06100289 Performance optimization of a solar driven heat engine with finite-rate heat transfer Sogut, O. S. and Durmayaz, A. Renewable Energy, 2005, 30, (9), 1329 1344. An optimal performance analysis for an equivalent Carnot-like cycle heat engine of a parabolic-trough direct-steam-generation solar driven Rankine cycle power plant at maximum power and maximum power density conditions is performed. Simultaneous radiation-convection and only radiation heat transfer mechanisms from solar concentrating collector, which is the high temperature thermal reservoir, are considered separately. Heat rejection to the low temperature thermal reservoir is assumed to be convection dominated. Irreversibilities are taken into account through the finite-rate heat transfer between the fixed temperature thermal reservoirs and the internally reversible heat engine. Comparisons proved that the performance of a solar driven Carnot-like heat engine at maximum power density conditions, which receives thermal energy by either radiation-convection or only radiation heat transfer mechanism and rejects its unavailable portion to surroundings by convective heat transfer through heat exchangers, has the characteristics of (1) a solar driven Carnot heat engine at maximum power conditions, having radiation heat transfer at high and convective heat transfer at low temperature heat exchangers respect- ively, as the allocation parameter takes small values, and of (2) a Carnot heat engine at maximum power density conditions, having convective heat transfer at both heat exchangers, as the allocation parameter takes large values. Comprehensive discussions on the effect of heat transfer mechanisms are provided.

06•00290 Reciprocating heat-engine cycles Ge, Y. et al. Applied Energy, 2005, 81, (4), 397~408. The performance of a generalized irreversible reciprocating heat- engine cycle model consisting of two heating branches, two cooling branches and two adiabatic branches with heat-transfer loss and friction-like term loss was analysed using finite-time thermodynamics. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between the power output and the efficiency of the cycle are derived. Moreover, analysis and optimization of the model were carried out in order to investigate the effect of the cycle process on the performances of the cycles using numerical examples. The results obtained herein include the performance characteristics of irreversible reciprocating Diesel, Otto, Atkinson, Brayton, Dual and Miller cycles.

06•00291 Regenerative steam-injection gas-turbine systems Nishida, K. et al. Applied Energ;y, 2005, 81, (3), 231 246. There is a demand for developments of the distributed energy system using a small-scale gas turbine. The steam injection configuration can improve the thermal efficiency of simple and regenerative gas-turbine cycles. In this paper, the performance characteristics of two types of regenerative steam-injection gas-turbine (RSTIG) systems are analysed and they are compared with the performances of the simple, regenerative, water injection and steam injected gas-turbine (STIG) cycles. The thermal efficiencies of the RSTIG systems are higher than those of the regenerative, water injection and STIG systems and the specific power is larger than that of the regenerative cycle. The optimum pressure-ratio for maximum efficiency of the RSTIG systems is relatively low. Furthermore, the steam-injection configuration can be applied in the flexible heat-and-power cogeneration system and the total efficiency of the RSTIG cogeneration system reaches more than 70% (HHV).

06•00292 Research and development of a Iow-BTU gas- driven engine for waste gasification and power generation Ando, Y. et al. Energy, 2005, 30, (11 12), 2206 2218. Combustion characteristics of low-BTU gases (about 1000 kcal/N m 3) were experimentally investigated in order to develop engine generators for waste gasification and power generation systems. Two simulated Iow-BTU gases, obtained from one-step high temperature gasification (hydrogen rich) and two-step pyrolysis/reforming gasification (methane rich), as well as natural gas, were tested in a small-scale spark ignition engine. Compared to the natural gas driven engine, the hydrogen rich Iow-BTU gas driven engine showed similar thermal efficiency but with significantly lower NOx and hydrocarbon emissions and wider equivalence ratio range for stable engine operation. On the other hand, the methane rich low-BTU gas engine showed narrower equivalence ratio range for stable operation. The test results show engine performance more depends on combustion characteristics than on the heating value of the fuel gas. For better engine performance, hydrogen rich fuel gas is desirable.

06/00293 Stator flux optimised Direct Torque Control system for induction motors Arias, A. ef al. Elecfric Power ~vsfems Research, 2005, 73, (3), 257 265.

10 Engines (power generation and propulsion, electrical vehicles)

Direct torque control (DTC) has, over the years, become one of the most popular methods of control for induction motors drive systems. There still remain, however, many disadvantages with this method of control, which have to be overcome. In the present paper we, therefore, consider a method of improving conventional DTC by reducing the undesirable torque ripple that can occur in the output torque. This new method, which is fully described in the paper, also has the additional advantage of maintaining the switching frequency of the power switching devices constant. The average torque ripple reduction achieved by this new method of control can be greater than 50%. This significant reduction in torque ripple is realized by the introduction of a two state modulation process between the active selected state from conventional DTC and an additional null state. The control of the two state modulation process is achieved by the application of an adaptive fuzzy logic controller. Additionally, a novel flux optimizer strategy is also introduced into the new DTC system, which together with the two state modulation process further reduces the torque ripple. Simulation and experimental results for the drive system presented are included in the paper and it is shown that not only good agreement exists between both sets of results but they also support the claims made in the paper.

06•00294 The modification of the fuel injection rate in heavy-duty diesel engines, Part 1: Effects on engine performance and emissions Desantes, J. M. et al. Applied Thermal Engineering, 2004, 24, (17 18), 2701 2714. An experimental study has been performed on the effects of injection rate shaping on the combustion process and exhaust emissions of a direct-injection diesel engine. Boot-type injections were generated by means of a modified pump-line-nozzle system, which is able to modulate the instantaneous fuel injection rate. The interest of the study reported here was the evaluation of the effective changes produced in the injection rate at different engine operating conditions, when the engine rotating speed and the total fuel injected were changed. In addition, the influence of these new injection rates was quantified on the global engine performance and pollutant emissions. In particular, the focus was placed on producing 'boot-like' injection rate shapes, with the main objective of reducing NO~ emissions. Results show how this system is capable of achieving boot-type injections tit different boot pressures and boot durations. Also, even though the general trend of the system is to reduce NO,. and to increase soot and fuel consumption, emissions and performance trade-offs can be improved for some specific boot shapes. On the contrary, the modulation of the injection rate showed to be ineffective at medium engine load, since the increase in soot was greater than the relative decrease in NO~. The analysis of the modifications produced by these strategies on the combustion process, and on the rate of heat release are the base of a second paper.

06•00295 The modification of the fuel injection rate in heavy-duty diesel engines, Part 2: Effects on combustion Desantes, J. M. et al. Applied Thermal Engineering, 2004, 24, (17 18), 2715 2726. An experimental study has been performed on the effects of injection rate shaping on the combustion process and exhaust emissions of a direct-injection diesel engine. Boot-type injections were generated by means of a modified pump-line-nozzle system, which is able to modulate the instantaneous fuel injection rate. The influence of different values of boot length and boot pressure has been evaluated by analysing the apparent rate of heat release and flame temperatures. Engine operating conditions at different rotating speed and injected fuel mass were considered in order to assess their effect on the injection rate shape. Results show how all the changes in the injection rate agree with changes in the diffusion combustion phase. Medium- load conditions presented larger increases in the dry soot emissions since the boot was longer and it was produced at lower pressure. Changes in engine speed at high load did not show major changes in the combustion evolution. Longer boots produced high soot emissions probably due to less efficient mixing conditions.

06•00296 Thermo-economics for endoreversible heat- engines Chen, L. et al. Applied Energy, 2005, 81, (4), 388 396. The thermo-economics of endoreversible heat engines has been studied based on the linear phenomenological heat-transfer law [i.e. the heat flux Q o(A(1/T), where T is the absolute temperature]. Analytical formulae for profit, the maximum profit and the corresponding efficiency are derived.

06/00297 Utilization of liquid biofuels in automotive diesel engines: An Indian perspective Subramanian, K. A. el al. Biomass and Bioenergy, 2005, 29, (1), 65 72. This paper deals the policy and planning issues for utilization of ethanol find biodiesel in antomotive diesel engines in Indian context in view of environmental benefits, energy self-sufficiency and boosting of

Fuel and Energy Abstracts January 2006 41