Laser induced incandescence and high speed imaging in hydra optical diesel engine

Abstract

The aim of this thesis is to investigate ways to reduce soot emission from compression ignition engines by investigating the combustion processes within the diesel engine. The approach is to include computational and experimental work. In order to investigate the trade-off between the amount and stratification of the premixing and the consequent rate of pressure rise, and in particular the effects of changing the autoignition properties of the fuel blend, a multizone code capable of representing the ignition of a premixed charge consequent on multiple injection of fuel is presented. As part of this investigation, this thesis began the process of looking into the potential of gasoline fuel. Experimentally, investigations of soot distribution were carried out in an optically-accessed single cylinder “Hydra” engine. The soot was visualized using high speed imaging and laser induced incandescence in the optical engine to look at the effect of injection pressure on combustion luminosity and soot distribution. An extensive parametric study was carried out on the Hydra engine to look at the effect of engine load, injection timing and pressure, number of injections, intake temperature and combustion phasing. High speed imaging was carried out to measure injection tip penetration and soot luminosity as a function injection pressure. The combustion luminosity was studied, with proper orthogonal decomposition (POD) analysis, at different injection pressures. It was found that increase of injection pressure decreases combustion luminosity. The technique of laser induced incandescence (LII) was used to visualize the soot. As a preliminary to the use of the LII in the engine, fundamental work on the technique itself was carried out at Heriot-Watt University to isolate the radiative emission component of heat loss from the soot and measure the complex refractive index of soot. Results on soot particle sizes were compared to scanning electron micrograph of the soot collected. The LII measurement was found to be much larger, due to the high signal to noise ratio and the bias towards detection of larger particles. The investigation also showed that the soot agglomerates could undergo micro-explosions on being exposed to laser irradiance. It is speculated that the soot molecules become ionized and mutually repel each other.