to reduce by about 5% the fuel consumption of regional trains.

Three main research themes were identified at the beginning of the project.

1. Studying the best control and supervision approach for an ORC (Organic Rankine Cycle) system equipped with a turbine in an application with variable heat source. «Model-based« control approaches will be favoured, by developing «moving boundary « exchanger models. For supervision, dynamic programming will be used to obtain an offline benchmark, while model predictive control should provide an online strategy implementable in real-time.

2. Designing a compact high-efficiency low-power turbine. Robust stochastic optimization approaches will be developed and tested as part of a PhD thesis.

3. Evaluating a more environmentally friendly working fluid than those currently being tested for transport applications. This evaluation will be carried out through an optimization campaign based on a series of simulations of the waste heat recovery system on a wide range of working fluids.

From typical mission profiles of a regional train IFPEN showed that exergy available in the exhaust gas of diesel engines amounts to 7-17% of the energy consumed by the train.

IFPEN then pursued a campaign of ORC simulations to evaluate a large range of working fluids, optimize the system architecture and estimate the optimal operating parameters. After consultation with suppliers, ENOGIA completed the task of integrating components into the template provided by ALSTOM for installation aboard a train.

It appeared that, for railway applications, Rankine cooling system significantly impacts the overall effectiveness of the recovery. In this case, the estimated potential gain in fuel consumption for a train equipped with Rankine technology will be less than 5%.

On the supervision and control side, IFPEN investigated the recovery potential in transient conditions with the ORC schemes considered and the influence of component sizing, using optimal control techniques (DP implemented on GPU). IFPEN and ENOGIA designed a hierarchical control system consisting of a rapid-prototyping PC that hosts high-level strategies and a PLC which provides low-level servos.

ENOGIA completed the turbine wheels design study, the electric generator integration study, and the CAD detailed study of the turbine-generator ensemble. After manufacture and assembly of components, the turbine has been tested successfully in the workshop. ENOGIA also supplied all other components before assembling them into a system meeting the dimensions allocated by ALSTOM for integration on board the train.

IFPEN also carried out the integration study of the ORC in the exhaust line of a diesel engine of ALSTOM Power Pack. IFPEN then installed the diesel engine supplied by ALSTOM in one of its engine test benches.

At the time of writing, ENOGIA ORC system is almost complete in the workshop and Alstom Diesel engine is almost ready to start-up at the test bench.

Compared to the initial objective, it seems possible, in the longer term, to reach the 5% fuel savings, namely by optimizing the cooling system on board the train.

[1] Peralez, J., Tona, P., , Sciarretta, A., Dufour, P., Nadri, M. (IFPEN), “Optimal control of a vehicular organic rankine cycle via dynamic programming with adaptive discretization grid”. In: Proc. of 19th IFAC World Congress, Cape Town, South Africa, August 2014 [International conference with proceedings, accepted]

[2] Peralez, J., Tona, P., Nadri, M., Dufour, P., Sciarretta, A. (IFPEN), “Optimal Supervisory Control for an Organic Rankine Cycle on board a Diesel-Electrical Railcar”, Journal of Process Control
[International journal with peer-review, under submission]

In Europe today, more than half of the railway network is not electrified. Especially for regional transportation, diesel electric trains (called Diesel Multiple Unit: DMU) are then widely used. ALSTOM will release next year its new regional train called Regiolis. A Regiolis train may use up to 6 diesel engines of 338 kW each, which represent a total onboard power of about 2 MW.

In this context, TRENERGY project aims at evaluating the interest of using a Rankine cycle in order to recover some lost heat and to increase the efficiency of the Diesel power packs. Rankine-cycle systems (and their derivatives like Organic Rankine Cycles, ORC) have already been investigated in the past for transportation means (train, trucks and more recently cars), but the fact is that up to now they have been mainly used for stationary equipments (power plants, heat recovery for boilers, furnaces and ovens…) or for heavy ships. For lighter transportation means, several scientific and technical bottlenecks still have to be addressed before Rankine systems may represent profitable devices for increasing energy efficiency. This is especially due to the transient behaviour of the heat source that characterizes this kind of applications.

TRENERGY will focus onto:
• the selection of the best control approach for an ORC system using a turbine in a varying heat source application, based on the analysis of the impact of component choice on control authority and system controllability, and on the design of a control strategy which can cope with the resulting limitations and make the most of the final architecture;
• the design of a compact high-efficient low-power turbine, with a robust optimization of the internal fluid flow, and a strong focus towards high rotational speed, bearing systems and thermal management in order to improve the performance/cost ratio as well as the reliability of the component.;
• the testing of a more environmentally friendly working fluid than current mediums tested for transportation applications like pentafluoropropane (R245fa) that may be banned in the next years.

This joint work of ALSTOM, ENOGIA small business, ARTS ET MÉTIERS PARISTECH-DynFluid Laboratory and IFP Energies nouvelles will materialize at the end of the project through the testing, at the engine test cell, of a prototype Rankine system, equipped with a dedicated turbine, that may prefigure a future device to be fitted onboard high energy-efficient Diesel electric locomotives. As such, the project has strong industrial potential, and should lead to strategic advantages for the partners.

As significant advances in research will be needed to attain the goals and obtain exploitable results, we expect that this project will not only increase competitiveness of the industrial partners, but also highlight the excellence of the academic partners.

Project coordination

Paolino TONA (IFP Energies Nouvelles) – paolino.tona@ifpen.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

IFPEN IFP Energies Nouvelles
Alstom Alstom Transport
DynFluid LABORATOIRE DE DYNAMIQUE DES FLUIDES
ENOGIA ENOGIA

Help of the ANR 1,218,993 euros
Beginning and duration of the scientific project: December 2012 - 36 Months

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