This research aims to improve the understanding of the interaction between air motion, spray trajectory and atomization in internal combustion engines conditions.
The results will be provided in a form suitable for use in the evaluation of calculation methods. Calculation will be performed to evaluate the influence of initial conditions and model assumptions.
The research of four partners was experimental with the fifth partner making use of the results to develop a multi-dimensional computer-based prediction method which, on occasion, also provided guidance for the experiments. Velocity and size characteristics of Diesel and gasoline sprays were obtained by phase-Doppler velocimetry and the experiments extended to consideration of impingement of the sprays on a valve stem and a valve head; they showed the nature of secondary atomization as a result of impingement, and perhaps of greater importance the liquid films which could be formed with the consequence of substantial increase in droplet size. Attempts were made to extend the phase-Doppler method to detect the droplets from one spray in another, as for example would result from the effects of swirl on a multi-hole spray. Thus, for fundamental studies of spray interaction, the individual sprays were generated with fluids of different refractive indexes, in such way that the mixing process between the two two-phase flows could be studied by identifying the droplets according to their refractive index. Results were obtained though it was evident that the droplets formed by coalescence could not readily be separated at the present stage of development of the technique; ie the extended PDA technique requires further development.
In-cylinder results were obtained with laser-Doppler velocimetry, particle-image velocimetry and Mie-scattering based tomography. The emphasis of the laser velocimetry experiments were to determine the nature of the swirl and squish flows in an operating Diesel engine and to make use of these results in a phenomenal model as well as in the multi-dimensional model. The spin-up of the swirl velocity within the bowl was successfully quantified although squish velocities were measured lower than those predicted by the phenomenological model. On other hand, and due to the fact that test flow rig based evaluation methods are commonly the only way to get information on the behaviour of a certain cylinder head geometry, intense efforts have been also made to evaluate and to improve the accuracy or prediction ability of this kind of techniques by applying more accurate velocimetry techniques (laser-Doppler anemometry) and extending them to pulsating flow.
Particle image velocimetry and Mie scattering were successfully used in free jets, the former produced successful images of the flow in a model engine and the latter was shown to be too insensitive to assist the quantification of the consequences of mixture preparation at top- dead-centre of compression but proved to be a useful tool for the better understanding of the scalar field during the intake stroke.
The multi-dimensional model was initially developed with two independent variables and latterly with three independent variables. It incorporates turbulence, heat-transfer and droplet models and has been shown to correctly represent the trends of almost all of the experiments, with differences between measurement and calculation which are only slightly greater than the uncertainty in the former. It has proved to be useful in the guidance of the experimental work and shows every promise of providing similar benefits to the engine industry.
A theoretical and experimental approach will be applied for the improvement of the understanding of the interaction between air motion, spray trajectory and atomization in engine sprays. Five tasks must be undertaken :
Task 1 - calculation of spray-aerodynamic interactions :
assembling of a computer model to allow the calculation of the velocity and size distribution of droplets, the velocity of air and the consequent trajectories.
Task 2 - interaction of multiple sprays :
by an extended phase doppler anemometer, the size, the velocity and refractive index of individual droplets will be measured and used to distinguish the origin of each droplet in two fuel sprays using fluids of different refractive index. Measurements will include the impingement. A two-dimension, three parameter log-hyperbolic distribution must be presented in function of primary operational conditions.
Task 3 - spray-aerodynamic interactions and its effect on performance :
laser velocimeter measurements will be carried out in a single cylinder. Several combinations of swirl number, bowl geometry and spray characteristics will be tested.
Task 4 - visualisation of the gaseous gasoline air mixture by laser tomography :
the objectives are to visualise and measure the local fuel concentration before ignition and to study the atomization at the inlet valve during its closure. Laser tomography and Mie diffusion will be used.
Task 5 - the relationship between primary and secondary atomization:
with a phase doppler anemometer, the purpose is to quantify the atomization when the sprays come into contact with solid bodies.
Funding SchemeCSC - Cost-sharing contracts