High pressure and high temperature measurements on diesel sprays

Abstract

Environmental, financial and legal reasons demand the development of cleaner diesel engines. Atomization, evaporation and mixing phenomena observed during injection of Diesel fuel affect the produced emissions. To study these phenomena, under engine-like conditions (50bar, 1000K), a chemically preheated constant volume chamber was built. A system of sensors, driven in real-time by a FPGA (Field Programmable Gate Array) and controlled by a Real Time Controller, was built to monitor and control the operations. A modern common rail fuel injection system (Bosch CP3) was driven by a purpose-modified Hartridge 1100 test stand and controlled by the FPGA (Field Programmable Gate Array). Chemical heating is a technique used widely to simulate the ambient conditions of an industrial combustor in a constant volume vessel. A flammable mixture is ignited in an optically accessible vessel, attempting to produce a post-combustion high pressure and high temperature environment. The flammable mixture usually consists of Hydrogen and a Hydrocarbon. Hydrogen is added, to assist with the ignitability of the pre-ignition mixture and to simulate the water present in industrial combustors as a result of exhaust gas recirculation. To this direction, the mole ratio of Hydrogen to Hydrocarbon and the mixture molecular weight were introduced as independent variables for the first time in the literature of constant volume combustion. An initial computer model, assuming perfect combustion, was used for calculation of adiabatic temperature and pressure. A second computer model investigated the effect of chemical dissociation by solving for the minimization of Gibbs energy and was compared to the former one. To verify the calculations, a dual pressure transducer technique and a High-Speed Schlieren technique were used to validate the combustion conditions inside the vessel To further understand the atomization, evaporation and mixing phenomena in sprays, a Diesel spray was visualized using back-illumination and Schlieren High-Speed cinematography at high pressure and room temperature. To understand the evaporation behaviour of a spray and map the vapour fuel distribution, a tracer Laser Induced Fluorescence was applied on a Dodecane/Methyl-naphthalene spray under evaporating and non-evaporating conditions. To compare the experimental findings to the theoretical models in literature, the evaporation of a single droplet in post-combustion vessel gases was simulated using a purpose-programmed FORTRAN code. A supercritical phase change was suggested to explain the sudden phase change and large differences between the theoretical model and the experimental results.