The effects of squish and swirl interaction on performance and emissions of a spark ignition engine
Creators: name: Law, Michael
Publisher: name: University of British Columbia
Year: 2009

description: In an attempt to reduce emissions and enhance the performance of a lean - burn, spark ignition engine, the effect of charge motion within the combustion chamber has been examined. The two most prominent charge motions are those of intake generated swirl and compression generated squish. A great deal of previous research work has focused individually on these charge motions, but very little has been done with respect to a detailed study of the combined effects of these phenomenon. The objective of this research is to determine if an optimum combination of squish and swirl intensity exists, and if so what the effects on performace and emissions are. The method by which this would be achieved was entirely experimental. The tests were run using a Ricardo - Hydra Research engine fuelled by natural gas. It required the design and construction of a swirl producing intake system followed by calibration on a steady flow test bench by means of a paddle- wheel anemometer. This resulted in swirl numbers in the range of 0 -1.6 at speeds in the range of 1000 - 2500 rpm. The variation in squish intensity was achieved by the insertion of piston crowns with the desired squish intensity. The squish was radial in nature produced by a bowl-in-piston configuration and a flat cylinder head. Squish ratios used were 0% , 30% , 50% and 70% which could be achieved using a 10.2:1 compression ratio. The testing was cycled through all possible squish and swirl combinations producing a set of emissions and performance data. Initially tests were conducted at WOT, using SAE correction factors for minor fluctuations in intake temperature and pressure. However a second set of part load tests conducted at an intake manifold pressure of 95 kPa produced more meartingful results due to less variations in intake conditions. definite optimization of engine torque and emissions was determined at various squish and swirl intensities and noted at all speed conditions. The effects were most prominent at higher relative air - fuel ratio (RAFR) where improvements in performance were up to 5%. Over the range of RAFR 1.0 - 1.4 benefits were found to vary from 1% - 5% in torque. The exhaust emissions results were less promising due to the increase in NO[sub x] as torque increased, and only a slight THC reduction with increased swirl intensity was noted. Noticeable trends were the benefit of a higher squish ratio as the charge became leaner, as well as when the speed was increased. Increased swirl intensity produced beneficial results with the higher squish requiring a lower swirl intensity to reach the optimum combination. A significant reduction in MBT timing was found as swirl no. was increased at all operating conditions. This reduction in MBT timing persisted after performance optimization had occurred indicating the beneficial effect of swirl on the initial burn time, but less benefit is obtained from the main burn time. The research project has brought to light a number of unexpected aspects of squish and swirl interaction, and has consolidated trends which were expected from previous research.