Abstract :

Concerns about energy conservation, global warming from emissions of CO2 and atmospheric pollution by oxides of nitrogen, hydrocarbons and particulates have prompted far-reaching remedial measures. In the short to medium term, the spark ignition engine, burning hydrocarbon fuels, will remain a dominant propulsion device for private transport. Energy generation in this engine is usually by deflagration burning in which the flame front propagates through homogeneous reactants. However, recent attempts to improve SI engine efficiency have included concepts such as gasoline direct injection (GDI) which raises the prospect of droplet combustion being relevant to these engines as well as to gas turbines and diesel engines. In all engines, it is necessary to avoid severe auto-ignition, or knock, which will ultimately, damage the engine. Many of the combustion related issues of burning rate, flammability limits, emissions and overpressures also have relevance to hazards and their mitigation. Hence, studies of combustion should not be confined to those relating to engines. Fundamental studies in ‘real’ engines are difficult due to the multiplicity of variable which are difficult to control and because of the limited access for diagnostic tools. The sparse data that does exit has often been obtained from pressure records without detailed photographic observations. Work at Leeds, and elsewhere, has shown that this can lead to incorrect interpretation because flame instabilities can develop that are not evident from pressure records but that significantly affect analysis. The present presentation describes some of the experimental apparatus developed at Leeds to elucidate the problem at realistic pressures and temperatures. These include two fan stirred combustion vessels, a rapid compression machine and several novel research engines. A recently developed time resolved 3D imaging technique also will be discussed. Widely used laser diagnostics that include high speed PIV, LDV and PLIF also are used at Leeds.  Important experimental data include laminar and turbulent burning velocities, ignition delay times, effects of flame stretch and flame instabilities. Data for homogeneous mixtures, aerosols and sprays are required. The presentation includes descriptions and photographic/movie examples of equipment and combustion experiments together with some important recent findings.