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EPSRC Reference: EP/H049967/1
Title: A Fundamental Study on CH* and OH* Flame Emissions as Indicators of Heat Release and AFR at Engine Relevant Conditions of Temperature and Pressure
Principal Investigator: Stone, Professor CR
Other Investigators:
Ewart, Professor P
Researcher Co-Investigators:
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Department: Engineering Science
Organisation: University of Oxford
Scheme: Standard Research
Starts: 15 March 2010 Ends: 14 September 2010 Value (£): 26,395
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Summary on Grant Application Form
Over 95% of the UK energy needs utilize combustion, so advanced combustion monitoring and measurement techniques are essential to the development of clean and efficient engines, boilers and furnaces. Flame chemiluminescence, which is light emitted from intermediate (radical) chemical species formed during combustion, has long been thought to hold detailed information about the chemical processes occurring in the reaction zone, such as the local air-fuel ratio and fuel consumption rate. However, there is conflicting information within the published literature as to the interpretation of chemiluminescence measurements as indicators of local heat release rate and air fuel ratio - parameters that are of tremendous interest and importance to combustion researchers of engines and burners. Accordingly, the overall objective of this work is to determine whether the chemiluminescence intensity emitted from two radical species that commonly occur in hydrocarbon flames (OH* and CH*) can be used as a measure of heat release rate under 'engine relevant' conditions, and also whether their relative intensities can be used to determine the air fuel ratio.Fundamental combustion experiments will be performed in a spherical vessel with central ignition and windows - otherwise known as a combustion bomb. Homogeneous mixtures of air, fuel, and residual combustion gases (representative of the range of conditions typically encountered in combustion engines) will be prepared and burnt in the vessel. The resultant OH* and CH* light emissions will be recorded by photomultiplier tubes fitted with appropriate spectral filters. The combustion bomb method is highly advantageous for this work in many respects: after ignition, a spherical flame propagates radially through the mixture compressing the unburned gas ahead of the flame front. Thus, flame chemiluminescence data is obtained for a sequence of linked temperatures and pressures from a single experiment. The combustion bomb allows data collection across a wide range of pressure and temperature (pressures up to 30 bar and unburned gas temperatures up to 850 K can be investigated). Moreover, by varying the initial temperature and pressure, the effects of pressure and temperature can be decoupled and correlations generated for the effect of temperature and pressure on the OH* and CH* chemiluminescence intensity. The Internal Combustion Engines Group (ICEG) at Oxford University has substantial experience (over 16 years) with combustion bomb experiments. The experience gained from these previous works has led to 3 notable innovations in the field:+ The use of free-fall experiments to eliminate the effect of buoyancy.+ The introduction of a multi-zone combustion model for data analysis, so that the effect of dissociation and the temperature gradient in the burned gas (typically 500 K) is incorporated into the analysis of flame front position and pressure rise.+ The use of 'real residuals' by retaining part of the previous combustion event as residuals, as opposed to the conventional approach of using a fixed composition N2/CO2 mixture to represent the residuals.Compared to engines, the combustion bomb provides a simplified (but not simple) experiment with combustion that can be accurately controlled and analysed - unlike an engine the temperature of the unburned gas can be calculated accurately, there is no moving piston, and no heat transfer to the enclosure before the end of the experiment.No major hardware purchases are required for the work. The existing combustion bomb facility, which uses a comprehensive LabVIEW interface for setting-up the experimental conditions and data logging, is available, as are photomultiplier tubes and a well-validated multi-zone combustion model and previously developed MATLAB routines for data analysis.
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