The potential of vortex amplifiers to improve mixture preparation in spark ignition engines
Spark ignition engines are a significant source of air pollution. Emissions are most severe in the period after the engine has been started from cold. This is because fuel enrichment is needed to ensure reliable combustion in the cold cylinder. The problem is compounded by the exhaust treatment catalyst not reaching operating temperature until some minutes after starting. As the majority of car usage is for short journeys, engines spend much of their time in this high emission operating regime. One route to reducing emissions is to improve mixture preparation. This is Particularly effective after a cold start as less enrichment is required to ensure combustion. The aim of this project has been to evaluate a Vortex'Amplifier as a route to improving mixture preparation. The vortex amplifier is a no moving parts fluidic control device. It regulates a large volume supply flow by imparting swirl to it with a small volume control flow. The control flow vortex creates a region of highly turbulent flow at the device outlet which possesses the potential to atomise a fuel spray. The VA has been tested experimentally. The sprays produced by the vortex amplifier were measured by a laser diffraction technique. Numerical analysis has also been undertaken to determine the motion of droplets within the vortex chamber and the potential of the flow to disrupt a fuel spray. The vortex amplifier has been found to be a highly effective atomiser. It produces sprays with a Sauter mean diameter approximately half the size of the best current technology. However the spray impacts on the walls of any pipework downstream of the VA due to the high tangential velocities in the flow exiting the VA. This problem currently precludes engine us'e, but suggestions for improving the situation are contained in the recommendations for future work.