Proceedings of the Institution of Mechanical Engineers,Part A: Journal of Power and Energy

A variable compression ratio concept that can give a different expansion ratio to the compression ratio has been evaluated by means of a simulation of a turbocharged diesel engine. The compression ratio is controlled by varying the ratio of the connecting rod length to the crank throw, hence the name variable crank radius/connecting rod length engine (VR/LE). The VR/LE mechanism kinematics have been defined and described, and the compression ratio and expansion ratio have been presented as a function of the eccentric phase angle (α_o). A zero-dimensional engine simulation that has been the subject of comprehensive validation has been used as the basis of the VR/LE study. The effect of the compression ratio on the engine performance at fixed loads is presented. The principal benefits are a reduction in fuel consumption at part load of about 2 per cent and a reduction in ignition delay that leads to an estimated 6 dB reduction in combustion noise. The study has been conducted within the assumption of a maximum cylinder pressure of 160 bar.

The influence of nozzle sac volume and associated changes in the fuel hole upstream flow on the spray atomization, velocity and penetration were studied. Four injectors, designed for applications in 1 litre per cylinder diesel engines, were investigated with the same 215 bar injector nozzle opening pressure and fuel flow quantity. A Malvern 2600c Series diesel spray laser diffraction spray analyser was used. Significant differences in the spray characteristics were found which helped to explain some of the emission differences between the four injectors.

Demand for natural gas in Europe is expected to grow rapidly, particularly for use in power generation, as a result of technological developments and regulatory action to protect the environment.

While there is no shortage of gas reserves to meet this potential demand, there is uncertainty over how rapidly such reserves can be developed and marketed, and at what level of cost. It seems probable that incremental gas supplies will be available only at higher prices than those being paid today, as a result of rising gas supply costs. However, it would appear that gas prices can rise further before other fuels become more commercially attractive in the power generation sector.

For most thermal power plant, the Carnot cycle efficiency is not the true ideal. Matching the cycle to the source leads to alternative limits and improved perceptions of how practical power plant can be improved. A method of including the work ratio into an ideal cycle analysis is presented which simplifies the estimation of practical power plant efficiencies and highlights the historic course of thermal efficiency improvement.

In situ decommissioning (ISD) is a radical approach to the disposal of nuclear reactors by burying them on-site beneath a mound of suitable material. The engineering and construction of the mound is dealt with and the selection of suitable material. The radiological impact of leaving radioactive materials on-site is studied and it is concluded that ISD could be a solution for some sites.

The decision-making process involving the decommissioning of the British graphite-moderated, gas-cooled Magnox power stations is complex. There are timing, engineering, waste disposal, cost and lost generation capacity factors and the ultimate uptake of radiation dose to consider and, bearing on all of these, the overall decision of when and how to proceed with decommissioning may be heavily weighed by political and public tolerance dimensions. These factors and dimensions are briefly reviewed with reference to the ageing Magnox nuclear power stations, of which Berkeley and Hunterston A are now closed down and undergoing the first stages of decommissioning and Trawsfynydd, although still considered as available capacity, has had both reactors closed down since February 1991 and is awaiting substantiation and acceptance of a revised reactor pressure vessel safety case. Although the other first-generation Magnox power stations at Hinkley Point, Bradwell, Dungeness and Sizewell are operational, it is most doubtful that these stations will be. able to eke out a generating function for much longer.

It is concluded that the British nuclear industry has adopted a policy of deferred decommissioning, that is delaying the process of complete dismantlement of the radioactive components and assemblies for at least one hundred years following close-down of the plant. In following this option the nuclear industry has expressed considerable confidence that the decommissioning technology required will he developed with passing time, that acceptable radioactive waste disposal methods and facilities will be available and that the eventual costs of decommissioning will not escalate without restraint.

Traditionally, the simple Brayton–Joule cycle has been optimized for maximum output and for minimum compressor work with inter-cooling and maximum turbine work with reheat. To these Woods et al. (1) have added optimization for peak efficiency of the simple cycle with internal irreversibilities. The results now presented include both maximum output and peak efficiency for both regenerative and intercool/reheat cycles with internal irreversibilities. Two special cases, for a regenerative cycle and for a non-regenerative cycle with both reheat and intercooling, are identified where the conditions for maximum output and peak efficiency coincide.