Dynamic modeling and optimal control strategy of waste heat recovery Organic Rankine Cycles

in Applied Energy (2011)

Organic Rankine Cycles (ORCs) are particularly suitable for recovering energy from low-grade heat sources. This paper describes the behavior of a small scale ORC used to recover energy from a variable ... [more ▼]

Organic Rankine Cycles (ORCs) are particularly suitable for recovering energy from low-grade heat sources. This paper describes the behavior of a small scale ORC used to recover energy from a variable flow rate and temperature waste heat source. A traditional static model is unable to predict transient behavior in a cycle with a varying thermal source, whereas this capability is essential for simulating an appropriate cycle control strategy during part-load operation and start and stop procedures. A dynamic model of the ORC is therefore proposed focusing specifically on the time-varying performance of the heat exchangers, the dynamics of the other components being of minor importance. Three different control strategies are proposed and compared. The simulation results show that a model predictive control strategy based on the steady-state optimization of the cycle under various conditions is the one showing the best results. [less ▲]

A parametric study on the emissions from an HCCI alternative combustion engine resulting from the auto-ignition of primary reference fuels

in Applied Energy (2008), 85(8), 755-764

The homogeneous charge compression ignition is an alternative combustion technology that can reduce automobile pollution, provided that the exhaust emission can be controlled. A parametric study can be ... [more ▼]

The homogeneous charge compression ignition is an alternative combustion technology that can reduce automobile pollution, provided that the exhaust emission can be controlled. A parametric study can be useful in order to gain more understanding in the emission reduction possibilities via this new combustion technology. For this purpose, the inlet temperature, the equivalence ratio and the compression ratio are changed, respectively, from 30 to 70 degrees C, 0.28 to 0.41 and 6 to 14. Also the diluting, thermal and chemical effects of exhaust gas recirculation were studied. The emission of CO, CO2, O-2 and hydrocarbons has been measured using primary reference fuels. It appears that an increase in the inlet temperature, the EGR temperature, the equivalence ratio and the compression ratio results into a decrease of the emissions of CO and the hydrocarbons of up to 75%. The emission of CO2 increased, however, by 50%. The chemical parameters showed more complicated effects, resulting into a decrease or increase of the emissions, depending on whether the overall reactivity increased or not. If the reactivity increased, generally, the emissions of CO and hydrocarbons increased, while that of CO2 increased. The increase of CO2 emissions could be compensated by altering the compression ratio and the EGR parameters, making it possible to control the emission of the HCCI engine. (c) 2008 Elsevier Ltd. All rights reserved. [less ▲]