Roy J. Crookes

Assessment of simulated biogas as a fuel for the spark ignition engine

Results are presented of tests with a variable compression ratio Ricardo E6 single-cylinder spark-ignition engine operating on simulated biogas formed from different mixtures of domestic natural gas and carbon dioxide. The fraction of carbon dioxide in the simulated biogas was changed from 0 to about 40% by volume to cover the range typically encountered in sources of biogas in practice. The tests covered a range of air:fuel ratios from rich to the lean operating limit at four speeds and a number of compression ratios. Measured results are given for power, exhaust temperature, thermal efficiency and the mole fractions of the regulated emissions carbon monoxide (CO), oxides of nitrogen (NOx) and total unburnt hydro-carbon (HC) in the exhaust gases. Experimental results indicate that the presence of carbon dioxide can improve NOx emissions, but since lower cylinder pressures result, engine power and thermal efficiency are reduced and the level of unburnt HC is increased. Measured data, however, suggest that it is possible to significantly increase the compression ratio as an effective means of improving biogas-fuelled engine performance when CO2 is present. While this would normally raise the emissions of both NOx and HC, the former is offset by the CO2 content of the biogas.

Systematic assessment of combustion characteristics of biofuels and emulsions with water for use as diesel engine fuels

Abstract Measurements of the combustion performance of biofuel oils, blends with diesel fuel and emulsions with water have been made, using a variety of experimental techniques. Photographic examination of single droplets demonstrated similar burning rates to diesel fuel. High speed records revealed the explosive combustion of oil-water emulsion droplets. Spray-flame photography showed up the poor combustion efficiency at atmospheric pressure, of the seed oils compared with diesel fuel. Combustion of sprays at elevated pressure, in a steady-flow combustor, of fuels, blends and emulsions showed improved combustion under these conditions though still poorer for vegetable oil than for diesel fuel. Soot formation levels were also higher, though these were reduced by emulsification with water. Under the more extreme conditions of the environment in a diesel engine combustion chamber, the performance of a commercially available biofuel matched more closely that of diesel fuel. In single-cylinder engine tests at relatively low power and speed, the ignition delay was longer for the biofuel. The difference became less at higher loads and speeds and also in a production line multi-cylinder engine under normal operating conditions. Soot levels were generally higher than for diesel fuel and oxides of nitrogen lower. Unlike most operating modifications which result in a trade-off between these species, emulsification of the biofuel with water reduced levels of both soot and oxides of nitrogen.

Study on energy use in China

AbstractRapidly rising energy consumption in China has attracted worldwide attention. This paper provides some insights into future energy supply and demand based on an analysis of the current situation and unique features of energy use in China. With a population of over 1·3 billion, China will need a massive amount of energy to maintain its high economic growth rate. Fast development, in the transportation sector, in particular, has resulted in continuing growth in oil imports, threatening Chinas energy security. Heavy reliance on coal has caused serious environment problems in China and possibly more widely, mainly by the emission of greenhouse gases such as carbon dioxide, a major contributor to global warming. The Chinese government has been taking measures to improve energy efficiency and energy conservation to control energy consumption as well as promoting the use of clean energy such as hydroelectricity and natural gas, to replace coal, to reduce energy related pollution.

Assessment of combustion in natural gas dual-fuelled compression ignition engines with dimethyl ether and rapeseed methyl ester pilot ignition

Abstract Compression-ignition engines are known to be more efficient than similar-sized spark-ignition engines because of the higher compression ratios and leaner combustion. The emissions of soot and nitrogen oxides remain the main hurdle in the complete exploitation of these engines. Dual-fuelling is one means favoured for solving the emission problem, in which high-octane fuels are used as the main fuel which is ignited by a smaller pilot injection of diesel or another high-cetane fuel. These dual-fuel engines produce less particulate matter and nitrogen oxides than spark-ignition engines, while retaining the desired compression-ignition engine efficiency. In the present investigation, tests were conducted using a variety of renewable and non-renewable fuels for pilot injection. The pilot fuels employed were conventional diesel, rapeseed methyl ester (known as biodiesel), and dimethyl ether, while natural gas was used as the main fuel. Biogas, or landfill gas, would be the renewable alternative. Pressure versus crank angle traces were obtained, together with their first and second derivatives. These were analysed to determine the crank angle at which ignition began. Diagrams that show the rate of reaction were also plotted for the same purpose. Here, the start of ignition is determined by the trace suddenly changing slope and rising above zero. Using these methods, the ignition delay was determined for different operating conditions and comparisons drawn for different pilot fuels. The characteristic shapes of rate-of-reaction curves were analysed highlighting differences in the combustion processes occurring in single- and dual-fuel diesel engine operation. Emissions data for different operating conditions were also obtained and analysed, showing a tendency for lower emissions of smoke and oxides of nitrogen but increased carbon monoxide and unburnt hydrocarbons to be produced in dual-fuelling. Carbon dioxide was also reduced.

Soot and gaseous species formation in a water-in-liquid fuel emulsion spray—a mathematical approach

The use of water-in-fuel emulsions as the combustible matter in various combustion systems has been advocated as a means of achieving cleaner combustion. Several experimental investigations have shown that adoption of this technique will result in marked reductions in NOx emissions and in the levels of smoke and soot particulate produced from spray-based combustion systems. Little effort has been directed towards modelling the combustion of water-in-oil emulsion, though understanding the underlying reasons for the aforementioned improvements will be enhanced by modelling the processes involved. This paper attempts to provide an understanding of the effects of the presence of water in the fuel on spray combustion and soot and gaseous product formation by modelling the relevant processes. The simplified model described below is capable of predicting soot and gaseous species concentrations in a burning water-in-liquid fuel emulsion. It is based on the Adler and Lyn treatment of an evaporating spray in a co-flowing air stream where the spray domain is considered to be a continuous medium allowing the conservation equations of continuity, momentum and energy to be represented in a classical differential form. The evaporating droplet is modelled through a quasi-steady gas phase approach enabling the lifetime of the droplet to be determined. The presence of water inside the emulsified fuel droplet is accounted for and the onset of micro-explosions is predicted by the droplet model. The spray analysis incorporates the droplet model and makes use of a probability function to determine to what extent the micro-explosion predicted by the droplet analysis affects the spray development. The computer model is organized in distinct subroutines facilitating easy use and the possibility of replacing one sub-model by another (such as soot formation sub-model). This allows for parametric studies and for prediction of the burning spray behaviour at various conditions of water content, pressure, temperature and input air–fuel ratio. A collection of results obtained using the model are presented and discussed in the paper. One particular set is compared with experimental results obtained on a specially designed combustion chamber running at conditions similar to the ones used in the model.

An Effective Property, LHF-Type Model for Spray Combustion

A mathematical model capable of describing the evaporation, mixing and burning characteristics of a confined reacting two-phase flow is presented. The flow field is described by solving the partial differential equations of continuity, momentum, and energy transport, together with the k-e equations of turbulence. Evaporation is accounted for via a droplet evaporation sub-model which runs in parallel with the gas-phase solver exchanging data with it. Effective properties are calculated in each control volume and the property changes resulting from the evaporation are allowed to propagate according to the turbulent mixing model. Combustion follows the mixing process and is assumed to proceed to equilibrium. The model is validated against experimental results, and its applicability over a wide range of conditions is investigated.

Experimental studies of autoignition and soot formation of diesel surrogate fuels

Computational simulation has undergone vast development for internal-combustion engine research as a time- and cost-saving tool. Yet combustion simulation for conventional hydrocarbon petroleum fuels faces difficult challenges since such fuels have very complex compositions, consisting of many different molecular species, for which data are sparse. The use of surrogate fuels for combustion simulation could provide a solution to this problem. In this investigation, n-heptane and mixtures of n-heptane and toluene were studied within a broad range of potential surrogate diesel fuels, and the ignition delay and soot formation trends were compared with those of diesel fuel. Ignition delays show good agreement with those for diesel fuel and it was also possible to replicate partially the soot formation behaviour for certain engine conditions. Further investigation is needed to find a surrogate fuel that closely matches over the range of operating conditions of a diesel engine.