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Abstract:The poor performance of internal combustion (IC) engines can be attributed to the departure from equilibrium in the combustion process. This departure is expressed numerically, as the difference between the working fluid's temperature and an ideal 'combustion temperature', calculated using a simple expression. It is shown that for combustion of hydrocarbons to be performed reversibly in a single reaction, impractically high working fluid temperatures are required -typically at least 3500 K.Chemical-looping combustion (CLC) is an alternative to traditional, single-stage combustion that performs the oxidation of fuels using two reactions, in separate vessels: the oxidizer and reducer. An additional species circulates between the oxidizer and reducer carrying oxygen atoms. Careful selection of this oxygen carrier can reduce the equilibrium temperature of the two redox reactions to below current metallurgical limits. Consequently, using CLC it is theoretically possible to approach a reversible IC engine without resorting to impractical temperatures. CLC also lends itself to carbon capture, as at no point is N 2 from the air allowed to mix with the CO 2 produced in the reduction process and therefore a post-combustion scrubbing plant is not required.Two thermodynamic criteria for selecting the oxygen carrier are established: the equilibrium temperature of both redox reactions should lie below present metallurgical limits. Equally, both reactions must be sufficiently hot to ensure that their reaction velocity is high. The key parameter determining the two reaction temperatures is the change in standard state entropy for each reaction.An analysis is conducted for an irreversible CLC system using two Rankine cycles to produce shaft work, giving an overall efficiency of 86.5 per cent. The analysis allows for irreversibilites in turbine, boiler, and condensers, but assumes reactions take place at equilibrium. However, using Rankine cycles in a CLC system is considered impractical because of the need for high-temperature, indirect heat exchange. An alternative arrangement, avoiding indirect heat exchange, is discussed briefly.

The mechanical hybrid vehicle: an investigation of a flywheel-based vehicular regenerative energy capture system. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 222(11), pp. 2087-2101. doi: 10.1243 This is the accepted version of the paper.This version of the publication may differ from the final published version. Abstract: Capturing braking energy by regeneration into an on board energy storage unit, offers the potential to reduce significantly the fuel consumption of vehicles. A common technique is to generate electricity in the motors of a hybrid electric vehicle when braking, and use this to charge an on board electrochemical battery. However, such batteries are costly, bulky and generally not amenable to fast charging as this affects battery life and capacity. In order to overcome these problems, a mechanical energy storage system capable of accepting and delivering surges of power is proposed and investigated. A scale physical model of the system, based around a flywheel, a planetary gear set and a brake, was built and operated in a laboratory. Tests showed that the proposed system could be used to store and provide braking energy between a flywheel and a vehicle, the latter emulated by an air-drag dynamometer. This validated the operating principle of the system and its computational model. Further, a computational analysis of a full size vehicle incorporating the mechanical energy storage system was conducted. The results showed that the utilisation of this system in a vehicle, when compared to a conventional vehicle, led to reductions in emissions and fuel consumption. PermanentKeywords: regenerative braking, braking energy, hybrid vehicle, planetary gear set, epicyclic, flywheel.

This paper describes the availability analysis of a generic, post-combustion carbon capture plant. The analysis first establishes the minimum work input required in an ideal plant with a flue gas inlet temperature equal to the sink temperature. The analysis shows that the ideal work input is surprisingly low and that, roughly equal amounts of work are required to first separate and then compress the CO 2 contained in a typical flue gas stream. The analysis is then extended to include the effects of variable inlet temperature and extraction efficiency. This extended analysis shows that there is a considerable quantity of available energy in the flue gas of a normal power station. Indeed, in principle, carbon capture is theoretically possible without any external work input for fuels of low carbon/hydrogen ratio such as heavy fuel oil and natural gas. When burning coal, the minimum work input would be significantly reduced if the flue gases' availability were utilized.The final section of the paper compares the actual work input of a variety of carbon capture schemes found in the literature, with the minimum work input for an ideal process. This comparison shows that the techniques presently found in the literature have a low second-law efficiency.