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

The trends of energy consumption and the sources of the associated emissions over the past two decades in the United Kingdom have been analysed. There are indications that the levels of emission of CO ₂, NO_x, CO, VOCs (volatile organic compounds) and black smoke are rising steadily as a result of energy consumption. The road transport sector emerges as the current overall major contributor of these pollutants and the likely candidate to remain as the fastest growing energy consumer and polluter for some years to come. With the current rate of increase in the number of motor cars, that is 3.9 per cent per annum, and the likely environmental consequences, immediate technological solutions to reduce transport pollution are strongly recommended.

Combined heat and power (CHP) can, in the most suitable cases, reduce a consumer's total energy costs by up to 40 per cent. It is important to stress that CHP is not viable at all sites and further that poor choice of CHP plant often results in inefficient and uneconomic operation. It is therefore vitally important to build a clear picture of what specific factors determine the profitability of a CHP scheme. The development of an accurate, reliable economic model is necessary for any sector where a potential market for CHP exists. Conventional economic models have a number of limitations, particularly where situations involve a high degree of risk and uncertainty. This paper shows how decision analysis techniques can be combined with a conventional spreadsheet to overcome these weaknesses and demonstrates the power and flexibility of the resulting model with a case study.

This paper describes the design considerations that were involved in the production of a prototype Stirling engine, primarily intended for use in a domestic scale combined heat and power (CHP) system. These are discussed in terms of the specification of basic design parameters—configuration, working fluid, etc. First the particular requirements of this application are considered, primarily a power output of 1 kW or less, suitability for high-volume mass production, ultra long life and as high an efficiency as possible. The design that emerges is relatively simple, of low specific power output and with rather conservative operating parameters—temperature, pressure and speed.

This paper describes work directed at characterizing the dynamic behaviour of a small gasifying fixed-bed biomass stove. The system comprises a primary gasification chamber, followed by a multi-stage secondary combustor which can allow for the considerable variation in quantity and calorific value of fuel gas produced by forming a series of flamelets which move along the length of the secondary combustor as a function of the local mixture ratio. The typical cycle time is about 60 minutes and once warmed up the unit is capable of operating with low emissions, providing appropriate guidelines are followed.

Correlation of temperature and gas concentration measurements on the unit with velocity and flow visualization measurements on a perspex model of the secondary combustor show that improvements can be made to the flow patterns in the bottom of the secondary combustion chamber by reducing the size and shape of the recirculation zones formed and revising the location of the mid-section secondary air inlet. Control of the system is indicated using a simple measurement of temperature in the secondary combustor to determine appropriate air supply rates.

The high cost of energy supplies as well as the concern over the availability of oil have brought much pressure on many countries to search for renewable energy sources, especially after the oil crisis in 1973. Vegetable oil fuels such as palm oil fuel provide one of the alternative forms of energy that are currently being studied, particularly as a diesel fuel substitute.

The purpose of this note is to review the potential of palm oil as an alternative fuel in automotive and industrial diesel engines with respect to its performance and tribological, environmental, economic and social implications.

This paper describes a new research facility designed to study the effect of rotation on heat transfer in the cooling channels of gas turbine rotor blades. Rotation influences cooling performance via secondary flows generated because of Coriolis forces and centripetal buoyancy. The resulting complex three-dimensional flow creates asymmetric heat transfer over the channel surface. The research facility has been designed to permit experiments to be undertaken that are near to actual engine conditions. The paper includes details of the design philosophy, construction and commissioning of the facility, together with a selection of experimental data.

The recent development of an unsteady, three-dimensional aerodynamic model has provided the opportunity to determine the influence of detailed blade geometry on the performance of straight-bladed vertical axis wind turbines. In particular, the present paper examines the effect of blade pitch, twist, taper and aerofoil section by comparison with a simplistic baseline configuration. The study concentrates on the low tip-speed ratio regime where the blade aerodynamics are inherently unsteady and the most severe loadings are experienced. In general, the effects of pitch and twist are similar, with both presenting only limited scope for enhanced design. Moderate taper is shown to improve the overall aerodynamic performance while having the structural benefit of reducing the bending moment at the cross-arm. The potential of a blade with varying cross-section to produce passive stall regulation is also demonstrated. Finally, the influence of unsteady blade stall is considered in more detail for each of the configurations.

An extensive research and development programme carried out at City University, London, has led to an improved level of understanding of how Lysholm twin screw machines may be used to recover power from two-phase flash expansion processes. The mode of operation of such machines is described together with the various types of rotor shapes used. Details are given of a computer simulation of the expansion process which was used to analyse 636 test results. These were obtained from earlier investigations as well as those of the authors and include three different working fluids, varying rotor profiles and sizes and power outputs of 5–850 kW. Good agreement was obtained between predicted and measured performance parameters and statistical analyses of the results indicate that this is unlikely to be improved without the development of more refined methods of two-phase flow analysis than are currently in use. Included in the tests are a set of measurements of pressure-volume changes within the expander carried out by the authors which confirmed a hitherto unappreciated feature of the expansion process. This is the relatively large pressure drop associated with the initial filling of the volume trapped between the rotors and the casing. The analytical technique thus developed was used both to explain the poor results of earlier studies with water expanders and to estimate optimum design performance. It is shown that, when expanding wet organic fluids, adiabatic efficiencies of over 70 per cent may be obtained at outputs of only 25 kW while multi-megawatt outputs are possible from machines no bigger than large compressors with efficiencies of more than 80 per cent. Two-phase screw expanders may be used not only for large-scale power generation in trilateral flash cycle (TFC) systems, but also in place of throttle valves in vapour compression systems to drive screw compressors in sealed ‘expressor’ units. The coefficient of performance of large refrigeration, air conditioning and heat pump systems may thereby be raised by up to approximately 8 per cent.

By the introduction of an insulating liner, the efficiency of a low pressure reciprocating steam engine has been increased and fuel consumption reduced by some 28 per cent.